Viral Infections PDF

307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 307 VIRAL INFECTIONS 18 CHAPTER OUTLINE Infections of the Lower Respiratory Viral Gastroenteritis (Vi...

307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 307 VIRAL INFECTIONS 18 CHAPTER OUTLINE Infections of the Lower Respiratory Viral Gastroenteritis (Viral Enteritis, Tract Having Multiple Causes Viral Diarrhea) INTRODUCTION Viral Infections of the Lower Viral Hepatitis HOW DO VIRUSES CAUSE DISEASE? Respiratory Tract VIRAL INFECTIONS OF THE VIRAL INFECTIONS OF THE SKIN VIRAL INFECTIONS OF THE ORAL GENITOURINARY SYSTEM VIRAL INFECTIONS OF THE EARS REGION VIRAL INFECTIONS OF THE VIRAL INFECTIONS OF THE EYES Cold Sores (Fever Blisters, CIRCULATORY SYSTEM VIRAL INFECTIONS OF THE Herpes Labialis) VIRAL INFECTIONS OF THE CENTRAL RESPIRATORY SYSTEM VIRAL INFECTIONS OF THE NERVOUS SYSTEM Viral Infections of the Upper GASTROINTESTINAL TRACT RECAP OF MAJOR VIRAL INFECTIONS Respiratory Tract Infections of the Gastrointestinal OF HUMANS The Common Cold (Acute Viral Tract Having Multiple Causes APPROPRIATE THERAPY FOR VIRAL Rhinitis, Acute Coryza) INFECTIONS LEARNING OBJECTIVES Certain of the viral diseases described in this chapter are nationally notifiable infectious diseases, meaning that AFTER STUDYING THIS CHAPTER, YOU SHOULD BE ABLE TO: when a patient is diagnosed with one of these diseases in the United States, the information must be reported to Correlate various viral diseases with body systems (e.g., the Centers for Disease Control and Prevention (CDC). rhinoviruses with the respiratory system) As of 2007, there were approximately 21 nationally noti- Correlate a particular viral disease with its major charac- fiable viral diseases (see Table 18-1). Most of them are teristics, etiologic agent, reservoir(s), mode(s) of trans- described in this chapter, as are some viral diseases that mission, and diagnostic laboratory procedures are not nationally notifiable. Name several nationally notifiable viral diseases Briefly describe how viruses cause disease Describe Koplik spots and state the disease with which HOW DO VIRUSES CAUSE DISEASE? they are associated Recall from Chapter 4 that viruses can only infect cells Characterize the various hepatitis viruses as being either bearing appropriate surface receptors (i.e., surface recep- DNA or RNA viruses tors that the virus is able to recognize and bind to). Thus, List several viral diseases that are sexually transmitted viruses are specific as to the type of cell(s) that they can infect. For this reason, certain viruses only cause respira- INTRODUCTION tory infections, whereas others only cause gastrointesti- nal (GI) infections, and so on. It would be impossible in a book this size to describe all Viruses multiply within host cells, and it is during of the human infectious diseases caused by viruses. their escape from those cells—by either cell lysis or bud- Thus, only selected viral diseases are described in this ding—that the host cells are destroyed. This cell chapter. destruction leads to most of the symptoms of the viral 307 307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 308 308 SECTION VIII Major Infectious Diseases of Humans TABLE 18-1 Nationally Notifiable Viral Diseases NUMBER OF NEW U.S. CASES VIRAL DISEASE REPORTED TO THE CDC IN 2007* AIDS 37,503 Domestic arthropod-borne viral (arboviral) diseases: Encephalitis caused by members of the California 55 serogroup Eastern equine encephalitis 4 Powassan virus encephalitis 7 St. Louis encephalitis 9 West Nile virus encephalitis 3,630 Western equine encephalitis 0 Hantavirus pulmonary syndrome 32 Hepatitis A 2,979 Hepatitis B 4,519 Hepatitis C 845 Influenza-associated pediatric mortality 77 Measles 43 Mumps 800 Poliomyelitis 0 Rabies, human 1 Rubella 12 SARS 0 Smallpox 0 Varicella (chickenpox) 40,152 Yellow fever 0 Source: http://www.cdc.gov. *These figures provide insight as to how frequently these diseases occur in the United States. For updated information, go to the CDC web site; click on “Morbidity & Mortality Weekly Report”; then click on “Notifiable Diseases”; then click on the most recent year that is listed. infection, which vary depending on the location of the STUDY AID infection. Other symptoms are the result of immunolog- What to Learn? ical injury (i.e., injury that results from the immune re- This chapter contains a large amount of information. sponse to the viral pathogen). In the case of the acquired Of primary importance will be your ability to later re- immunodeficiency syndrome (AIDS) virus (human im- call the name of the virus that causes a particular viral munodeficiency virus [HIV]), the virus destroys cells of disease and the manner in which the disease is trans- the immune system. This renders the patient unable to mitted. If applicable, you should be able to state the ward off various viral, bacterial, fungal, and parasitic vector that is involved in the transmission of the dis- pathogens. The AIDS patient’s death results from over- ease. For example, if your teacher says “dengue fever,” whelming infections caused by these pathogens. you should be able to state the name of the virus that causes the disease (dengue virus), the manner in which dengue fever is transmitted (mosquito bite), and the VIRAL INFECTIONS OF THE SKIN vector that is involved in the transmission of dengue Table 18-2 contains information pertaining to viral in- fever (mosquitoes in the genus Aedes). fections of the skin. 307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 309 CHAPTER 18 Viral Infections 309 TABLE 18-2 Viral Infections of the Skin DISEASE ADDITIONAL INFORMATION Chickenpox and Shingles. (a) Chickenpox (also known as Pathogen. Chickenpox and shingles are caused by varicella) is an acute, generalized viral infection, with varicella-zoster virus (VZV); a herpes virus (family fever and a skin rash (Fig. 18-1). Vesicles also form in Herpesviridae) that is also known as human mucous membranes. It is usually a mild, self-limiting herpesvirus 3; a DNA virus. disease, but can be severely damaging to a fetus. Reservoirs and Mode of Transmission. Infected humans Serious complications include pneumonia, secondary serve as reservoirs. Transmission is from person to per- bacterial infections, hemorrhagic complications, and son by direct contact or droplet or airborne spread of encephalitis. Reye’s (pronounced “rize”) syndrome vesicle fluid or secretions of the respiratory system of (a severe encephalomyelitis with liver damage) may persons with chickenpox. follow clinical chickenpox if aspirin is given to children Laboratory Diagnosis. Diagnosis is usually made on clini- younger than 16 years of age. Chickenpox is the leading cal and epidemiologic grounds. Immunodiagnostic and cause of vaccine-preventable death in the United molecular diagnostic procedures are available, as are States. (b) Shingles (also known as herpes zoster) is a cell culture and electron microscopy. reactivation of the varicella virus, often the result of immunosuppression. Shingles involves inflammation of sensory ganglia of cutaneous sensory nerves, producing fluid-filled blisters, pain, and paresthesia (numbness and tingling). Shingles may occur at any age, but is most common after age 50. Patient Care. Use Airborne and Contact Precautions for hospitalized patients until their lesions become dry and crusted. German Measles (Rubella). German measles is a mild, Pathogen. Rubella is caused by rubella virus, an RNA virus febrile viral disease. A fine, pinkish, flat rash begins 1 in the family Togaviridae. or 2 days after the onset of symptoms (Fig. 18-2). The Reservoirs and Mode of Transmission. Infected humans rash starts on the face and neck and spreads to the serve as reservoirs. Transmission occurs by droplet trunk, arms, and legs. Rubella is a milder disease than spread or direct contact with nasopharyngeal secretions hard measles with fewer complications. If acquired dur- of infected people. ing the first trimester of pregnancy, rubella may cause Laboratory Diagnosis. Immunodiagnostic and molecular congenital rubella syndrome in the fetus. This can lead diagnostic procedures are available for diagnosis of to intrauterine death, spontaneous abortion, or congen- rubella. The virus can be propagated in cell culture. ital malformations of major organ systems. Patient Care. Use Droplet Precautions for hospitalized pa- tients until 7 days after the onset of rash. Measles (Hard Measles, Rubeola). Measles is an acute, Pathogen. Measles is caused by measles virus (also known highly communicable viral disease with fever, conjunc- as rubeola virus). It is an RNA virus in the family tivitis, cough, photosensitivity (light sensitivity), Koplik Paramyxoviridae. spots in the mouth, and red blotchy skin rash (Fig. 18-3). Reservoirs and Mode of Transmission. Infected humans Koplik spots are small red spots, in the center of which serve as reservoirs. Airborne transmission occurs by can be seen a minute bluish white speck when observed droplet spread, direct contact with nasal or throat under a strong light (Fig. 18-4). The rash begins on the secretions of infected persons, or with articles freshly face between days 3 and 7 and then becomes general- soiled with nose and throat secretions. ized. Complications include bronchitis, pneumonia, otitis Laboratory Diagnosis. Diagnosis of measles is usually made media, and encephalitis. Rarely, autoimmune, subacute, on clinical and epidemiologic grounds. Immunodiagnostic sclerosing panencephalitis (SSPE) may follow a latent and molecular diagnostic procedures are available, and period of several years. SSPE is characterized by gradual the virus can be isolated in cell culture. progressive psychoneurological deterioration, including personality changes, seizures, photosensitivity, ocular abnormalities, and coma. Patient Care. Use Airborne Precautions for hospitalized patients until 4 days after the onset of rash. (continues) 307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 310 310 SECTION VIII Major Infectious Diseases of Humans TABLE 18-2 Viral Infections of the Skin (continued) DISEASE ADDITIONAL INFORMATION Monkeypox. Monkeypox is a rare viral disease that causes Pathogen. Monkeypox is caused by monkeypox virus, fever, headache, muscle aches, backache, lymphadeni- which is in the same group of viruses (orthopoxviruses) tis, malaise (fatigue), and a rash (Fig. 18-5). A milder as smallpox virus (variola virus) and the virus used in disease than smallpox, monkeypox occurs primarily in the smallpox vaccine (vaccinia virus). central and western Africa, although several people in Reservoirs and Mode of Transmission. Infected animals the United States became ill in 2003 after handling serve as reservoirs. Transmission occurs via animal bite infected prairie dogs. Unlike smallpox, monkeypox is or contact with an infected animal’s blood, body fluids, rarely fatal. or rash. Person-to-person transmission does occur. Patient Care. Use Airborne and Contact Precautions for Laboratory Diagnosis. Monkeypox can be diagnosed by hospitalized patients; Airborne Precautions until mon- molecular diagnostic procedures, cell culture, electron keypox is confirmed and smallpox is excluded; Contact microscopy, or immunodiagnostic procedures. (see Precautions until lesions become crusted. http://www.cdc.gov/ncidod/monkeypox for more information) Smallpox. Smallpox is a systemic viral infection with Pathogen. Smallpox is caused by two strains of variola fever, malaise, headache, prostration, severe backache, virus: variola minor (with a fatality rate of ⬍1%), and a characteristic skin rash (refer back to Fig. 11-10 in variola major (with a fatality rate of 20%–40% or Chapter 11), and occasional abdominal pain and higher). Variola virus is a double-stranded DNA virus in vomiting. The rash is similar to, and must be distin- the genus Orthopoxvirus, family Poxviridae. Smallpox guished from, the rash of chickenpox. Smallpox can virus is a potential biological warfare and bioterrorism become severe, with bleeding into the skin and mucous agent. membranes, followed by death. Reservoirs and Mode of Transmission. Before smallpox Patient Care. Use Airborne and Contact Precautions for was eradicated, infected humans were the only source hospitalized patients until all scabs have crusted and of the virus. There are no known animal or environ- separated (3–4 weeks). Use N95 or higher respiratory mental reservoirs. Person-to-person transmission is protection. via the respiratory tract (droplet spread) or skin inocu- lation. Patients are most contagious before eruption of the rash, by aerosol droplets from oropharyngeal lesions. Laboratory Diagnosis. Because of the potential danger of the use of smallpox virus as a bioterrorism agent, physicians must become familiar with the clinical and epidemiologic features of smallpox and how to distin- guish smallpox from chickenpox. Laboratory diagnosis is by cell culture, virus neutralization tests, molecular diagnostic procedures, or electron microscopy. These procedures are performed only in biosafety level 4 (BSL-4) facilities. Warts. Warts consist of many varieties of skin and mucous Pathogens. Warts are caused by at least 70 types of membrane lesions, including common warts (verrucae human papillomaviruses (HPV). They are classified in vulgaris), venereal warts, and plantar warts. Most are the genus Papillomavirus within the family harmless, but some can become cancerous. Venereal or Papovaviridae. They are DNA viruses. genital warts are discussed in more detail later in the Reservoirs and Mode of Transmission. Infected humans chapter. serve as reservoirs. Transmission usually occurs by direct contact. Genital warts are sexually transmitted. They are easily spread from one area of the body to another, but most are not very contagious from person to person (genital warts are an exception). Laboratory Diagnosis. Diagnosis is made on clinical grounds. 307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 311 CHAPTER 18 Viral Infections 311 FIGURE 18-3. Child with measles. (Courtesy of the CDC.) FIGURE 18-1. Chickenpox, with lesions at all stages of development. (From Harvey RA, et al. Lippincott’s Illustrated Reviews: Microbiology, 2nd ed. Philadelphia: Lippincott Williams & Wilkins, 2007.) Koplik spots FIGURE 18-4. Koplik spots. Koplik spots, an early sign of measles, usually appear prior to the onset of skin rash. Koplik spots are irregularly shaped, bright-red spots, often having a bluish white central dot. (From Harvey RA, et al. Lippincott’s Illustrated Reviews: Microbiology, 2nd ed. Philadelphia: Lippincott Williams & Wilkins, 2007.) FIGURE 18-2. Child with rubella. The lesions are not FIGURE 18-5. Child with monkeypox. (Courtesy of as intensely red as those of measles. (Courtesy of the CDC.) the CDC.) 307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 312 312 SECTION VIII Major Infectious Diseases of Humans VIRAL INFECTIONS OF THE RESPIRATORY SYSTEM STUDY AID Beware of Similar-Sounding Names Viral Infections of the Upper Do not confuse varicella, variola, and vaccinia viruses. Respiratory Tract Varicella virus (which is a type of herpes virus) is the cause of chickenpox. Variola virus is the cause of The Common Cold (Acute Viral Rhinitis, smallpox and is often referred to as smallpox virus. Acute Coryza) Vaccinia virus is the cause of cowpox; it is used to Disease. The common cold is a viral infection of the lin- make the vaccine that protects against smallpox. The ing of the nose, sinuses, throat, and large airways. words vaccine and vaccination are derived from vacca, Symptoms include coryza (profuse discharge from nos- Latin for cow. trils), sneezing, runny eyes, sore throat, chills, and malaise. Additionally, laryngitis, tracheitis, or bronchitis may ac- company a cold. Secondary bacterial infections, including sinusitis and otitis media, may follow. The common cold VIRAL INFECTIONS OF THE EARS occurs most frequently in fall, winter, and spring. On average, most people have one to six colds annually. It is Information about viral and bacterial ear infections can not a nationally notifiable disease in the United States. be found in Table 19-3 in Chapter 19. Patient Care. Use Droplet Precautions for hospitalized patients. VIRAL INFECTIONS OF THE EYES Pathogens. Many different viruses cause colds. Rhino- Table 18-3 contains information about viral infections of viruses, of which there are more than 100 serotypes, are the eyes. the major cause in adults. Other cold-causing viruses TABLE 18-3 Viral Infections of the Eyes DISEASE ADDITIONAL INFORMATION Adenoviral Conjunctivitis and Keratoconjunctivitis. Pathogens. Adenoviral conjunctitivis and keratoconjunc- These are acute viral diseases of one or both eyes, tivitis are caused by various types of adenoviruses. associated with inflammation of the conjunctiva, edema Herpes simplex and varicella-zoster viruses can also eyelid and periorbital tissue, pain, photophobia, and cause keratoconjunctivitis. blurred vision. The cornea is involved in about 50% of Reservoirs and Mode of Transmission. Infected humans cases, with permanent scarring of the cornea in severe serve as reservoirs. Transmission occurs via direct con- cases. tact with eye secretions or contact with contaminated Patient Care. Use Contact Precautions for hospitalized surfaces, instruments, or solutions. People with viral patients for the duration of the illness. infections (e.g., cold sores) should wash their hands thoroughly before inserting or removing contact lenses or otherwise touching their eyes. Laboratory Diagnosis. Diagnosis is made by cell culture orimmunodiagnostic or molecular diagnostic procedures. Hemorrhagic Conjunctivitis. This viral disease has a sud- Pathogens. Hemorrhagic conjunctivitis is caused by den onset, with redness, swelling, and pain in one or adenoviruses and enteroviruses. both eyes. Small, discrete subconjunctival hemorrhages Reservoirs and Mode of Transmission. Infected humans may enlarge to form confluent subconjunctival hemor- serve as reservoirs. Transmission occurs by direct or rhages. One adenoviral syndrome, called pharyngocon- indirect contact with discharge from infected eyes. junctival fever, is characterized by upper respiratory Adenovirus transmission may be associated with poorly disease, fever,and minor degrees of corneal epithelial chlorinated swimming pools; this “swimming pool inflammation. conjunctivitis” can reach epidemic proportions. Patient Care. Use Contact Precautions for hospitalized Laboratory Diagnosis. Diagnosis is made by cell culture or patients for the duration of the illness. immunodiagnostic or molecular diagnostic procedures. 307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 313 CHAPTER 18 Viral Infections 313 include coronaviruses, parainfluenza viruses, respiratory trauma, fever (hence the name), physiologic changes, or syncytial virus (RSV ), influenza viruses, adenoviruses, disease. The infection may be severe and extensive in im- and enteroviruses. munosuppressed individuals. Cold sores are usually caused by herpes simplex virus type 1 (HSV-1), although they can Reservoirs and Mode of Transmission. Infected hu- also be caused by herpes simplex virus type 2 (HSV-2). mans serve as reservoirs of infection. Transmission is via HSV-1 and HSV-2 are also known as human her- respiratory secretions by way of hands and fomites or di- pesvirus 1 and human herpesvirus 2, respectively. They rect contact with or inhalation of airborne droplets. are DNA viruses in the family Herpesviridae. Either of these viruses may also infect the genital tract, although Laboratory Diagnosis. Laboratory diagnosis of the genital herpes infections are most often caused by HSV-2. common cold usually is not required, but cell-culture tech- niques can often demonstrate the specific viral pathogen. VIRAL INFECTIONS OF THE Infections of the Lower Respiratory Tract GASTROINTESTINAL TRACT Having Multiple Causes Infections of the Gastrointestinal Tract Information pertaining to infections of the lower respi- ratory tract having multiple causes can be found in Having Multiple Causes Chapter 19. Diarrhea can have many causes. It may or may not be the result of an infectious disease. When diarrhea is the Viral Infections of the Lower Respiratory result of an infectious disease, the pathogen may be a Tract virus, a bacterium, a protozoan, or a helminth. Dysentery Table 18-4 contains information pertaining to viral in- (a severe form of diarrhea) may also be caused by various fections of the lower respiratory tract. pathogens, including bacteria (e.g., Shigella spp. cause bacillary dysentery) and protozoa (e.g., those that cause VIRAL INFECTIONS OF THE amebiasis and balantidiasis; see Chapter 21). ORAL REGION Viral Gastroenteritis (Viral Enteritis, Viral Diarrhea) Cold Sores (Fever Blisters, Herpes Labialis) Disease. Viral gastroenteritis may be an endemic or Cold sores are superficial clear vesicles on an erythema- epidemic illness in infants, children, and adults. Symptoms tous (reddened) base, which may appear on the face or lips include nausea, vomiting, diarrhea, abdominal pain, myal- (refer back to Fig. 14-2 in Chapter 14). They crust and gia, headache, malaise, and low-grade fever. Although heal within a few days. Reactivation may be caused by most often a self-limiting disease lasting 24 to 48 hours, viral gastroenteritis (especially when caused by a rotavirus) can be fatal in an infant or young child. In developing countries, rotavirus infections are responsible for more HISTORICAL NOTE than 800,000 diarrheal deaths per year. Although viral gas- The World’s Worst Influenza Pandemic troenteritis is sometimes referred to as “stomach flu” or The 1918–1919 Spanish flu pandemic (also known as “24-hour flu,” keep in mind that flu is an abbreviation of the swine flu pandemic) killed an estimated 20 to 100 influenza, which is a respiratory disease. Viral gastroenteri- million people, worldwide—between 2.5% and 5% of tis is not a nationally notifiable disease in the United States. the world population. The pandemic killed between 2% and 20% of those infected compared with a mortal- Patient Care. Use Standard Precautions for hospitalized ity rate of about 0.1% for modern-day flu epidemics. patients. Add Contact Precautions for diapered or incon- Although most victims of modern-day flu epidemics are tinent patients and for patients with rotavirus infections. very young, very old, and immunosuppressed people, the 1918–1919 pandemic killed primarily healthy Pathogens. The most common viruses infecting chil- young adults. Scientists have recovered the virus (desig- dren in their first years of life are enteric adenoviruses, nated A/H1N1) that caused the pandemic from frozen astroviruses, caliciviruses (including noroviruses), and tissue samples, and are currently studying it. They have rotaviruses. Those infecting children and adults include discovered that the virus kills by causing an overreac- norovirus-like viruses and rotaviruses. tion of the body’s immune system. This could explain why healthy young adults with strong immune systems Reservoirs and Mode of Transmission. Infected hu- were affected to a greater extent than those with weaker mans are reservoirs of these viruses; contaminated water immune systems—very young, very old, and immuno- and shellfish may also be reservoirs. Transmission is most suppressed individuals. often via the fecal–oral route. Airborne transmission and contact with contaminated fomites may cause epidemics 307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 314 314 SECTION VIII Major Infectious Diseases of Humans TABLE 18-4 Viral Infections of the Lower Respiratory Tract DISEASE ADDITIONAL INFORMATION Acute, Febrile, Viral Respiratory Disease. This disease is Pathogen. Acute, febrile, viral respiratory disease can be characterized by fever and one or more of the following caused by one of many viruses, including parainfluenza systemic reactions: chills, headache, general aching, viruses, respiratory syncytial virus (RSV), adenovirus, malaise, anorexia, and sometimes gastrointestinal (GI) rhinoviruses, certain coronaviruses, coxsackieviruses, disturbances in infants. The disease may include rhinitis, and echoviruses. RSV is the major viral respiratory tract pharyngitis, tonsillitis, laryngitis, bronchitis, pneumonia, pathogen of early infancy. RSV may cause pneumonia, conjunctivitis, otitis media, and/or sinusitis. Acute, croup, bronchitis, otitis media, and death. febrile, viral respiratory diseases are not nationally Reservoirs and Mode of Transmission. Infected humans notifiable diseases in the United States. serve as reservoirs. Transmission occurs via direct oral Patient Care. Use Standard Precautions for adult patients; contact or by droplets; indirectly via handkerchiefs, add Contact Precautions for infants and young children eating utensils, or other fomites; or for some viruses, for the duration of the illness. via the fecal–oral route. Laboratory Diagnosis. Diagnosis is made by isolation of the etiologic agent from respiratory secretions, using cell cultures. Immunodiagnostic and molecular diagnos- tic procedures are available. Hantavirus Pulmonary Syndrome (HPS). HPS is an acute Pathogens. At least five hantaviruses (Sin Nombre, Bayou, viral disease characterized by fever, myalgias (muscular Black Creek Canal, New York-1, Monongahela) have pain), GI complaints, cough, difficulty breathing, and caused HPS in the United States. Other strains have hypotension (decreased blood pressure). The Sin Nombre caused HPS in South America. virus—literally, the “virus with no name”—was the Reservoirs and Mode of Transmission. Rodents, including cause of the epidemic that occurred in the Four Corners deer mice, pack rats, and chipmunks serve as reservoirs. area of the United States in the spring and summer of Transmission occurs via inhalation of aerosolized rodent 1993. Since then, sporadic cases have been reported in feces, urine, and saliva. Person-to-person transmission many states as well as in South America. does not occur. Patient Care. Use Standard Precautions for hospitalized Laboratory Diagnosis. HPS can be diagnosed by patients. immunodiagnostic and molecular procedures and by cell culture. Influenza (Flu). Influenza is an acute, viral respiratory Pathogens. Influenza is caused by influenza viruses types infection with fever, chills, headache, aches and pains A, B, and C. They are single-stranded RNA viruses in throughout the body (most pronounced in the back and the family Orthomyxovirus. Influenza A virus cause legs), sore throat, cough, nasal drainage. Influenza severe symptoms and is associated with pandemics sometimes causing bronchitis, pneumonia, and death in and severe disease and more localized outbreaks. severe cases. Nausea, vomiting, and diarrhea may occur, Influenza C virus usually does not cause epidemics or particularly in children. Although the term stomach flu is significant disease. often heard, influenza viruses rarely cause GI symptoms. Reservoirs and Mode of Transmission. Infected humans Stomach flu, also known as the 24-hour flu, is caused by are the primary reservoir; pigs and birds also serve as viruses other than influenza viruses. reservoirs. Because pig cells have receptors for both Patient Care. Use Droplet Precautions for hospitalized avian and human strains of influenza virus, pigs serve patients, usually for 5 days from onset of symptoms. as “mixing bowls,” resulting in new strains containing RNA segments from both avian and human strains. It is thought that the 1918 pandemic was caused by an avian influenza virus that jumped directly from birds to humans. Transmission occurs via airborne spread and direct contact. Laboratory Diagnosis. Influenza is diagnosed by isolation of influenza virus from pharyngeal or nasal secretions or washings using cell culture techniques, antigen detec- tion, and demonstration of a rise in antibody titer (con- centration) between acute and convalescent sera (see Chapter 16), or by molecular diagnostic procedures. 307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 315 CHAPTER 18 Viral Infections 315 TABLE 18-4 Viral Infections of the Lower Respiratory Tract (continued) DISEASE ADDITIONAL INFORMATION Avian Influenza (Bird Flu). Avian influenza, commonly re- Pathogens. Bird flu is caused by avian influenza virus ferred to as bird flu, is primarily a disease of birds, but type A. The three prominent subtypes of the virus are can cause human disease. In humans, the virus causes a designated H5, H7, and H9. The strain known as H5N1 respiratory infection with manifestations ranging from is the most virulent strain. influenza-like symptoms (fever, cough, sore throat, and Reservoirs and Mode of Transmission. Infected wild and muscle aches) to eye infections, pneumonia, acute and domesticated birds serve as reservoirs. Bird-to-human severe respiratory distress, and other severe and life- transmission occurs via contact with infected poultry or threatening complications. surfaces that have been contaminated with excretions Patient Care. Use Droplet Precautions for hospitalized pa- from infected birds. Person-to-person transmissions are tients (see http://www.cdc.gov/flu/avian/professional/ relatively rare. However, influenza viruses commonly infect-control.htm for more information). mutate, and increased instances of person-to-person transmission are likely to occur in the future. Laboratory Diagnosis. Molecular diagnostic procedures or cell culture are the means of diagnosis. Note: Additional information about bird flu can be found on the CD-ROM. Severe Acute Respiratory Syndrome (SARS). SARS is a viral Pathogen. SARS is caused by SARS-associated coronavirus respiratory illness with high fever, chills, headache, a gen- (SARS-CoV) (Fig.18-6). eral feeling of discomfort, body aches, and sometimes di- Reservoirs and Mode of Transmission. Infected persons arrhea. Most patients develop a dry cough followed by serve as reservoirs. It is possible that an unknown mam- pneumonia. SARS was first reported in Asia in February malian reservoir exists. Transmission occurs by respira- 2003. Over the next few months, the illness spread to tory droplets or by touching the mouth, nose, or eye more than 2 dozen countries in Asia, Europe, South after touching a contaminated surface or object. America, and North America. During the 2003 outbreak, a Laboratory Diagnosis. Immunodiagnostic or molecular di- total of 8,098 people developed SARS, 774 of whom died. agnostic procedures or cell culture can be used to diag- No cases of SARS have been reported since 2004. nose SARS. Patient Care. Use Standard, Airborne, Droplet, and Contact Precautions for hospitalized patients for the duration of the illness plus 10 days after resolution of fever. Use N95 or higher respiratory protection and eye protection (see http://www.cdc.gov/ncidod/sars for more information). in hospitals or cruise ships. Foodborne, waterborne, and shellfish transmission have been reported. Laboratory Diagnosis. Diagnosis is by electron micro- scopic examination of stool specimens or by immunodiag- nostic or molecular procedures. Viral Hepatitis Hepatitis, or inflammation of the liver, can have many causes, including alcohol, drugs, and viruses. Viral hepa- titis refers to hepatitis caused by any one of about a dozen different viruses, including hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV), hepa- titis D virus (HDV), hepatitis E virus (HEV), hepatitis G virus (HGV), hepatitis GB virus A (HGBV-A), hepatitis GB virus B (HGBV-B), and hepatitis GB virus C FIGURE 18-6. SARS-associated coronavirus virions. (HGBV-C). Hepatitis can also occur as a result of viral Notice the crownlike halo surrounding each virion, which diseases such as infectious mononucleosis, yellow fever, gives rise to the corona in coronavirus. (Courtesy of and cytomegalovirus infection. See Table 18-5 for infor- Dr. F.A. Murphy and the CDC.) mation about viral types, modes of transmission, and 307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 316 316 SECTION VIII Major Infectious Diseases of Humans TABLE 18-5 Common Types of Viral Hepatitis NAME AND TYPE NAME OF DISEASE OF VIRUS MODE OF TRANSMISSION TYPE OF DISEASE Type A hepatitis HAV, a nonenveloped, Fecal–oral transmission; Abrupt onset; varies in clinical (also known as HAV linear ssRNA virus in the person-to-person; infected severity from a mild illness lasting infection, infectious genus Hepatovirus, family food handlers; fecally 1–2 weeks to a severe, disabling hepatitis, and Picornaviridae contaminated foods and disease lasting several months; no epidemic hepatitis) water chronic infection Type B hepatitis HBV, an enveloped, circular Sexual or household contact Usually has an insidious (gradual) (also known as HBV dsDNA virus in the genus with an infected person; onset; severity ranges from infection and serum Orthohepadnavirus, family mother-to-infant before or inapparent cases to fulminating, hepatitis) Hepadnaviridae; the only during birth; injected drug fatal cases; chronic infections DNA virus that causes use; tattooing; needlesticks occur; may lead to cirrhosis or hepatitis and other types of healthcare- hepatocellular carcinoma associated transmission. Type C hepatitis HCV, an enveloped, linear Primarily parenterally Usually an insidious onset; (also known as HCV ssRNA virus in the genus transmitted (e.g., via blood 50%–80% of patients develop a infection and non-A, Hepacivirus, family transfusion); rarely sexually chronic infection; may lead to cir- non-B hepatitis) Flaviviridae transmitted rhosis or hepatocellular carcinoma Type D hepatitis HDV or delta virus, an Exposure to infected blood Usually has an abrupt onset; may (also known as enveloped, circular ssRNA and body fluids; contaminated progress to a chronic and severe delta hepatitis) viral satellite (a defective needles; sexual transmission; disease RNA virus) in the genus coinfection with HBV is Deltavirus necessary Type E hepatitis HEV, a spherical, Fecal–oral transmission; Similar to type A hepatitis; no nonenveloped, ssRNA virus primarily via fecally contami- evidence of a chronic form in the genus Calcivirus, nated drinking water; also family Calciviridae from person to person Type G hepatitis HGV, a linear ssRNA virus Parenteral Can cause chronic hepatitis in the genus Hepacivirus, family Flaviviridae. ds, double-stranded; ss, single-stranded types of disease. Use Standard Precautions for hospital- homosexual and bisexual men, and users of illicit drugs), it ized patients; add Contact Precautions for diapered or is now also routinely administered to U.S. children. It is re- incontinent patients. Various immunodiagnostic proce- quired for healthcare workers exposed to blood. dures are available for diagnosis of viral hepatitis. In addition to vaccination against HBV, healthcare The World Health Organization (WHO) estimates personnel practice Standard Precautions (described in that 350 million people are chronically infected with Chapter 12). Hepatitis B immune globulin can be given HBV worldwide, that about 1 million people die each to unvaccinated people who have been exposed to HBV, year as a result of HBV infections, and that more than perhaps by accidental needlestick injury. 2 million new acute clinical cases occur annually. Vaccines are available for HAV and HBV. The HAV VIRAL INFECTIONS OF THE vaccine, which contains inactivated virus grown in cell cul- GENITOURINARY SYSTEM ture, is recommended for people at increased risk of acquir- ing hepatitis A (including military personnel and others Information pertaining to viral sexually transmitted dis- traveling to regions where HAV is endemic, homosexual eases (STDs) is contained in Table 18-6. and bisexual men, and users of illicit drugs). The HBV vac- cine is a subunit vaccine, produced by genetically engi- VIRAL INFECTIONS OF THE neered Saccharomyces cerevisiae (common baker’s yeast). At CIRCULATORY SYSTEM first, only recommended for persons at high risk of ac- quiring HBV infection (such as infants born to HBV anti- Information pertaining to viral infections of the circula- gen-positive mothers, household contacts of HBV carriers, tory system is contained in Table 18-7. 307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 317 CHAPTER 18 Viral Infections 317 TABLE 18-6 Viral Sexually Transmitted Diseases DISEASE ADDITIONAL INFORMATION Anogenital Herpes Viral Infections (Genital Herpes). In Pathogens. Genital herpes is usually caused by HSV-2, but general, herpes simplex infections are characterized by is occasionally caused by HSV-1. a localized primary lesion, latency, and a tendency to Reservoirs and Mode of Transmission. Infected humans localized recurrence. In women, the principal sites of serve as reservoirs. Transmission occurs via direct sexual primary anogenital herpes virus infection are the cervix contact or oral–genital, oral–anal, or anal–genital con- and vulva, with recurrent disease affecting the vulva, tact during presence of lesions. Mother-to-fetus or perineal skin, legs, and buttocks. In men, lesions appear mother-to-neonate transmission occurs during pregnancy on the penis (Fig. 18-7), and in the anus and rectum of and birth. those engaging in anal sex. The initial symptoms are Laboratory Diagnosis. Genital herpes is diagnosed by ob- usually itching, tingling, and soreness, followed by a servation of characteristic cytologic changes in tissue small patch of redness and then a group of small, scrapings or biopsy specimens, and the presence of painful blisters. The blisters break and fuse to form multinucleated giant cells with intranuclear inclusions, painful, circular sores, which become crusted after a few and confirmation by immunodiagnostic and molecular days. The sores heal in about 10 days but may leave diagnostic procedures. scars. The initial outbreak is more painful, prolonged, and widespread than subsequent outbreaks and may be associated with fever. Patient Care. Use Standard Precautions for hospitalized patients; add Contact Precautions for severe dissemi- nated or primary mucocutaneous herpes. Genital Warts (Genital Papillomatosis, Condyloma Pathogens. Genital warts are caused by HPVs of the Acuminatum). Genital warts start as tiny, soft, moist, Papovaviridae family of DNA viruses (human wart pink or red swellings, which grow rapidly and may viruses). HPV genotypes 16 and 18 have been develop stalks. Their rough surfaces give them the associated with cervical cancer. appearance of small cauliflowers. Multiple warts often Reservoirs and Mode of Transmission. Infected humans grow in the same area, most often on the penis in men serve as reservoirs. Transmission occurs via direct con- and the vulva, vaginal wall, cervix, and skin surrounding tact, usually sexual; through breaks in skin or mucous the vaginal area in women. Genital warts also develop membranes; or from mother to neonate during birth. around the anus and in the rectum in men or women who Laboratory Diagnosis. Genital warts are usually diagnosed engage in anal sex. These warts can become malignant. clinically. Molecular diagnostic procedures are available. FIGURE 18-7. Herpes simplex lesions on a penile shaft. (From Harvey RA, et al. Lippincott’s Illustrated Reviews: Microbiology, 2nd ed. Philadelphia: Lippincott Williams & Wilkins, 2007.) 307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 318 TABLE 18-7 Viral Infections of the Circulatory System DISEASE ADDITIONAL INFORMATION HIV Infection and AIDS. The signs and symptoms of acute Pathogens. AIDS is caused by HIV (refer back to Fig. 4-13 in HIV infection (i.e., infection with “the AIDS virus”) usually Chapter 4). Two types have been identified: type 1 (HIV- occur within several weeks to several months after infec- 1), which is the most common type, and type 2 (HIV-2). tion with HIV. Initial symptoms include an acute, self- HIV viruses are single-stranded RNA viruses in the family limited mononucleosis-like illness lasting 1 or 2 weeks. Retroviridae (retroviruses). Unfortunately, acute HIV infection is often undiagnosed or Reservoirs and Mode of Transmission. Infected humans misdiagnosed, because anti-HIV antibodies are usually not serve as reservoirs. Transmission occurs via direct sexual present in a high enough concentration to be detected dur- contact (homosexual or heterosexual); sharing of con- ing this early phase of infection. Other signs and symptoms taminated needles and syringes by intravenous drug of acute HIV infection include fever, rash, headache, lym- abusers; transfusion of contaminated blood and blood phadenopathy, pharyngitis, myalgia (muscle pain), arthral- products; transplacental transfer from mother to child; gia (joint pain), aseptic meningitis, retro-orbital pain, breast-feeding by HIV-infected mothers; transplantation weight loss, depression, GI distress, night sweats, and oral of HIV-infected tissues or organs; and needlestick, or genital ulcers. Without appropriate anti-HIV treatment, scalpel, and broken glass injuries. There is no evidence approximately 90% of HIV-infected individuals ultimately of HIV transmission via biting insects. Most likely, HIV-1 develop AIDS. AIDS is a severe, life-threatening syndrome first invades dendritic cells in the genital and oral that represents the late clinical stage of infection with HIV. mucosa. These cells then fuse with CD4⫹ lymphocytes Invasion and destruction of helper T cells (see Chapter 16) (helper T cells) and spread to deeper tissues. leads to suppression of the patient’s immune system (im- Laboratory Diagnosis. Immunodiagnostic procedures are munosuppression). Secondary infections caused by viruses available for detection of antigen and antibodies. Most (e.g., cytomegalovirus, herpes simplex), protozoa (e.g., HIV-infected patients develop detectable antibodies Cryptosporidium, Toxoplasma), bacteria (e.g., mycobacteria), within 1–3 months after infection. However, there may and/or fungi (e.g., Candida, Cryptococcus, Pneumocystis) be- be a more prolonged interval of up to 6 months, or even come systemic and cause death. Persons with AIDS die as a longer in some cases. The most commonly used screening result of overwhelming infections caused by a variety of test is an enzyme-linked immunosorbent assay (ELISA). If pathogens, often opportunistic pathogens. Kaposi’s sar- the screening test is positive, a confirmatory test such as coma, a previously rare type of cancer, is a frequent com- the Western blot analysisa or indirect fluorescent plication of AIDS, thought to be caused by a type of herpes antibody test is usually performed. Antigen detection virus called human herpesvirus 8. Previously considered to procedures detect an HIV antigen known as p24. be a universally fatal disease, certain combinations of Molecular diagnostic procedures are also available. drugs, referred to as cocktails, are extending the life of Quantitative assessment of viral RNA is used to monitor some HIV-positive patients. In the absence of effective the effectiveness of antiviral therapy. anti-HIV treatment, the AIDS case–fatality rate is very high—approaching 100%. (Chapter 11 contains informa- tion about the current AIDS pandemic.) Patient Care. Use Standard Precautions for hospitalized patients and appropriate Transmission-Based Precautions for specific infections that occur in AIDS patients. Infectious Mononucleosis. Infectious mononucleosis (also Pathogen. The etiologic agent of infectious mononucleosis is called “mono” or the “kissing disease”) is an acute viral Epstein-Barr virus (EBV), which is also known as human disease that may be asymptomatic or may be character- herpesvirus 4. It is a DNA virus in the family Herpesviridae. ized by fever, sore throat, lymphadenopathy (especially EBV infects and transforms B cells, although it also infects posterior cervical lymph nodes), splenomegaly (enlarged other types of cells. EBV is known to be oncogenic (cancer spleen), and fatigue. Infectious mononucleosis is usually causing), causing or being associated with lymphomas a self-limited disease of 1 to several weeks’ duration. It is (e.g., Hodgkin disease and Burkitt lymphoma), carcinomas rarely fatal. (e.g., nasopharyngeal carcinoma and gastric carcinoma), Patient Care. Use Standard Precautions for hospitalized and sarcomas, among other cancers. patients. Reservoirs and Mode of Transmission. Infected humans serve as reservoirs. Transmission occurs from person to person by direct contact with saliva. Kissing facilitates spread among adolescents. EBV can be transmitted via blood transfusion. Laboratory Diagnosis. Patients with infectious mononucleosis usually present with a lymphocytosis (abnormally high pe- ripheral lymphocyte count), including 10% or more abnor- mal lymphocyte forms, and abnormalities in liver function tests. Specific diagnosis is usually made by detection of an- tibodies. Molecular diagnostic procedures are also available. EBV can be cultured from the buffy coat—the layer of white blood cells that appears in centrifuged blood. 318 307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 319 CHAPTER 18 Viral Infections 319 CHAPTER 18 Viral Infections 319 TABLE 18-7 Viral Infections of the Circulatory System (continued) DISEASE ADDITIONAL INFORMATION Mumps (Infectious Parotitis). Mumps is an acute viral Pathogen. Mumps is caused by mumps virus, an RNA virus infection characterized by fever and swelling and in the genus Rubulavirus, family Paramyxoviridae. tenderness of the salivary glands (Fig. 18-8). Reservoirs and Mode of Transmission. Infected humans Complications can include orchitis (inflammation of the serve as reservoirs. Transmission occurs via droplet testes), oophoritis (inflammation of the ovaries), spread and direct contact with the saliva of an infected meningitis, encephalitis, deafness, pancreatitis, arthritis, person. mastitis, nephritis, thyroiditis, and pericarditis. Laboratory Diagnosis. Diagnosis of mumps is made using Patient Care. Use Droplet Precautions for hospitalized immunodiagnostic procedures or cell culture. patients until 9 days after onset of swelling. Viral Hemorrhagic Diseases. Viral hemorrhagic diseases Pathogens. Viral hemorrhagic fevers are caused by many dif- are extremely serious, acute viral illnesses. Initial symp- ferent viruses, including dengue virus, yellow fever virus, toms include sudden onset of fever, malaise (a feeling Crimean-Congo hemorrhagic fever virus, Lassa virus, Ebola of general discomfort; feeling “out of sorts”), myalgia, virus, and Marburg virus. Ebola virus and Marburg virus are and headache, followed by pharyngitis, vomiting, diar- filamentous viruses in the family Filoviridae. Both are ex- rhea, rash, and internal hemorrhaging. Case fatality tremely large viruses. Ebola virus is about 80 nm in width rates for Marburg virus infection and Ebola virus infec- and up to 1 mm or longer in length. Marburg virus is tion have been 25% and 50%–90%, respectively. All about 80 nm in width and 790 nm in length. known cases of both diseases occurred in or could be Reservoirs and Mode of Transmission. Infected humans traced back to Africa. serve as reservoirs; infected African green monkeys also Patient Care. Exercise Standard, Droplet, and Contact serve as reservoirs of Marburg virus. Transmission is from Precautions for hospitalized patients for the duration person to person via direct contact with infected blood, of the illness. Emphasize (a) use of sharps safety secretions, internal organs, or semen, or by needlestick. devices and safe work practices, (b) hand hygiene, The risk is highest when the patient is vomiting, having (c) barrier protection against blood and body diarrhea, or hemorrhaging. Crimean-Congo hemorrhagic fluids, and (d) appropriate waste handling. Use N95 fever is a tickborne disease. Dengue fever and yellow fever or higher respirators when performing aerosol- are mosquito-borne diseases, transmitted primarily by generating procedures. mosquitoes in the genus Aedes. Laboratory Diagnosis. Viral hemorrhagic diseases are diagnosed using immunodiagnostic and molecular proce- dures, cell culture, or electron microscopy. Laboratory studies of viral hemorrhagic fevers represent an extreme biohazard and should be conducted only in BSL-4 containment facilities. a A Western blot analysis is a laboratory procedure in which proteins separated by electrophoresis in polyacrylamide gels are trans- ferred (blotted) onto nitrocellulose or nylon membranes and identified by specific complexing with tagged antibodies. STUDY AID Viremia The presence of viruses in the bloodstream is known as viremia. The viruses either may be free in the plasma, or attached to or within red blood cells or white blood cells, such as lymphocytes and monocytes. The number of viruses in the bloodstream is referred to as the viral load, which may be described as being heavy or light. The degree of viremia varies from one viral disease to another, and often from one stage of a particular viral infection to another. FIGURE 18-8. Child with mumps. (Courtesy of Barbara Rice, the National Immunization Program, and the CDC.) 307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 320 320 SECTION VIII Major Infectious Diseases of Humans VIRAL INFECTIONS OF THE APPROPRIATE THERAPY FOR VIRAL CENTRAL NERVOUS SYSTEM INFECTIONS Table 18-8 contains information pertaining to viral in- Recommendations for the treatment of infectious fections of the central nervous system (CNS). diseases change frequently. The viral infections described in this chapter must be treated using appropriate antivi- ral drugs. Sources of updated information include The RECAP OF MAJOR VIRAL Merck Manual (http://www.merck.com/pubs) and INFECTIONS OF HUMANS WebMD (http://www.webmd.com). For certain diseases, serum immune globulins (e.g., varicella-zoster immune Table 18-10 provides a recap of some major viral infec- globulin) are available for treatment. Additional informa- tions of humans. tion about antiviral agents can be found in Chapter 9. TABLE 18-8 Viral Infections of the Central Nervous System DISEASE ADDITIONAL INFORMATION Lymphocytic Choriomeningitis. Lymphocytic horiomeningi- Pathogen. Lymphocytic choriomeningitis is caused by tis is a rodentborne viral disease that presents as aseptic lymphocytic choriomeningitis virus (LCMV), a member of meningitis, encephalitis, or meningoencephalitis. the family Arenaviridae. Asymptomatic or mild febrile disease also occurs. Some Reservoirs and Mode of Transmission. Infected rodents, patients develop fever, malaise, suppressed appetite, primarily the common house mice serve as reservoirs. muscle aches, headache, nausea, vomiting, sore throat, Humans become infected following exposure to mouse coughing, joint pain, chest pain, and salivary gland pain. urine, droppings, saliva, or nesting materials. The virus Possible complications of CNS involvement include deaf- can enter broken skin; through nose, the eyes, or ness and temporary or permanent neurological damage. mouth; or via the bite of an infected rodent. Organ An association between lymphocytic choriomeningitis transplantation is a possible means of transmission. virus infection and myocarditis has been suggested. Person-to-person transmission does not occur. Patient Care. Use Standard Precautions for hospitalized Laboratory Diagnosis. Diagnosis is primarily by immunodi- patients. agnostic procedures and cell culture. Poliomyelitis (Polio, Infantile Paralysis). In most patients, Pathogens. Poliomyelitis is caused by polioviruses, RNA poliomyelitis causes a minor illness with fever, malaise, viruses in the family Picornaviridae (pico ⫽ small, headache, nausea, and vomiting. In about 1% of patients, RNA viruses). the disease progresses to severe muscle pain, stiffness of Reservoirs and Mode of Transmission. Infected humans the neck and back, with or without flaccid paralysis. Major serve as reservoirs. Transmission is from person to person, illness is more likely to occur in older children and adults. primarily via the fecal–oral route; also by throat secretions. Although once a major health problem in the United Laboratory Diagnosis. Diagnosis of poliomyelitis is made States, vaccines became available in the 1950s. The WHO by isolation of polio virus from stool samples, cere- is attempting to eradicate polio worldwide. brospinal fluid (CSF), or oropharyngeal secretions using Patient Care. Use Contact Precautions for hospitalized pa- cell culture techniques or by immunodiagnostic or mo- tients for the duration of illness. lecular diagnostic procedures. Rabies. Rabies is a usually fatal, acute viral en- Pathogen. Rabies is caused by rabies virus, a bullet-shaped, cephalomyelitis of mammals, with mental depression, enveloped RNA virus in the family Rhabdoviridae. restlessness, headache, fever, malaise, paralysis, saliva- Reservoirs and Mode of Transmission. Reservoirs are tion, spasms of throat muscles induced by a slight breeze various wild and domestic mammals, including dogs, or drinking water, convulsions, and death caused by res- foxes, coyotes, wolves, jackals, skunks, raccoons, mon- piratory failure. The paralysis usually starts in the lower gooses, and bats. Transmission is usually via the bite of legs and moves upward through the body. Rabies is en- a rabid animal, which introduces virus-laden saliva. demic in every country of the world except Antarctica and Airborne transmission from bats in caves also occurs. in every state except Hawaii. Worldwide, an estimated Person-to-person transmission is rare. 35,000–40,000 people die of rabies annually. Laboratory Diagnosis. Diagnosis of rabies is made by cell Patient Care. Use Standard Precautions for hospitalized culture, antibody detection in serum or CSF, antigen de- patients. tection in tissue samples, molecular diagnostic procedures for brain tissue, or observation of Negri bodies in brain or other tissues. Negri bodies are viral RNA-nucleoprotein complexes found in the cytoplasm of virus-infected cells (i.e., they are intracytoplasmic inclusions). 307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 321 CHAPTER 18 Viral Infections 321 TABLE 18-8 Viral Infections of the Central Nervous System (continued) DISEASE ADDITIONAL INFORMATION Viral Meningitis. Viral meningitis is also known as aseptic Pathogens. The most common causes of viral meningitis in meningitis and nonbacterial or abacterial meningitis. It the United States are enteroviruses. Other causes include is a relatively common disease but, fortunately, is rarely coxsackie viruses, arboviruses, measles virus, mumps virus, serious. Acute illness rarely exceeds 10 day’s duration. herpes simplex and varicella-zoster viruses, lymphocytic Viral meningitis is characterized by sudden onset of choriomeningitis virus, and adenoviruses. Leptospirosis febrile illness with the signs and symptoms of (a bacterial disease) can also cause aseptic meningitis. meningeal involvement. CSF findings include the Reservoirs and Mode of Transmission. Reservoirs and presence of mononuclear white blood cells, increased modes of transmission vary with the specific etiologic protein levels, normal glucose levels, and the absence agent. of bacteria. A rash may develop. When caused by an Laboratory Diagnosis. During the early stages of the enterovirus, GI and respiratory symptoms may occur. disease, the viral pathogen may be isolated from throat Patient Care. Use Standard Precautions for hospitalized washings and stool, and occasionally from CSF and patients. Add Contact Precautions for infants and blood. Diagnosis is made by immunodiagnostic or young children. molecular diagnostic procedures or cell culture. Viral Encephalitis (Arthropod-borne Viral Encephalitis; Pathogens. See Table 18-9. Over the years, St. Louis Table 18-9). Arthropod-borne viral encephalitis is an encephalitis virus has been the most common mosquito- acute inflammatory viral disease. A patient with this transmitted pathogen in the United States. The situation disease may be asymptomatic or have mild fever and changed in 2002, when West Nile virus took over the headache. Severe infection is also possible, with number one spot. headache, high fever, stupor, disorientation, coma, Reservoirs and Mode of Transmission. See Table 18-9. tremors, occasional convulsions, spastic paralysis, and Person-to-person transmission is rare; possibly by trans- death. The term arboviruses is sometimes used in fusion, organ transplant, breast milk, or transplacentally. reference to viruses that are transmitted by arthropods. Laboratory Diagnosis. Many of the viruses that cause en- Patient Care. Exercise Standard Precautions for hospital- cephalitis, including arboviruses, are difficult to isolate ized patients. Transmission-Based Precautions may be from CSF by cell culture. Appropriate containment facilities necessary, depending on the etiologic agent. must be used when attempting to cultivate arboviruses. Viral encephalitis caused by arboviruses is usually diag- nosed using immunodiagnostic or molecular diagnostic procedures, or sometimes by electron microscopy. Note: Additional information about West Nile virus can be found on the CD-ROM. TABLE 18-9 Selected Arthropod-borne Viral Encephalitides of the United States DISEASE PATHOGEN RESERVOIRS VECTORS Eastern equine EEE virus, an RNA virus in the Birds, horses Aedes, Coquilletidia, Culex, encephalitis (EEE) family Togaviridae and Culiseta mosquitoes California encephalitis California encephalitis virus, an RNA Rodents, Aedes and Culex RNA virus in the family Bunyaviridae rabbits mosquitoes La Crosse encephalitis La Crosse encephalitis virus, an RNA Chipmunks, Aedes mosquitoes virus in the family Bunyaviridae squirrels St. Louis encephalitis St. Louis encephalitis virus, an RNA Birds Culex mosquitoes virus in the family Flaviviridae West Nile virus encephalitis West Nile virus, an RNA virus in the Birds, perhaps Culex mosquitoes family Flaviviridae horses Western equine encephalitis WEE virus, an RNA virus in the Birds, horses Aedes and Culex (WEE) family Togaviridae mosquitoes 307-322_18283_CH18.qxd 10/8/09 7:01 PM Page 322 322 SECTION VIII Major Infectious Diseases of Humans Recap of Some Major Viral c. variola virus TABLE 18-10 d. none of the preceding choices Infections of Humans 2. Which of the following are considered to be DISEASE VIRAL PATHOGEN oncogenic? a. Epstein-Barr virus and HPVs AIDS HIV b. HIV and Ebola virus Avian influenza (bird flu) Avian influenza viruses c. rubella and rubeola viruses Chickenpox Varicella-zoster virus d. variola and varicella viruses 3. Laboratory diagnosis of HIV infection is usually Cold sores (fever blisters) HSVs made by which of the following? Genital herpes HSVs a. electron microscopy Hantavirus pulmonary syndrome Hantaviruses b. growth of HIV in cell culture c. growth of HIV in embryonated chicken eggs Infectious mononucleosis Epstein-Barr virus d. immunodiagnostic procedures for the detection Influenza Influenza viruses of antigen and antibodies Monkeypox Monkeypox virus 4. Which of the following is also known as infectious hepatitis? Mumps Mumps virus a. HAV Poliomyelitis Polioviruses b. HBV Rabies Rabies virus c. HCV d. HDV Rubella (German measles) Rubella virus 5. Mosquitoes serve as vectors in all of the following Rubeola (hard measles) Rubeola virus viral diseases, except: Severe acute respiratory SARS-associated a. dengue fever. syndrome (SARS) coronavirus b. hepatitis. c. West Nile virus disease. Smallpox Variola virus d. yellow fever. Swine flu Swine flu viruses 6. Which of the following viruses is/are not transmitted Viral hepatitis Various hepatitis sexually? viruses a. hantavirus Warts Papillomaviruses b. HSVs c. HIV West Nile virus encephalitis West Nile virus d. papillomaviruses 7. Which of the following is a DNA virus? a. HAV b. HBV ON THE CD-ROM c. HCV Terms Introduced in This Chapter d. HDV Review of Key Points 8. Which of the following is a type of herpes virus? Insight: a. Epstein-Barr virus A Closer Look at Bird Flu b. measles virus A Closer Look at Swine Flu c. mumps virus A Closer Look at West Nile Virus d. rabies virus Increase Your Knowledge 9. Which of the following viral diseases has been Critical Thinking acquired in the United States by handling pet prairie Case Study dogs? Additional Self-Assessment Exercises a. chickenpox b. hantavirus c. monkeypox SELF-ASSESSMENT EXERCISES d. smallpox 10. The disease known as severe acute respiratory syn- After studying this chapter, answer the following multiple- drome (SARS) is caused by a type of: choice questions. a. coronavirus. 1. Which of the following is the cause of smallpox? b. herpes virus. a. vaccinia virus c. papillomavirus. b. varicella virus d. picornavirus.