Infectious Disease Class Notes PDF

Systems- Infectious Disease INFECTIOUS DISEASE The invasion of the human body by pathogen and microorganisms can produce harmful and potentially lethal consequences. The illnesses caused by such means are known as infectious diseases....

Systems- Infectious Disease INFECTIOUS DISEASE The invasion of the human body by pathogen and microorganisms can produce harmful and potentially lethal consequences. The illnesses caused by such means are known as infectious diseases. Handy Terminology Microorganisms – Organisms so small they are invisible to the naked eye and can only be seen with a microscope. Microorganisms can be pathogens or non-pathogens. All microbes are microorganisms, but not all microorganisms are microbes Infection – The presence and multiplication within a host of another living organism with subsequent injury to the host. Infectivity – The ability of an organism to enter, multiply, and survive in a host. Host – Any organism capable of supporting the nutritional and physical growth requirements of another organism. (For this class, the term host refers to humans supporting the growth of microorganisms.) Colonization – The act of establishing a presence within a host. Virulence – The disease producing potential of an invading organism. Pathogen – An organism so virulent that it is rarely found in the absence of disease. Microflora – A multitude of non-harmful bacteria inhabiting the internal and external exposed surfaces of the human body. Saprophytes – Free living organisms that obtain nutrition from dead or decaying organic materials in the environment. Opportunistic Pathogen – An organism which produces an infectious disease only when the health and immunity of the host have been severely compromised. 1 Systems- Infectious Disease Types of Interactions Between Host and the Colonizing Microorganisms Commensalism – The multitude of non-harmful bacteria inhabiting the internal and external exposed surfaces of the human body (microflora) acquire survival needs from the host, but the host is not adversely affected by this relationship. This is known as commensalism, and the microflora is also referred to as commensal flora, normal flora, resident microbiotica. Locations of normal flora in the human body are: Skin Nose/Pharynx Mouth Colon/Rectum Vagina/Distal Urethra/Perineum Mutualism – An interaction in which colonizing organism and host both derive benefits. E.g., Some bacteria that live in the intestines and feed off of undigested food also produce vitamins beneficial to humans. Parasitic – An interaction in which a colonizing organism benefits and the host sustains injury. Agents of Infection Disease Prions Protein particles that lack any kind of demonstrable genetic material. They are mutated forms of a normal host protein. Prions may affect other normal proteins and alter them. They aggregate in the brain and form plaques. They have been identified in a number of incurable and transmissible degenerative neurological diseases o Creutzfeldt-Jakob disease o Kuru o Mad Cow disease The defective protein may be inherited. Cannibalism has also been implicated as a transmission mechanism. It is hypothesized that humans can acquire prions by eating animals that are infected by a prion disease like Mad Cow Disease. Because prions lack reproductive and metabolic functions, the current antimicrobial agents are useless against them. Treatment is palliative. 2 Systems- Infectious Disease Rickettsia, Chlamydia, Coxiella, Mycoplasma These organisms combine the characteristics of viruses and bacteria. All are obligate intracellular pathogens like viruses Most produce a rigid peptidoglycan cell wall, reproduce asexually, and contain RNA and DNA like bacteria. Rickettsia – Tiny gram negative bacteria that live inside a host cell (obligate intracellular parasites). They are transmitted by insect vectors and cause diseases like typhus, and Rocky Mountain Spotted Fever. They cause a typical rash, and cause small hemorrhages. Chlamydia – A primitive organism related to bacteria that lack many of the enzymes needed for metabolic processes. It causes a very common sexually transmitted infection which can lead to pelvic inflammatory disease, and sterility in women. Infants born to infected mothers can develop eye infections and pneumonia. Coxiella – Causes Q fever, and illness that presents with flu-like symptoms, and cause progress to become systemic affecting the heart, lungs, and GI. Mycoplasmas – Commonly cause pneumonia. These organisms lack a cell wall, therefore they are not affected by antimicrobial drugs. Fungi Fungi – Free living eukaryotic saprophytes found in every habitat on earth. Some are part of the normal human microflora. Few fungi are capable of causing disease in human, and most of these are limited infections of skin and subcutaneous tissue. Candida is a harmless fungus normally present on the skin. It may cause infection in the oral cavity and is a common cause of vaginal infection. Candida can also become opportunistic in immunosuppressed patients. Serious fungal infections are rare, but can be life threatening when host defences have been disabled. There are two types of fungi: 1. Yeast – Single celled organisms about the size of RBCs. They reproduce asexually through a budding process. 2. Molds – Grow in long filaments called hyphae. A limited number of fungi are capable of growing as yeasts at one temperature, and molds at another. Yeasts and molds produce a rigid cell wall layer that is chemically unrelated to the peptidoglycan of bacteria and is therefore not susceptible to the effects of antibiotics. 3 Systems- Infectious Disease Parasites The term parasite has evolved to designate members of the animal kingdom that infect and cause disease in other animals. They include Protozoa – unicellular eukaryotes that may reproduce sexually or asexually. Most are saprophytes. Some are pathogenic to humans (e.g., malaria, amoebic dysentery, giardiasis, trichomonas vaginitis) Helminths (a.k.a. worms) – Roundworms, tapeworms, flukes. They reproduce sexually. Arthropods – Tics, mosquitoes, biting flies, lice, fleas, mites. Mechanism of Infection Epidemiology - The study of factors, events, and circumstances that influence the transmission of infectious disease in human populations. It focuses on: Incidence of disease (number of new cases) Prevalence of disease (number of active cases at any given time) The source of infection The portal of entry The site of infection Virulence factors Signs and symptoms The clinical course of a disease. The ultimate goal of epidemiologic studies are the interruption of the spread of infectious disease and its eradication. Source of Infection – Refers to the host, object, location, or substance from which an infectious agent is acquired. This involves different modes of transmission as well. Endogenous – Acquired form the host’s own microbial flora, as in the case of opportunistic infection. Exogenous – Acquired from sources in the external environment, such as water, food, soil, and air. Source of infection can be another person. E.g., transmission of illness from mother to child during gestation (congenital infections). Contact transmission occurs from transfer of microbes by physical contact. This may be direct or indirect. Droplet transmission occurs when microbes are spread across a short distance (less than one meter) by droplets. This happens after someone sneezes or coughs. Airborne transmission occurs when microbes are transmitted by air currents across long distances (more than one meter). Microbes are carried on evaporated droplets, or dust particles. 4 Systems- Infectious Disease Vector born transmission – animals, or biting arthropods transmit microbes to humans. Vehicle born transmission occurs when infection is transmitted by a contaminated source (vehicle). Common vehicles of transmission are food, water, medication, and invasive medical equipment, as well as bodily fluids. Locations may be sources of infection. When infection is acquired during hospitalization, or from a health care facility, they are known as nosocomial infections (or hospital acquired infections). Infections acquired outside of health care settings are called community acquired. Portal of Entry refers to the process by which a pathogen enters the body and gains access to susceptible tissue. Penetration – Any disruption in the integrity of the body’s surface barrier (skin or mucous membrane) is a potential site for invasion. This can happen from: Abrasions, burns, penetrating wounds Medical procedures such as IV administration, or catheterization Primary infectious process that produces surface lesions such as chicken pox Arthropod bite Direct contact – Pathogens are transmitted directly from infected tissue or secretions to exposed, intact mucous membranes. This includes: Sexual contact Congenital infections – when a pathogen crosses the placenta to infect a fetus during birth when the baby comes in contact with infected vaginal secretions. Ingestion – Entry of infectious agent occurs through oral cavity and GI tract. Contaminated food or water Through breast feeding Inhalation – Entry of infectious agents through respiratory tract. Droplet infection Airborne infection Site of Infection – refers to the part of the body that is infected. Local infection occurs in one body part e.g., an eye infection Systemic, or generalized infection involves the whole body. 5 Systems- Infectious Disease Pathogenicity and Virulence Pathogenicity is the capacity of a microorganism to cause disease (can make you sick). Virulence is the degree of pathogenicity of a pathogen (how easily can you get sick with it). Virulence is based on the following: Invasive qualities Toxic qualities Adherence to tissue Ability to avoid host defences Control of Transmission of Infection Universal precautions include hand washing, wearing gloves, and personal protective clothing. Hand washing is the most effective way to stop the spread of most common pathogens. Reservoir or source of infection must be located and removed. Portal of exit of microbes should be blocked (like by covering your mouth when you cough) Knowledge of the mode or modes of transmission of a pathogen is essential to block transmission. Reduce host susceptibility by immunization, proper diet, and nutrition. Adequate cleaning of surroundings and clothing. Use of disinfectants (that destroy microorganisms and their toxins on inanimate objects) and antiseptics (that are applied to the skin, to destroy microorganisms) Sterilization of fomites – inanimate objects capable of transmitting pathogens – by methods such as autoclaving. 6 Systems- Infectious Disease Symptomatology Symptomatology (a.k.a. clinical picture; disease presentation) – Refers to the collection of signs and symptoms expressed by the host during the disease course. They include: Fever and chills Increased pulse and respiratory rates Aches, pain, or tenderness Fatigue and loss of energy Loss of appetite, nausea, vomiting, and diarrhea Rash, redness, and swelling of a body part Sores on mucous membrane Disease Course The disease course can be divided onto several distinguishable phases. 1. Incubation period – pathogen begins active replication without producing symptoms 2. Prodromal stage – initial appearance of symptoms 3. Acute stage – the host experiences maximum impact of the infectious process – host experiences the most symptoms. 4. Convalescent stage – containment of infection, progressive elimination of the pathogen, repair of damaged tissue, and resolution of associated symptoms 5. Resolution stage total elimination of pathogen from the body with no residual s/s. There are some exceptions to the classical presentation. Chronic infections – continuous s/s for months or years without a convalescent stage Subclinical (sub-acute) illness – progresses from infection to resolution without clinically apparent symptoms Insidious – prodromal phase is gradual Fulminant – abrupt onset of illness with little or no prodromal phase. 7 Systems- Infectious Disease Diagnosis and Treatment Diagnosis (Dx) is based on: History Physical examination Culture Serology Treatment (Tx) Antimicrobial agent Immunotherapy Surgical intervention 8 Systems- Infectious Disease BACTERIAL INFECTIONS Bacteria are microscopic, single celled organisms (prokaryotes). There are thousands of different kinds, and they live in every conceivable environment. Only a few kinds of bacteria cause disease. Sometimes the bacteria that usually reside harmlessly in the human body may cause disease. Bacteria can cause disease by producing toxins, invading tissue, or both. Classification of Bacteria Scientific Names Bacteria are classified by species. Within a species there may be different types called strains. Strains differ in genetic makeup, and chemical components. Staining Bacteria may be classified by the colour they turn after they are treated with certain chemicals (stains). The most common stain is Gram Stain. Gram-positive bacteria turn purple when stained. Gram-negative turns pink when stained. Gram-positive and -negative bacteria have differences in their cell wall structure. They cause different infections, and they response differently to antibiotics. Shapes All bacteria may be classified as one of 3 basic shapes. 1. Spheres (cocci) 2. Rods (bacilli) 3. Spirals (spirillum) Oxygen Need Bacteria are classified by whether they need oxygen to live and grow. Aerobes need oxygen Anaerobes live without oxygen Facultative can live with and without oxygen 9 Systems- Infectious Disease Bacterial Structure Outer ridge cell wall – protects the bacteria and provides a specific shape. Cell membrane – located inside the cell wall, it controls movement of nutrients, other materials, and metabolic processes. External capsule- an external capsule is found on some bacteria outside of the cell wall. Flagella – some bacteria have flagella (whips) attached to the cell wall to provide motility. Pili or fimbriae – tiny hair like structures found on some bacteria, usually the gram- negative class. Spores – a latent form of bacteria with a coating that is highly resistant to heat and other adverse conditions. It provides bacteria with a long survival time. Tetanus and botulism can remain dormant as spores in soil. If they enter the body, they may return to a vegetative state. Toxins and enzymes may be secreted by bacteria. There are two types of toxins: Exotoxins – usually secreted by gram positive bacteria. They diffuse through the body. Examples include neurotoxins secreted by tetanus bacillus, and enterotoxins secreted by enteric bacteria. Endotoxins – are present in the cell wall of gram negative bacteria. They are released when the bacteria dies. Endotoxins cause fever, general weakness, and serious circulatory effects like endotoxic shock. Enzymes – produced by some bacteria and cause damage to the host tissue. E.g. hemolysin produced by hemolytic streptococci cause damage to red blood cells. 10 Systems- Infectious Disease Bacterial Defences Bacteria have different ways to defend themselves from the host’s immune system. Biofilm – Some bacteria secrete a substance that helps them to attach to other bacteria, cells, or body tissues. Dental plaque is an example of biofilm. Capsule – Some bacteria are enclosed in a protective capsule. This helps to protect them from ingestion by macrophages. Outer membrane/cell wall – Gram-negative bacteria have an outer membrane that protects them from effects of antibiotics. When disrupted, this membrane releases endotoxins. Spores – Some bacteria produce spores. Spores enable bacteria to survive when environmental conditions are difficult. When reintroduced to a hospitable environment, spores germinate and become active bacteria. Flagella – Long thin filaments that project from a cell wall and enable bacteria to move from one place to another. Antibiotic resistance – Bacteria can develop resistance to drugs because their genes can mutate. E.g., Certain types of staphylococcus aureus have developed resistance to penicillin, and methicillin. These are known as Methicillin Resistant Staphlococcus Aureus (MRSA). Bacterial Diseases Staphylococcal (Staph) Infections There are more than 30 strains of staphylococcus. Most infections are produced by staph aureus. Common infections are: Skin infections, like furuncles (boils) Cellulitis, an acute infection of subcutaneous tissue Pneumonia Food Poisoning Breast abscesses in nursing mothers Postoperative infections Toxic shock syndrome Blood infections (bactemia) 11 Systems- Infectious Disease Streptococcal (Strep) Infections Strep comes in strains from A to G. The most common infections arise from group A and group B strep. Group A strep is a bacterium commonly found in the throat and on the skin. Group A strep bacteria can cause a range of infections from relatively mild sore throats and skin infections to life threatening invasive disease. Strep A is spread by person to person contact Symptoms usually start 1-3 days after exposure9 S/S depend on type of infection, but typically strep infections present with cardinal S/S of inflammation Strep A causes: Strep throat – Bacteria resides in the nose and throat. May spread person to person from inhaling droplets that are coughed or sneezed out of an infected person. Droplets on the hand of an infected person may be spread to another by hand shaking (wash your hands). S/S of strep throat usually develop within 3 days of exposure. They include red and white patches on the throat, difficulty swallowing, tender, swollen glands, enlarged tonsils, HA, fever, abdominal pain, anorexia, nausea, and general malaise. Scarlet fever – bacterial toxins cause a scarlet coloured rash. Impetigo – a skin infection Toxic Shock Syndrome Necrotizing Fasciitis (fleshing eating disease) – Severe inflammation and tissue necrosis due to infection by a highly virulent strain of strep A. It invades tissues rapidly, reducing the blood supply and secretes enzymes that digest tissue. Systemic toxicity may lead to organ failure. Group B strep is carried by most people without causing illness. However, when the body’s immune system is weakened, it can cause serious infection. Group B strep may be transmitted to newborns from their mothers. It is the most common cause of blood infections and meningitis in newborns. Strep B causes: Urinary Tract Infections (UTI) Blood infections Skin infections Pneumonia 12 Systems- Infectious Disease Some Common Diseases Caused by Bacteria Rheumatic Fever An inflammatory disease that may develop after a strep infection (e.g., strep throat or scarlet fever). The disease may affect the heart, joints, skin, and brain. It may lead to endocarditis, and be an issue later in life. Rheumatic fever mainly affects children from ages 6-15. S/S include: Abdominal pain Fever Cardiac problems that may be asymptomatic, or present with dyspnea (shortness of breath) or chest pain Joint pain, joint swelling Nosebleeds (epistaxis) Shin nodules A ring, or snakelike rash Bacterial Meningitis A serious infection of the protective membranes of the brain and spinal cord (meninges). (Often caused by hemophilus influenzae type b, Neisseria meningitdis, or streptococcus pneumoniae bacteria (DW)). S/S includes high fever, headache, stiff neck, nausea, and vomiting. Patients will be positive for Brudzinski’s Sign (neck flexion will cause hip and knee flexion) or Kernig’s Sign (extreme pain with hip flexion and knee extension) Bacteria may spread by direct close contact with the discharges from the nose or throat of an infected person. Treated with antibiotics Prevention depends on the use of vaccines, rapid diagnosis, and prompt Tx of close personal contacts. 13 Systems- Infectious Disease Respiratory Tract Infections Upper respiratory tract infections include infections like strep throat. Lower respiratory infections include bacterial pneumonia and bronchitis. Pneumonia is infection of lung parenchyma. It is commonly caused by strep pneumoniae, staph aureus, and hemophilus influenza. The bacteria may be inhaled, or enter the lungs via the blood stream. S/S include high fever, cough, dyspnea, and chest pain. Acute bronchitis is infection of the bronchioles. It has similar S/S to pneumonia, although it is generally less painful, and breathing is easier than with pneumonia. Tx for both is antibiotics. Tuberculosis is an infection caused by mycobacterium tuberculae. It is a bacteria with a waxy capsule that makes it hard for macrophages to destroy them. The bacteria may remain dormant in granulomas in the lungs called Ghon Foci. If the Ghon Foci rupture, then an active case of tuberculosis begins. The bacteria may spread to any part of the body, and cause inflammation and damage to lunch parenchyma. Enteric Bacterial Infections These are infections of the intestines. Some of the bacteria that cause enteric selections are: Escherichia coli (e. coli) Vibrio cholera (causes cholera) Salmonella Shigella Anaerobic streptococci Salmonella Infection – There are more than 2000 varieties of salmonella. Little more than ten of them are pathogenic to humans. Most salmonella infections are known as gastroenteritis. S/S start 12-72 hours after exposure to bacterium. They last for 507 days. It usually resolves without treatment in most people. Symptoms include nausea, vomiting, diarrhea, abdominal cramps, and fever. 14 Systems- Infectious Disease A few varieties of salmonella can lead to typhoid fever. This is sometimes a deadly disease more common in developing countries. Incubation period ranges from 5-21 days. S/S lasts 7-10 days. Symptoms include diarrhea or constipation, high fever, bradycardia, raised red spots on the upper chest, and enlargement of the liver and spleen. Tx with antibiotics. Shigella Infection (a.k.a. Shillosis) is a common infection settings where hygiene is poor. It is spread via the fecal oral route (gross). S/S start 2 days after exposure and resolve after 5-7 days. Symptoms include fever, diarrhea (often blood) abdominal cramps and dehydration. Tx is usually palliative, and antibiotics may be used. Anti-diarrheals should be avoided. Prevention is by hygienic food preparation, and hand washing. Bacterial Infections of the Urinary Tract These infections affect the urethra, urinary bladder, ureters, and kidneys. They are commonly caused by e. coli, pseudomonas aeruginosa, and klebsiella. S/S include urinary frequency and urgency, dysuria, lower abdominal pain, and flank pain. Dx based on urine test and culture Proper hygiene may prevent UTIs. Tx with antibiotics. Lyme’s Disease The most common tick-borne infection in the northern hemisphere. Early S/S include headache, fever fatigue, depression. These are followed by a target shaped rash known as erythema migrans or “bulls-eye rash” Later may involve joints, heart and CNS. Tx is by antibiotics- is a difficult illness to treat. Some patients must be treated with doses of antibiotics for years. 15 Systems- Infectious Disease VIRAL INFECTIONS Viruses are the smallest obligate intracellular pathogen. They have no organized cellular structure. Rather, they consist of a protein coat (a.k.a. capsid) surrounding a nucleic acid core of RNA or DNA. Some viruses are enclosed within a lipoprotein envelope derived from the cytoplasmic membrane of a parasitized host cell. How do Viruses Work? Viruses are incapable of replication outside of a living cell. They must penetrate a living cell and use the biosynthetic machinery of the host cell to produce viral progeny. The virus will attach to a host cell, enter it, and then release its genetic material. The virus’s genetic material takes control of the cell and forces it to replicate the virus. The host cell will usually die as it can’t perform its normal function. When the infected cell dies, it releases the viral replications, which can go on to infect other cells. Sometimes the virus will not kill the infected cell, but alter the cell’s function. The cell is at risk of becoming cancerous. Some viruses leave their genetic material in a host cell. It may remain dormant there for an extended period of time. The virus will begin replicating after this dormancy period and cause disease. Routes of Viral Invasion Nasal and respiratory Oral and gastrointestinal Through blood and bodily fluids (needles, bites, STI’s) The Body’s Response to Viral Infections Inflammatory response – vascular congestion and leakage of exudate Immune response – collection of lymphocytes in infected tissue. Medical treatment is supportive and may involve the use of anti-viral drugs. Prevention is by immunization. Because viruses are not bacteria, antibiotics do not work against them. 16 Systems- Infectious Disease Types of Viral Infection Childhood Viral Infections Poliomyelitis An acute viral infection that can affect the nervous system. It may lead to full or partial paralysis. Caused by poliovirus There are 2 types – paralytic, and non-paralytic Highly contagious – can spread by contact with infected mucous or phlegm, or from infected feces The virus enters through the mouth and nose. Multiplication occurs in lymphoid tissue of the throat and GI tract. This is followed by invasion of the CNS. The incubation period is 5-35 days. Prophylaxis is by immunization. Rubeola (Measles) A highly contagious respiratory inflection Caused by paramyxovirus Causes a total body skin rash with flu like symptoms including fever, cough, and runny nose Treatment is palliative Prophylaxis is by immunization Rubella (German Measles) Caused by rubella virus (CA – this is not the same as rubeola in spite of similar names) Primarily affects skin and lymph nodes Can be spread by inhaling infected droplets It can also pass through the placenta from the mother to the foetus. This can lead to congenital rubella syndrome – may lead to visual and hearing impairments, heart disease, spleen, liver, bone marrow abnormalities, and thrombocytic purpura (blueberry muffin rash) Symptoms include fever, headache, general malaise, runny nose, skin rash. S/S are more severe in adults than in children Infection results in lifelong immunity Prophylaxis is by immunization 17 Systems- Infectious Disease Mumps Viral infection that is spread through saliva. Primarily affects parotid glands. S/S – fever, headache, arthralgia, loss of appetite, followed by pain and swelling of parotid glands Infection is uncommon under 1 year of age Very unusual to have a second infection – the first infection will yield lifelong immunity Tx aimed at reducing pain Chicken Pox A common, preventable childhood infection caused by the Varicella-Zoster virus. Usually mild, but uncomfortable in children. More sever in adults. Spreads by direct contact, and droplet transmission Can be spread to fetus from infected mother S/S – fever, followed by an itchy rash which changes to fluid filled blisters which break and scab Most cases result in lifelong immunity. There are some instances where it can occur more than once. Prophylaxis by immunization Shingles aka Zona aka Herpes-Zoster This is not a childhood illness, but only occurs in people who have had a chicken pox. The virus remains dormant in the dorsal root ganglia for years. It usually gets activated by stress. Less contagious, as it does not spread through droplet transmission It leads to an acute CNS infection involving primarily the DRG. S/S include neuralgic pain, and vesicle eruption on the skin. Rash resembles chicken pox. It presents in a dermatomal pattern consistent with the DRG in which the virus was dormant. If you are susceptible to Chicken Pox (i.e., you aren’t immune) you can catch Chicken Pox from Shingles. You cannot catch Shingles from Shingles. 18 Systems- Infectious Disease Common Viral Infections The Common Cold A mild infection of the upper respiratory tract. Caused by several different viruses including rhinovirus, adenovirus and coronavirus. S/S – sneezing, stuffy nose, sore throat, coughing They may last 2-14 days Highly contagious – can be spread in droplets that are spread by sneezing or coughing, direct or indirect contact Influenza (the Flu) A viral infection of the lower respiratory tract. May be mild, or life threatening. There are three types of influenza virus – A, B, and C. They are further sub-categorized based on two surface antigens: hemagglutinin and neuraminidase (DW). Examples of Types A Influenza include H1N1, H5N1, and H3N2. Occurs every two to three years in epidemics. Has a high mortality rate among the elderly S/S – chills, fevers, headache, arthralgia, sore throat, cough Can lead to life threatening complications, and lead to secondary infections like pneumonia Spread in the same manner as the common cold Influenza virus is constantly mutating. This gives rise to different antigen presentations. For this reason, you may become infected with ‘flu many times. The genetic material inside a virus may also mutate so that a virus that previously couldn’t infect humans can now be infectious. These viruses often come from birds and pigs. These viruses are quite virulent as they are a brand new entity to the immune system. SARS and MERS Severe acute respiratory syndrome (SARS) is an illness caused by a new form of coronavirus. It is thought to have originated in civets (a type of cat) in China. The virus is spread by close person to person contact. Between 2002 and July 2003 it had spread to infect people in 37 different countries. Toronto was a hot spot for the disease which caused the WHO to issue a travel advisory to anyone wanting to visit Toronto. Initially SARS infection presents with cold like symptoms A high fever – over 38C is a key diagnostic sign The virus will eventually spread to the lower respiratory tract causing pneumonia that is fatal in 10% of cases Treatment is palliative with special attention to the reduction of fever. No vaccines or specific medications are available; O2 supplied as needed 19 Systems- Infectious Disease Since 2004, there have been no reported cases of SARS anywhere in the world. However, in 2012, a new corona virus was identified in Qatar and Saudi Arabia. This new virus cases a SARS like illness in those infected with it. It has been dubbed Middle East respiratory syndrome (MERS). Intestinal Flu (Viral Enteritis, Gastroenteritis – Con Al – while the names are similar, this is not the same as influenza) The most common type of gastrointestinal infection Spread through contaminated food or water. Also, the dreaded fecal oral route. Children are usually affected. Lasts one to two days (sometimes called 24-hour flu) S/S – nausea, vomiting, diarrhea, malaise, low grade fever, abdominal pain Tx is palliative Herpes Simplex Infections There are 2 types of herpes infections: Type 1 Causes oral and skin lesions on or near the lips called “cold sores” or “fever blisters” After initial infection, the virus stays dormant in nerve cells Flare ups are precipitated by stress or febrile illness Transmitted by direct contact Can cause fata encephalitis Type 2 Causes genital infection After initial infection, the virus stays dormant in nerve cells, just like Type 1 May be transmitted during childbirth. Can produce a fatal disseminating neonatal infection. Human Papilloma Virus (HPV) There are more than 100 types of HPV. Most are harmless, and cause warts (verrucae). Only 30 types give risk of cancer. These types usually affect genitals, and are spread through sexual contact. Warts cause proliferative lesions of squamous epithelium. HPV is associated with an increased risk of developing cervical cancer. In recent years, a marked increase in oral and pharyngeal cancers in men has been attributed to HPV. There is a vaccine that can prevent HPV infection. 20 Systems- Infectious Disease Mononucleosis (the kissing disease) Mono is caused by the Epstein-Bar virus. Saliva is the primary method of transmitting mono (which is where it gets its nickname from), but it can also be spread by coughing and sneezing, or by sharing infected eating utensils or drinking glasses. Incubation period is 4-6 weeks S/S – fever, sore throat, generalized lymphadenopathy (swollen lymph glands), lethargy, splenomegaly, hepatitis, and atypical lymphocytes. Lasts for weeks, in some people months to years. Generally, more common amongst teenagers and young adults. Virus remains in the body and can become active without symptoms later in life Human Immunodeficiency Virus (HIV) HIV is the virus that leads to Acquired Immune Deficiency Syndrome (AIDS). Spread by contact with infected bodily fluids (blood, or semen) Virus first presents with mild flu like symptoms and then lies dormant until a later time The virus remains dormant for years. When it reactivates, it attacks T-cells As T-cells die, the immune system is unable to defend the body against infection. Death is usually due to pneumonia, or other opportune infection. Viral Hepatitis A diffuse inflammatory disease of the liver. It is caused by several different viruses (HAV, HBV, HCV, HDV, HEV). General S/S are nausea, vomiting, malaise, fever, headache, dark urine, jaundice, enlarged liver, excess bruising, and pain in the abdomen. Hep A Caused by enterovirus An acute infection – there is no chronic stage, is not progressive, and does not cause permanent liver damage. Spread by contaminated food and water Occurs sporadically, or in epidemics Incubation is roughly 30 days Immune system makes antibodies that confer immunity to future infection Prophylaxis through immunization 21 Systems- Infectious Disease Hep B A more serious health problem – has chronic stage/carrier state. 2-6 month incubation period Spread by contaminated feces, bodily fluids including saliva, contaminated breaks in the skin, sex, or contaminated tissue transplant. Prophylaxis through immunization leads to cirrhosis Hep C Serious disease – often becomes chronic and leads to cirrhosis of the liver, and liver cancer Incubation period is 2 weeks to 6 months Spread is similar to Hep B Hep D Hep D virus is only present with Hep B infection Fulminant hepatitis and liver cirrhosis are more common with Hep D infection than with a Hep B infection Hep E Clinically resembles Hep A – no chronic stage Transmitted by fecal oral route. SEXUALLY TRANSMITTED INFECTIONS Sexually Transmitted Infections (STIs) is a term to describe any infectious condition that is spread through sexual contact. The agents of infection include bacteria, viruses, chlamydia fungi, protozoa, and parasites. Portals of entry include the genitals, mouth, urinary meatus, rectum, and skin. Rates of STIs are highest among adolescents, but any sexually active person may contract one. Rates are higher with people who have more than one sex partner. Incidence of STIs are increasing, and it is estimated that many cases go unreported. Good sexual hygiene is important to control the spread of STIs. This includes the use of condoms – a new one each time – and proper cleaning of sex toys between uses. Sexually active people in non-monogamous should get regular STI tests. 22 Systems- Infectious Disease Condylomata Acuminata (Genital Warts) Caused by Human Papilloma Virus Most cases are asymptomatic, and resolve without treatment Some infections result in warts on the genitals May lead to cervical cancer – possible link to oropharyngeal cancers There is currently a vaccine to prevent HPV infection. Candidiasis (Yeast Infection, Thrush) Not strictly an STI Candida albicans is the most common yeast to cause infection Common vaginal infection – 75% of women of reproductive age will experience one in their lifetime Men may have candida on their penis, but usually do not experience s/s The yeast may also be in the gastrointestinal tract – auto-inoculation is possible Causes vaginal pruritis, erythema, swelling, dysuria, and dyspareunia Typical vaginal discharge is usually thick, white, and odourless Treated with anti-fungal medications. Trichomoniasis Caused by an anaerobic protozoa. A more common infection than Gonorrhea – often considered a marker for high risk sexual behaviour. The protozoa can live in the paraurethral glands of both sexes. Men generally remain asymptomatic. In women, greater than > 75% develop symptoms. Symptoms include copious, frothy, malodorous, green or yellow discharge. Small hemorrhagic areas may appear on the cervix – known as “strawberry spots”. May lead to tubal infertility in women, and atypical pelvic inflammatory disease. Can lead to infertility, altered sperm motility, and chronic prostatitis in men. Treated with systemic anti-protozoan medications. 23 Systems- Infectious Disease Chlamydia Infection One of the most common STIs in North America. In women, typical symptoms include mucopurulent cervical discharge, urinary frequency, and dysuria. The cervix hypertrophies, and becomes erythematous, edematous, and extremely friable. May lead to fallopian tube damage. Left untreated it may lead to PID. In men, s/s include urethritis, meatal tenderness and rubor, urethral pruritis, discharge, and dysuria. Prostatitis and epididymitis may develop and lead to infertility. Left untreated may lead to Reiter syndrome – a reactive arthritis that leads to conjunctivitis, urethritis, and mucocutaneous lesions (can’t see, can’t pee, can’t dance with me). 75% of women and 50% of men have no symptoms, so many cases go untreated – it is a good idea for every sexually active person to undergo routine STI screening. May be treated with antibiotics. Gonorrhea Caused by Nisseria Gonorrhea bacteria 90% of cases occur in those between 15 and 44 years old, women are more likely to be infected compared to men. After years of declining rates of infection, incidence is now on the rise. Usually spread through intercourse (vaginal or anal), but auto-inoculation to the conjunctiva is possible. Babies born to infected mothers are at risk of contracting gonorrheal conjunctivitis – may lead to permanent blindness. In men, the infection starts in the anterior urethra, and may spread proximally in the genital tract. Symptoms include urethral pain, dysuria and creamy yellow or blood urethral discharge. May become chronic and infect the epididymis, and prostate. In women, symptoms include unusual vaginal discharge, dysuria dyspareunia, pelvic pain, proctitis, and fever. Symptoms may fluctuate with menses. Chronic infections may lead to salpingitis with subsequent scarring and infertility. May invade the circulatory system of both men and women and cause sequelae in joint spaces, heart valves, meninges, and other tissues of the body. Many cases are asymptomatic – people may unwittingly spread the infection. Currently, gonorrhea is considered to be resistant to all know antibiotics (pretty scary!) 24 Systems- Infectious Disease Syphilis Caused by Treponema pallidum bacteria. Incidence has been increasing over the past ten years. Has three stages. Primary, secondary and tertiary. Primary Stage Primary syphilis is characterized by a lesion on the site of sexual contact (penis, scrotum, vagina, anus). The lesion starts as a button like papule called a chancre that erodes to become a clean ulceration on an elevated base. It is apparent between 1 week and three months after exposure – usually in the first 3 weeks. The lesion is generally more obvious on men, so it may go untreated in women. The chancre usually heals in 3 to 12 weeks even without treatment. Secondary Stage The timing of the second stage varies greatly. S/S include maculopapular rash, especially on the palmer surfaces of the hand and plantar surfaces of the feet, fever, sore throat, nausea, anorexia, and conjunctivitis. Alopecia may develop. Also there may be elevated, red-brown lesions on the genitals called Condylomata lata. Condylomata lata may produce a foul discharge and are highly contagious. The infection then enters a latency period. Infected persons are still contagious for up to two years of the latency period. The latency period may last for life, or develop into tertiary syphilis. Tertiary Stage Tertiary syphilis may develop as long as 20 years after the initial infection. Only 1 in 3 untreated cases will develop the tertiary stage. Lesions may include: Destructive lesions called gumma – rubbery, non-inflammatory, necrotic lesions commonly found on the liver testes, or bone. Cardiovascular (CV) lesions – usually cause scarring of the medial layer or the thoracic aorta with aneurysm formation. The aneurysm may lead to aortic valve insufficiency, and CHF. CNS lesions may lead to dementia, blindness, spinal cord injury, ataxia, and sensory loss. 25 Systems- Infectious Disease Treatment is with antibiotics. Treatment may have to be continued for several weeks. Pregnant women infected with syphilis may experience premature birth, or still birth. The baby may be born with congenital defects, or an active infection. 26