Chapter 7 Viruses of Clinical Significance PDF

Chapter 7 Introduction to Viruses of Clinical Significance 1. Respiratory Viruses Carina O. Barlongo, RMT 08 October 2024  Organ / System Categorization of Viruses practical approach to understanding the clinical impact of viruses and the diseases they cause...

Chapter 7 Introduction to Viruses of Clinical Significance 1. Respiratory Viruses Carina O. Barlongo, RMT 08 October 2024  Organ / System Categorization of Viruses practical approach to understanding the clinical impact of viruses and the diseases they cause this method makes it easier to correlate the viral pathogens with their symptoms, diagnostic methods, treatments, and preventive measures for the medical technologists or medical lab scientists, the association helps in identifying the appropriate sample specimen and lab tests  Viruses of Clinical Significance 1. Respiratory Viruses primarily affect the respiratory tract, causing illnesses ranging from the common cold to severe pneumonia. crucial in managing respiratory outbreaks and pandemics Examples: Influenza, RSV, and SARS-CoV-2  Viruses of Clinical Significance 2. Gastrointestinal Viruses primarily infect the digestive system, leading to gastroenteritis, diarrhea or hepatitis. Common examples: Norovirus and Rotavirus  Viruses of Clinical Significance 3. Nervous System Viruses target the central and peripheral nervous systems, causing neurological diseases like encephalitis or meningitis Examples: Rabies virus, Poliovirus, and Herpes Simplex Virus  Viruses of Clinical Significance 4. Dermatological Viruses manifest through skin lesions or rashes. Examples: Human Papillomavirus (HPV) Varicella-Zoster virus (VZV) Molluscum contagiosum  Viruses of Clinical Significance 5. Hepatic Viruses primarily affect the liver, leading to conditions such as hepatitis. Examples: Hepatitis A, B, C, D, and E viruses  Viruses of Clinical Significance 6. Cardiovascular System Viruses Coxsackie B Virus: Associated with myocarditis and pericarditis Enteroviruses: Can cause viral myocarditis, leading to heart inflammation and damage.  Viruses of Clinical Significance 7. Reproductive System Viruses Human Papillomavirus (HPV): Linked to cervical, anal, and genital cancers, as well as genital warts Herpes Simplex Virus (HSV-2): Causes genital herpes  Viruses of Clinical Significance 8. Ocular Viruses Adenovirus: Can cause viral conjunctivitis (pink eye) Herpes Simplex Virus: can lead to ocular herpes, causing keratitis or more severe eye infections.  Viruses of Clinical Significance 9. Systemic Viruses HIV affects multiple systems but primarily targets the immune system Cytomegalovirus (CMV) can cause systemic infections in immunocompromised patients, affecting the liver, lungs, brain, and gastrointestinal tract.  Viruses of Clinical Significance 10. Arthropod-borne viruses, or arboviruses are viruses transmitted by arthropods such as mosquitoes, ticks, and sandflies typically affect multiple organ systems, depending on the virus, but they are often categorized based on their primary clinical manifestations arboviruses can cause a range of diseases, including febrile illness, encephalitis, hemorrhagic fever, and joint/muscle pain Examples: Dengue, Zika 1. Respiratory Viruses  Respiratory viruses primarily target the respiratory tract (upper and/or lower airways), leading to a wide range of diseases, from mild colds to severe pneumonia. Clinical significance: ability to cause widespread outbreaks, especially during colder seasons, and their potential to cause serious complications, particularly in vulnerable populations such as young children, the elderly, and immunocompromised individuals. Major routes of transmission: - airborne droplets - direct contact and fomites (contaminated surfaces)  1. Influenza Virus A, B, C (Orthomyxoviridae) 1.Orthomyxovirus virions contain a segmented RNA genome (sdRNA) and have a helical- shaped virion with an envelope. Size range from 75 to 125 nm. 2.Orthomyxoviruses have hemagglutinin (HA) and neuraminidase (NA) on their surface. 3.The influenza viruses, A, B, and C, are the only members of the family Orthomyxoviridae. Influenza A and B viruses are most clinically significant. 1. Influenza Virus A, B, C (Orthomyxoviridae) Hemagglutinin (HA): A glycoprotein on the surface of the influenza virus that allows the virus to bind to and enter host cells by attaching to sialic acid receptors on the cell surface. It’s crucial for the virus’s ability to infect host cells. Neuraminidase (NA): Another surface protein that helps the virus to release from the infected host cell after replication. It cleaves sialic acid, allowing the virus to spread to other cells. These proteins are the basis for classifying different strains of influenza A virus, such as H1N1 (swine flu, 2009 pandemic, 1918 Spanish flu) or H3N2 (seasonal flu), where the numbers correspond to specific subtypes of HA and NA proteins. 1. Influenza Virus (Orthomyxoviridae) Type: A, B, C Influenza A: The most virulent and known for causing pandemics (e.g., H1N1, H3N2). Influenza B: Causes seasonal epidemics but is generally less severe than type A. Influenza C: Causes mild respiratory illness. Mode of Transmission: Airborne via respiratory droplets from coughs and sneezes and direct contact by touching surfaces contaminated with the virus. Diseases: Causes influenza (trangkaso), characterized by symptoms such as fever, chills, cough, sore throat, body aches, and fatigue. Complications: Can lead to pneumonia, bronchitis, sinus infections, and worsening of chronic health conditions. Clinical Significance: Influenza has seasonal epidemics with significant morbidity and mortality, particularly among the elderly, young children, and those with chronic health issues. Vaccination is critical for prevention. 1. Influenza Virus (Orthomyxoviridae) Laboratory Diagnosis Rapid influenza diagnostic tests (RIDTs): Detects viral antigens, provides results in about 15 minutes but can be less sensitivity RT-PCR: Gold standard, highly sensitive, detects and differentiates between influenza types and subtypes. Viral culture: Less commonly used but can be done for confirmation.  1. Influenza Virus (Orthomyxoviridae) Treatment: Antiviral medications: Oseltamivir (Tamiflu): Most common antiviral for influenza. Zanamivir (Relenza) and Peramivir are alternatives. Should be administered within 48 hours of symptom onset for maximum efficacy. Prevention: Annual influenza vaccination: Recommended for everyone, particularly vulnerable groups (children, elderly, healthcare workers). Hand hygiene and respiratory etiquette Isolation of infected individuals during outbreaks  Reconstruction of 1918 Influenza Virus PCR technology has yielded gene fragments of influenza virus from archival lung tissue specimens from victims of the 1918 Spanish flu epidemic. The complete coding sequences of all eight viral RNA segments have been determined, and the sequences document that it was an H1N1 influenza A virus. It appears that the 1918 virus was not a reassortant (not a combination of the RNA segments) but was derived entirely from an avian source that adapted to humans. Source: Jawetz, 28th edition  2. Rhinovirus (Picornaviridae) The picornaviruses have a naked virion ranging in size from 20 to 30 nm. The family Picornaviridae includes a number of viruses such as the enteroviruses, hepatitis A virus, and the rhinoviruses. Rhinoviruses Rhinoviruses are a frequent cause of the common cold. Other viruses, including coronaviruses, are also associated with colds. The rhinoviruses grow better at temperatures just below core body temperature (e.g., 33°C). This is near the typical temperature of the nasal passage. Over 100 serotypes are known, and immunity to one does not provide immunity to the others. This is why colds are so common.  Important Properties of Picornaviruses 2. Rhinovirus (Picornaviridae) Source: Jawetz, 28th edition 2. Rhinovirus (Picornaviridae) Mode of Transmission Direct contact with infected secretions (e.g., touching hands, objects, surfaces) Inhalation of respiratory droplets Laboratory Diagnosis: Typically, clinical diagnosis based on symptoms. RT-PCR: Can be used for detection in severe cases, especially in vulnerable populations, but is not routine.  2. Rhinovirus (Picornaviridae) Treatment Supportive care: Hydration, rest, over-the- counter pain relievers (e.g., acetaminophen, ibuprofen), decongestants. No specific antiviral therapy for rhinovirus. Prevention Hand hygiene and avoidance of close contact with infected individuals. Disinfection of surfaces during cold outbreaks.  3. The Three Major Coronaviruses: SARS, MERS, and SARS-CoV-2 Coronaviruses are large, enveloped RNA viruses. The human coronaviruses cause common colds, may cause lower respiratory tract infections, and have been implicated in gastroenteritis in infants. Virus Structure: Enveloped, positive-sense single- stranded RNA viruses with spike proteins that give them a crown-like appearance. Types: Infect humans and animals, causing respiratory, gastrointestinal, and neurological diseases. Very little is known about the epidemiology of enteric coronavirus infections.  SARS-CoV (Severe Acute Respiratory Syndrome Coronavirus) First Identified: 2002 in Guangdong, China. Outbreak: Caused a global epidemic in 2002-2003. Transmission: Respiratory droplets, close contact. Symptoms: Fever, cough, difficulty breathing, and pneumonia; can lead to ARDS (Acute Respiratory Distress Syndrome). Mortality Rate: ~10%. Diagnosis: RT-PCR, viral culture, serology. Treatment: Supportive care; no specific antivirals; corticosteroids in some severe cases. Prevention: Isolation of infected patients, quarantine, and public health measures. Source: WHO, CDC  MERS-CoV (Middle East Respiratory Syndrome Coronavirus) First Identified: 2012 in Saudi Arabia. Outbreaks: Primarily in the Middle East but also seen in other countries through travel. Transmission: Zoonotic transmission from camels to humans; limited human-to-human spread, mostly in healthcare settings. Symptoms: Fever, cough, shortness of breath, and gastrointestinal symptoms; can progress to pneumonia and kidney failure. Mortality Rate: ~34%. Diagnosis: RT-PCR, serology, viral culture. Treatment: Supportive care; investigational antivirals in some cases. Prevention: Avoiding contact with camels, infection control in healthcare settings, and travel precautions. Source: WHO, CDC  SARS-CoV-2 (COVID-19) First Identified: December 2019 in Wuhan, China. Pandemic: ` Global pandemic 2020. Transmission: Primarily through respiratory droplets, aerosols, and close contact; also via contaminated surfaces. Symptoms: Wide range, from asymptomatic to severe pneumonia; common symptoms include fever, cough, loss of taste/smell, and fatigue. Severe cases may involve ARDS, multi-organ failure, and death. Mortality Rate: Varies by region and healthcare capacity; generally lower than MERS but highly infectious. Diagnosis: RT-PCR, antigen tests, serology for past infections. Treatment: Antivirals (e.g., remdesivir), monoclonal antibodies, corticosteroids (e.g., dexamethasone), oxygen therapy, and mechanical ventilation in severe cases. Prevention: Vaccination (Pfizer, Moderna, AstraZeneca, Janssen, Sinovac), masks, physical distancing, hand hygiene, and travel restrictions Source: WHO, CDC  4. Adenovirus (Adenoviridae) Adenoviruses can replicate and produce disease in the respiratory, gastrointestinal, and urinary tracts and in the eye. Many adenovirus infections are subclinical, and virus may persist in the host for months About one-third of the 57 known human serotypes are responsible for the most cases of human adenovirus disease A few types serve as models for cancer induction in animals Adenoviruses are valuable systems for molecular and biochemical studies of eukaryotic cell processes They are also useful vectors for gene therapy approaches. Adenoviruses 1–7 are the most common types worldwide and account for most instances of adenovirus associated illness  4. Adenovirus (Adenoviridae) Adenoviruses belong to the family Adenoviridae. There are four genera: Mastadenovirus, Aviadenovirus, Atadenovirus and Siadenovirus At present 57 antigenic types of human adenoviruses have been described. Human adenoviruses have been classified into seven groups (A–G) on the basis of their physical, chemical and biological properties. All of the human adenoviruses are classified in the Mastadenovirus genus Structure and Properties  Clinical Significance Infection with one of the many adenoviruses may be asymptomatic or result in specific syndromes: 1. Respiratory tract infections, especially in young children 2. Urinary tract and gastrointestinal infections, and pharyngitis 3. Eye infections in newborns, patients who are immunocompromised, 4. and military recruits (because of close living conditions) are common. 5. Adenoviruses have been associated with epidemics of keratoconjunctivitis.  Gene Therapy Adenoviruses are being used as gene delivery vehicles for cancer therapy, gene therapy, and genetic immunization studies. http://transhumanismwr10206.weebly.com/uploads/1/8/3/4/18346115/136503 1098.jpg Laboratory Diagnosis A. Detection, Isolation, and Identification of Virus Samples should be collected from affected sites early in the illness to optimize virus detection. Depending on the clinical disease, virus may be found in respiratory samples, conjunctiva, throat, blood, stool, or urine. Duration of adenovirus excretion varies among different illnesses ex: respiratory infection of adults (1–7 days) and children (3–6 weeks) Virus isolation in a cell culture requires susceptible cell types. Primary human embryonic kidney cells are most susceptible but usually unavailable. Polymerase chain reaction (PCR) assays are routinely used for diagnosis of adenovirus infections in respiratory samples, blood, tissues, or body fluids, usually by using primers from a conserved viral sequence (eg, hexon and VA I) that can detect all serotypes.  Laboratory Diagnosis B. Serology The complement-fixation test is an easily applied method for detecting infection by any member of the adenovirus group but the test has low sensitivity If specific identification of a patient’s serologic response is required, antibody neutralization or hemagglutination inhibition tests can be used. The neutralization test is the most sensitive.  Treatment, Prevention and Control § There is no specific treatment for adenovirus infections. § Careful hand washing is the easiest way to prevent infections. § Environmental surfaces can be disinfected with sodium hypochlorite. § In group settings, paper towels may be advisable because dirty towels can be a source of infection in outbreaks. § The risk of waterborne outbreaks of conjunctivitis can be minimized by chlorination of swimming pools and waste water. § Strict asepsis during eye examinations, coupled with adequate sterilization of equipment, is essential for the control of epidemic keratoconjunctivitis. 5. Paramyxo Viruses (Paramyxoviridae) Genome: Non-segmented, negative-sense single- stranded RNA (ssRNA). Shape: Enveloped, pleomorphic (can have various shapes, typically spherical or filamentous). Replication: Occurs in the cytoplasm of the host cell. 5. Paramyxo Viruses (Paramyxoviridae) Key Viruses: Respiratory Syncytial Virus (RSV): A leading cause of bronchiolitis and pneumonia in infants and the elderly. Parainfluenza Virus: Causes croup (laryngotracheobronchitis), especially in children, as well as bronchiolitis and pneumonia. Measles Virus: Causes measles, a highly contagious viral disease characterized by fever, cough, and a widespread rash. Mumps Virus: Causes mumps, characterized by fever and swelling of the salivary glands.  5. Paramyxo Viruses (Paramyxoviridae) Diseases: Paramyxoviruses cause a range of respiratory illnesses, from the common cold to severe diseases such as bronchiolitis, pneumonia, and croup in children. Measles and mumps are also notable systemic diseases caused by paramyxoviruses. (both will be discussed in succeeding chapters) Transmission: Primarily through respiratory droplets and close person-to-person contact.  Respiratory Syncytial Virus (RSV) (Paramyxoviridae) Mode of Transmission: Airborne droplets Direct contact with infected secretions (e.g., saliva, nasal discharge) Fomites (contaminated surfaces) Laboratory Diagnosis: RT-PCR: Highly sensitive and specific for RSV. Antigen detection tests: Common in pediatric settings but less sensitive than PCR. Rapid antigen tests: Can detect RSV in nasopharyngeal swabs or secretions, commonly used in clinical settings. Viral culture: Rarely performed due to the slow growth of the virus in culture.  Respiratory Syncytial Virus (RSV) (Paramyxoviridae) Treatment Supportive care: Hydration, oxygen supplementation, mechanical ventilation in severe cases. Ribavirin: Antiviral used in severe cases, particularly in high-risk individuals. Monoclonal antibody (Palivizumab): Used prophylactically in high-risk infants to prevent severe RSV infections. Prevention: Hand hygiene: Critical in preventing the spread of RSV in hospitals and homes. Palivizumab: Given to high-risk infants during RSV season as prophylaxis. Infection control measures: In healthcare settings, isolating RSV patients can prevent transmission.  Human Parainfluenza Viruses (HPIV) (Paramyxoviridae, Respirovirus Genus and Rubulavirus Genus) Treatment: Supportive care: Management of symptoms such as fever, cough, and breathing difficulty (e.g., cool mist humidifiers, hydration). In severe cases, oxygen therapy or intubation may be required. Corticosteroids: May be used in severe croup to reduce inflammation and ease breathing. Antivirals: No specific antiviral therapy is currently available for HPIV. Prevention and Control: Infection control: Hand hygiene, avoiding close contact with infected individuals, and surface disinfection are key measures. No vaccine: Unlike measles and mumps, there is no available vaccine for HPIV, although vaccine development is ongoing.  Human Parainfluenza Viruses (HPIV) (Paramyxoviridae, Respirovirus Genus and Rubulavirus Genus) Laboratory Diagnosis: Rapid antigen tests: Commonly used for detecting HPIV in respiratory specimens. PCR: Sensitive and specific detection of HPIV RNA in nasopharyngeal or throat swabs. Viral culture: Occasionally used, though PCR is preferred due to its faster results.  Knowledge Check Adenoviruses can cause eye infections that are highly contagious. Which of the following is least likely to be a means of transmission during an outbreak of epidemic keratoconjunctivitis? A. Swimming pools B. Hand towels C. Mosquito bites D. Hand-to-eye E. Contaminated ophthalmic equipment