Clinical Virology: Part Two The Viruses MLAB 2434 – Microbiology Keri Brophy-Martinez
Feb 24, 2016
Clinical Virology: Part TwoThe Viruses
MLAB 2434 – MicrobiologyKeri Brophy-Martinez
Respiratory Viruses• Influenza Viruses– ssRNA virus– Causes crucial health problems• epidemics and pandemics
– Antigenic drifts and shifts• Major or minor changes in viral surface
glycoproteins– Attack ciliated epithelial cells of
respiratory tract
Respiratory Viruses(cont’d)• Parainfluenzae Viruses– Enveloped RNA– Major cause of respiratory disease in young
children• Respiratory Syncytial Virus (RSV)– Enveloped RNA– Most common virus isolated from infants with
LRT infections– Spread by contact with respiratory secretions
Respiratory Viruses(cont’d)• Adenoviruses– Half of all infections are asymptomatic– Causes 10% of all pneumonia cases– Causes 5% - 15% of all gastroenteritis in
children– dsDNA, nonenveloped
Respiratory Viruses (cont’d)• Rhinoviruses– Major cause of common cold– Infect nasal epithelial cells and activate
inflammatory response– ssRNA, small and naked– No cure
• Coronaviruses– ssRNA– Cold-like infections
Exanthemas
• Definition = skin eruption accompanying certain infectious diseases
• Mumps– ssRNA– Swelling of parotid
glands, testes, ovaries and pancreas
– Vaccine available
Exanthemas (cont’d)
• Measles (Rubeola)– ssRNA virus– Abrupt onset with sneezing,
runny nose and cough, red eyes and high fever, followed by maculopapular (flat discolored area of skin with raised bump) rash on head and trunk
– Also see Koplik’s spots- bright red spots with white centers
– Easily diagnosed clinically; lab requests rare
Exanthemas (cont’d)• Rubella– Enveloped ssRNA– Mild febrile illness with rash and
lymphadenopathy; many cases asymptomatic– Rash starts on face and spreads to trunk and
limbs; no rash on palms and soles– Causes birth defects in first trimester– Vaccine strongly recommended– Serologic titer for immune status
Exanthemas (cont’d)• Parovirus B19– ssRNA– Causes Erythema
Infectiosum, also known as “Fifth Disease”
– “Slapped cheek” appearance, spreading to trunk and limbs
Immunodeficiency Viruses• Human Immunodeficiency Virus Type
1– AIDS– ssRNA– Target cells are CD4+ T cells– Destruction of these cells results in
opportunistic infections
Central Nervous System Viruses
• Enteroviruses– ssRNA virus– Includes poliovirus, coxsackie A and B, and
echovirus– Transmission: Fecal-oral/respiratory– Causes a variety of infections and conditions,
including paralysis– Resistant to disinfectants
Agents of Gastrointestinal Infections
• Known to cause the “stomach flu”• Includes adenovirus, norovirus, rotavirus• Rotaviruses– dsRNA with double-layer protein capsid– Most common cause of gastroenteritis in
infants, children– Oral-fecal route– Hand washing and vaccines for prevention
Agents of Gastrointestinal Infections (cont’d)
• Norovirus– Originally called Norwalk and Norwalk-Like
Agents– Gastroenteritis in older children and adults– Outbreaks in camps, schools, and on cruise
ships– Nausea, vomiting, diarrhea and low-grade
fever– Highly infectious
Family Arenaviridae• Causes hemorrhagic fevers– Lassa Fever
• Transmitted by rodents• Acquired by aerosol or skin abrasion
Family Filoviridae
• Includes Ebola and Marburg viruses• Human infections may result from
contact with infected monkeys• High mortality rates• Unknown reservoirs in nature
Rabies• Transmitted by bite or scratch from infected
animal• Pain at site of infection, followed by flu-like
symptoms• CNS system changes, followed by death• Vaccine and postexposure prophylaxis
available• Detected in brain of source animal
Human Papilloma Virus• dsDNA virus• Causes– Leading cause of sexually transmitted
disease– Common and plantar warts– Genital warts– Associated with cervical cancers
Hepatitis Viruses• Hepatitis A (HAV)– oral-fecal– Person-person contact, contaminated
food/water– RNA– Anti-HAV antibodies emerge around 10
days
Hepatitis Viruses Hepatitis B (HBV)
Blood and body fluids
DNA Hardy organism
Hepatitis Viruses• Hepatitis C (HCV)
– Blood and body fluids– RNA– For diagnosis- Anti-HCV serology
• Hepatitis D (HDV)– Blood and body fluids– RNA– Requires HBV for replication
• Hepatitis E (HEV)– Oral-fecal– RNA
Herpesviruses• HSV Type 1– Oral herpes– “Cold sores”– Can cause encephalitis– Recurrent
• HSV Type 2– Genital herpes– Neonatal herpes– Can cause encephalitis– Recurrent
Herpesviruses (cont’d)• Varicella-zoster
– Varicella causes chicken pox– Zoster is clinical manifestation of reactivated
varicella virus, which can be latent in nerve tissue (“Shingles”)
• Epstein-Barr– Mononucleosis– Associated with Burkitt’s lymphoma,
nasopharyngeal carcinoma, Hodgkins lymphoma
Herpesviruses (cont’d)• Cytomegalovirus (CMV)–Most common congenital infection in
U.S.–Most adults have antibodies to CMV
• Herpesvirus 6 – Causes Roseola Infantum or “Sixth
Disease”
Herpesviruses (cont’d)• Herpsevirus 7– Infects CD4 + cells– Viruses present in 75% of adult saliva
• Herpsevirus 8– Detected in Kaposi’s sarcoma– Not culturable
Arboviruses• Derive name from mode of
transmission (arthropod born)• Humans are dead-end hosts
• Families– Bunyaviridae family• Vector- mosquito• Hemorrhagic fever, including Hanta virus• Encephalitis
Arboviruses (cont’d)• Togaviridae family– Encephalitis
• Reoviridae family– Colorado tick fever
• Flaviviridae family– Most common cause of arboviral encephalitis in
the world, including St. Louis encephalitis (SLE)– West Nile– Dengue fever (Classic and hemorrhagic)– Yellow fever
Antiviral Therapy• Like bacteria and antibiotics, the use of
antivirals can result in virus resistance• Some viral infections are treatable,
especially if therapy is given early in infection
• Antivirals must be designed to target a viral replication mechanism without destroying host cells
• Vaccinations
References• Kiser, K. M., Payne, W. C., & Taff, T. A. (2011). Clinical Laboratory
Microbiology: A Practical Approach . Upper Saddle River, NJ: Pearson Education.
• Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.
• http://www.fifthdisease.org/general.html• http://www.idph.state.il.us/about/immunepics/measles.htm• http://www.idph.state.il.us/about/immunepics/mumps.htm• http://www.mc3cb.com/viruses.html