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