Chapter Capsule

A. Orthomyxoviruses: Influenza viruses have a segmented genome and glycoprotein spikes (hemagglutinin, neuraminidase); are subject to antigenic shift and drift that creates new viral subtypes. Influenza A is spread in epidemics and pandemics from human to human and from animal (pigs, poultry) to human. Clinical disease is marked by respiratory symptoms, fever, aches, sore throat; secondary pneumonia is frequent cause of death; long-term complications are Guillain-Barré syndrome and Reye syndrome; controlled with anti-flu drugs and vaccination.

B. Bunyaviruses are zoonotic viruses widely associated with insects and rodents. One type is the Hantavirus; cause of Korean hemorrhagic fever worldwide and hantavirus pulmonary syndrome, a newly described disease in the United States; spread by dried animal excreta.

C. Paramyxoviruses: Nonsegmented genome; glycoprotein spikes facilitate development of multinucleate giant cells; are spread through droplets.

1. Paramyxovirus causes parainfluenza, a common, mild form of influenza or coldlike illness, mostly in children; mumps or parotitis, inflammatory infection of salivary glands, sometimes testes; occurs often in children; can cause deafness; prevented by live, attenuated vaccine (MMR).

2. Morbillivirus, the viral agent of measles or rubeola, is highly contagious respiratory infection that produces a maculopapular rash over the body and in the oral cavity (Koplik’s spots); usually mild, but can threaten life in a small number of children; other complication is progressive brain disease called SSPE; attenuated vaccine administered in combination (MMR) or alone.

3. Pneumovirus, or respiratory syncytial virus (RSV), causes croup, an acute respiratory syndrome in newborns that is a problem in hospital nurseries; treated with aerosol ribavirin.

D. Rhabdoviruses: The main human pathogen is bullet-shaped Lyssavirus, the cause of rabies, a nearly 100% fatal infection encephalitis; a zoonosis carried by wild carnivores; contracted through an animal bite or scratch or inhaled; virus enters nerves and is carried to brain and salivary glands; symptoms include hyperactivity or paralysis, also hydrophobia; death results from cardiac or respiratory arrest; treatment requires cleaning of wound, passive immunization with rabies immune globulin, and active immunization with human diploid cell vaccine.

A. Coronaviruses: Have distinctive crown of spikes; human coronavirus (HCV) is one cause of the common cold.

B. Togaviruses: Rubella (German measles) virus is a teratogenic virus that crosses the placenta and causes developmental disruptions; virus is spread through contact with droplets; period of respiratory symptoms is followed by rash; infection during pregnancy can lead to congenital rubella with severe heart and nervous system damage; control by live, attenuated vaccine (MMR), preferably given in childhood or prior to pregnancy.

A. Arenaviruses: Spread by rodent secretions, droppings; example is Lassa fever, a severe and often fatal African hemorrhagic fever.

B. Arboviruses: Loose grouping of 400 viruses spread by arthropod vectors and harbored by numerous birds and mammals; include togaviruses, bunyaviruses, and reoviruses; distribution is determined by vector location; cause febrile infections (tick-borne fever), mosquito-borne encephalitis in horses and humans (WEE, EEE) and in humans and birds (St. Louis encephalitis); hemorrhagic fevers include yellow fever and dengue fever, sometimes deadly mosquito-borne diseases.

C. Retroviruses

Retroviruses are enveloped, single-stranded RNA viruses with reverse transcriptase that converts their single-stranded RNA into double-stranded DNA genome; insertable into host cell, so viruses are latent and can be oncogenic.

1. Human immunodeficiency virus (HIV, types 1 and 2): Causes acquired immunodeficiency syndrome (AIDS), an HIV antibody-positive state with some combination of opportunistic infections, fever, weight loss, chronic lymphadenitis, neoplasms, diarrhea, brain dysfunction. HIV appears to have originated in Africa; AIDS occurs as a pandemic and is the sixth prevalent cause of death.

2. Virus occurs in blood, semen, and vaginal secretions; is transmitted through homosexual and heterosexual contact and shared needles; risk groups or behaviors include (1) male homosexuals or bisexuals practicing unsafe sex, (2) intravenous drug abusers, (3) heterosexual partners of drug users and bisexuals, (4) blood transfusion and organ transplant patients, (5) persons with unknown risk factors, (6) fetuses or newborns of infected mothers.

3. HIV attacks cells with CD4 receptors (macrophages, T cells, and other lymphocytes); virus becomes latent; long-term infection brings the levels of T-helper cells down.

4. First signs of AIDS are opportunistic infections: Pneumocystis carinii pneumonia (PCP) and serious opportunistic diseases caused by protozoa, fungi, mycobacteria, and viruses; Kaposi sarcoma and lymphoma cancers; coinfections with HIV and other agents can hasten the destruction and weakening of immunities; the death rate is nearly 50%.

5. Treatment for AIDS includes drug cocktails that combine azidothymidine (AZT), ddI, 3TC, and d4T and protease inhibitors; drugs must be given for secondary infections; prevention measures are safe sexual practices; numerous vaccines are in clinical trials.

6. Other retroviruses and diseases: HTLV I causes adult T-cell leukemia or mycosis fungoides, a fatal cancer; HTLV II causes another cancer with high mortality rate, hairy-cell leukemia.

A. Picornaviruses are the smallest human viruses.

1. Enteroviruses: Spread primarily by the oral-fecal route. Poliovirus, cause of polio; virus can spread through close contact, contaminated food, water; occasionally leads to paralysis caused by infection and destruction of spinal neurons; bulbar type requires life support; disease controlled through vaccination with inactivated polio vaccine (IPV) and oral polio vaccine (OPV).

2. Coxsackievirus causes respiratory infection, hand-foot-mouth disease, conjunctivitis.

3. Hepatitis A virus causes short-term, mild hepatitis; spread through close institutional contact, contaminated food or shellfish; disease is initially flulike, followed by liver discomfort and diarrhea; prevented by immunization with vaccines and gamma globulin.

4. Rhinovirus: Most prominent cause of common cold; spread by droplets; confines itself to respiratory membranes; virus exists in over 110 forms; symptoms are nasal drainage, cough, sneezing, sore throat; treatment is symptomatic.

5. Calicivirus: Norwalk agent, a common cause of viral gastroenteritis.