Caused by varicella-zoster virus, a member of Herpesviridae; is acquired by inhaling virus-laden droplets into the respiratory system
Incubation period is 10 to 23 days after which small vesicles appear on face and upper trunk
Can be prevented or infection shortened with attenuated vaccine or the drug acyclovir
Infection confers permanent immunity from chickenpox, but does not rid individual of virus; instead, virus enters a latent stage in the nuclei of sensory nerve roots
Shingles
When an adult who harbors the virus is under stress, the virus can emerge and cause sensory nerve damage and painful vesicle formation, a condition known as shingles
Treated with acyclovir or famciclovir in immunocompromised patients
Influenza (flu)
Caused by orthomyxoviruses that can undergo frequent antigenic variation
Antigenic drift-small variation
Antigenic shift-large variation
Animal reservoirs are important (e.g., chickens and pigs) and contribute to antigenic shifts
Virus is acquired by inhalation or ingestion of virus-contaminated respiratory secretions; it enters host cells by receptor-mediated endocytosis
Influenza is characterized by chills, fever, headache, malaise, and general muscular aches and pains; diagnosis can be confirmed by rapid serological tests
Treatment is focused on alleviating symptoms, but some antiviral drugs have been shown to decrease duration and symptoms of type A influenza
Measles (rubeola)
A skin disease with respiratory spread caused by Morbillivirus, a member of family Paramyxoviridae
After 10-21 day incubation, cold-like symptoms develop, followed by a rash; on rare occasions can develop into subacute sclerosing panencephalitis
MMR (measles, mumps, and rubella) vaccine is used for prevention
Mumps
Caused by mumps virus, a member of the genus Rubulavirus in the family Paramyxoviridae
Spread in saliva and respiratory droplets; portal of entry is the respiratory tract
Causes swelling of salivary glands; meningitis and inflammation of testes are complications, especially in postpubescent male
Therapy is supportive and the MMR vaccine is used for prevention
Respiratory syndromes and viral pneumonia
Acute respiratory syndromes
Caused by a variety of viruses collectively referred to as acute respiratory viruses
Associated with rhinitis, tonsillitis, laryngitis, and bronchitis; immunity resulting from infection is incomplete and reinfection is common
Viral pneumonia is clinically nonspecific, and symptoms may be mild or severe (death is possible)
Respiratory syncytial virus (RSV) is the most dangerous cause of respiratory infection in young children; is a member of the RNA virus family Paramyxoviridae
Rubella (German measles)
Caused by rubella virus, a ssRNA virus of family Togoviridae
Virus is spread by respiratory droplets, and the resulting infection is mild in children (a rash), but disastrous for pregnant women in first trimester; in pregnant women it causes congenital rubella syndrome, which leads to fetal death, premature delivery, and congenital defects
No treatment is indicated; a vaccine (MMR) is available
Smallpox (variola)
Caused by variola virus, a dsDNA virus belonging to the family Poxviridae
Virus is transmitted by aerosol or contact; symptoms include severe fever, prostration, rash, toxemia, and septic shock
Virus was eradicated as the result of a vigorous worldwide vaccination program; eradication was made possible for several reasons
Disease has easily identifiable clinical features
There are virtually no asymptomatic carriers
It infects only humans (there are no animal or environmental reservoirs)
It has a short period of infectivity
Arthropod-Borne Diseases
General features of arthropod-borne diseases
Viruses multiply in tissues of insect vectors without producing disease, and vector acquires a lifelong infection
Three clinical syndromes are common
Undifferentiated fevers, with or without a rash
Encephalitis-often with a high case fatality rate
Hemorrhagic fevers-frequently severe and fatal
Infection provides permanent immunity; for many of the diseases, no vaccines are available; treatment is usually supportive
Colorado Tick Fever
Caused by Coltivirus (RNA virus)
Tick-borne; main reservoirs are ground squirrels, rabbits, and deer
Symptoms include abrupt onset of fever, chills, severe headaches, photophobia, and muscle pain
Serology is used to confirm diagnosis
Yellow Fever
Mosquito-borne; there are two patterns of transmission
Urban cycle-human-to-human transmission
Sylvan cycle-monkey-to-monkey and monkey-to-human transmission
Early symptoms include fever, chills, headache, backache; these are followed by nausea and vomiting; in severe cases jaundice, lesions and hemorrhaging occur
Prevention and control is by vaccination and vector control
Direct Contact Diseases
Acquired immune deficiency syndrome (AIDS)
Caused by human immunodeficiency virus (HIV), a lentivirus within the family Retroviridae; believed to have evolved in Africa from viruses that infect other primates
Disease occurs worldwide, but certain groups are more at risk; these include homosexual/bisexual men, intravenous drug users, transfusion patients and hemophiliacs, prostitutes, and newborn children of infected mothers
Virus is acquired by direct exposure of the person's bloodstream to body fluids containing the virus; can also be transmitted via breast milk
Virus targets CD4+ cells such as T-helper cells, macrophages, dendritic cells, and monocytes
Precise mechanism of pathogenesis is unknown
Four types of pathological changes may ensue
AIDS-related complex (ARC)-mild fever, weight loss, lymph node enlargement, and presence of antibodies to HIV; can develop to full-blown AIDS
AIDS-antibodies not sufficient to prevent infection; virus establishes itself in CD4 immunocompetent cells, which then proliferate in the lymph nodes and cause the lymph nodes to collapse; leads to depletion of T-cell progenitors, which cripples the immune system; this leaves the person open to opportunistic infections
AIDS dementia and other evidence of central nervous system damage; the virus can cross the blood-brain barrier
AIDS-related cancer-Kaposi's sarcoma (caused by human herpesvirus 8; HHV-8), carcinoma of the mouth and rectum, B-cell lymphomas
Diagnosis is by viral antigen detection or by viral antibody detection (seroconversion)
Three types of antiviral agents are used to treat HIV disease
Nucleoside anologues that inhibit HIV reverse transcriptase (RT)
Nonnucleoside inhibitors of HIV RT
Inhibitors of HIV protease
Vaccines to stimulate production of neutralizing antibodies are currently under investigation
Prevention and control involves screening of blood and blood products, education, and protected sexual practices (use of condoms)
Cold sores-fever blisters
Caused by herpes simplex type 1 (HSV-1), a dsDNA virus; transmission is by direct contact
Blister at site of infection is due to viral- and host-mediated tissue destruction
Lifetime latency is established when virus migrates to trigeminal nerve ganglion; is periodically reactivated in times of physical or emotional stress
Herpetic keratitis-recurring infections of the cornea; can result in blindness
Drugs are available that are effective against cold sores; diagnosed by cell culture and immunological tests
Common cold
Caused by many different rhinoviruses as well as other viruses; many do not confer durable immunity
Understanding rhinovirus structure has suggested approaches to developing vaccines and drugs
At one time, common cold was thought to be spread by explosive sneezing, but now it is believed to be primarily spread by hand-to-hand contact; treatment is supportive
Cytomegalovirus inclusion disease
Most infections are asymptomatic but infection can be serious in immunologically compromised individuals; virus persists in the body and is shed for several years in saliva, urine, semen, and cervical secretions
Infected cells have intranuclear inclusion bodies
Diagnosis is by viral isolation and serological tests
Some antiviral agents are available for treatment; these are only used in high-risk patients; prevention is by avoiding close personal contact with infected individual and by using blood or organs from seronegative donors
Genital herpes
Caused by herpes simplex type 2 (HSV-2), a dsDNA virus that is a member of Herpesviridae; virus is most frequently transmitted by sexual contact
Disease has active and latent phases
Active phase-the virus rapidly reproduces; can be symptom free or painful blisters in the infected area may occur, as well as other symptoms (fever, burning sensation, genital soreness); blisters heal spontaneously
Latent phase-after resolution of active phase virus retreats to nerve cells; the viral genome resides in the nuclei of host cells and can be periodically reactivated
Congenital (neonatal) herpes is spread to an infant during vaginal delivery; therefore, infected females should deliver children by caesarean section
There is no cure, but acyclovir decreases healing time, duration of viral shedding, and duration of pain
Human herpesvirus 6 infections
Etiologic agent of exanthem subitum (rash) in infants, a short-lived disease characterized by a high fever of 3 to 4 days duration, followed by a macular rash; CD4 cells are the main sites of viral replication and the tropism of the virus is wide and includes CD8+ T cells, natural killer cells, and probably epithelial cells; transmission is probably by way of saliva
Virus produces latent and chronic infections and can be reactivated in immunocompromised individuals, leading to pneumonitis; virus has been implicated in a variety of other diseases, including chronic fatigue syndrome and lymphadenitis; diagnosis is by immunofluorescence or enzyme immunoassay; there is neither treatment nor prevention currently available
Human parvovirus B19 infections
Mild symptoms (fever, headaches, chills, malaise) in most normal adults; erythema infectiosum in children; joint disease in some adults; serious aplastic crisis in immunocompromised individuals or those with sickle-cell disease or autoimmune hemolytic anemia; anemia and fetal hydrops (the accumulation of fluid in the tissues) in infected fetuses
Spread by a respiratory route
Antiviral antibodies are the principal means of defense, and treatment is by means of commercial anti-B19 immunoglobulins; infection is usually followed by lifelong immunity
Leukemia-certain leukemias (adult T-cell leukemia and hairy-cell leukemia) are caused by retroviruses (HTLV-1 and HTLV-2, respectively) and are spread similarly to AIDS; they are often fatal and there is no effective treatment, although interferon (INF-a) has shown some promise
Mononucleosis (infectious)
Caused by the Epstein-Barr virus (EBV), a herpesvirus (dsDNA virus), which is spread by mouth-to-mouth contact ("kissing disease") or by shared bottles and glasses; virus replicates in lymphatic tissue, eventually infects B cells, and causes enlargement of lymph nodes and spleen, sore throat, headache, nausea, general weakness and tiredness, and a mild fever; disease is self-limited
Treatment is largely supportive and requires plenty of rest; diagnosis is made by serological tests
EBV is also associated with Burkitt's lymphoma and nasopharyngeal carcinoma in certain parts of the world
Rabies
Caused by a number of different strains of neurotropic viruses of the family Rhabdoviridae (negative-strand RNA viruses)
Transmitted by bites of infected animals; aerosols in caves where bats roost; or by scratches, abrasions, open wounds, or mucous membranes contaminated with saliva of infected animals
Virus multiplies in skeletal muscle and connective tissue, then migrates to central nervous system, causing a rapidly progressing encephalitis
In the past, diagnosis depended on the observation of characteristic Negri bodies (masses of virus particles or unassembled viral subunits); today diagnosis is based on immunological tests, virus isolation, as well as the detection of Negri bodies
Symptoms progress and death results from destruction of the part of the brain that regulates breathing
Vaccines conferring short-term immunity are available and must be given soon after exposure (postexposure vaccination is effective because of the long incubation period of the virus); prevention and control involves annual preexposure vaccination of dogs and cats, postexposure vaccination of humans, and frequent preexposure vaccination of humans at special risk
Viral hepatitides
Hepatitis is any inflammation of the liver; currently nine viruses are recognized as causing hepatitis; some have not been well characterized
Hepatitis B (serum hepatitis)
Caused by hepatitis B virus (HBV), a dsDNA virus with a circular genome
Virus is transmitted by blood transfusions, contaminated equipment, unsterile needles, or any body secretion; also transplacental transmission to fetus occurs
Most cases are asymptomatic; sometimes fever, appetite loss, abdominal discomfort, nausea, and fatigue develop; death can result from liver cirrhosis or HBV-related liver cancer
Control measures involve excluding contact with contaminated materials, passive immunotherapy within seven days of exposure, and vaccination of high-risk groups
Hepatitis C
Caused by hepatitis C virus (HCV) an ssRNA virus within the family Flaviviridae
Virus is spread by intimate contact with virus-contaminated blood, in utero from mother to fetus, by the fecal-oral route, or through organ transplants
Diagnosis is by serological tests
Has reached epidemic proportions
Treated with interferon
Hepatitis D
Is caused by hepatitis D virus (HDV) (formally called the delta agent), which only causes disease if the individual is coinfected with hepatitis B virus; coinfection may lead to a more serious acute or chronic infection than that normally seen with HBV alone
Diagnosis is by serological tests; treatment is difficult and often involves administration of alpha interferon; prevention and control is by the use of the hepatitis B vaccine
Recently, hepatitis F and hepatitis G have been identified and are currently being investigated
Caused by Norwalk and Norwalk-like viruses, rotaviruses, caliciviruses, and astroviruses
Main transmission route is fecal-oral route; disease is leading cause of childhood death in developing countries
Seen most frequently in infants; disease severity may range from asymptomatic infection, to mild diarrhea, to severe and occasionally fatal dehydration
Viral gastroenteritis is usually self-limited; treatment is supportive
Hepatitis A-caused by the hepatitis A virus (HAV)
Spread by fecal contamination of food or drink, or by infected shellfish that live in contaminated water
Caused by the hepatitis A virus (HAV), a plus-strand RNA virus of family Picornaviridae
Mild intestinal infections sometimes progress to liver involvement; most cases resolve in four to six weeks and produce strong immunity
Control is by hygienic measures and sanitary disposal of excreta; a killed vaccine (Havrix) is now available
Hepatitis E
Implicated in many epidemics in developing countries in Asia, Africa, and Central and South America
Caused by hepatitis E virus (HEV), an ssRNA virus
Infection is associated with fecal-contaminated drinking water; HEV enters the blood from the gastrointestinal tract, replicates in the liver, is released from hepatocytes into the bile, and is subsequently excreted in the feces
HEV, like HAV, usually runs a benign course and is self-limiting; can be fatal (10%) in pregnant women in their last trimester
There are no specific measures for prevention other than those aimed at improving the level of health and sanitation in affected areas
Poliomyelitis
Caused by poliovirus, a member of the family Picornaviridae; is a plus-strand RNA virus that is stable and remains infectious in food and water
Once ingested, virus multiplies in throat and intestinal mucosa; subsequently enters bloodstream and causes viremia (99% of viremia cases are transient with no clinical disease); can enter central nervous system (less than 1% of cases), leading to paralysis
Vaccines have been extremely effective (less than 10 cases per year; no endogenous reservoir) in preventing and controlling the disease; global eradication may be possible in the next few years
Slow Virus and Prion Diseases
Progressive pathological process caused by a virus or a prion that remains clinically silent for months or years; this is followed by progressive clinical disease, ending in profound disability or death
Four of the six recognized human diseases are caused by prions; these diseases are called spongiform encephalophathies
Other Diseases
Diseases that do not fit into any of the previous categories; includes diabetes mellitus, viral arthritis and warts
Warts are caused by papillomaviruses; treatment involves removal of warts, physical destruction, or injection of interferon; some papillomaviruses play a major role in the pathogenesis of epithelial cancers of the male and female genital tracts
