Microbial Diseases Of The Skin And Eyes
Objectives: Viral Diseases of the Skin
For each microbial disease listed give the following if applicable.
Papillomaviruses cause skin cells to proliferate and produce a benign growth called a wart or papilloma.
Warts are spread by direct contact.
Warts may regress spontaneously or be removed chemically or physically.
Variola virus causes two types of skin infections: variola major and variola minor. Variola major has a mortality rate of 20% or higher while variola minor has a mortality rate of less than 1%.
Smallpox is transmitted by the respiratory route, and the virus is moved to the skin via the bloodstream.
Twelve to fourteen days after infection patients become febrile and exhibit severe aching pains and prostration.
Two to three days after the appearance of first symptoms a papular rash appears, which soon becomes vesicular and then pustular. Pustules expand, eventually scab, and heal leaving deep pitted scars.
Patients remain febrile throughout the development of the rash and experience severe pain. Death usually occurs during the second week.
The only host for smallpox is humans.
Smallpox has been eradicated as a result of a vaccination effort by the WHO (yeah, except for those bioterror stockpiles everybody's holding on to).
Lesions of Smallpox
Endemic in small mammals in Africa and East Asia, first showed up in zoo monkeys.
There are occasional outbreaks in those areas and have been cases in the U.S.
Symptoms are similar to small pox, with a death rate of 1-10% (although there have been no deaths in the U.S.).
The smallpox vaccine appears somewhat protective, and while the virus jumps from animals to humans human to human transmission has been rare.
Chickenpox (Varicella) and Shingles (Herpes Zoster)
Varicella-zoster virus is transmitted by the respiratory route and is localized in skin cells, causing a vesicular rash. Vesicles fill with pus, rupture, and form a scab within 3-4 days. The disease is usually mild.
Complications of chickenpox include encephalitis, pneumonia, and Reye's syndrome.
After chickenpox, the virus can remain latent in nerve cells and subsequently activate as shingles.
Shingles (herpes zoster) is characterized by a vesicular rash along the affected cutaneous sensory nerves.
The virus can be treated with acyclovir. An attenuated live vaccine is available.
Chickenpox and Shingles
Herpes simplex infection of mucosal cells results in cold sores and occasionally encephalitis and genital herpes.
The virus remains latent in nerve cells (HSV-1 in the trigeminal nerve ganglion), and cold sores can recur when the virus is activated.
HSV-1 is transmitted primarily by oral and respiratory routes.
Herpes encephalitis occurs when herpes simplex viruses infect the brain.
Acyclovir has proven successful in treating herpes encephalitis.
Latency of HSV-1
Measles is caused by measles virus and transmitted by the respiratory route.
Vaccination provides effective long-term immunity.
After the virus has incubated in the upper respiratory tract, macular lesions appear on the skin, and Koplik's spots appear on the oral mucosa.
Complications of measles include middle ear infections, pneumonia, encephalitis, and secondary bacterial infections. Rarely subacute sclerosing panencephalitis occurs (mostly in males) anywhere from 1-10 years after recovery from measles, causing severe neurological symptoms and death within a few years.
Macular Lesions of Rubeola
Reported Cases of Measles in U.S.
Rubella (German measles)
The rubella virus is transmitted by the respiratory route.
A red rash and light fever might occur in an infected indivitual; the disease can be asymptomatic.
Congenital rubella syndrome can affect a fetus when a woman contracts rubella during the first trimester of her pregnancy.
Damage from congenital rubella syndrome includes stillbirth, deafness, eye cataracts, heart defects, and mental retardation.
Vaccination with live rubella virus provides immunity of unknown duration.
Other Viral Rashes
Human parvovirus B19 causes fifth disease (erythema infectiosum) and HHV-6 causes roseola.