transmittable spongiform encephalopathies (TSEs).
Some prion diseases are inherited and others are
acquired. The most notorious prion illness is vari-
ant Creutzfeldt-Jakob disease (vCJD), acquired
through the consumption of beef from cattle that
have bovine spongiform encephalopathy (BSE),
commonly called mad cow disease. Prions are
highly resistant to disinfectants and sterilization
procedures. Many hospitals now use disposable
instruments for brain surgery to reduce the risk for
transmitting a prion disease through an OPERATION.
See also CREUTZFELDT-JAKOB DISEASE(CJD); FOOD
SAFETY.
prodrome The stage of illness immediately
before the emergence of full symptoms. Prodrome
is particularly prominent in herpesvirus INFECTION,
which features tingling and irritation at the sites
where herpes blisters are about to erupt. Pro-
drome occurs with many viral infections, such as
MEASLESand CHICKENPOX. Often these infections are
most contagious during the prodrome.
See also BLISTER; HERPES SIMPLEX; HERPES ZOSTER;
GENITAL HERPES.
protozoa Single-celled organisms such as ame-
bas. Many protozoa are parasitic and require host
organisms for survival. Some protozoa are patho-
genic, notably those that cause MALARIAand infec-
tions such as AMEBIASIS, BABESIOSIS, and GIARDIASIS.
Some protozoal infections are self-limiting and
others require treatment with medications such as
antibiotics.
See also ANTIBIOTIC MEDICATIONS; BACTERIA; FUN-
GUS; PARASITE; VIRUS.
rabies A potentially fatal illness resulting from
INFECTIONwith the rabies VIRUS, which belongs to
the Lyssavirusviral family. Rabies is very rare in
people though a common infection in wild ani-
mals who can transmit the infection to unvacci-
nated pets such as dogs and cats or to people
through bites. Raccoons, skunks, coyotes, and bats
are reservoirs for the rabies virus; though infected
with the rabies virus, these animals do not them-
selves become ill with rabies. Nearly any animal
may acquire rabies infection as a result of contact
with saliva or other secretions from an infected
animal, usually a bite.
In animals and humans the rabies virus infects
the CENTRAL NERVOUS SYSTEM. It travels via the
PERIPHERAL NERVESto the BRAIN, where it replicates
within brain neurons (NERVEcells). Symptoms of
illness generally appear one to three months after
exposure, though the INCUBATION PERIODmay be as
short as a few days or as long as several years.
Once symptoms appear rabies is fatal. The illness
of rabies is ENCEPHALITIS.
The most effective treatment for rabies infec-
tion in people is postexposure prophylaxis, which
consists of one injection of human rabies
IMMUNOGLOBULINand five injections of rabies VA C-
CINEadministered at regular intervals after a bite
from a potentially infected animal. The vaccine
injections are given in the upper arm and are sim-
ilar in discomfort to receiving a tetanus shot. The
course of postexposure prophylaxis covers 28 days
and appears to be 100 percent effective. People at
high risk for rabies exposure, such as those who
work with animals, can receive rabies vaccinations
to prevent infection, though they also need post-
exposure prophylaxis if bitten.
See also IMMUNIZATION.retroviruses See VIRUS.Rocky Mountain spotted fever An illness result-
ing from INFECTION with the bacterium Rickettsia
rickettsii. Tick bites spread Rocky Mountain spotted
FEVER, so-named because of the characteristic RASH
the illness causes. Symptoms generally appear
within five days of a tick bite and include- fever
- slight RASH
- NAUSEAand VOMITING
- severe HEADACHE
- MUSCLE PAIN
Symptoms become rapidly more severe as the
illness progresses. Diagnosis is primarily clinical,
based on the presentation of symptoms in combi-
nation with a history of tick bite or exposure to
settings where tick bites are possible (such as hik-
ing or camping in wooded areas). Treatment is
prompt administration of doxycycline or tetracy-
cline, ANTIBIOTIC MEDICATIONS that are especially350 Infectious Diseases