D–E

diphtheria An illness that results from INFECTION
with the bacterium Corynebacterium diphtheriae.
Routine childhood IMMUNIZATIONhas made diph-
theria rare in the United States, though the infec-
tion can occur in people who do not receive a
booster VACCINEevery 10 years and is common in
other parts of the world.
Infection may involve the NOSEand THROAT(res-
piratory diphtheria) or the SKIN(cutaneous diph-
theria). C. diphtheriae BACTERIA that infect the
throat produce a toxin that causes a thick layer of
cells and mucus to accumulate in the throat,
forming a membrane that impairs BREATHING. Res-
piratory diphtheria is life threatening and requires
urgent administration of diphtheria ANTITOXIN,
which counters the toxin the C. diphtheriaebacte-
ria produce, in combination with ANTIBIOTIC MED-
ICATIONSto kill the C. diphtheriaebacteria (typically
erythromycin or penicillin G). Diphtheria that
occurs in the United States is most often cuta-
neous. Cutaneous diphtheria causes painful, red
sores on the skin. Antibiotic therapy is often ade-
quate to treat the infection, though sometimes
doctors also administer diphtheria antitoxin.
The INCUBATION PERIODfor either type of diph-
theria is two to five days after exposure. The infec-
tion is contagious for up to two weeks after
symptoms emerge. The course of uncomplicated
illness is four to six weeks. Respiratory diphtheria
(especially when untreated) may result in compli-
cations that include MYOCARDITIS (INFLAMMATION
and infection of the HEART MUSCLE), NEURITIS,RESPI-
RATORY FAILURE, and death. Childhood immuniza-
tion with booster vaccines every 10 years is the
most effective means of prevention. Some people
are carriers of C. diphtheriae bacteria, which
requires human hosts for survival. Carriers have

the infection present in their bodies but do not

become ill, though they can pass the infection to

others. ANTIBIOTIC PROPHYLAXISprevents infection in

people who are exposed to C. diphtheriae.

See also CHILDHOOD DISEASES; PREVENTIVE HEALTH

CARE AND IMMUNIZATION.

encephalitis INFLAMMATION and INFECTIONof the

BRAIN. Encephalitis usually results from infection

with a VIRUS and is potentially life threatening.

Infection can enter the brain via pathogens that

are small enough to pass across the BLOOD–BRAIN

BARRIERor that are able to follow neural pathways

(the routes of nerves) into the brain. The most

common cause of encephalitis is infection with an

arbovirus transmitted through the bite of a mos-

quito or tick. Other viruses that typically cause

common infections may affect the brain to cause

encephalitis, and encephalitis may develop as a

complication of viral infection (and less commonly

bacterial infection) elsewhere in the body. TOXO-

PLASMOSIS, a parasitic infection, may also cause

encephalitis.

VIRUSES THAT CAN CAUSE ENCEPHALITIS

CYTOMEGALOVIRUS(CMV) California VIRUS

eastern equine virus EPSTEIN-BARR VIRUS

HERPES SIMPLEXvirus (HSV) LaCrosse virus

MUMPSvirus Powassan virus

RUBELLAvirus rubeola (MEASLES) virus

St. Louis virus varicella zoster viruses

West Nile virus western equine virus

Symptoms and Diagnostic Path

The symptoms of encephalitis differ somewhat in

children and in adults. Children often become

lethargic, confused, irritable, and sensitive to light;

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