See Chp 5 for parasitic/fungal/helminthic infections
A.
BACTERIAL:
1. Plague
– Yersinia
pestis;
zoonosis; spread from infected rodents to humans by fleas; incidence of disease is low;
bacilli travel in lymphatics to lymph nodes where they cause enlargements caused buboes (especially in armpits and groin);
hemorrhages turn skin black (“Black Death”); deaths can be prevented with
antibiotic treatment.
2. Tularemia
– Francisella
tularensis – zoonosis;
reservoir: usually cottontail rabbits (number
of causes rises during rabbit-hunting season); first isolated in Tulare County, CA in
1911; low incidence in US; disease is an hazard for taxidermists, hunters, trappers;
transmission: breaks in skin, bite from
arthropod vector (tick, deer fly), inhalation of aerosols during skinning, consumption of
contaminated meat; clinical signs: ulcer
formation at the entry site, fever, severe headache, and buboes (enlargement of lymph
nodes); one form can lead to a septicemia that resembles typhoid fever; vaccine does exist
but frequent boosters are required.
3. Relapsing
Fever
– Borrelia recurrentis (spirochete) and
other species of this same genus; transmitted by ticks and human body and head lice; lice
are crushed and their body contents scratched into the skin; ticks transmit bacteria in
their salivary secretions several days of high fever, respites, and shorter periods of
fever due to changes in organisms’ antigens; can cross placenta; treat with
antibiotics; syphilis patients were once purposely infected with relapsing fever to kill
syphilis bacteria.
4. Lyme
Disease
– Borrelia burgdorferi (spirochete);
transmitted by deer ticks (Ixodes damini);
white-tailed deer are a reservoir; develop flu-like symptoms; the rash erythema chronicum
migrans characterizes the disease (“bull’s-eye” rash – concentric
rings around initial site of tick bite); other symptoms include arthritis, myocarditis,
etc.; there is a vaccine for dogs; treat with antibiotics.
a. Endemic
(murine) typhus – murine
refers to rats and mice; Rickettsia typhi
(obligate intracellular parasite); does occur in Texas; transmitted by fleas (fleas
defecate while biting, infecting the humans); fever, chills, crushing headache; disease is
self-limiting and lasts about 2 weeks if untreated; mortality is low.
b. Epidemic
typhus
(classic or louseborne typhus) – Rickettsia prowazekii (obligate intracellular
parasite); epidemics were halted with discovery of pesticide DDT during WWII; transmitted
by body lice (when a louse bites, it defecates; as victim scratches bite, they inoculate
the microorganisms into the wound); fever and headache; rash starts on trunk and spreads
to extremities (rarely affects palms or soles); vaccine is available; treat with
antibiotics; mortality can range to 40% if untreated.
c. Brill
Zinsser disease
(recurrence of epidemic typhus) – disease has milder symptoms, in shorter in
duration, and often does not cause a skin rash; caused by reactivation of latent
microorganisms harbored in lymph nodes.
6. Rocky
Mountain Spotted Fever
– Rickettsia rickettsii (obligate
intracellular parasite); transmitted to humans by dog ticks; fever, headache, weakness;
rash begins on ankles and wrists and progresses toward trunk (reverse of progression in
typhus); rash is prominent on palms and soles; blood vessel damage cause hemorrhages
throughout the body; treat with antibiotics.
7. Rickettsial
pox
– Rickettsia akari (obligate intracellular
parasite); transmitted by mites fond on house mice; disease is mild and lesions resemble
those of chickenpox; often misdiagnosed as chicken pox.
B.
VIRAL:
1. Yellow
Fever
– monkeys are reservoirs of the disease; transmitted to humans by mosquitoes; many
victims suffer severe liver damage and become jaundiced.
2. Encephalitis
–
discussed under nervous system diseases; transmitted by mosquitoes.