Misc 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.

5. Typhus Fever – occurs in a variety of forms:

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.