Microbial Diseases Of The Cardiovascular and Lymphatic Systems |
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Plague is caused by Yersinia pestis. The vector is usually the rat flea (Xenopsylla cheopis).
Reservoirs for plague include European rats and North American rodents (ground squirrels and prairie dogs).
Signs of bubonic plague include bruises on the skin and enlarged lymph nodes (buboes).
Bubonic Plague
The bacteria can enter the lungs via blood and cause pneumonic plague. Pneumonic plague is easily spread by airborne droplets from humans or animals.
Laboratory diagnosis is based on isolation and identification of the bacteria.
Sstreptomycin is effective in treating plague, but must be administered promptly after exposure to the disease. Prevention is accomplished by controlling rat populations.
U.S. Geographic Distribution of Human Plague, 1970-1997
Relapsing fever is caused by Borrelia species and transmitted by soft ticks (Ornithodoros).
The reservoir of the disease is rodents.
Signs include fever, jaundice, and rose-colored spots. Signs recur three or four times after apparent recovery,
Laboratory diagnosis is based on the presence of spirochetes in the patient’s blood.
Treatment is with penicillin or cephalosporins.
Lyme disease is caused by Borrelia burgdorferi and is transmitted by a tick (Ixodes).
Lyme disease is prevalent on the U.S. Atlantic Coast.
Field mice provide the most important animal reservoir.
Early symptoms are rash at the bite site and flu-like symptoms. Later signs are irregular heartbeat, neurological signs, and arthritis.
Diagnosis is based on serological tests and clinical symptoms.
Antibiotics are effective when administered early in the disease. Later stages require large amounts of intravenous antibiotics.
Doxycycline or amoxicillin are used early, ceftriaxone or cefotaxime are used for late complications.
Lyme Disease in the United States, Reported Cases by County
Life Cycle of the Tick Vector of Lyme Disease
Bull's-eye Rash of Lyme Disease
Human ehrlichiosis (human granulocityc - HGE, and human monocytic - HME) is a flu-like disease caused by Ehrlichia species. It is similar to typhus, and like typhus is occasionally fatal.
HGE is found primarily in the northeast and is transmitted by Ixodes ticks - it occasionally occurs as a coinfection with Lyme disease.
HME is more prevalent in southern states. It is caused by a different species of Erlichia and transmitted by a different tick (the Lone Star tick)
The treatment is doxycycline.
Ehrlichiosis
Typhus is caused by rickettsias, obligate intracellular parasites of eukaryotic cells.
The human body louse Pediculus humanus corporis transmits Rickettsia prowazekii in its feces, which are deposited while the louse is feeding.
Epidemic typhus is prevalent in crowded and unsanitary living conditions that allow the proliferation of lice.
The signs of typhus are rash, prolonged high fever, and stupor.
Tetracyclines and chloramphenicol are used in treatment.
Endemic murine typhus is a less severe disease caused by Rickettsia typhi and transmitted from rodents to humans by the rat flea.
Rickettsia rickettsii is a parasite of ticks (Dermacentor spp.) in the southeastern U.S., Appalachia, and the Rocky Mountain states.
The rickettsia may be transmitted to humans, in whom it causes tickborne typhus fever. (The reservoir and the vector are ticks).
Chloramphenicol and tetracyclines effectively treat Rocky Mountain spotted fever, or tickborne typhus.
Serological tests are used for laboratory diagnosis.
U.S. Geographic Distribution of Rocky Mountain Spotted Fever By State, 1994-1998
Life Cycle of The Tick Vector of Rocky Mountain Spotted Fever
Rash Caused by Rocky Mountain Spotted Fever
