Microbial Diseases Of The Cardiovascular and Lymphatic Systems |
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Tularemia is caused by Francisella tularensis. The reservoir is small wild mammals, especially rabbits (it is often referred to locally as rabbit fever).
Signs include ulceration at the site of entry, followed by septicemia. Multiple organs may be infected and if inhaled pneumonia may result.
Humans contract tularemia by handling diseased carcasses, eating undercooked meat of diseased animals, and being bitten by certain vectors (such as deer flies).
F. tularensis is resistant to phagocytosis.
Laboratory diagnosis is based on an agglutination test on isolated bacteria.
Treatment is with streptomycin.
Tularemia Cases in the United States
Brucellosis can be caused by Brucella abortus, B. melitensis, and B. suis.
In the United States, elk and bison constitute the reservoir of B. abortus, which is the most common species in the U.S.
The disease is usually mild and self-limiting. Formerly acquired mostly by ingesting cow or other milk, now mostly by contact with animal carcasses.
The bacteria enter through minute breaks in the mucosa or skin, reproduce in macrophages, and spread via lymphatics to liver, spleen, or bone marrow.
Signs include malaise and fever that spikes each evening (undulant fever).
Brucellosis caused by B. suis causes the occasional formation of destructive abscesses.
The most common species in the rest of the world, B. melitensis, causes the most severe form of brucellosis, undulant fever.
The disease is severe, often resulting in disability or death. Fever typically spikes to about 104 F each evening.
Diagnosis is based on serological tests.
Treatment is prolonged because the bacteria are intracellular. Tetracycline (doxycycline) and streptomycin are used in combination.
Bacillus anthracis causes anthrax. In soil, endospores can survive for up to 60 years.
Grazing animals acquire an infection after ingesting the endospores.
Humans contract anthrax by handling hides from infected animals. The bacteria enter through cuts in the skin or through the respiratory tract.
Entry through the skins causes cutaneous anthrax and results in a pustule that can progress to septicemia. Over 90% of naturally occuring cases in humans are cutaneous.
Cutaneous Pustule of Anthrax
Entry through the respiratory tract results in inhalational or pulmonary anthrax, the most dangerous form. Endospores inhaled into the lungs have a high probability of entering the bloodstream, where they may proliferate and cause septic shock. This usually kills the patient within 24 - 36 hours (the mortality rate is nearly 100%).
Gastrointestinal anthrax is caused by ingestion of undercooked food containing the spores. This form is fairly rare but usually has a mortality rate of greater than 50%.
Diagnosis is based on isolation and identification of the bacteria.
Treatment is with ciprofloxacin or doxycycline.
Gangrene
Soft tissue death from ischemia (loss of blood supply) is called gangrene.
Microorganisms grow on nutrients released from gangrenous cells.
Gangrene is especially susceptible to the growth of anaerobic bacteria such as Clostridium perfringens, the causative agent of gas gangrene.
C. perfringens can invade the wall of the uterus during improperly performed abortions.
Surgical removal of necrotic tissue, hyperbaric chambers, amputation, and antibiotics (penicillin) are used to treat gas gangrene.
Gangrene
Hyperbaric Chambers Used to Treat Gas Gangrene
Systemic Disease Caused by Bites and Scratches
Pasteurella multocida, introduced by the bite of a dog or cat, can cause septicemia.
Anaerobic bacteria such as Clostridium, Bacteroides, and Fusobacterium infect deep animal bites.
Cat-scratch disease is caused by Bartonella henselae. It is a systematic infection characterized by prolonged fever. It is usually self-limiting, although in some cases may be fatal.
Treatment is with azithromycin.