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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Corynebacterium,Listeria,and Bacillus

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Anthrax : Clinical Aspects

Cutaneous anthrax usually begins 2 to 5 days after inoculation of spores into an exposed part of the body, typically the forearm or hand.

ANTHRAX :   CLINICAL   ASPECTS

Cutaneous anthrax usually begins 2 to 5 days after inoculation of spores into an exposed part of the body, typically the forearm or hand. The initial lesion is an erythematous papule, which may be mistaken for an insect bite. This papule usually progresses through vesicular and ulcerative stages in 7 to 10 days to form a black eschar (scab) surrounded by edema. This lesion complex is known as the “malignant pustule,” although it is neither malignant nor a pustule. Associated systemic symptoms are usually mild, and the lesion typically heals very slowly after the eschar separates. Less commonly, the disease progresses with massive local edema, toxemia, and bacteremia; it has a fatal outcome if untreated.

Pulmonary anthrax is contracted by inhalation of spores. Historically, this occurred when contaminated hides, hair, wool, and the like are handled in a confined space (wool-sorter’s disease) or following laboratory accidents. Today it is the form we would expect from the dissemination of a spore aerosol in biologic warfare. In the pulmonary syndrome, 1 to 5 days of nonspecific malaise, mild fever, and nonproductive cough lead to progressive respiratory distress and cyanosis. Massive spread to the bloodstream and CNS follow rapidly. Mediastinal edema was a prominent finding in the postal workers. If untreated, pro-gression to a fatal outcome is usually very rapid once bacteremia has developed.

DIAGNOSIS

Culture of skin lesions, sputum, blood, and CSF are the primary means of anthrax diag-nosis. Given some suspicion on epidemiologic grounds, Gram stains of sputum or other biologic fluids showing large numbers of Gram-positive bacilli can indicate the diagnosis. In September of 2001, diagnosis of the first case in Florida was speeded by an infectious disease specialist who knew such rods were extremely rare in the spinal fluid. Such bacilli are also unusual in sputum.

B. anthracis and other Bacillus species are not difficult to grow. In fact, clinical labo-ratories frequently isolate the nonanthrax species as environmental contaminants. The saprophytic species are usually -hemolytic and motile; these features can be used to ex-clude B. anthracis. Blood cultures are positive in most cases of pulmonary anthrax.

TREATMENT

Antimicrobial treatment has little effect on the course of cutaneous anthrax but does pro-tect against dissemination. Almost all strains of B. anthracis are susceptible to penicillin, which remains the treatment of choice for all forms of anthrax. Doxycycline or ciprofloxacin are alternatives and are also recommended for chemoprophylaxis in the case of known or suspected exposure.

PREVENTION

The most important preventive measures are those that eradicate animal anthrax and limit imports from endemic areas. Vaccines are also useful. Pasteur’s vaccine used a live strain attenuated by repeated subculture that resulted in the loss of a plasmid encoding toxin production. A similar live vaccine is still effective for animals, but inactivated human vac-cines have a less certain efficacy. The vaccine used by the US military is prepared from filtrates of a nonencapsulated B. anthracis strain that produces the protective antigen component of the toxin complex. Its acceptance is complicated by fears that the architects of biological warfare may have crafted strains for which this vaccine is not protective. Proof of the efficacy of the vaccine in humans is neither practical nor ethical.

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