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Diagnosis of Anthrax

The most critical aspect in making a diagnosis of anthrax is a high index of suspicion associated with a compatible history of exposure. Cutaneous anthrax should be considered following the development of a painless pruritic papule, vesicle, or ulcer—often with surrounding edema (swelling)—that develops into a black eschar. With extensive or massive edema, such a lesion is almost pathognomonic. Gram’s stain or culture of the lesion will usually confirm the diagnosis. The differential diagnosis should include tularemia, staphylococcal or streptococcal disease, and orf (a viral disease of sheep and goats, transmissible to humans).

The diagnosis of inhalational anthrax is extraordinarily difficult, but the disease should be suspected with a history of exposure to a B anthracis–containing aerosol. The early symptoms are entirely nonspecific. However, (1) the development of respiratory distress in association with radiographic evidence of a widened mediastinum due to hemorrhagic mediastinitis, and (2) the presence of hemorrhagic pleural effusion or hemorrhagic meningitis should suggest the Diagnosis. Sputum examination is not helpful in making the diagnosis, since pneumonia is not usually a feature of inhalational anthrax.

Gastrointestinal anthrax is exceedingly difficult to diagnose because of the rarity of the disease and its nonspecific symptoms. Only with a history of ingesting contaminated meat in the setting of an outbreak is Diagnosis usually considered. Microbiologic cultures are not helpful in confirming the diagnosis. The diagnosis of oropharyngeal anthrax can be made from the clinical and physical findings in a patient with the appropriate epidemiological history.

Meningitis due to anthrax is clinically indistinguishable from meningitis due to other causes. An important distinguishing feature is that the cerebral spinal fluid is hemorrhagic in as many as 50% of cases. The diagnosis can be confirmed by identifying the organism in cerebral spinal fluid by microscopy, culture, or both.

Serology is generally only of use in making a retrospective diagnosis. Antibody to protective antigen or the capsule develops in 68% to 93% 1, 2, 3, 4 of reported cases of cutaneous anthrax and 67% to 94% 5, 6 of reported cases of oropharyngeal anthrax.  A positive skin test to anthrax (an undefined antigen derived from acid hydrolysis of the bacillus that was developed and evaluated in the former Soviet Union) has also been reported 7 to be of value in the retrospective diagnosis of anthrax. Western countries have limited experience with this test 8.

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1.  Turnbull PCB, Leppla SH, Broster MG, Quinn CP, Melling J. Antibodies to anthrax toxin in humans and guinea pigs and their relevance to protective immunity. Med Microbiol Immunol. 1988;177:293–303.

2.  Buchanan TM, Feeley JC, Hayes PS, Brachman PS. Anthrax indirect microhemagglutination test. J Immunol. 1971;107:1631–1636.

3.  Sirisanthana T, Nelson KE, Ezzell J, Abshire TG. Serological studies of patients with cutaneous and oral-oropharyngeal anthrax from northern Thailand. Am J Trop Med Hyg. 1988;9:575–581.

4.  Harrison LH, Ezzell JW, Abshire TG, Kidd S, Kaufmann AF. Evaluation of serologic tests for Diagnosis of anthrax after an outbreak of cutaneous anthrax in Paraguay. J Infect Dis. 1989;160:706–710.

5.  Sirisanthana T, Nelson KE, Ezzell J, Abshire TG. Serological studies of patients with cutaneous and oral-oropharyngeal anthrax from northern Thailand. Am J Trop Med Hyg. 1988;9:575–581.

6.  Harrison LH, Ezzell JW, Abshire TG, Kidd S, Kaufmann AF. Evaluation of serologic tests for Diagnosis of anthrax after an outbreak of cutaneous anthrax in Paraguay. J Infect Dis. 1989;160:706–710.

7.  Shlyakhov EN, Rubinstein E. Human live anthrax vaccine in the former USSR. Vaccine. 1994;12:727–730.

8.  Pfisterer RM. Retrospective verification of the Diagnosis of anthrax by means of the intracutaneous skin test with the Russian allergen “anthraxin” in a recent epidemic in Switzerland. Salisbury Med Bull Suppl. 1990;68:80.

(This material has been derived from the Virtual Naval Hospital web site ww.vnh.org)

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