MM 209-210; ID 1003-1008
NAMES OF DISEASE:
The spores of Bacillus
anthracis are commonly found on animal pelts. When the spore is deposited
on an open wound, it germinates and produces a dermatotoxin which causes
the formation of a malignant pustule with a black eschar.
This is a Gram+ sporeforming rod that grows aerobically. It
is non-motile and encapsulated. The capsule is made of polyglutamic acid.
The virulence of B. anthracis is directly related to the presence of a capsule (D-glutamic acid). Even avirulent strains produce an exotoxin. The toxin is comprised of three distinct, antigenically active components. All are thermolabile proteins or lipoproteins:
Factor I (Edema factor) - necessary for the edema-producing activity of the toxin
Factor II (Protective antigen) - induces protective antibodies
Factor III (Lethal factor) - essential for lethal effect
Edema factor plus protective antigen = edema
factor plus protective antigen = death
The primary lesion usually develops at the site of a minor scratch or abrasion in an exposed area of the face, neck or upper extremities after an incubation period of 1-7 days. It begins as a small, inflamed papule which later becomes vesicular. Eventually the vesicle breaks down and is replaced by a black eschar. A striking "gelatinous" non-pitting edema surrounds the eschar for a considerable distance. At no stage is the lesion particularly painful. In severe cases of cutaneous anthrax the regional lymph nodes become enlarged and tender and the blood stream is eventually invaded.
Cutaneous anthrax should be considered whenever a painless, pruritic papule on an exposed part of the body progresses through a vesicular stage to become a black, depressed eschar, regardless of antimicrobial therapy. The recovery of B. anthracis from vesicular fluid or exudate from the ulcer confirms the diagnosis. A differential diagnosis should include:
2. Staphylococcal skin lesions
- more pyogenic, spread more rapidly, usually multiple lesions. Painful,
only small black
3. Tularemia - the most common
type is ulceroglandular. The skin is ulcerated at the point of entry and
the regional lymph
nodes become enlarged. This can be differentially diagnosed by serological techniques or isolation of the organism.
Etiological agent is gram negative (Francisella tularensis).
4. Plague. Symptoms are similar to tularemia. Etiological agent is gram negative. (Yersinia pestis).
5. Milker's nodules. These occur only on the hands and do not generally form an eschar.
6. Orf. Generally occurs
on the fingers. The orf virus is a poxvirus which shows characteristic
intracytoplasmic inclusion bodies).
In the past there was a vaccine
available for those with occupational exposure to anthrax. More recently
the U.S. military has signed an agreement with the sole producer of the
vaccine for exclusive use of the vaccine. If the military vaccine is the
same as the vaccine previously used to prevent occupational anthrax then
it is an alum precipitate of the protective antigen. There is some speculation
that the military has added the lethal factor and the edema factor to the
preparation. The military schedule calls for 3 injections, 2 weeks apart
followed by injections at 6, 12 and 18 months with an annual booster.