Anthrax natural history, complications and prognosis
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]
Overview
Natural History
Cutaneous Anthrax
Anthrax eschars are generally seen on exposed unprotected regions of the body, mostly on the face, neck, hands and wrists. Generally cutaneous lesions are single, but sometimes two or more lesions are present. For example, with infection resulting from skinning an infected dead animal, multiple lesions may be seen on hands, wrists or arms.
The incubation period ranges from as little as 9 hours to 3 weeks, mostly 2 to 6 or 7 days.
The general scenario is as follows:
- Day 0 entry of the infecting B. anthracis (usually as spores) through a skin lesion (cut, abrasion, etc.) or (possibly as vegetative forms or vegetative forms and spores) by means of a fly-bite.
- Days 2-3 A small pimple or papule appears.
- Days 3–4 A ring of vesicles develops around the papule. Vesicular fluid may be exuded. Unless the patient was treated, capsulated B. anthracis can be identified in appropriately stained smears of this fluid, and the bacterium can be isolated by culture. Marked oedema starts to develop. Unless there is secondary infection, there is no pus and pathognomonically the lesion itself is not painful, although painful lymphadenitis may occur in the regional lymph nodes and a feeling of pressure may result from the oedema. The lesion is usually 1–3 cm in diameter and remains round and regular. Occasionally a lesion may be larger and irregularly shaped.
- Days 5–7 the original papule ulcerates to form the characteristic eschar. topical swabs will not pick up B. anthracis. Detection in smears or by culture requires lifting the edge of the eschar with tweezers (this gives no pain unless there is secondary infection) and obtaining fluid from underneath. The fluid will probably be sterile if the patient has been treated with an antibiotic. Edema extends some distance from the lesion. Systemic symptoms are low-grade fever, malaise and headache. If the cutaneous reaction is more severe, especially if located on the face, neck or chest, clinical symptoms may be more severe with more extensive edema extending from the lesion, toxamia, a change in mental status, high fever, hypotension, regional lymphadenomegaly and the patient unable to eat or drink. Tracheotomy is a life-saving procedure in patients having a cutaneous lesion on the face or neck with an extensive oedema leading to compression on the trachea. this clini- cal manifestation is very dangerous (doganay et al., 1987; doganay, 1990).
- Day 10 the eschar begins to resolve; resolution takes several weeks and is not hastened by treatment. Clinicians unaware of this suffer from concern that the treatment has been inef- fective. A small proportion of untreated cases develop sepsis or meningitis with hyperacute symptoms.
Time to resolution will depend on the size, location and local severity of the lesion. The initial crust separates several weeks after onset, with subsequent healing by granulation. Sometimes the separation of the crust is delayed and the lesion may become secondarily infected. In this situation, the crust should be excised surgically. Lesions characterized by “malignant edema” can be expected to take months to heal. Very large lesions may require skin grafts, and lesions in locations such as the eyelid may require surgical intervention due to scarring.
Complications
Prognosis
The anthrax prognosis will depend on a number of factors, including:
- The type of anthrax
- How early the anthrax is diagnosed
- The strain of anthrax bacteria
- The patient's age and health condition