Anthrax

by Daniela Gera, DVM
Resident in Applied Epidemiology
Virginia-Maryland Regional College of Veterinary Medicine
University of Maryland, College Park, MD

10/17/2001

Summary:Anthrax is an acute febrile infectious disease that can affect virtually all mammals, including humans.
Etiology:A spore forming Gram positive non-motile, encapsulated bacterium Bacillus anthracis

In Humans
Transmission:Transmission via direct contact with tissues from animals soil, inhaling spores, biting insects (infrequent), or eating undercooked meat from an infected animal. Often an occupational exposure in those exposed to animals and animal products ("woolsorters disease").
Diagnosis:Diagnosis is made by finding the organism in blood, lesions, or discharges; culture,; or paired serology.
Symptoms:

Cutaneous form (Malignant Carbuncle)

  • About 95% of human cases.
  • First pruritis (itchiness), then a lesion develops. The lesion is at first papular, then vesicular. After 2-6 days it develops into a black eschar (depressed ulcer) that is surrounded by edema. The primary lesion is not usually painful, but secondary edema or infection may be painful.
  • Areas normally affected: forearms, head, and hands.
  • Untreated infection can spread to regional lymph nodes, cause septicemia, or even cause meningitis.
  • Normally the bacterium will enter through an abrasion or cut.
  • Case Fatality is between 5 and 20%.

Respiratory form

  • Initially, mild nonspecific respiratory tract infection, in 3-5 days there can be acute symptoms of respiratory distress, fever, and shock.
  • Radiographic changes may be seen in the chest, including evidence of mediastinitis.
  • Transmission is by inhalation of spores.
  • Case fatality is between 95 to 100% (often because of delays in diagnosis and treatment).

Gastrointestinal

  • Rare form of the disease.
  • Normally an explosive outbreak, like food poisoning.
  • Relatively common in developing countries.
  • Signs are: abdominal distress, fever, septicemia, and death.
  • Transmission is via ingestion of contaminated meat.
  • Case fatality is between 50 and 100%.

Occupations that place people at increased risk: processing hides, hair, bone, bone products, or wool; veterinarians, wildlife workers, agricultural workers who come into contact with infected animals.
Incubation period:A few hours to 7 days. Normally within 48 hours, in some cases up to 60 days.
Communicability:Very unlikely
Treatment:Antibiotics (such as ciprofloxacin)
NOTE: Exposure to anthrax spores is necessary for development of disease, HOWEVER such exposure frequently does not lead to disease. Exposure does not equal disease!

In Wildlife
Hosts:Antelopes, camels, sheep, goats, cattle, and other herbivores. When carnivores or humans are infected, they are incidental hosts.
Resevoir:Anthrax spores can live in the soil for many years, and are resistant to extremes of temperature, chemical disinfectants, and desiccation.
Occurrence:Can be found globally. Anthrax is endemic in South and Central Americas, southern and eastern Europe, Asia, Africa, the Middle East, and the Caribbean. Primarily in agricultural regions. In the United States, it is rare, but found primarily in South Dakota, Nebraska, Arkansas, Mississippi, Louisiana, Minnesota, Texas, and California.
Seasonality:Outbreaks from soil-born infection usually occur during warmer seasons, when the lowest daily temperature is >60 F. Sometimes outbreaks occur after heavy rainfall, flooding, or drought (times of climatic change.)
Clinical Signs:

Peracute form: staggering, dyspnea, trembling, collapse, convulsions, and death. Body temperature may be very high.

Acute form: Fever, period of excitement followed by depression, stupor, respiratory and cardiac distress, staggering, convulsions, and death.

Chronic form: localized subcutaneous edematous swelling in ventral neck, thorax, and shoulders.
Lesions:

The carcass of an animal that died from anthrax should not be necropsied in the field for human health reasons.

Rigor mortis is usually absent or incomplete, lesions of septicemia may be seen, with multiple hemmorhages. Blood is thick and fails to clot, spleen is large, soft, dark in color, and semi-fluid.
Transmission:Livestock become infected when grazing where soil contains infectious spores.
Incubation Period:Typically, 3-7 days, although can range from 1-14 days.
Sample Submission:Lab should be contacted first, then sample submission of blood or lymph node for culture; antigen and antibody tests are available.
Diagnosis: Isolation of Bacillus anthracis from the blood, skin lesions, or respiratory secretions; polymerase chain reaction, IF, Western blot, and ELISA. (last two for antibodies.)
Treatment:Antibiotics such as penicillin, oxytetracycline, and others.
Prevention/Control:Livestock vaccination, notification of regulatory officials if there is an outbreak, quarantine, disposal of dead animals, sanitation, control of scavengers, and prevention of over-grazing (which increases access to spores in general).

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