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Anthrax: What is it?

Dr. Lila Miller, D.V.M., ASPCA

What is anthrax?
Anthrax is a systemic bacterial disease caused by a spore-forming organism known as bacillus anthracis.

Why is it so dangerous?

Anthrax: What is it?


The bacillus forms spores that are extremely resistant to chemical disinfection and natural environmental decontamination (extremes of temperature or drying out). It can persist in soil for years. The spores form when the bacillus is discharged from an infected animal or exposed to oxygen from an opened carcass. The most common form of anthrax is the cutaneous form, which is easily treated with many readily available antibiotics. If the spores are inhaled, however, this normally rare form of the disease has a high mortality rate if not diagnosed and treated early. An effective disinfectant is bleach, diluted 1:10.

Who gets it?
Anthrax is a soil borne disease that primarily affects domestic animals, most commonly herbivores (sheep, goats, horses, cattle, antelope, etc). It can cause disease in all warm-blooded mammals, although dogs, cats and carnivores are fairly resistant to it.

It occurs worldwide. It is not very common in the US, but when it does occur, it is found primarily in agricultural regions in South Dakota, Nebraska, Arkansas, Mississippi, Louisiana, Texas and California. The disease also occurs in small areas in other states. Natural outbreaks occur when floods or other natural environmental phenomena, including drought, allow anthrax organisms in the soil to multiply and spread.

It is contagious to people, and most commonly seen in people who process the hides and hair, wool, bone and bone products of sheep and goats. It is commonly known as the “woolsorter’s disease”. It is also seen in veterinarians and other agricultural workers as an occupational hazard.

What is the incubation period?
The incubation period is usually 7 days or less.

How is it diagnosed?
There are several tests available to diagnose the disease. Diagnosis is made by examining stained smears of blood, needle aspirates or swabs of infected tissue. Blood tests and bacterial cultures also provide means of diagnosis. Extreme care must be taken when handling tissue samples of infected animals to make certain not to spread the bacteria. Veterinarians are often advised not to perform necropsies on animals in the field they suspect of having died of anthrax because of the risk of spreading the spores.

How is it transmitted?
It is not transmitted from human to human or from animals to humans. Infection is acquired

  1. through direct contact with the infected tissues of an animal, or contaminated hair, wool, hides or soil. The organism can penetrate cuts in the skin and form skin lesions. This is referred to as cutaneous form.
  2. The spores can be inhaled. This inhalation form is particularly deadly if not treated promptly and aggressively.
  3. The organism can be spread by ingesting contaminated meat, bone meal or other feed products. This is known as the gastrointestinal form. Current concerns about the spread of the disease as a biological weapon revolve around objects being coated with a powdery substance containing the anthrax spores. The spores are either inhaled or enter through breaks in the skin.

What are the signs in man?
As described above, there are three forms, cutaneous, gastrointestinal and inhalation. The inhalation and gastrointestinal forms are rare and have a high mortality rate compared to the cutaneous form.
This is the most common form of the disease. Bacteria in infected blood or tissues penetrate broken skin and form skin lesions (fluid filled blisters, carbuncles, skin ulcers).
This is a rare but highly fatal hemorrhagic form of the disease that occurs when spores from infected hair or wool are inhaled.(woolsorter’s disease) The disease starts off with mild respiratory signs and fever and chest pains, which progress to septicemia and death within a few days if not treated soon after exposure.
The intestinal form can be acquired from eating contaminated meat. The signs include nausea, vomiting, diarrhea, loss of appetite, cramps and fever. The diarrhea can become bloody later in the course of the disease.

What are the signs in animals?
The signs in animals vary.

Dogs and cats:
The most common form of anthrax seen in dogs is the gastrointestinal form acquired from eating contaminated meat. The signs include swelling of the head and neck, local inflammation, necrosis and edema of the upper gastrointestinal tract, including the liver. There may also be enlargement of the lymph nodes. The non-specific signs include vomiting, diarrhea, constipation and loss of appetite.

The signs are fever, chills, colic, loss of appetite, depression, weakness, bloody diarrhea, and swelling around the neck, sternum, lower abdomen and external genitalia. Death usually occurs within 2 or 3 days.

Cattle, sheep and goats:
The signs commonly feature fever, loss of appetite, depression, staggering, difficulty breathing, convulsions and death.

The signs are usually either sudden death or swelling around the throat.

There are a few distinct features to anthrax. The blood is very dark and does not clot, and bloody discharges are seen from the mouth, nose and rectum. After death, there is bloating and a lack of rigor mortis.

How is it treated?

Penicillin is the antibiotic of choice in most cases. Many other antibiotics such as tetracycline or doxycycline are also effective. In the case of inhalation anthrax, the most effective antibiotic is ciprofloxacin. The course of treatment is 60 days. Cipro and other antibiotics should not be taken unless prescribed by a veterinarian or physician. Taking the drug randomly just in case leads to the chance of drug side effects and the development of antibiotic resistance.

Is there a vaccine?
There are both human and animal vaccines, but the human vaccine is not available to the general public. The animal vaccine cannot be used on humans. The human vaccine can be used in conjunction with antibiotics to shorten the course of antibiotic treatment from 60 to 30 days.

What should be done in case of an exposure?
The following steps should be taken.

  2. Call 911. Explain the situation carefully and follow their directions.
  3. Isolate the animal (or object) and restrict access to only one or two people at most.
  4. Make certain that any workers who have contact with the animal are wearing a surgical mask, hat, gloves and protective garments. If the shelter does not have these items they should obtain them.
  5. Get as complete a history as possible, but do not touch the animal or take any samples until the appropriate authorities arrive or give you other instructions.
  6. Make a list of any and all people that you know have had contact with the animal. This will aid the authorities in their investigation.
  7. Follow instructions for disinfecting the premises afterward.

While anthrax is a serious problem, it should be remembered that in some areas of the country, veterinarians and other agricultural workers have been dealing with the disease for years. Understanding the facts about the disease, staying calm and following the instructions from the authorities should help keep both the staff and animals in our care safe and healthy in case of an exposure.

Sources: Greene, Infectious Diseases of the Dog and Cat
Merck Veterinary Manual
Garvey, Michael- Animal Medical Center
Haynes, Keeping Livestock Healthy

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