Pamela A. Davol, 76 Mildred Avenue, Swansea, MA  02777-1620.
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ANTHRAX:

What Dog Owners Want to Know

Anthrax, a highly fatal infectious disease that may infect all warm-blooded animals including dogs and humans, is acquiring much attention in relation to recent terrorist attacks on the United States because of its potential use as a biological weapon. Though obviously of great concern in regard to implications toward humans, many dog owners are also understandably concerned by the threat that anthrax may pose to their companion dogs. The following article provides information on this bacterial disease in regard to infection in dogs.

Cause: Anthrax is caused by infection with a gram-positive, non-motile, spore-forming bacterium known as Bacillus anthracis. The spore-forming characteristic of B. anthracis makes this bacteria extremely resistant to environmental conditions, such as heating, freezing, chemical disinfection or dehydration that typically destroy other types of bacteria. Thus, B. anthracis may persist for long periods of time within or on an infected environment or product. Under optimum growth conditions that often occur in neutral or alkaline, calcium or lime-rich soils, the spores vegetate, multiply and produce more spores that may be spread to transmit infection. Once the bacteria infect an animal or human, the organisms multiply and spread throughout the body. Anthrax bacterium produce a potent and lethal toxin that causes cellular death and breakdown of the tissues infected with the bacteria. This results in malignant systemic ulcers, inflammation, and organ damage eventually leading to organ failure. The bacteria spread throughout the body through the blood and lymphatic (immune) system. If the organisms gain access to the central nervous system (spinal chord, brain), meningitis occurs. If spores are inhaled, propagation of bacteria in the lungs results in a fatal pneumonia (inhalation anthrax). If spores gain access to the skin through wounds or abrasions, deep skin ulcerations develop (cutaneous anthrax). If spores are ingested, severe gastrointestinal and oral mucosal lesions develop (gastrointestinal anthrax). Under normal circumstances, anthrax outbreaks in the United States are an extremely rare occurrence.

Anthrax as a Biological Weapon: Several characteristics of the anthrax bacterium make it suitable for use as a biological weapon. Anthrax is extremely potent: inhalation of just one millionth of a gram of spores results in fatality; one kilogram has the potential to kill hundreds of thousands of people in a metropolitan area. In 1979, accidental release of anthrax spores from a military microbiology facility in the former Soviet Union caused an anthrax epidemic (inhalation anthrax) in humans living within a 4-km (approx. 2.5-mile) zone downwind of the facility with an approximate 86% mortality rate. Furthermore, livestock within a 50-km (approx. 32-mile) distance of the facility also died. In the event of terrorist attacks or warfare utilizing anthrax spores, inhalation anthrax and cutaneous anthrax are expected to be the primary mode of infection in targeted regions and would result in high incidence of casualties.  Potential spread of infection to regions not initially contaminated could occur through migration of wildlife and pose infection risk to dogs or humans who may come in contact with infected animal remains.

Transmission: Under normal conditions, outbreaks of anthrax infection occur during warm weather and typically following heavy rains. Livestock (cattle, horses, mules, sheep, goats) become infected when they graze in areas contaminated with bacterial spores. Flies and other insects may further spread the disease from infected animals to other animals. Infection may also occur if livestock are fed natural or artificial feeds that contain bonemeal derived from infected animals. Dogs and humans may acquire the disease by eating undercooked meat of infected animals, or by coming in contact with the blood, tissues, or body fluids of infected animals that harbor spores. Humans are also at risk to infection from inhaling spores when handling contaminated animals or remains. Anthrax is not directly communicable from an infected animal to another animal, between animal to human, or between human to human, even in the case of anthrax pneumonia, by usual social contact. For infection to occur, spores must gain access to the body by ingestion, inhalation, or through open wounds. When transmission occurs between individuals it is usually through exposure to infected tissue or body fluids, therefore, humans should practice universal precautions (wearing gloves, protective clothing, protective eye-gear, and masks) when handling remains, tissue, blood or other body fluids from potentially infected animals.

General Symptoms: Symptoms of anthrax may present similar to symptoms of many other conditions and may occur as an acute illness or chronic illness. In the acute form, symptoms occur rapidly in a previously healthy animal. High fever and an agitated state are quickly followed by chills, loss of appetite, depression, disorientation, difficulty breathing or exercise intolerance, muscle weakness, seizures, and death. Bloody diarrhea or bloody discharge from natural body orifices may be observed. In chronic cases, pustular lesions develop on the tongue and in the throat and swelling around the neck is typically observed and may lead to death by suffocation. Swelling in the areas of the chest, lower abdomen and external genitalia may also occur. If spores infect open cuts or abrasions, a localized skin infection occurs.

Cutaneous anthrax: Skin lesions caused by anthrax begin as an itchy papule resembling an insect bite, which enlarges and ulcerates within 1 to 2 days. The center of the lesion will turn black and localized swelling usually occurs around the ulceration. The lesion will dry in 1 or 2 weeks and leave a scar. Antibiotic treatment does not alter the course of cutaneous anthrax but may help to reduce accompanying systemic symptoms.

Inhalation anthrax: Anthrax infection of the lungs is insidious and typically fatal. Symptoms do not appear immediately but only after lymphatic spread of the infection has occurred. Symptoms may present over a 1 to 3 day period producing vague flu-like symptoms of fatigue, low-grade fever, chest pain and dry cough. Thereafter, signs of systemic infection are sudden in onset producing shock, coma, and typically death.

Gastrointestinal Anthrax: Symptoms of infection following ingestion of spore-infected meat present as common gastrointestinal symptoms of nausea, vomiting, loss of appetite and fever. Eventually as lesions progress, abdominal pain and bloody diarrhea develop. Systemic infection eventually develops as bacteria spread to other systems and results in shock, coma and eventually death. Oropharyngeal anthrax may also develop alone or concurrently with gastrointestinal anthrax infection in which case lesions develop in the oral cavity producing sore throat, difficulty breathing, fever, and lymph node enlargement of the neck. Swelling may compromise respiration and lead to suffocation, thus tracheotomy may be necessary. In most cases, however, death occurs due to systemic spread.

Diagnosis: Many systemic infections such as other bacterial infections (i.e. Leptospirosis, etc.) as well as other conditions (i.e. bloat, poisoning, etc.) may present symptoms similar to anthrax. Diagnosis of anthrax, therefore, is not based upon clinical observations alone, but requires laboratory analysis of blood samples from the potentially infected animal or human to confirm the presence of the organism.

Treatment and Control: Recognition of symptoms, rapid diagnosis, and early intervention are key factors for the treatment and control of outbreaks of anthrax. Antibiotics like penicillin and tetracyclines provide the best responses in infected animals but must be administered in the early stages of the disease. Other antibiotics such as chloramphenicol, erythromycin and sulfonamides can also be used but are less effective. Use of penicillin as a prophylactic against infection should be carefully considered in regard to history or risk of exposure to anthrax in light that prophylactic use might select for a strain of penicillin-resistant anthrax against which no treatments would be available. Vaccines that provide effective immunity against anthrax are available for livestock, but anthrax vaccines are not currently available for use in dogs or humans (human anthrax vaccines have not been approved by the FDA and are only available for high-risk military personnel). When infection with anthrax is suspected the following steps should be initiated:

References:

G.L. Mandell et al. Bacillus anthracis. In: Principles and Practices of Infectious Disease, 5th ed., Churchill Livingstone, New York, 2000. pp. 2215-2220.

For more information on Anthrax please visit the following website:

Center for Disease Control Anthrax Information Page

Recommended reading:

Shirin Shafazand, MD; Ramona Doyle, MD, FCCP; Stephen Ruoss, MD; Ann Weinacker, MD, FCCP and Thomas A. Raffin, MD, FCCP. Inhalational Anthrax: Epidemiology, Diagnosis, and Management. Chest. 1999;116:1369-1376.