Anthrax: vaccination considerations

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Nearly every summer, cases of anthrax in cattle are reported from pastures in South Dakota.  Anthrax is a disease that can strike quickly, usually causing death losses without prior noticeable clinical signs in the animals.  Anthrax is caused by bacteria, Bacillus anthracis, which has the ability to form very resistant spores in the soil.  These spores can remain viable for many years on pasture, and become reactivated when the right environmental conditions exist.  Fortunately for cattle producers, losses due to anthrax can be prevented through use of a vaccine that has proven its effectiveness through the years. 

Anthrax was among the first animal diseases for which a vaccine was developed.  In 1881, Louis Pasteur developed a vaccine consisting of two different preparations given two weeks apart.  This procedure gained widespread use and was only slightly modified over the next 50 years.  In the late 1930’s a vaccine using a weakened, non-disease causing strain of B. anthracis was developed (the “Sterne” strain) and it is in fact the strain used in today’s vaccines.

Today’s “Anthrax Spore Vaccine” (Colorado Serum Company) consists of live, non-disease causing spores of the B. anthracis bacterium.  It is a vaccine widely available through veterinarians and is relatively inexpensive.  It is labeled for use in all domestic farm animals at a dose of 1 cc subcutaneously in the neck.  It has proven very safe for animals; however horses are at higher risk for painful swellings following vaccination; the vaccine manufacturer advises that administering the vaccine in the brisket area may minimize adverse reactions in horses.  Consultation with a veterinarian is recommended before using anthrax vaccine on any group of animals for the first time. 

Since the anthrax vaccine is a live spore preparation, and anthrax is a potential human disease, a physician should be consulted if accidental human exposure to the vaccine occurs.  This vaccine is different from the vaccine available for certain people (e.g. military personnel), which only contains portions of the anthrax spores. 
As is the case with most vaccines, animals should ideally be vaccinated 2-4 weeks before exposure to pasture, but maximum immunity may be achieved in as little as 5-8 days.  Duration of immunity studies have not been performed with this vaccine; however animals are believed to have at least six months and possibly up to a year of solid immunity from one vaccine dose—at least enough to get through the grazing season.

The common question most cow-calf producers face is, “Should I vaccinate my cattle for anthrax?”  The question is easy to answer for producers grazing cattle in endemic areas.  Cattle grazing pastures or geographical locations that have previously reported anthrax should vaccinate cattle every year.  The recommendations of the International Working Group on anthrax indicate that cattle grazing pastures within 6 miles (10 km) of a known previously infected area should be vaccinated as well, due to the potential for wildlife or biting flies to transmit anthrax spores to adjacent herds. 

But in short, it is difficult to predict where anthrax may occur in a given year, so cattle producers anywhere in South Dakota should at least give anthrax vaccination careful consideration. 

When outbreaks of anthrax occur, vaccination may play a role in reducing future losses within the affected herd.  Vaccinating in the face of an outbreak should be undertaken only with guidance from proper regulatory authorities (the state Animal Industry Board in South Dakota) and may include concurrent administration of antibiotics in order to treat cattle that may be in the early stages of the incubation period for the disease. 

Anthrax is a reportable disease in South Dakota, as it has implications for human health as well as the health of future cattle grazing these pastures.  Cattle producers faced with unusual cases of death loss on pastures during the summer should work with their local veterinarian to promptly rule out anthrax as a cause of death.

Source: Dr. Russ Daly


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