July 28, 2011
Anthrax is caused by a gram-positive bacterium, Bacillus anthracis, similar to gram-positive clostridial bacteria that cause redwater, blackleg, malignant edema. They all cause sudden death, yet can be easily prevented by vaccination. Anthrax occurs worldwide, and can infect all warm-blooded animals. It is generally not spread from live animal to live animal, but typically transmitted via spores from carcasses of animals that died of the disease.
Once the animal dies and the carcass is opened and bacteria are exposed to air, they form spores. These spores are resistant to heat, cold, freezing, disinfectants or drying and can survive in contaminated soil as much as 100 years or more. The carcass may be long gone – scattered by predators or decomposed and disappeared – but the spores are still viable in surrounding soil. This is why it’s crucial to find dead animals quickly, have a proper diagnosis (by having a veterinarian take a blood sample) and dispose of all anthrax-killed carcasses by burning/burying to halt the spread of spores.
Dr. Tasha Epp, Western College of Veterinary Medicine in Saskatchewan was involved in a study of anthrax during an outbreak in western Canada in 2006. “We found that areas with heavy rainfall and flooding in the spring and hot, dry conditions later were more likely to see cases of anthrax. Moisture draws spores from the ground and when the flooded areas dry out the cows go into those areas of lush grass, and ingest spores that ended up on grass. That combination of wet, then hot and dry makes a bad year for anthrax.” Many regions are experiencing that same weather pattern this year, so ranchers should be aware of the risks.
In 2006 in Saskatchewan alone, more than 800 animals were confirmed with anthrax – the largest number ever recorded. “Every few years, and sometimes a couple years in a row, there are reports of cases, but not to the extent we had in 2006,” she said.
“Cattle seem to be one of most prominent species in which it shows up, but bison were also hit hard in 2006. On many bison farms we saw more deaths than we would have seen with cattle,” Epp said.
This disease probably affected bison in North America long before there were cattle here. “A researcher who is now in Florida has looked at potential distribution of anthrax spores – in Mexico, the U.S. and Canada. He mapped it out, and it seems to follow old cattle trails and bison migration routes – where animals died in years past,” she explained.
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“There were also a couple pigs lost to anthrax in 2006, some horses, and a few sheep and goats. Basically any warm-blooded animal that grazes can become exposed,” Epp continued.
“The majority of anthrax cases are not found in time to treat; the animal is usually found dead because it’s such a fast onset of disease,” she noted. Penicillin is effective, but has to be given in very early stages.
“The vaccine is effective, but because we don’t see cases very often, most ranchers don’t vaccinate. If there was a way to predict where and when anthrax would occur, perhaps more people would do it. Even this year, when we’ve been saying there’s risk because of flooding and subsequent hot weather, many people still take the risk. If we have a year like 2006, however, their choice might be different,” she said.
“It takes 7-14 days to gain full immunity after vaccination. In some instances, one vaccination may not be sufficient. Your vet may recommend a booster – especially if it’s a bad year. Australian researchers looked at whether vaccination would be quick enough to prevent disease in cattle once cases are seen in an area. They thought it would, but it depends on whether everyone vaccinated their animals,” Epp said.
Immunity lasts about a year, so producers can vaccinate annually in the spring or even at preg-checking in the fall and have protection through the summer months. Dr. Kevin Smykowski with Hovland Veterinary Services in Lisbon, ND, advises clients to vaccinate every year – especially in a year like this one, with flooding in many areas. “We haven’t seen any cases yet this year, but it’s still a bit early. After the outbreak we had here in 2006, most ranchers aren’t taking chances.”
Anthrax also appears in wildlife – especially deer, elk and bison. An outbreak in 2008 near Bozeman, MT, affected many bison and elk on one large ranch. Ranchers who raise bison or farmed elk should consider vaccinating them, according to Dr. Jason Blackburn with the University of Florida, who has studied anthrax all across the U.S. and around the world.