Anthrax: An ancient disease continues to plague livestock and wildlifeWritten by Heather Smith Thomas
This disease is a swift killer, caused by a gram-positive bacterium, Bacillus anthracis, which is similar in many ways to the gram-positive clostridial bacteria that cause redwater, blackleg and malignant edema. They all cause sudden death, yet they 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 is typically transmitted via spores from carcasses of animals that died of the disease.
Once the animal dies and the carcass is opened, bacteria are exposed to air, and they form spores. In this dormant stage, the bacteria can survive a long time. These spores are resistant to heat, cold, freezing, disinfectants or drying and can survive in the 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 the surrounding soil. As a result, it’s crucial to find dead animals quickly and have a proper diagnosis. Your veterinarian can diagnose the disease by taking a blood sample. It’s imperative to dispose of all anthrax-killed carcasses by burning or burying to halt the spread of spores.
Tasha Epp of the 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 in the year 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 the spores that ended up on grass,” she explains. “That combination of wet, then hot and dry makes a bad year for anthrax.”
Many regions experience this type of weather pattern, 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 so far not to the extent we had in 2006,” Epp says.
“Cattle seem to be one of most prominent species in which this disease 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,” says Epp.
This disease probably affected bison in North America long before there were cattle here.
“A researcher who is now in Florida has looked at the potential distribution patterns 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 explains.
“There were also a couple pigs lost to anthrax in the outbreak we investigated in 2006, some horses, and a few sheep and goats. Basically any warm-blooded animal that grazes can become exposed,” she says.
Treating and vaccinating
“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,” according to Epp.
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 vaccinate.
Even in the years when we tell ranchers there’s a risk because of flooding and subsequent hot weather, many people still take the risk and don’t bother to vaccinate. If we have a bad year, however, their choice might be different,” she says.
“It takes seven to 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 a certain region. They thought it would, but it depends on whether everyone vaccinated their animals,” Epp says.
Any animals left unvaccinated could serve as potential victims and continue to spread the disease.
Research in Texas and Africa has shown that the bacteria and their spores can be spread from sick, dying and dead animals by flies. The flies that feed on a fresh carcass can also pass the bacteria in their droppings when they land on nearby vegetation. Wildlife and livestock eating the fly-contaminated foliage may be at risk for anthrax.
Immunity from vaccination 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.
Anthrax also appears in wildlife, especially deer, elk and bison. An outbreak in 2008 near Bozeman, Mont. affected many bison and elk on one large ranch.
Ranchers who raise bison or farmed elk should consider vaccinating them, according to Jason Blackburn of the University of Florida, who has been studying anthrax all across the U.S. and around the world. He says Texas ranchers who raise bison or wildlife for hunting generally vaccinate their bison, deer and exotic wildlife. Since this is off-label use of the vaccine, Blackburn recommends that ranchers discuss this with their veterinarian.