In late June, 30 hippopotamuses died of anthrax in Queen Elizabeth National Park, Uganda, a popular safari location. These hippopotamuses likely contracted Bacillus anthracis, the causative agent of anthrax, from spores that had been lying dormant in the lake shore soil for 6 years, originating from an anthrax outbreak in 2004 which killed approximately 300 hippos. Because B. anthracis spores are hardy and can survive for decades in the soil, proper disposal of infected carcasses is very important to control future outbreaks. The New Vision reports that the State Minister for the Animal Industry in Uganda, Major Rwamirama, recommended that the carcasses should be moved and the infected areas sprayed – the article did not mention with what. Major Rwamirama also mentioned that burying the carcasses was expensive, ~$440 per carcass, and unreliable, since burial does not kill the hardy spores.
Spraying chemicals such as formaldehyde would kill surface B. anthracis spores, but the quantity of chemical needed to penetrate the soil to kill all spores would likely be too great. Gruinard Island, used by the former British bioweapons program as an anthrax testing site, required hundreds of tones of a formaldehyde solution to disinfect one portion of the island. This disinfection strategy is not an option for Uganda, since the large quantity of chemicals would contaminate the water, killing many animals in the National Park.
A concurrent anthrax outbreak, in the Northwest Territories, Canada, has killed at least 21 bison. Canadian authorities are covering the carcasses with formaldehyde as they are found to prevent scavengers from spreading the disease. Then the carcasses are completely burned, a feat that requires approximately 1000 lbs of coal and 3500 lbs of wood. This method of disposal is more effective than burial, but may not be ecnomically viable for Ugandan hippopotamuses. Bison weigh roughly 1,000-2,000 lbs and a hippopotamus is easily three times larger (roughly 3,000-7,000 lbs), so the cost of coal alone required to burn a hippopotamus could easily be three times more than the cost of burial, which is already considered expensive. Other methods to control anthrax outbreaks are needed in developing countries.
Because natural anthrax outbreaks among grazing animals are common throughout the world, domesticated livestock are commonly vaccinated against anthrax. In the United States, it costs approximately $10 per head of cattle annually for vaccination – the dose would likely be higher and more expensive for a hippopotamus. As scientists develop more effective, longer-lasting, cheaper and easier to deliver anthrax vaccines, it may become viable to vaccinate wildlife in “at risk” areas. Once these vaccines are available, the large costs of carcass disposal will no longer be a major issue.