Climate Change and Anthrax Outbreaks

Climate change may have a whole lot of consequences that aren’t yet foreseen by anyone, and also some that are known possible risks within scientific communities, but not yet known among the general public. One of these surprising risks has come to people’s attention lately – the risk of anthrax outbreaks as tundra permafrost thaws.

The Guardian recently reported on the death of a boy in Siberia related to an anthrax outbreak there. This outbreak is the first since 1941, and has sickened dozens of people and killed thousands of reindeer, which the nomadic groups there depend on for their livelihood.

In the USA people tend to think of anthrax as a biological weapon, but it is primarily a zoonotic disease, meaning that it usually infects animals but can be transmitted to humans. It is most common in grazing herbivores, like cattle, horses, and deer (including Siberian Reindeer). It is caused by a bacteria that can last in soil for years, so in most industrialized nations livestock herds are routinely vaccinated for anthrax in areas where the spores are known to have been present.

Catching anthrax naturally in the United States is extremely rare, with only a few natural cases in the last several decades. Worldwide it is more common, and there have been outbreaks of various sizes, from a few cases up to more than ten thousand people infected in Zimbabwe between 1979 and the mid-1980’s. It is usually caught through the process of butchering infected animals, handling dead animals, or processing animal skins. These routes of infection generally result in cutaneous (skin) infection, though more deadly respiratory infections occur as well. Rarely, indigestion of infected meat can cause it if the meat is raw or undercooked, causing the disease in the digestive system.

Anthrax bacteria exist in the environment as spores that can survive for long periods of time. When animals that have died from Anthrax are buried the spores can remain viable for decades, or centuries in frozen ground. In the case of the recent Siberian outbreak it seems that animals from a previous outbreak were buried in frozen ground, not very deeply. As the permafrost thawed in this year’s unusually high temperatures it may have brought these spores back into the ecosystem, causing the outbreak in the Siberian reindeer herds and then the people who depend on them.

The thawing of permafrost poses many problems, including accelerating climate change through the release of stored methane gas and decay of previously frozen biomass. Now apparently Siberia needs to worry about stored anthrax too. I doubt this will be the last surprise climate change brings.

Sources:
http://www.who.int/csr/resources/publications/anthrax_web.pdf
https://www.cdc.gov/mmwr/preview/mmwrhtml/rr4915a1.htm
https://www.theguardian.com/world/2016/aug/01/anthrax-outbreak-climate-change-arctic-circle-russia
http://www.merckvetmanual.com/mvm/generalized_conditions/anthrax/overview_of_anthrax.html
http://www.cattlenetwork.com/cattle-news/Anthrax-vaccination-considerations-152715445.html

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Climate Change and Anthrax Outbreaks
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