Epidemiology

Bacillus anthracis is found in soil worldwide. Anthrax still occurs in agricultural regions of the Americas, southern and eastern Europe, central and southwestern Asia, and sub-Saharan Africa. In the US, wildlife and livestock anthrax still occurs sporadically in an area from southwest Texas to Colorado, North and South Dakota, and Montana. However, it has almost been eliminated in the US through livestock vaccination. Only nine confirmed or probable cases have been reported in the US since 2006.[1] A large-scale outbreak is ongoing in Zambia.[9]

Infection usually occurs in grazing livestock who come into contact with or ingest the spores. Humans may acquire anthrax from contact with infected animals (e.g., sheep, cattle, goats, other herbivores) or their products (i.e., meat, hides, wool, and tusks). Historically, inhalation anthrax, or woolsorters' disease, has been linked to large-scale processing of hides and wool, which results in aerosolized spores. Several such cases have been linked to the preparation and use of animal hides contaminated with B anthracis spores.[10][11][12]

Roughly 10,000 cases of cutaneous infection occurred in Zimbabwe from 1979 to 1985, in the largest known anthrax outbreak.[13] In 1979, the accidental release of B anthracis spores from a military research facility in Sverdlovsk, Russia, resulted in 66 deaths.[7] A large animal outbreak in Texas in 2019 resulted in concerns about increased human transmission risk, with one reported patient developing cutaneous anthrax.[14]

Only 18 cases of inhalation anthrax were reported in the US from 1900 to 2000.[15] The potential of anthrax as a biologic weapon was highlighted in 2001 following intentional contamination of US mail; a total of 11 inhalation anthrax cases and 11 cutaneous anthrax cases were identified, 5 of which were fatal.[16][17] Since then, only 2 cases of inhalation anthrax have been reported in the US, in 2006 and 2011.

Isolated ingestion anthrax is rare. The last case reported in the US was in 2009. Data on ingestion anthrax are often extrapolated from 100 human cases reported in the Bekaa Valley, Lebanon from 1960 to 1974.[18]

Anthrax may occur from injection drug use. An outbreak of anthrax was seen among intravenous drug users in Scotland, resulting in several deaths.[19] Infection was related to injection, ingestion, or inhalation (snorting) of contaminated heroin. Similar, smaller outbreaks have been reported in England, Germany, and Norway.[20] Anecdotal evidence suggests that this has also occurred periodically in the Middle East in the 1970s and beyond. In 2010, cutaneous and subcutaneous anthrax infections affected 47 intravenous drug users in the UK; the outbreak resulted in 13 infection-related deaths.[21] There have been no reports of injection anthrax in the US to date.

CDC: history of anthrax Opens in new window

Use of this content is subject to our disclaimer