Billions of people live in areas where they are at risk of being exposed to anthrax, research suggests.
The bacteria behind the killer infection lurks in the soil of every inhabited continent, with its spores getting taken up by grazing livestock.
Scientists used existing data to calculate that up to 1.83billion all over the world could be exposed to the bacteria behind the infection.
Handling or eating contaminated meat can spread the infection to humans, which may trigger inflammation of the brain and life-threatening bleeding.
The research was carried out by The National Socio-Environmental Synthesis Center in Annapolis, Maryland.
B. anthracis’ worldwide distribution is poorly understood. Scores of countries have inadequate surveillance systems, even in endemic regions.
To uncover how prevalent the bacteria is, the researchers analysed global data of the infection in humans, livestock and other animals across 70 countries.
They looked at records collected by scientists, national surveillance data and online statistics. This was then extrapolated to predict how many people may be at risk.
Results revealed an estimated 1.83billion people live in regions that are at risk of an anthrax outbreak. The ‘vast majority’ reside in rural areas in Africa, Europe and Asia.
However, the researchers add most people are not exposed to infected animals and will unlikely come into contact with spores in the soil.
They therefore estimate 63.8million people face a genuine risk, who tend to be livestock keepers living in poor anthrax-endemic areas.
Worldwide, 1.1billion livestock are thought to be at risk, including 320million sheep, 294.9 million pigs, 268.1million cattle, 211.2million goats and 0.6 million buffalo.
Many of these animals are not vaccinated against anthrax, the researchers wrote in the journal Nature Microbiology.
Immunisation rates vary from 90 per cent in eastern Europe and central Asia to just less than one per cent in parts of east and south Asia.
Jabs are often given once an outbreak has taken hold rather than as a preventative measure.
But ‘proactive vaccination in under-vaccinated, hyperendemic countries could help bring anthrax outbreaks under control’, the researchers wrote.
Between 2,000 and 20,000 cases of anthrax occur worldwide each year, particularly in rural areas, according to estimates.
Risk of death varies according to how the infection spreads. Most cases are spread via skin-to-skin, which is easier to treat, but spores can be inhaled.
Anthrax has also been used in bioterrorism attacks, with five Democratic senators dying in the week after 9/11 when they opened letters containing the bacteria’s spores. ,
The second most common route of transmission is via the gastrointestinal tract, which has ‘intermediate to high fatality rates’.
These cases usually come about by handling or slaughtering infected livestock or eating contaminated meat.
A person’s mortality risk is driven by the ‘dynamics at the wildlife-livestock interface’, the researchers wrote.
Animals are exposed to B. anthracis spores in the soil, which then get returned to the ground when the livestock die and decompose.
Anthrax spores can survive in soil for decades, researchers have previously revealed.