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Anthrax: ancient disease, modern threat


07 February 2012 - Anthrax has grabbed headlines in recent years for its sinister use in bioterrorism and the continued threat that it can be weaponized by groups or individuals wanting to harm and even kill people.

Anthrax, however, need not be weaponized to cause havoc, and it has effortlessly left indiscriminate destruction in its wake over several millennia. It has long been a fatal disease in livestock, thought by many scholars to have been the cause of the fifth and sixth plagues in ancient Egypt in 1491 B.C.

In fact, the bacterium that causes the disease, Bacillus anthracis, derives its name from the Greek word for coal, owing to the black-rimmed skin sores that form after infection. Anthrax is believed to be the root of livestock and human plagues described by Homer in the Iliad, and Virgil (70-19 B.C.) provided one of the earliest and most detailed descriptions of an anthrax epidemic in Georgics, an epic poem about agriculture. Virgil noted that anthrax is zoonotic, able to spread from animals to humans.

An epidemic known as the “Black Bane” now attributed to anthrax swept across Europe in the 17th century, killing 60 000 cattle and resulting in large numbers of human deaths.

No longer in Western Europe

Despite its lingering threat, anthrax is now a largely neglected infectious disease in animals, since there is no imminent threat to humans, especially in developed countries. Anthrax has been almost entirely eliminated in Western Europe, with what can be considered “incidental outbreaks” cropping up once every ten years or so. National authorities act swiftly to control outbreaks and eliminate any source of infection by burning animal carcasses, which is the only sure way of killing anthrax when it is still encased in its tough spore shell. The spores otherwise can lie dormant in the soil for decades, even in the most inhospitable of environments.

As decades go by, the cumulative effect has been a dying out of anthrax in Western Europe. But therein lies the rub for developing countries. Often, burning carcasses en masse just doesn’t happen in countries where veterinary services are weak and even wood can be in short supply.

Increasing levels of anthrax in Africa, the former USSR

In the countries of the former Soviet Union and across sub-Saharan Africa, there has instead been an exponential increase in the accumulation of environmental anthrax in soils, where it will lie dormant until released by heavy rains or even when someone unwittingly digs in an area where an animal carcass might have been buried.

In both the Eastern Europe and Africa regions, anthrax until recently was prevented from emerging by implementing wide-scale vaccination campaigns once a year in these endemic areas. In the early 20th century, colonial farmers in Africa would routinely vaccinate against anthrax (along with the related blackleg). Anthrax was the single most important disease to vaccinate against, since its spread is so quick and it kills the widest possible range of animal species. Death comes quickly once animals are infected: sometimes within two hours, animals die of internal swelling, bleeding and tissue death. Grazing mammal species – livestock included – have the weakest defenses against anthrax, while carnivores, for example, have lower mortality rates.

Ecosystems in upheaval

In addition to the colossal shifts in the political and economic landscape since the 1960s, in sub-Saharan Africa there is the additional factor of domestic animals’ ever increasing contact with wild animals. The disease can wipe out wildlife species as well, but even more importantly, anthrax can be perpetuated over time without man-made interventions to eliminate anthrax from the environment. If wildlife die from anthrax, carcasses are left above ground to infect other animals, and the spores contaminate the soil.

In southeastern parts of the African continent, big wild game species once made up the majority of the animal biomass in the ecosystem. Now, however, domestic cattle outnumber all species of big game by ten to one.

This is the trend as human populations increase: to ramp up agricultural production to feed and provide for more people. A rising middle class is also driving the demand for meat and animal-based products. As domestic animal populations expand and appropriate more land for grazing, the risk for spillover from wild animals becomes an imminent threat to livestock and to humans. In addition, in Africa’s big wildlife reserves, domestic animals and people come into direct contact with wildlife areas, with the disease risks that entails.

Vaccines the best first line of defense

In endemic regions, vaccination of livestock animals is the best way to protect domestic animals and humans from devastating outbreaks of anthrax. A vaccine developed by Dr. Max Sterne in 1937 is based on a strain of  Bacillus anthracis, and is still the most effective vaccine available today. A sound vaccination strategy for domestic animals when they are healthy, using quality controlled vaccines, will prevent anthrax outbreaks in livestock animals. In some areas with particularly strong veterinary services, there are also attempts to vaccinate wildlife species, but in most places, this approach just isn’t economically or technically feasible.

Solutions in One Health
It is exactly this sort of major transformation in ecosystems dynamics that FAO’s Animal Health Service is working to address via a One Health approach to tackling disease at source. In One Heath, the health of people, animals and the environments that support them are inextricably linked: the health of one is the health of all.

In sub-Saharan Africa, the sudden surge in domestic animal populations has forced encroachment into pristine environments, and the resulting increased contact with wild animal populations can be a recipe for disaster. Anthrax has more possibilities to pass to domestic animals from wildlife sources and vice versa. Livestock are increasingly kept in unhealthy environments, and the illnesses they pick up – anthrax included – become a greater risk to human health, people’s livelihoods and food supplies.

As the risks proliferate, FAO is working with veterinary services, public health services and natural resources managers to find a sustainable solution to the needs to increase production while protecting people from disease risks that increase when overexploitation puts ecosystems in disharmony.

As globalization links animal suppliers south of the Sahara with markets in North Africa, especially during high-volume live animal trade around religious feasts, anthrax could become a major threat to human health and food security once again. Its epic destruction throughout the ages shouldn’t be underestimated.

 

© FAO/Mat Yamage
© FAO/Mat Yamage
© FAO/C. Shiley
© FAO/Ahmed El Idrissi

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