African Hippopotamuses and Buffalo Threatened by Anthrax

Anthrax is a zoonotic infectious disease caused by the bacterium Bacillus anthracis. For a long time it has posed a serious threat to many domestic animals, and wildlife populations are not immune when outbreaks spread through natural ecosystems.

One anthrax outbreak has continued to affect the region up to 2025. The event occurred in Virunga National Park in eastern Democratic Republic of the Congo. As early as 2015, residents of the Kasongwere area began reporting large numbers of livestock deaths. Affected animals developed high fever, abdominal bloating, and dark blood flowing from the mouth and nose, while carcasses decomposed rapidly after death. Based on clinical symptoms and interviews with farmers, investigators concluded that Bacillus anthracis was spreading among livestock.

During this episode, pigs, cattle, dogs, and sheep all became victims of the disease. Mortality was highest in pigs. One possible explanation lies in their feeding behavior. Pigs are omnivorous and often roam freely while foraging, rooting through soil and carcass remains. In doing so they may ingest anthrax endospores present in contaminated soil or animal remains. Improperly buried carcasses can therefore become long-lasting reservoirs where endospores accumulate, silently preparing the conditions for future outbreaks.

Livestock production in this region largely relies on grazing systems, and many herders practice transhumance, moving their animals seasonally in search of pasture and water. During certain seasons, herds are driven into areas within the national park. Such movements bring domestic livestock into close contact with wildlife that share the same habitat, increasing the opportunity for anthrax transmission.

In 2021, multiple deaths of hippopotamuses and African buffalo (Syncerus caffer) were suddenly reported inside Virunga National Park. Field observers recorded the carcasses of sixteen hippopotamuses and three buffalo along the banks of the Ishasha River and floating on the surface of Lake Edward. Infected hippopotamuses emitted distress calls and showed symptoms including reddened skin and severe respiratory difficulty before dying. Some carcasses were surrounded and guarded by other members of the herd. Dark, non-coagulated blood seeped from natural body openings. This blood and the fluids released during decomposition contain anthrax endospores, which subsequently entered the river and lake water. Carried by currents, these spores may reach downstream ecosystems and human settlements, expanding the geographic range of exposure.

Hippopotamus that died from anthrax（Courtesy of Virunga National Park/ REUTERS）

Hippopotamus that died from anthrax（Courtesy of Virunga National Park/ REUTERS）

In May 2025, a report from the World Health Organization summarized the scale of the outbreak. Since the beginning of the event, 54 hippopotamuses and 10 African buffalo had died from anthrax. Among humans, 24 suspected infections were reported, including one confirmed case and one death. Public awareness of anthrax among local communities remains limited, and some farmers reportedly smoke the meat of animals that died from disease and sell it for consumption.

Environmental conditions also influence anthrax outbreaks. The rainy season appears particularly important. Heavy rainfall can transport endospores from deeper soil layers to the surface through runoff, contaminating grasslands where grazing animals feed. Rainfall also increases earthworm activity, and these soil-dwelling organisms may help move spores upward through the soil. In addition, the decomposition of infected carcasses enriches surrounding soil with nutrients, promoting plant growth. The resulting lush vegetation attracts herbivores, which then graze in areas contaminated with spores, creating a cycle that sustains transmission.

Government authorities have implemented several control measures, including animal quarantine, vaccination of livestock, safe disposal of wildlife carcasses, and disease surveillance and reporting systems. These efforts aim to reduce the spread of anthrax and limit future outbreaks.

(a, b) Hippopotamuses along the Ishasha River; (c) African buffalo（Image source：Eddy Syaluha， CC BY 4.0 ）

Author: Shui-Ye You

References:

1. Désire SM et al. (2024). Verbal Autopsy and Outbreak Investigation of Anthrax in Livestock and Wildlife at the Virunga National Park Interface Area, Democratic Republic of the Congo. Fortune Journal.

2. World Health Organization. (2025). Human anthrax outbreak in North Kivu province, DRC and Uganda.