First reported case of anthrax in African desert wildlife
Using GPS telemetry data, a team of scientists from the Cheetah Research Project at the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) reconstructed a special case of anthrax infection in Namibia: three free-roaming cheetahs in the Namib Desert died within 24 hours of feeding on a mountain zebra that tested positive for the disease. The zebra is the first described case of a wild animal infected with anthrax in this arid region. The case also shows that there could be previously unknown risks to cheetah populations in the desert. It is described in detail in Frontiers of veterinary science.
Since 2015, scientists from the Leibniz-IZW Cheetah Research Project (CRP) have been conducting a national cheetah survey in collaboration with the Namibian Ministry of Environment, Forestry and Tourism (MEFT). The aim is to obtain data on the density and distribution of cheetahs across the country. In this context, a coalition of three male cheetahs was captured in the Namib Desert and an animal fitted with a GPS collar. The recorded location and movement data were regularly uploaded during aerial tracking flights. On one of these flights, on October 5, 2019, the carcass of a collared cheetah, one of the coalition members, was located from the plane. During the subsequent ground inspection, the other two cheetahs were also found dead.
“Collared cheetah’s GPS data revealed that it died within six hours of days before we found it,” says Ruben Portas, a CRP scientist. “By evaluating their most recent movements, we identified a cluster of GPS locations about two kilometers from where they were found dead. “
In this place, the cheetahs spent 20 hours the day before their death. While visiting this group, Portas found the carcass of an adult mountain zebra. GPS and collar activity data suggested the cheetahs were feeding on it. Bacillus anthracis, the cause of anthrax infections, was isolated from oral and nasal swabs taken from the dead zebra, making it the first confirmed anthrax infection in a wild species of the Namib Desert.
Carnivores are generally less sensitive to smut than herbivores. Cheetahs in particular have high constitutive innate immunity which provides them with a rapid first line of defense against pathogens such as Bacillus anthracis.
“However, when a high load of bacteria is ingested, for example with meat from a contaminated carcass, their potent constitutive innate immunity can be overloaded,” said Bettina Wachter, head of the CRP project. “Cheetahs rarely shed, which reduces their exposure to prey infected with anthrax. Therefore, they do not produce high antibody titers which would be another line of defense. So, cheetahs die quickly when infected, as studies conducted in Etosha National Park in northern Namibia have shown.
The pathogen was not detected in any of the three cheetahs found in the Namib, but scientists consider it very likely that anthrax was the direct cause of their death. Bacterial cultures from highly susceptible animals that die quickly are often anthrax negative because animals can already die if there is a low presence of bacteria in the blood or a high load of toxin released by the bacteria. Bacillus anthracis when destroyed by the immune system. In addition, the vegetative form of the pathogen only develops when exposed to air soon after the death of the host. The cheetahs were left untouched for 11 days after death, and their bodies were not opened by scavengers, which could also explain the negative lab test results for anthrax.
Anthrax is a disease not studied in arid habitats. When wildlife dies in the Namib Desert, the causes are often attributed to drought, hunger and harsh desert conditions.
“The few reported cases in which diseases such as anthrax have been tested in Namibia’s arid environments are when livestock or people have been directly affected,” says Portas. “We don’t know the prevalence of anthrax in the Namib Desert and how wildlife populations are affected by the disease. For other habitats, such as Etosha National Park, much research shows that anthrax has a key ecological role in the environment.
This first confirmed case of anthrax in the Namib Desert in wildlife demonstrates that the disease may be endemic in the desert and other arid environments. Most of the Namib Desert is included in protected areas where cheetahs and other species find important refuge from conflict with humans. Thus, this new knowledge may be important in assessing the risks to the species.
“Although little data is available, no other disease has shown such an impact on the cheetah population and certainly requires further research that can lead to appropriate conservation measures,” Wachter concludes. “This study shows that the data recorded by the GPS collars has the potential to disclose additional important information in addition to information on spatial movements.”
Republished courtesy of Leibniz Institute for Zoo and Wildlife Research. Photo: A collared cheetah in the Namib Desert, as part of the National Cheetah Survey in Namibia conducted by the Cheetah Research Projekt of Leibniz-IZW. Credit: Ruben Portas / Leibniz-IZW