The Tiny Threats Facing the Kings of the Savannah

Lions are often celebrated as symbols of strength and resilience, but new research led by Yale School of the Environment scientists suggests that some of the most serious threats facing West Africa’s critically endangered lions are too small to be seen with the naked eye.

A study published this month in Royal Society Open Science offers the first comprehensive look at the parasites living in West African lions, a subspecies that now occupies just 1.1% of its historic range.

Faculty

Nyeema Harris Knobloch Family Associate Professor of Wildlife and Land Conservation

“Parasites are truly the unappreciated majority, a grand puppeteer that regulates behavior, immune responses, and even biodiversity,” said lead author Nyeema Harris, the Knobloch Family Associate Professor of Wildlife and Land Conservation. “Some might think there is little left to learn from such an iconically charismatic and well-studied species, but there is a dearth of understanding of the parasite communities that plague African lion populations.”

The research team used advanced DNA metabarcoding techniques to analyze fecal samples collected from lions in four national parks across Benin, Burkina Faso, and Senegal. By extracting and sequencing environmental DNA, the researchers detected thousands of organisms such as gastrointestinal worms, blood parasites, and bacteria. 

“Hookworms were among the most common parasites we found,” said Jane Hallam, a molecular ecology postdoctoral researcher at YSE and study co-author. “In other carnivores, heavy loads can cause anemia and reduced fitness, which is a potential concern for small, endangered populations.” 

The team also detected blood parasites such as Sarcocystis and Babesia, which have been linked to reduced reproduction in other carnivores. Lungworms and other gastrointestinal parasites were also present. “These findings point to possible health risks,” Hallam said, “but they should be seen as warning signs rather than proof of illness.”

Why parasites matter for conservation

Parasites are often overlooked in conservation, but they can influence host survival, behavior, and reproduction, and their effects extend through prey communities and ecological networks. By studying parasite diversity, scientists can better understand animal health, ecosystem resilience, and even early warning signs of disease outbreaks.

The West African lion is one of the planet’s most threatened large carnivore populations, with perhaps only a few hundred individuals remaining across its fragmented range. Unlike their East and Southern African counterparts, these lions tend to live in smaller prides, which can consist of fewer than 10 individuals. The study found that the diversity of the lions’ parasites reflected their population sizes: Senegal’s small, isolated population showed lower overall parasite diversity than lions in Burkina Faso and Benin, which have larger populations.

At the same time, DNA metabarcoding allowed researchers to identify individual lions from their feces, revealing that parasite communities varied widely from one animal to another. This diversity means that even within a single population, each lion harbors a distinct assemblage of parasites, highlighting both population-level trends and the complexity of individual host-parasite interactions.

Crossing boundaries: lions, livestock, and people

The research team also identified DNA from parasites, such as the hookworm Ancylostoma duodenale, which can also infect humans and livestock.

Hallam noted that this does not mean lions are actively transmitting diseases. 

Newsletter

Subscribe to “YSE 3”

Biweekly, we highlight three news and research stories about the work we’re doing at Yale School of the Environment.

“It’s important to emphasize that our study only shows DNA from these parasites was present in lion feces; it does not confirm that lions were actively infected or capable of transmitting disease,” she said. “Still, as pressures on protected areas grow, the risk of cross-species exposure also rises. This doesn’t mean there is an immediate public health crisis, but it emphasizes the need for careful monitoring at the human–livestock–wildlife interface.”

Although the study findings greatly expanded the knowledge of parasites, Harris emphasized that policy recommendations would be premature at this stage and more research was needed. 

“Now that we’ve characterized what parasites are present across multiple West African populations, we need to know where they come from,” Harris said. “Parasites from prey versus from livestock have very different management implications. We also need to know what the parasites do — in other words, what is the consequence of their presence for lions?”