Ivermectin could help beat malaria, veterinary college researcher finds in running the numbers

When a stranger from Spain called Cassidy Rist in her first months at Virginia Tech, she almost didn't take the meeting.

The caller was Carlos Chaccour, a physician at the University of Navarra who worked on global health and tropical diseases. He told her he was working on ivermectin for malaria. 

Rist, an associate professor of population health sciences at the Virginia-Maryland College of Veterinary Medicine, had spent years studying how animal and human diseases interact across communities. But she had never considered ivermectin as a tool for fighting mosquito-borne illnesses.

"Ivermectin doesn't treat malaria," she recalled thinking. "At first, I thought the idea was a little wacky." 

It wasn't. The collaboration that followed produced a paper published in The Lancet Global Health and the first economic analysis of ivermectin mass drug administration using real-world trial data — establishing that the approach can be a cost-effective supplementary strategy for malaria control in communities where other tools are already in place but still falling short.

The finding gives health ministries and international funders the economic evidence they need to consider adding ivermectin to the malaria toolbox. For Rist, it is also the product of a career built on the recognition that human and animal health cannot be separated. 
 
The economic analysis builds on results from the BOHEMIA cluster-randomized trial, published in The New England Journal of Medicine, which found that ivermectin mass drug administration reduced malaria infections by 26 percent in children in coastal Kenya. Rist and collaborators then used those trial data to model whether the intervention would be cost-effective if added to existing malaria-control measures.

The mosquito problem nobody solved 

Malaria kills about 600,000 people a year, according to World Health Organization estimates, the vast majority of them children under age 5 in sub-Saharan Africa. The tools that drove dramatic progress in reducing that toll, principally insecticide-treated bed nets and indoor residual spraying, still save millions of lives. But over the past decade, progress has stalled.

One major reason is evolution. 

"Mosquitoes were becoming resistant," Rist said. "Mosquitoes were changing their behavior, so now they're biting at different times of the day."

Some of the mosquito species that carry malaria have increasingly shifted toward feeding on livestock — animals such as cattle, goats and other domesticated species that live near or with families — referred to by researchers as peri-domestic animals. 

Under bed nets at night, humans are protected. But when mosquitoes can shift to feeding on cattle, they can survive long enough to transmit malaria when they find a human host. This residual transmission means malaria persists even in communities doing everything right.

That's where ivermectin enters the picture, and where the connection to veterinary medicine becomes impossible to miss.

Ivermectin is a drug veterinarians have used for decades. It kills internal and external parasites in animals and is widely used in human medicine to treat conditions like river blindness and lymphatic filariasis.

Early research in the 1980s and 1990s showed something unusual: Mosquitoes that fed on the blood of people or animals who had recently received ivermectin were killed by the drug. Certain species, including those that transmit malaria, failed to survive long enough to reproduce. 

"It is a vector control tool," Rist said. "It has nothing to do with the parasites that cause malaria. It's treating the vector."

The idea was largely set aside when bed nets became the dominant strategy. But as residual transmission emerged as a stubborn barrier, Chaccour and his colleagues in the Broad One Health Endectocide-based Malaria Intervention in Africa consortium, known as BOHEMIA, decided it was time to test the approach at scale. 

The BOHEMIA consortium ran a phase 3 cluster-randomized trial in Mozambique and Kenya. Cluster-randomized means groups of people — rather than individuals — were assigned to different treatments.

In Kenya's Kwale County, a coastal region near the Tanzanian border, field teams administered ivermectin monthly for three consecutive months to eligible community members, aiming to reach roughly 64% of the population. The trial covered nearly 29,000 people across 84 clusters and tracked how often malaria occurred in a group of children aged 5 to 15. 

The Mozambique arm faced significant implementation challenges, including logistical delays and severe flooding that prevented teams from reaching parts of the study area. The Kenya trial proceeded effectively.

The results were meaningful. Children in communities that received ivermectin had 26 percent fewer malaria infections than children in control communities, on top of the protection already provided by their bed nets. 

But a clinical finding, even a strong one, doesn't automatically change policy. Health ministries in low-income countries operate with constrained budgets and must make hard choices among interventions. To make the case for scaling up any new tool, you need to show not just that it works, but that it's worth the money.

That is where Rist and her team came in. 

Building the economic case

The cost-effectiveness analysis Rist led was the first of its kind. No previous study had assessed the cost-effectiveness of ivermectin mass drug administration using real-world implementation data from a randomized controlled trial. 

The team included Virginia Tech graduate student Kexin Xie and collaborators from institutions including the University of Virginia, the Kenya Medical Research Institute, and ISGlobal in Barcelona.  Using data from the clinical trial, along with direct economic surveys of households in the area, they built a decision-tree model to simulate the intervention's impact across an entire population, accounting for intervention costs, household out-of-pocket expenses, health system costs, and productivity lost to illness.

Delivering ivermectin to the eligible population in Kwale cost $11.83 per person, covering administration, training, targeting and implementation. 

The study used a cost-effectiveness threshold equal to half of Kenya’s gross domestic product per capita — a benchmark for judging whether the health benefits are worth the added cost. The intervention came in just below this threshold. The base-case incremental cost-effectiveness ratio, which compares the added cost and health outcome of one intervention to another, was $905 per disability-adjusted life year averted. Kenya's threshold is $974.65.

"That study was just published, and I'm very proud of it -  it took a long time," Rist said. "It's a cost-effectiveness analysis, which is critical for policy decision making.  I received training in health economics and disease ecology during my postdoctoral research, and as a veterinarian I bring cross-cutting skills that allow me to work closely with economists, statisticians, and malaria experts to serve as the mentoring author on the manuscript.”  

The analysis also identified where the economics could improve. Sharing logistics with existing programs, such as seasonal malaria chemoprevention campaigns that already send field workers to households, or overlapping with neglected tropical disease programs that already distribute ivermectin for other conditions, could significantly reduce the cost per person. In communities where diseases such as river blindness are also present, ivermectin distribution could potentially be aligned with neglected tropical disease programs, while additional seasonal doses could target malaria transmission.

"So there are all these opportunities for overlap and co-use of resources that could improve the costs and benefits associated with it," Rist said. 

The livestock question

The original BOHEMIA design included an arm that would have treated both humans and livestock simultaneously, making both human and animal blood meals lethal to malaria-carrying mosquitoes at the start of the rainy season.  
 
Mathematical models suggest that treating both species could about double the impact seen from treating humans alone. And giving ivermectin to livestock does not just reduce the mosquito population — it treats the animals themselves, clearing parasites and preventing certain tick infestations. Field workers already making household visits to administer ivermectin to livestock could simultaneously vaccinate against other diseases, layering animal health benefits onto the public health mission.

"It actually can be extremely beneficial to the animals as well," she said. "So it's truly a One Health intervention." 

A trial testing the livestock component is now moving forward in northern Kenya, led by veterinary entomologist Marta Maia, a BOHEMIA collaborator, despite a tightening funding landscape for U.S. investigators in global malaria research. One of the researchers Rist worked alongside in Kenya, Almudena Sanz Gutierrez, who served as a field manager during the trial, is now a Ph.D. student at Virginia Tech.

"I'm not a malaria researcher, per se," Rist said. "I'm interested in the One Health aspect where human and animal health interventions can be designed to share resources, reduce costs, and multiply benefits.”