Rats have long been notorious for spreading disease, but a new study reveals just how much human-altered landscapes can influence their viral payloads.
Researchers investigating Madagascar’s forests and farmlands discovered that black rats — an invasive species — are the sole carriers of a dangerous hantavirus strain. Surprisingly, while these rats thrive in agricultural settings and frequently carry the virus there, none of their rainforest counterparts tested positive. The study sheds light on how land use, not just the animals themselves, can shape disease risk.
Black Rats Linked to Hantaviruses in Madagascar
Invasive species can wreak havoc on ecosystems, and sometimes, on human health too. When animals enter new environments, they may bring unfamiliar pathogens with them. Some of these diseases can spill over to humans, as the COVID-19 pandemic powerfully reminded us.
A recent study from UC Santa Barbara, the University of Réunion, and Duke University has identified the black rat as a likely source of hantavirus transmission in rural Madagascar. These areas, once forested, have been increasingly cleared for agriculture and settlements. The findings were published today (April 7) in the journal Ecology and Evolution.
Rodent Stowaways and Their Global Journey
Rats have long lived alongside humans, raiding our food stores, settling in our towns, and traveling with us across continents. Their role in spreading disease is well known. The black rat (Rattus rattus), originally from southern Asia, spread through Europe via the spice trade and eventually reached Madagascar between the 10th and 14th centuries.
Disease ecologists were curious about which species in Madagascar could transmit Hantaviruses and how human land use impacted the number of infected animals across the landscape. Hantaviruses are a group of viruses that can cause potentially deadly illnesses. The pathogens mainly spread to people via exposure to rodent urine and feces.
Unique Viral Strains and Local Exposure
“We were particularly interested in hantaviruses here because Madagascar has unique hantaviruses that are not well studied,” said co-lead author Kayla Kauffman, a doctoral student in Professor Hillary Young’s lab at UCSB. There’s also extremely high evidence of past exposure in Malagasy people.
The authors engaged with communities living alongside the boundary of Marojejy National Park, in northeastern Madagascar. Community members allowed the team to trap small mammals and bats in their homes and fields, which included agroforests where vanilla is grown, hillside crop fields, and flooded rice fields. They also obtained permission to trap animals in the rainforest located just inside the boundary of the national park.
Thousands of Samples, One Infected Species
The team collected samples from nearly 2,000 animals, which they shipped to their lab in La Réunion to be tested for the presence of hantavirus. They sequenced the viral genome in samples that came back positive to determine how related the viruses were between animals in the study, as well as to other hantaviruses globally. The sequencing results will help determine the origins of hantavirus in Madagascar in future work. Models helped the authors track different factors — like location, sex, weight, and age — to see how they correlated with the likelihood an animal was infected.
After taking samples from 17 species of small mammals and 11 species of bats, the team found the virus exclusively in rats. “We were surprised to find that only black rats were infected with hantaviruses because the other non-native species of small mammals are commonly infected in other parts of the world,” Kauffman said.
Agriculture Hotspots for Infection
Larger, adult rats were more likely to be infected and were more commonly trapped in agricultural lands than inside people’s homes. “This means that people are less likely to be exposed to the virus at home than in their fields,” Kauffman added.
What’s more, while many rats in the agroforests carried the disease, not one of the rats captured in the rainforest was infected. These findings demonstrate how human land use impacts infection in these animals, and in turn human exposure to this virus.
A Global Collaboration on Zoonotic Threats
This research project, funded by the National Institutes of Health and Duke University, connected scientists from around the world with diverse specialties, including disease ecology, social sciences, and veterinary health. Over the last eight years, the international team has studied zoonotic pathogens in wildlife, domestic animals, and people, comparing how pathogen prevalence and human exposure vary among animals across native and highly disturbed landscapes.
The authors are currently dating the introduction of hantavirus to Madagascar using the samples from this and other studies in the country. They also plan to further investigate how habitat fragmentation and human land use impact small mammals and the parasites they carry.
Reference: “Effect of Land-Use on Hantavirus Infection Among Introduced and Endemic Small Mammals of Madagascar” by Jérémy Dubrulle, Kayla Kauffman, Voahangy Soarimalala, Toky Randriamoria, Steven M. Goodman, James Herrera, Charles Nunn and Pablo Tortosa, 7 April 2025, Ecology and Evolution.
DOI: 10.1002/ece3.70914
Never miss a breakthrough: Join the SciTechDaily newsletter.
Follow us on Google and Google News.
1 Comment
“Some of these diseases can spill over to humans, as the COVID-19 pandemic powerfully reminded us.”
You forgot to add “when humans intentionally manipulate the virus to spill over to humans”