In the U.S., some 300,000 people are diagnosed with Lyme disease annually. Thousands also suffer from babesiosis and anaplasmosis, tickborne ailments that can occur alone or as co-infections with Lyme disease. According to a new paper published in PLOS ONE, when small, fast-living mammals abound, so too does our risk of getting sick.
In eastern and central North America, blacklegged ticks are the primary vectors for Lyme disease, babesiosis and anaplasmosis. The pathogens that cause these illnesses are widespread in nature; ticks acquire them when they feed on infected animals.
Richard S. Ostfeld, the paper's lead author and a scientist at the Cary Institute of Ecosystem Studies, has researched the ecology of Lyme disease since 1992. "A pattern emerged in our long-term studies. Ticks that fed on certain rodents and shrews were much more likely to pick up multiple pathogens, making the environment riskier for people."
To investigate why mammals differ in their 'reservoir competence' or ability to transmit pathogens to ticks, Ostfeld and his co-authors from Bard College, Oregon State University, the University of South Florida, and EcoHealth Alliance took a two-pronged approach.
First, they looked at life history traits for nine mammals known to harbor Lyme disease, babesiosis, and anaplasmosis. Attributes like body size, litter size, and life span were taken into consideration.
Then they looked at the role of mammal population density. As 'sit and wait' parasites, ticks are much more likely to encounter animals with dense populations. This, in turn, could help pathogens evolve to exploit specific hosts, resulting in more effective transmission rates.
For Lyme disease and anaplasmosis, fast life history features were a strong predictor of an animal's ability to transmit infection to ticks. Body size was inversely related to reservoir competence. Raccoon, skunk, opossum, squirrel, and deer infected fewer ticks than their mouse, chipmunk, and shrew counterparts.
Ostfeld notes, "This is consistent with past research on Lyme disease, West Nile virus, and Eastern Equine encephalitis. There is evidence that animals that mature early and have frequent, large litters invest less in some immune defenses, making them better pathogen hosts."
Population density was the best predictor of species' abilities to transmit all three pathogen groups, with animals that ticks encountered most frequently being the most effective at transferring infection. Co-author Felicia Keesing of Bard College explains, "Fast life history and high population density often go hand-in-hand. In rodents and shrews, pathogen adaptation and poor immune defense may be working together to amplify disease spread."
Ostfeld adds, "In our struggle to manage the ever-growing list of tick-borne diseases, we need to understand which animals magnify human disease risk. Our results suggest when generalist pathogens emerge, small mammals with large populations and a fast pace of life warrant careful monitoring."
Research and analyses were made possible through grants from the National Science Foundation's Divisions of Environmental Biology and Emerging Frontiers.
Source: Cary Institute of Ecosystem Studies
The Next Frontier in Infection Control: AI-Driven Operating Rooms
Published: July 15th 2025 | Updated: July 15th 2025Discover how AI-powered sensors, smart surveillance, and advanced analytics are revolutionizing infection prevention in the OR. Herman DeBoard, PhD, discusses how these technologies safeguard sterile fields, reduce SSIs, and help hospitals balance operational efficiency with patient safety.
Targeting Uncertainty: Why Pregnancy May Be the Best Time to Build Vaccine Confidence
July 15th 2025New national survey data reveal high uncertainty among pregnant individuals—especially first-time parents—about vaccinating their future children, underscoring the value of proactive engagement to strengthen infection prevention.
CDC Urges Vigilance: New Recommendations for Monitoring and Testing H5N1 Exposures
July 11th 2025With avian influenza A(H5N1) infections surfacing in both animals and humans, the CDC has issued updated guidance calling for aggressive monitoring and targeted testing to contain the virus and protect public health.
IP LifeLine: Layoffs and the Evolving Job Market Landscape for Infection Preventionists
July 11th 2025Infection preventionists, once hailed as indispensable during the pandemic, now face a sobering reality: budget pressures, hiring freezes, and layoffs are reshaping the field, leaving many IPs worried about their future and questioning their value within health care organizations.