Annual Review: Vector-Borne Disease in 2024 and What To Expect in 2025
Vector-borne disease screening is essential for early detection and treatment of diseases that can have asymptomatic presentations. In addition to the well-being of your patient, screening helps prevent the spread of these infections to other animals. It also supports public health surveillance by identifying potential human health risks. Regular screening is a key component of preventive healthcare, and it helps veterinarians and researchers understand trends over time and predict future risks.
Looking back through 2024 data, the Companion Animal Parasite Council (CAPC) Parasite Prevalence Maps show that Lyme and anaplasma increased slightly, but heartworm and Ehrlichia positivity decreased slightly. These trends are influenced by various factors that are expected to remain relevant in 2025, such as climate change, changing human activities, and land use.
Vector-Borne Disease Trends in 2024
Transmitted by mosquitoes, heartworm disease has seen persistently high levels throughout the southern U.S. in recent years, with some of 2024's highest prevalence (3-5% of all dogs tested having a positive test) along the Gulf Coast.
Lyme disease remains one of the most common exposures to vector-borne disease in dogs, with over 7% of dogs tested in Wisconsin testing positive, and over 10% of dogs testing positive in parts of New England.
Transmitted by the same black-legged tick (Ixodes scapularis), anaplasmosis has a similar geographic distribution to Lyme, with the highest prevalence in the Northeast and Upper Midwest. However, trends in Anaplasma spp. exposure in 2024 continued to show increasing prevalence beyond those historically high-risk areas to areas along the West Coast and moving southward across the country, likely transmitted by the brown dog tick (Rhipicephalus sanguineus).
Finally, Ehrlichia spp. exposure in dogs remains high throughout much of the U.S., though the states with the largest proportion of tested dogs showing evidence of exposure included Missouri (11%) and Arkansas (17%). New species of Ehrlichia have been identified in parts of Wisconsin and Minnesota, emphasizing the importance of testing even in "low-risk" regions to minimize transmission and disease.
Contributing Factors in 2025
Several factors contribute to the trends in the prevalence and geographic spread of vector-borne diseases in dogs, and these will continue to play a role in disease distribution in 2025. Climate change is a major player, with warmer temperatures and shifting rainfall patterns allowing ticks and mosquitoes to expand their range and stay active longer.
Urbanization and changes in land use also play a role: When people build new neighborhoods or clear land, we often create ideal habitats for vectors and their wildlife hosts, as well as bring our pets into closer contact with these vectors.
Fluctuations in populations of deer, rodents, and other host animals also directly impact disease transmission. On top of that, human travel and pet relocation for adoption further exacerbate the spread of these diseases, as increased travel and relocation can introduce infected vectors or hosts to new areas.
Finally, the emergence or introduction of new vectors, such as the invasive Asian longhorned tick (Haemaphysalis longicornis), raises concerns about the potential for novel transmission patterns in the future.
How Can We Keep Dogs Safe?
The CAPC emphasizes the importance of year-round parasite prevention. Consistently recommending tick and heartworm prevention products can help decrease transmission risk. Routine annual testing for vector-borne diseases also allows for early detection and treatment before serious health problems develop. Vaccination is another crucial tool, adding an extra layer of protection; though Lyme disease is currently the only common vector-borne disease with a widely-available vaccine. Managing the environment also makes a difference. Pet owners should be mindful of high-risk areas, like tick-heavy woodlands or mosquito-infested swamps, and take steps to limit their dogs' exposure. By integrating these preventive measures, veterinarians and pet owners can work together to protect canine health and reduce the overall burden of vector-borne diseases.
