Vector-Borne Diseases: 5 Unexpected Regions of Increased Prevalence and the Responsible Vectors
Many factors—such as changes in climate, habitats, land use, and wildlife reservoir populations—are causing vector-borne diseases to spread across the U.S. This includes tick-borne diseases not previously seen in some areas.
Historically, the bacterial species Borrelia burgdorferi was thought to be limited to the northeastern U.S., while the Ehrlichia species were considered endemic in southeastern and southwestern states.
However, recent IDEXX data compiled from customer testing in sales regions throughout the U.S. for the Companion Animal Parasite Council's (CAPC) 2021 Parasite Prevalence Maps has demonstrated surprising findings, showcasing everything from how common tick-borne diseases in dogs are to the rising prevalence of Lyme disease and ehrlichiosis in some states in the U.S.
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Let's dissect this data and discover what we can learn from the findings to help support your patients' health and well-being.
Analysis of the VBD Data
CAPC educates veterinary professionals and pet owners by collecting and distributing credible, accurate, and timely information to improve diagnosis, treatment, prevention, and control of parasitic infections. One resource that the CAPC provides is a parasite prevalence map for counties in the U.S. with adequate volume of testing.
The IDEXX data compiled for the 2021 CAPC maps revealed a national heartworm disease prevalence of 1.22%, a Lyme disease prevalence of 4.2%, an anaplasmosis prevalence of 2.5%, and an ehrlichiosis prevalence of 2.5%, based on serologic testing. Despite heartworm having the lowest prevalence rate among these diseases, many veterinarians screen for heartworm alone rather than a more comprehensive screen that also includes Lyme disease, anaplasmosis and ehrlichiosis.
The IDEXX data also highlighted five regions with unexpectedly high vector-borne disease test results. The following interpretations are estimates.
- The Gulf Coast region: At 3.7%, ehrlichiosis prevalence here is 1.5 times higher than the national average. Data is based on testing from counties in Alabama, Arkansas, Lousiana, Mississippi and Texas.
- Memphis region: At 10.8%, ehrlichiosis prevalence is 4.2 times higher than the national average and 2.8 times higher than heartworm disease (3.8%). Data in this region comes from counties in Arkansas, Illinois, Indiana, Kentucky, Missouri, Mississippi, and Tennessee.
- The Great Lakes region: At 2.6%, Lyme disease is 3.5 times more prevalent than heartworm infection (0.7%). This is based on data from counties in Michigan and Indiana.
- Minneapolis region: At 7%, Lyme disease prevalence is 1.7 times higher than the national average and 16.7 times higher than heartworm disease (0.4%). This data is based on testing from counties in Iowa, Michigan, Minnesota, North Dakota, and Wisconsin.
- The Tennessee Valley region: At 6.3%, ehrlichiosis prevalence is 2.5 times higher than the national average and 5.5 times higher than heartworm disease (1.2%). This region's data comes from counties in Indiana, Kentucky, Ohio, Tennessee, Virginia, and West Virginia.
The Responsible Tick Species
Many tick species transmit diseases; however, according to CAPC, three species are responsible for spreading Lyme disease and ehrlichiosis in these areas.
- Ixodes scapularis: Also known as the deer tick, black-legged tick, and bear tick, this tick species is the main vector for Lyme disease in North America. This species can also transmit Ehrlichia muris, babesiosis, and anaplasmosis. Ixodes scapularis distribution is linked to the abundance and dispersal of the white-tailed deer, which is the species' preferred host. The ticks are found as far south as Florida, extending westward to central Texas, and as far north as Maine, extending to Minnesota and Iowa. The I. scapularis life cycle lasts about two years. Adult females lay between 1,000 to 3,000 eggs.
- Amblyomma americanum: Also known as the lone star tick, this tick species is the primary vector for Ehrlichia ewingii and Ehrlichia chaffeensis. They are widely distributed in the southeastern U.S. and were identified for the first time in New York State in the 1970s. Currently, the lone star tick's leading geographic distribution edge is considered to lie in the central midwestern U.S. White-tailed deer and wild turkey populations may be responsible for the lone star tick's expansion. This tick species has a similar life cycle to the deer tick, and an engorged female tick can lay approximately 5,000 eggs.
- Rhipicephalus sanguineus: Also known as the brown dog tick, this tick species is considered the most widespread tick in the world and is the primary vector for Ehrlichia canis. Brown dog ticks can also transmit Rocky Mountain spotted fever and babesiosis. According to CAPC, they live in and around homes and kennels, infesting both anywhere there are dogs. This includes the colder regions of North America. In addition, the brown dog tick's life cycle is significantly shorter compared to the deer tick and lone star tick. Specifically, it's 70-90 days as compared with 2-3 years to complete a life cycle.
The Importance of Comprehensive Screening
These results indicate that vector-borne diseases are spreading, and CAPC data reports heartworm disease, Lyme disease, Ehrlichia spp., and Anaplamsa spp. in all 50 states. However, many veterinarians don't routinely recommend comprehensive vector-borne disease screening every year, which may explain lack of prevalence data in certain regions.
The diseases are common and may go undetected if veterinarians do not screen for them. A look at CAPC 2021 data shows that screening for heartworm infection is much more commonplace, although vector-borne diseases are more prevalent conditions. In 2021, there were 17,680,518 dogs tested for heartworm with 215,392 positive cases (1.22%). But the same number of dogs was not tested for Lyme disease. Specifically, 10,323,420 dogs were tested for Lyme with 434,737 positive cases (4.21%).
Comprehensive screening for vector-borne diseases is in your patients' best interest, regardless of location. Unfortunately, historical data about the locality of these diseases may no longer be accurate as vectors spread across the nation. CAPC's Parasite Prevalence maps can help veterinarians encourage pet owners to have their pets tested regularly. Take advantage of the resources available to help you effectively communicate tick-borne disease risks to your clients. Ensure your patients are screened and protected—regardless of where you practice.