Risk of Exposure to Vector-Borne Pathogens: What to Expect in 2021

The risk of exposure to the pathogens that cause heartworm disease, Lyme disease, ehrlichiosis, and anaplasmosis continues to increase throughout the United States, particularly in areas where the agents are common.

Ticks and mosquitoes continue to expand their prevalence ranges. The 2021 forecasts, together with ongoing research, highlight areas of concern where more can be done to lower the risk of exposure of companion animals to vectors of disease. The best preventive measures that veterinarians and their clients can take is to prevent contact between companion animals and these vectors. Use of products that kill and/or repel mosquitoes and ticks, and the practice of year-round heartworm prevention are strongly recommended.

The 2021 national forecasts alert veterinarians and pet-owners to geographic regions where increased risk of transmission of vector-borne diseases is likely to occur.

20210406 Capc Forecast Maps Display V1 Heartworm

Heartworm Forecast

  • When we compare the 2021 heartworm forecast to the average prevalence over the past nine years, we expect the prevalence to be much higher in areas along the Mississippi river, throughout the southern portions of the interior Midwest, and along the Atlantic coast north into Virginia and southern New Jersey. As the prevalence of heartworm continues to increase in the mid-Atlantic region and into the megalopolis regions of the northeast, heartworm infections are more likely to impact the health of increasing numbers of dogs in those areas.
  • Veterinarians in states with historically lower prevalence are again cautioned about the increasing risk of heartworm infection and are encouraged to have a discussion with their clients about the changing prevalence. This is particularly important in the interior Midwest (Indiana, central and northern Illinois, and southern Iowa), and lower Michigan and Ohio in the Great Lakes region.
  • Additional areas likely to experience increased risk include the southwest (southern Arizona and New Mexico) and portions of Colorado, Kansas, Montana and North Dakota in the northern and central Great Plains.
  • Unique to this year’s forecast of increased risk include northern California and Idaho and western Montana in the northern Rocky Mountain west.
  • Much of the upper interior Midwest and the New England region is expected to have little change, but small increases in prevalence may be seen throughout.
  • An intriguing increase in risk is seen in much of central and southern Florida. These regions have had historically lower prevalence, likely due to more compliant use of preventive products. However, 2020 brought changes to pet disease prevention strategies in many parts of the US. Perhaps this and local changes in climate, testing, and veterinary visits contribute more significantly in this and other regions of emerging risk.
  • Very few regions are expected to have lower than average prevalence. It is important to remind clients that changes in local environments could create risks that might not be evident in the broader regional forecasts.

Year-round use of preventive products remains the best means of providing comprehensive internal and external parasite control throughout the year. Annual testing is recommended to monitor compliance and continuing preventive efficacy.

20210406 Capc Forecast Maps Display V1 Lyme

Lyme Disease Forecast

The tick vector (Ixodes scapularis) and Lyme disease (Borrelia burgdorferi) in dogs are expanding their ranges from the northeastern and mid-Atlantic states, the upper Midwestern states, and throughout Canada. These ticks (called deer ticks) also transmit other important agents such as Anaplasma phagocytophilum, Babesia spp., Borrelia miyamotoi, Ehrlichia muris eauclarensis, and possibly Bartonella spp. On-going research continues to recognize other disease agents transmitted by deer ticks.

  • The geographic prevalence of Lyme disease continues to expand southward and westward.
  • Particularly large increases are expected in eastern Kentucky, northeastern Tennessee, western Michigan, and Ohio. High-risk “hot-spots” are predicted in parts of northwestern and southwestern lower Michigan, and southern and northeastern Ohio.
  • High risks of Lyme disease persist in all portions of the Northeast, the upper mid-western states of Wisconsin, Minnesota and the upper peninsula of Michigan. A higher than normal risk of Lyme disease in North Dakota, northern South Dakota, Iowa, southern Illinois, and western Kentucky is consistent with the westward and southward expansion of Lyme Borreliosis.
  • The southward movement of Borrelia burgdorferi is also evident in the increasing risk in the Carolinas and Tennessee.
  • Veterinarians in regions of historically high prevalence and in forecasted regions of increased risk should reinforce their recommendations of aggressive tick control. Keep in mind that potential spread of Lyme Borreliosis can occur anywhere the tick vector is present. Always consider vaccinating high-risk patients. Annual testing can aid in assessing risk for dogs in hyper-endemic areas.
  • Veterinarians in regions where the prevalence of Lyme and other tick-borne diseases is low to moderate should also use these forecasts to explain the need for testing and prevention. Constant surveillance and more aggressive tick control will prevent an increase in prevalence of existing disease or slow the establishment of new diseases.

Ehrlichiosis and Anaplasmosis

Forecasts are also provided for these important tick-borne diseases of dogs. View the Ehrlichia spp. and Anaplasma spp. forecasts and learn more about the CAPC guidelines for prevention and treatment of ehrlichiosis and anaplasmosis.

2021 Anaplasma spp. forecast

2021 Ehrlichia spp. forecast

Year-Round Protection, Annual Testing

The best way to protect your patients is to advise owners of the importance of year-round prevention, even during the winter months. You can use the CAPC Parasite Prevalence Maps to support your recommendation by underscoring the risks in your area and in regions of the country your clients may travel with their pets. It is also critical to emphasize the importance of compliance and using products correctly.

CAPC Parasite Prevalence maps and Forecast maps are validated tools for increasing client willingness to engage in parasite prevention. Sign up to receive local alerts on parasite testing results down to the county level today by visiting the CAPC Parasite Prevalence Maps and selecting "Get Updates".

Monthly Pet Parasite Forecasts

Veterinary professionals and pet owners who want to monitor parasite activity in their county throughout the year, can also access 30-Day Parasite Forecast Maps at www.petdiseasealerts.org. These maps, developed exclusively by CAPC, provide a local forecast for every county in the continental United States on a monthly basis.

The Science Behind the Forecasts

Vector-borne disease is dynamic and ever changing, driven by multiple factors that affect the development of arthropod vectors and the pathogens they carry. Leading parasitologists work in collaboration with a team of statisticians to identify regions of the country that may experience higher parasite incidence in the months ahead. Numerous factors are analyzed, including the number of positive tests and the influence of weather patterns, vegetation indices, and human population density. Using this multi-disciplinary approach, we are leveraging everyone’s expertise to focus on a single common interest: forecasting the risk of exposure to vector-borne pathogens. While these forecasts predict the potential risk of a dog testing positive, they do not necessarily reflect the occurrence of clinical disease.

To learn more about the science behind the maps, a free review can be read here and full access to all of our manuscripts describing the methodology and fidelity of our forecasts can be found here.