Parasite Forecasts

2024 Pet Parasite Forecasts

Risk of Exposure to Vector-Borne Pathogens:  What to Expect in 2024

Pathogens that cause heartworm disease, Lyme disease, ehrlichiosis, and anaplasmosis continue to increase and spread throughout the United States. The risk of vector-borne disease is complex and involves the interaction of vectors, pathogens, hosts, host behaviors, and habitats. Land use and climate change, human population growth, urbanization, changes in wildlife host and vector densities and distributions, and increasing international trade and travel are all factors that directly impact vector-borne diseases. An interdisciplinary approach between human, animal, and ecosystem health, referred to as One Health, recognizes the diversity of factors involved in vector-borne disease risks.

Risks have increased due to rehoming of pets, changes in distribution and prevalence of vector populations, habitat changes, changes in wildlife populations and increased interactions with them in newly developed and reclaimed areas, and the short and long-term changes in climatic conditions.

Ticks and mosquitoes remain the principal transmitters of pet and human vector-borne pathogens. The recent discovery of the invasive Asian long-horned tick (Haemaphysalis longicornis) in the eastern United States, and the continuing recovery of H. longicornis southward and westward of the original site, adds to our concern about disease agents that might be transmitted by this tick. According to the CDC, between 2004 and 2016, mosquito-borne and tick-borne disease incidence in people in the United States tripled, with much of this increase due to tick-borne pathogens which were reported in higher numbers and across a larger geographic area. The CAPC 2024 forecasts for vector-borne diseases in dogs, supported by ongoing research, continued to highlight areas where we can do more to lower the risk of exposure of companion animals to vectors of concern. The best preventive measures that veterinarians and their clients can take is to prevent contact between companion animals and these vectors. The foundation of these prevention strategies are the recommended use of products that kill and/or repel mosquitoes and ticks, administration of approved vaccines, and the compliant use of year-round preventives.

Lyme Forecast

The tick vector (Ixodes scapularis) of Lyme disease (Borrelia burgdorferi) continues to expand its geographic range. These ticks (called black-legged ticks) also transmit other important agents such as Anaplasma phagocytophilum, Babesia spp., Borrelia miyamotoi, Ehrlichia muris eauclarensis, several viruses, and possibly Bartonella spp. On-going research is increasing the spectrum of disease agents transmitted by black-legged ticks. Lyme disease is an important One Health pathogen that impacts the health of both humans, dogs, and horses.

  • The 2024 forecast for Lyme disease in dogs is similar to the 2023 forecast with the geographic distribution of Lyme disease continuing to expand southward and westward outside of the historically high-risk areas (Northeast and Upper Midwest).
  • We expect minor increases beyond last year’s forecasts in eastern Tennessee, Indiana, and North Dakota. High-risk “hot-spots” are again predicted in northern and southwestern Lower Michigan, and southern Indiana.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 is expected to continue in North Dakota, northeastern South Dakota, southeastern Iowa, Illinois, and eastern Kentucky. For the first time, Lyme forecasts include eastern Montana.
  • The southward movement of Borrelia burgdorferi is also evident in the increasing risk in North Carolina and Tennessee. Higher risk areas in parts of coastal North Carolina continue as was reported in the 2022 and 2023 forecasts. The 2024 Lyme prevalence maps, indicate that one northern North Carolina county has a prevalence rate of 44% (72 positive of 163 tested). Although this number represents a small number of dogs tested to date, the emerging data validates and emphasizes our reminders that pets and pet owners do not have to travel to the traditional endemic areas of the Northeast to encounter substantial Lyme disease risks.

Pet owners living or traveling in areas endemic for Lyme disease, or those areas on the edges of Lyme disease endemic areas should talk to their veterinarian about testing and protecting their dogs against this disease that is a threat to both animals and their owners. A vaccination for Lyme disease should always be considered for pets in high-risk areas. Keep in mind that potential spread of Lyme Borreliosis can occur anywhere the tick vector is present.

What is Lyme disease?

Lyme disease is a bacterial infection transmitted through the bite of an infected black-legged tick (including eastern and western black-legged ticks). Infected dogs may show signs such as shifting-leg lameness, fever, lethargy and loss of appetite, although the majority of infected dogs show no signs at all. Lyme disease can lead to systemic complications including renal disease.

People and other pets in your household can’t catch Lyme disease directly from an infected dog. However, infected dogs do indicate that there are infected ticks in the area that may transmit the infection to other household members.

Year-round tick control and vaccination can help safeguard your dog

Within any geographic area, there are likely several different species of ticks and each tick can harbor more than one disease-causing agent.  Some species of ticks can also be active during the winter. While it helps to limit your dog’s exposure to ticks by avoiding tall grass and wooded areas, this approach may not always be feasible. That’s why CAPC recommends year-round tick control and regular screening tests for dogs. Also, don’t forget that cats can get ticks and there are important tick-borne pathogens of cats (e.g., cytauxzoonosis).

Keep your pets and family safe from tick-borne disease. Talk to your veterinarian about Lyme disease prevention, including year-round use of tick preventive and vaccination.

Heartworm Forecast

  • We expect the high risk of heartworm infection to continue along the Mississippi river, throughout the southern portions of the interior Midwest, and along the Atlantic coast north into Virginia and southern New Jersey. The prevalence of heartworm continues to increase in the mid-Atlantic region, pushing northward into the densely populated regions of the northeast. The number and diversity of mosquitoes teamed with the population densities of the region support that heartworm infections are more likely to affect the health of increasing numbers of dogs in those areas.
  • Pet owners 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 veterinarian about the changing prevalence. This is particularly important in southern Indiana, central and southern Illinois, southern Iowa, Kansas, and Lower Michigan and Ohio in the Great Lakes region.
  • Additional areas likely to experience increased risk include the southwest (New Mexico), large portions of Colorado, and the northern Great Plains.
  • Forecast of increased risk continues in northern California, with an additional increased likelihood of infection in western North Dakota, eastern Montana, and northwest South Dakota.
  • We expect that much of the upper Midwest and the Northeast will have little change, perhaps indicating that increased emphasis on vector control and compliant heartworm prevention are having an impact in these regions. It is important to remember that areas of greater local prevalence and increased risk are likely to remain in some areas within these regions.
  • The risk of heartworm infection reported during the previous years in much of central and southern Florida remains. However, the predicted prevalence in southcentral Florida decreased slightly. Perhaps increased post-pandemic veterinary visits and compliance has helped to lessen what was once a severe emerging risk.
  • Very few regions are expected to have lower-than-average prevalence. It is important to remember 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. Annual testing is recommended to monitor compliance and preventive efficacy.

What is Heartworm disease?

A serious and potentially fatal condition, heartworm disease has been diagnosed in all 50 states of the country. It only takes a single mosquito bite for pets to become infected with heartworm larvae.

In dogs, the larvae mature into adult worms in the heart and nearby blood vessels, often leading to heart and lung failure. Signs may include coughing, trouble breathing, and exercise intolerance, although some dogs may show no signs at all.

Cats and ferrets can get heartworm disease too. While cats are less likely to develop large numbers of adult worms, immature heartworms can damage the lungs, leading to coughing, asthma-like signs, or vomiting.  Even indoor cats are at risk — studies show that up to 30% of cats diagnosed with heartworm disease were described as strictly indoor.Year-round tick control and vaccination can help safeguard your dog

Should your pet be on year-round heartworm preventive, even during the winter months?

The answer is yes. Mosquito numbers are tied closely to heat and humidity. An early spring or warm, wet fall can cause mosquitoes to emerge early or be active later in the season. Activity may be noted sporadically in the winter during periods of warm weather. Major weather events, such as hurricanes can also cause extensive changes in mosquito prevalence. The single most effective way to avoid timing mistakes with heartworm preventive is to keep dogs, cats, and ferrets on medication year-round and have your dog tested at least once a year. Your veterinarian can recommend an effective preventive that’s right for your pet.

Annual Testing is critical for the health of your pet

CAPC recommends that all dogs be tested annually for both heartworm antigens and microfilariae, even if they are on year-round preventives. Cats should be tested for the presence of heartworm antigen and antibody before starting them on preventive.

The science behind the forecasts

How are the CAPC Forecast maps constructed? Numerous factors are analyzed, including the number of positive tests for the bacterial infection and the influence of weather patterns, vegetation types, and human population density. Leading parasitologists work in collaboration with a team of statisticians to identify regions of the country that may experience higher parasite numbers in the months ahead. While these forecasts predict the potential risk of a dog testing positive, they do not necessarily reflect clinical disease. The best source of information on parasitic disease is your local veterinarian: they are your local experts and the best provider of healthcare information for your pets.

Stay current on vector-borne disease

To help you identify the risk for parasite infection in your geographic area, CAPC provides Parasite Prevalence Maps down to the county level.  These maps report the number of dogs testing positive for infection in your area, as well as in other regions where you may travel with your pet.  Parasites that affect pets and people are dynamic and ever changing, and CAPC is your trusted resource for accurate, timely information.

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".

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

Click on the diseases to learn more about the 2024 forecasts for Ehrlichiosis and Anaplasmosis

Category: Parasite Forecasts