Parasite Forecasts

The Forecasts Are In: 2017 Will Be a Big Year for heartworm disease and Lyme disease

Heartworm Disease

This year, the Companion Animal Parasite Council (CAPC) is forecasting higher levels of heartworm transmission nationwide. The United States as a whole experienced above average precipitation and seasonal temperatures in 2016, leading to perfect breeding conditions for mosquitoes that transmit heartworms. Last year's forecasted heartworm outbreak in Northern California unfortunately came to fruition. Given the ongoing trend toward above average temperatures and rainfall, CAPC is forecasting high levels of heartworm disease activity in 2017 for most of the country, with an especially active year for the Western United States. Of great concern is the ongoing precipitation that the West observed this winter, leading to the prediction that heartworm disease will continue to increase even farther beyond its endemic range in 2017.

Overall, CAPC is forecasting above average heartworm disease activity nationwide. Key areas of concern include:


• The Lower Mississippi Valley, where heartworm disease is rampant, is expected to observe more cases of disease than normal.
• Locations in the Rockies and westward, where heartworm disease may not be foremost on the mind of pet owners, are forecasted to be problematic in 2017.
• New England, the Ohio River Valley, the Upper Midwest, and the Atlantic Coast States are predicted to see above normal heartworm disease activity.
• Western Texans from Amarillo to Laredo may observe static to lower than average burden of heartworm disease in 2017.

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 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.

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. Major weather events, such as hurricane Matthew last year, can also cause extensive changes in mosquito prevalence. The single most effective way to avoid timing mistakes with Heartworm preventive is to keep dogs and cats 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.

Lyme Disease

Nationwide, Lyme disease continues to expand beyond established endemic boundaries. Pet owners living or traveling to areas endemic for Lyme disease (Northeastern and Central Midwestern US), or those areas on the edges of Lyme disease endemic areas (The Dakotas, Iowa, Missouri, Southern Illinois, Ohio, Kentucky, Tennessee, North Carolina) should talk to their veterinarian about testing and protecting their dogs against this disease that is a threat to both animals and their owners.


• Western Pennsylvania, and Pittsburgh are of elevated concern: Lyme disease is now endemic in these regions and is forecasted to be even more problematic this year.
• New York State, North-western Wisconsin and Northern Minnesota, already endemic for Lyme disease, are expected to observe higher caseloads than in previous years.
• Lyme disease along the Atlantic seaboard (I-95 corridor) from Washington DC to Boston is forecasted to remain static this year.

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.

Testing for vector-borne disease

Because parasite prevalence is dynamic and ever changing, CAPC recommends all dogs be tested for Lyme disease, Anaplasmosis and Ehrlichiosis on an annual basis.

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, the changing distribution of wildlife that may harbor the parasite, 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 activity in your area

To help you identify the risk for parasite infection in your geographic area, CAPC provides Parasite Prevalence Maps down to the county level. The 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.

Learn more about 2017 Forecasts for Ehrlichiosis and Anaplasmosis: 

2017 Anaplasmosis Forecast

2017 Ehrlichiosis Forecast

Category: Parasite Forecasts