Park Hill Vet: The Forecast Is Heartworm

How To Beat the Bugs of Summer

By Margot K. Vahrenwald, DVM, CVJ

For the GPHN

As I write this column, we have a patient getting treatment for heartworm disease — it’s the second of three deep intramuscular injections of melarsomine. From beginning to the end of treatment is about six months. The average cost of diagnosis and treatment for a 40-pound dog is between $1,800 to $2,000, compared with the average cost of 12 months of heartworm preventative medicine being around $100 to $200.

As the winds die down and the threat of snow retreats, we can look forward to summer. But as you prepare, this month and next we’ll be digging into the forecasts of the bugs that plague us and our pets. It’s going to be a buggy summer. Prevention is the best medicine against disease-carrying mosquitos and ticks. This month we’ll discuss the flying menace of mosquitos.

For the past 20 years, the Companion Animal Parasite Council (CAPC) has issued annual forecasting maps for the most common parasites that are sources of disease for pets and people. Vector-borne pathogens are those that are transmitted by a vector such as mosquitos and can be harbored in the population of vector/s to create reservoir of persistent disease.

Mosquitos are the vectors for diseases that can impact people and/or animals such as West Nile virus, Eastern Equine Encephalitis, Dengue fever, Zika and new encephalitis viruses that have not yet become household names.

Impacting us in Colorado this year will be the highest percentage increases for risks for heartworm in the past 15 years. When creating their forecasting, CAPC uses test data from as many sources as possible, including national and local veterinary reference labs such as IDEXX, the Colorado Department of Environment and Public Health and the veterinary teaching hospital diagnostic labs. The CAPC is also quick to point out that these numbers are likely underestimations because they represent only about 30 percent of the pet population — the rest are not reported.

What animals get heartworm? Many is the short answer – including coyotes, ferrets, seals, sea lions, otters, skunks, red pandas, lions, tigers, other wild cats and, of course, domestic cats and dogs. Cats can get heartworm disease but are much harder to diagnose because the numbers of adult worms are very few versus dogs with many adult worms. We don’t commonly have cats on heartworm preventative in Colorado, but it is not wrong to consider it for your cat/s.

Heartworm Disease in Colorado has been increasing steadily and is most prevalent in our urban areas. Denver and all the counties along the Front Range have a two to greater than four percent increase in risk. While those numbers sound small, that translates on average to one in 100 dogs testing positive. Given known undercounted results from unreported and untested dogs, that likely means that there are potentially several hundreds of dogs that are heartworm positive and already suffering the damage caused by all life stages of heartworm.

Our biggest reasons for the rise are the huge influx of heartworm-positive dogs in and out of the state via shelter transfers — many dogs are sent to Colorado for rehoming from much more endemic areas of the country. In addition, some dog owners are not as vigilant as they should be for testing and year-round prevention. The fact is, no longer can we only give heartworm preventative seasonally, as we are home to all four species of mosquitos that carry heartworm — and they now overwinter rather than being killed off during the cold months.

The most insidious part of the disease is the long prepatent period from bite by an infected mosquito to the ability to diagnose via blood testing for heartworm antigen. In the meantime, the damage to the pet starts as soon as the larval heartworms arrive in the vessels of the heart, some 70-plus days after the dog is bitten by a microfilaria-infected mosquito. And, treatment is not fun for pet and owner due to extreme activity restrictions for several weeks to avoid complications from the die-off of adult worms.

Best practice is to have your dog heartworm tested annually. Most veterinary hospitals use a combined test that also screens for the three most common tick-borne diseases. Then, keep the dogs on preventative year-round – either oral, topical or injectable for their protection. Your veterinarian can review the options.

For more information on pets and parasites, visit capcvet.com. For more detailed information about heartworm, visit heartwormsociety.org.

Dr. Margot Vahrenwald is the owner of Park Hill Veterinary Medical Center at 2255 Oneida St. For more information, visit parkhillvet.com