In Connecticut, it is estimated that there are 6–25 cases of heartworm infection diagnosed per clinic per year. While most of these cases are dogs that have been transported from other areas of the country where heartworm infections are more common, like the Southeast, some are home-grown cases. There have been increasing numbers of cases over the past 15 years of heartworm disease. Incidence maps from 2010 from the American Heartworm Society show New England as having 1–5 cases diagnosed per clinic per year.
When a mosquito bites and feeds on an infected dog, the larval worms (microfilaria) are transmitted into the mosquito. When that mosquito feeds on another dog, it then transmits microfilaria to that dog. The worms mature into adults over a 6–month period and start producing microfilaria to continue the lifecycle. Adult worms can live 5–7 years while microfilaria live 1–2 years.
Prevention of heartworm disease is key. Preventatives kill larval worms that have already infected the pet rather than preventing the parasites. The preventative medications can only kill the larva at a certain stage of maturity which is why it is important to continue heartworm preventative medications year-round. If the larval worms can mature past the stage where medications can kill them, they could mature into adult worms. If you miss a month of heartworm prevention, it is typically recommended to test for heartworms six months later to catch infections as quickly as possible. We can only test for adult female worms, so we do not recommend testing animals before six months of age.
There are many different preventative medications consisting of oral, topical or injectable versions. I recommend discussing with your veterinarian about which is best for your pet if you are considering changing or starting heartworm prevention. While prevention can seem expensive, with a year’s worth of Heartgard or Interceptor costing around $175, treatment is much more expensive with many more side effects.
The treatment guidelines set by the American Heartworm Society consist of a 365-day protocol. This includes a regimen of antibiotics to kill a synergistic bacteria that lives within the heartworms, steroids to limit inflammation, and melarsomine to kill the adult worms. The melarsomine injections are painful and can cause abscesses and tissue damage. While being treated, dogs must stay exercise-restricted to limit side effects on the cardiopulmonary system. In severe infestations of heartworms, the worms may need to be surgically extracted if they are blocking the flow of blood through the heart.
Heartworm disease can affect cats and ferrets as well. There is no treatment for cats, so heartworm prevention is highly recommended. If you have questions or concerns about Heartworm prevention or disease, contact your veterinarian or visit heartwormsociety.org