Wrigley, an 8 year old female spayed Boder Collie Mix, presented for vaccines, a fecal exam, and a heartworm test as part of her routine annual exam. She was doing well at home and there were no abnormalities found on her physical exam.
A sample of Wrigley’s blood was submitted to look for the presence of heartworm antigens. Her test came back positive. A second test was submitted to make sure the result was real, but also came back positive and Wrigley was diagnosed with heartworm disease.
Heartworm disease is a serious and potentially fatal condition caused by parasitic worms living in the arteries of the lungs and sometimes in the right side of the heart of dogs, cats and other mammals. Dogs or other animals harboring adult worms are the recognized reservoir of heartworm infection. The disease is spread by mosquitoes that become infected while feeding from an infected dog. The mosquito can then go on to bite another dog, cat, or other susceptible animal, spreading infection. In the dog, the adult worms live in the vessels of the chest, where they cause extensive injury. In Wrigley’s case, radiographs, or X-rays, were taken of her chest to look for evidence of heartworm disease. Radiographs of the heart and lungs are the best tools available to evaluate the severity of the disease and to try to predict how well a patient might tolerate treatment for heartworm infection. Typical changes include enlargement of the pulmonary arteries of the lung and enlargement of the right side of the heart. Inflammation may be found in the lung tissue. Fortunately, Wrigley’s radiographs were largely unremarkable. Still, not treating the infection was not an option. Untreated infection will eventually lead to cardiopulmonary disease. and can also lead to liver or kidney failure. Death can result from one or a combination of these problems.
Wrigley was continued on monthly heartworm prevention to prevent new heartworm infection while being treated for her existing heartworm disease, and to prevent her from being a source of infection for mosquitoes to pick up and potentially infect other dogs. She was also started on Minocycline, an antibiotic, to treat a type of bacteria associated with heartworms.
Wrigley recently received her first injection of an arsenical drug called Melarsomine, which will kill the adult heartworms in her body. She will need 2 more injections to give her the best chance of clearly her infection.
The most concerning complication during treatment for heartworm disease is the development of pulmonary thromboembolism (PTE), as dead heartworms obstruct blood flow through the pulmonary arteries. It will be extremely important to restrict Wrigley’s activity while she is undergoing treatment to minimize her risk for complications.
The best way to prevent heartworm disease is through the use of heartworm preventatives. Even in colder climates the American Heartworm Society recommends year-round prevention. Most products are given monthly, either as topical or oral medications. It is important to give monthly preventatives the same day each month since it only takes one missed dose to put your pet at risk for infection.
Annual heartworm testing is also important, since we are often able to detect infection before the development of clinical signs and significant cardiopulmonary disease, as was the case with Wrigley.