Heartworm Disease and Your Pet
The following post is from Molly Foreman, DVM:
What causes heartworm?
Heartworm infection is caused by a filarial organism known as Dirofilaria immitis. Mosquitos serve as intermediate hosts which help to spread the disease to animals as the mosquito takes a blood meal and bites your dog or cat. Infections are possible in numerous wild and companion animals. Wild animal reservoirs can include wolves, coyotes, foxes, California gray seals, sea lions, and raccoons. In companion animals, heartworm infection is seen primarily in dogs and less commonly in cats and ferrets.
The heartworm life cycle
The life cycle of Dirofilaria immitis takes place with certain stages of growth while in the mosquito and then while in the infected host. Mosquito vector species acquire the first stage larvae (microfilariae) while feeding on an infected host. Development of microfilariae to the second larval stage and to the infective third stage, occurs within the mosquito in approximately 1 to 4 weeks, depending on environmental temperatures. When mature, the infective larvae migrate to the mouth parts of the mosquito so that as the mosquito feeds, the larvae can migrate into the bite wound, beginning the mammalian portion of their life cycle.
Once in the infected pet, the infective larvae molt into a fourth stage in 2-3 days. After remaining in the subcutaneous tissue for close to 2 months, they molt into young adults that migrate through host tissue, arriving in the pulmonary arteries approximately 50 days later. Adult worms develop primarily in the pulmonary arteries of the lung over the next 2 to 3 months. They reside mostly in the pulmonary arteries but can move into the right ventricle of the heart when the worm burden becomes high. Microfilariae are produced by gravid females approximately 6 to7 months post infection
Symptoms of heartworm disease
Live worms can have an immunosuppressive effect; however the presence of dead worms leads to immune and allergic reactions. Long term infections, due to all of the factors noted (ie, direct irritation, worm death, and immune response) result in chronic lesions and secondary scarring. Active dogs tend to develop more pathology than inactive dogs for any given worm burden. Frequent exertion increases the problems that occur in the heart and lungs, which can lead to overt clinical signs such as coughing, exercise intolerance, and even congestive heart failure.
When heartworm positive dogs are not administered a preventative and are not appropriately tested or treated, clinical signs such as coughing, exercise intolerance, unthriftiness, labored breathing, fainting, bleeding from nose, and excess fluid in the abdomen due to right-sided CHF are likely to develop. Infection can eventually lead to the death of your pet if left untreated. Treatment is very expensive and there are many complications that can occur.
This is a disease which is easily prevented, so please see your veterinarian today to have your pet tested for heartworm disease and started on the appropriate heartworm prevention medication.