Getting to the Heart of the Problem, or the Problem of the Heart
Heartworm is a parasitic roundworm that is spread by mosquitoes. The victims and hosts for these potentially deadly squatters are dogs, cats and other similar mammals; even humans can be affected. They are named “heartworms” because in the final stage of its life cycle, the parasite lives and reproduces within the heart of the host. The accumulation of parasites eventually causes congestive heart failure. Infected dogs that go untreated can die, and even treated dogs go through a long period of uncomfortable treatment and sometimes require surgery. The best defense comes in the form of a prophylactic treatment administered during the mosquito season. A course of heartworm prevention begins with a blood test to see if the parasite is present. If the dog is parasite free, a medication can be used to prevent heartworm infection. A positive test result, on the other hand, usually requires treatment to eradicate the worms.
Heartworms evolve through a series of stages before becoming adults and infesting the host’s heart. Infected blood is transferred from host to host through mosquito bites. Once inside the host, the parasite enters a larval stage and begins growing to adult size. After the parasites have matured, they begin reproducing and migrate to the heart. Heartworms bear live young, producing thousands of them every day. The offspring, called microfilarine, must be ingested by a mosquito for the next stage to be set into motion and before they can begin to grow to full size. Before becoming adults, they travel through the circulatory system and become lodged in the arteries, heart and lungs. Once in place, they increase in size; females can reach almost a foot in length with males reaching around nine inches.
The period between initial infection and when the worms have reached adult size sometimes takes six to seven months in dogs. Dogs show no indication of infestation during this period. Although it is rare, migrating heartworm larvae can get misdirected and end up in unusual locations such as the eye, brain, or arteries in the leg, which results in symptoms such as blindness, seizures and lameness. Some dogs will show little or no sign of infection even after the worms have matured. The presence of the heartworms leads to slow damage to areas such as the lungs, kidneys and liver; this causes the host to appear as if they are aging faster. Active dogs may experience more pronounced symptoms because of the excessive work carried out by their respiratory and circulatory systems.
Treatment is highly effective if the disease is diagnosed in the early stages. Before the worms can be treated, the dog must be evaluated to ensure the heart, liver and kidney are healthy enough for the dog to survive; problems with these organs will be addressed first. Adult worms are usually killed with an arsenic-based compound; the currently recommended medication has been reformulated to lessen side effects, making it safer for dogs with late-stage infections. The course of treatment is not completed until several weeks later when the microfilariae are dealt with in a separate course of treatment. Once heartworm tests come back negative, the treatment is considered a success. Surgical removal of the adult heartworms is also a treatment that may be indicated, especially in advanced cases with substantial heart involvement.
After treatment, the dog must rest and be restricted from exercise for several weeks for sufficient healing. Otherwise, when the dog is under exertion, dead worms may break loose and travel to the lungs, potentially causing respiratory failure and death. Although previously recommended for dogs with heartworm, aspirin is no longer thought to have a positive medical effect.
Prevention against heartworm can be obtained through a number or veterinary drugs, the most popular being ivermectin. This may remove adult heartworms from most dogs. It shouldn’t, however, be considered a legitimate treatment because not all dogs are cleared by this method. Secondly, adult heartworms do not begin to die until almost a year and a half of treatment has elapsed. The most popular brands of heartworm medication include Heartgard, Interceptor, ProHeart, Advantage, and Revolution.
Preventative drugs are highly effective, and when regularly administered, will protect more than 99 percent of dogs from infection. Failures often result from irregular and infrequent administration of the drug. If a dose is accidentally missed one month, adequate protection is usually provided so long as the next two monthly doses are administered on schedule. Monthly heartworm prevention should be administered beginning within a month of the onset of the local mosquito season and continued for a month after local mosquito activity has disappeared. In areas with warmer, more tropical climates, medication should be administered year-round.