Heartworm

Heartworm is a parasitic roundworm that is spread from host to host through the bites of mosquitoes. The heartworm is a type of filarial worm, a small thread-like worm, that causes heartworm disease. The definitive host is the dog, but it can also infect cats, wolves, coyotes, foxes, and other animals, such as ferrets, sea lions, and even, under rare circumstances, humans.

Life Cycle

The life cycle of the heartworm begins when an infected animal is bitten by a mosquito. The mosquito ingests the microfilariae during a blood meal. The microfilariae then develop further for 10 to 30 days in the mosquito's gut and then enter its mouth parts. When the mosquito bites another animal, the heartworm larvae are deposited on the skin and enter the new host through the mosquito bite wound. Once inside a new host, it takes approximately 6 months for the larvae to mature into adult heartworms. Once mature, heartworms can live for 5 to 7 years in dogs and up to 2 or 3 years in cats.

Symptoms

In the early stages of the disease, many dogs show few symptoms or no symptoms at all. The longer the infection persists, the more likely symptoms will develop. Active dogs, dogs heavily infected with heartworms, or those with other health problems often show pronounced clinical signs. Symptoms of heartworm disease may include a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss.

Treatment

The goal of treatment is to eliminate all stages of the heartworms with a minimum of harmful effects to the host. Serious complications can occur when the worms die, so it is important that the dog be kept quiet and closely monitored during the treatment period. Currently, there are two drugs approved by the FDA for the treatment of heartworm disease in dogs: melarsomine dihydrochloride and ivermectin.

Prevention

Prevention of heartworm disease can be obtained through a number of veterinary drugs. These drugs are generally given monthly and can be administered as a chewable oral tablet, a topical solution applied to the skin, or an injectable drug given every 6 months.

See Also

• Parasitic worms
• Mosquitoes
• Heartworm disease
• Filarial worms