What causes heartworm disease?
Heartworm disease or dirofilariasis is a serious and potentially fatal disease. It is caused by a blood-borne parasite known as Dirofilaria immitis.
Adult heartworms are found in the heart and adjacent large blood vessels of infected dogs. Rarely, worms may be found in other parts of the circulatory system. The female worm is 6 to 14 inches long (15 to 36 cm) and 1/8 inch wide (5 mm). The male is about half the size of the female. One dog may have as many as 300 worms present when diagnosed.
"Adult heartworms may live up to five years..."
Adult heartworms may live up to five years and, during this time, the female produces millions of offspring called microfilaria. These microfilariae live mainly in the small vessels of the bloodstream.
What is the life cycle of the heartworm?
"...the parasite requires the mosquito as an intermediate host..."
The life cycle of the heartworm is complicated; the parasite requires the mosquito as an intermediate host before it can complete its life cycle in the dog. As many as 30 species of mosquitoes can transmit heartworms.
The life cycle begins when a female mosquito bites an infected dog and ingests the microfilariae during a blood meal. The microfilariae develop further for 10 to 30 days in the mosquito's gut and then enter its mouthparts. At this stage, they are infective larvae and can complete their maturation when they enter a dog. The infective larvae enter the dog's body when the mosquito bites the dog. They migrate into the blood stream and move to the heart and adjacent blood vessels, maturing to adults, mating and reproducing microfilariae within 6-7 months.
Where is heartworm disease found?
"Canine heartworm disease occurs all over the world."
Canine heartworm disease occurs all over the world. In the United States, it was once limited to the south and southeast regions. The highest numbers of reported cases are still within 150 miles of the Gulf of Mexico and the Atlantic Ocean coastlines and along the Mississippi River and its tributaries. However, the disease is spreading and is now found in most regions of the United States, including California, Oregon and Washington. In Canada, the disease is problematic in areas where mosquitoes are prevalent, such as along waterways and coastlines in many provinces. The greatest number of cases in Canada occurs around the southern Great Lakes
