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Canine Heartworm Life Cycle | |||||||||
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Dog heartworm is a disease common in canines throughout most of the United States. It is caused by a roundworm with the scientific name Dirofilaria immitis. The adult female heartworm measures from 9 to 16 inches in length, with the males a little more than half that long. The males have cork screw turns of the posterior end that is often referred to as a "pigtail." Adult worms living within the heart
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The heartworm parasite has to have both a dog and a mosquito for a host before it can reach the adult stage. It cannot complete its’ life cycle without first being ingested by a mosquito. The development of the larvae starts when the mosquito sucks up the microfilariae during its’ feeding on an infected dog. The newly acquired larva migrates from the mosquito’s stomach to the abdominal region and into the mosquito kidney. Once there, it becomes immobile, shortens and becomes thickened. In about 4 to 5 days, it develops into a sausage-like form. At about 8 days, it molts and becomes a larva. During the second larval stage, it’s internal organs are formed. The third stage brings another molt at around 11 to 12 days, which results in a larvae which is a miniature adult which increases in length over the next few days and then breaks out of the kidney area to migrate through the mosquito’s body to its head, where it gathers in the proboscis (mouthparts). It is now capable of infecting another dog. The entire process in the mosquito takes only 2 to 3 weeks. | |||||||||
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As the mosquito feeds on the dog, After an increase in size and another molt into the 5th and final stage, the worms are young adults and leave the tissue and muscle to enter the bloodstream through the wall of a small vein. They then follow the bloodstream and eventually lodge in the right side of the heart and pulmonary arteries, where they grow into adult heartworms and start to mate and produce microfilariae (babies) of their own. From time of infection to production of baby larvae takes a little over 6 months. This is about the length of a normal winter. This is the reason your veterinarian wants to test your pet before starting heartworm pills in the spring. That last mosquito of last fall could have been a culprit that infected your dog. | |||||||||
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produce millions of microscopic larva that are about 1/800 of an inch long and are known as microfilariae. These circulate in the blood stream of the dog for up to three years. However, only a very few ever get a chance to mature in a mosquito. If they are not ingested during those 3 years, they die and disintegrate. The breeding adults, however, are continually replacing those that die.
Some studies have shown that the numbers of microfilariae in the blood appear to increase near the surface of the skin during the times of peak feeding activity for mosquitoes. They also appear to be more numerous during the day and during the summer than at night or during the winter.
the larvae emerge from the tip of its proboscis and are deposited on the skin. They stay moist and protected until they enter the dog by a drop of the mosquito’s blood. The larvae penetrate the skin through the wound that the mosquito has made after she withdraws her mouth. They’ll stay close to the area of the wound for a few days and then burrow into the dog, where they settle in the tissue. Around 6 to 10 days after entering the dog, there’s another molt and they become 4th stage larvae. They’ll stay in the tissue for a couple of months as they increase in size to about 1/10 inch in length.