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What is heartworm and how is it treated?

Heartworms, Dirofilaria immitis, belong to the same class of worms as roundworms. In fact, they look a bit like roundworms, but that is where the similarity ends. Heartworms spend their adult life in the right side of the heart and the large blood vessels connecting the heart to the lungs.

Adult heartworms in the heart lay very tiny larvae called microfilariae, which then live in the bloodstream. These microfilariae enter a mosquito when it sucks blood from an infected animal. In 2-3 weeks, the microfilariae develop into larger larvae in the mosquito and migrate to the mosquito's mouth.

When the mosquito bites another animal, the larvae enter the animal's skin. The larvae grow and after about three months finish their migration to the heart, where they grow into adults, sometimes reaching a length of 14 inches. The time from when an animal was bitten by an infected mosquito until adult heartworms develop, mate, and lay microfilariae is about 6-7 months in dogs and 8 months in cats.

Severely infected dogs can have up to several hundred heartworms in their hearts and vessels. Adult worms in dogs usually live up to 5-7 years. Thirty to eighty percent of infected dogs have microfilariae, and the microfilariae can live up to 2 years. Microfilariae cannot mature into adult heartworms unless they pass through a mosquito.

In dogs, the adult worms can obstruct the various large blood vessels leading from the heart to the lungs. Worms may also enter smaller vessels in the lung and obstruct those vessels, as well. In severe cases, called "caval syndrome" worms start to fill the right ventricle of the heart.

When the adult heartworms die as a result of treatment, they can obstruct blood vessels to the lungs (these are called pulmonary embolisms). If only a small part of the lung is involved, there may be no clinical signs. However, if the vessels to a large portion of the lung, or a small area of an already diseased lung are blocked, severe signs may result. These include fever, cough, coughing up blood, and even heart failure. Because of the risk of these embolisms, any dog being treated with an adulticide must be kept very quiet during treatment and for at least 4 weeks thereafter.

Meet Ally McBeagle

Sunday, June 27, 2010

Ally McBeagle at Play!

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