Heartworm in Dogs, Part 1: Overview

Photo by fabioberti.it.

With mosquito season now upon us, it is time to think about heartworm in dogs. This is a serious and potentially fatal disease that occurs in the United States and other countries.

The parasite that causes heartworm is called Dirofiliara immitis. It is transmitted from animal to animal by the bite of a mosquito that has picked it up from a dog already infected with heartworms. Heartworms cannot be transmitted from dog to dog without this mosquito.

The process starts with an infected dog that already has heartworms. The adult heartworms in these animals produce what are called microfilaria. The microfilaria circulate in the bloodstream and are sucked up by a mosquito when it bites the infected animal.

In the mosquito, the microfilaria develop into mature larvae over 10 to 14 days. These infective larvae now enter another dog when this mosquito bites this dog. Over the next six months, these larvae in the dog develop into adult heartworms and stay there up to seven years, causing damage to the heart and lungs.

Infected dogs can harbor large numbers of adult heartworms in the heart and lungs, and their numbers can increase as they are bitten by more mosquitoes in subsequent years. These worms can cause severe damage to the other organs even after successful elimination of the worms with medication.

Next week, Dr. Palazzolo will cover the prevalence of heartworm in dogs.

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