Heartworms by Debra Offenbacker, D.V.M.
Heartworms, or Dirofilaria immitis, causes serious and potentially
life-threatening cardiac disease in both dogs and cats. Heartworm infections have been diagnosed in both all around the world, including all 50 states in the USA. This worm is transmitted to the animals by mosquitoes and because infected mosquitoes can come inside your house, both outdoor and indoor pets are at risk. Adult heartworms are long and thin. Females can grow up to 10 inches while males only reach half that length. Although heartworms can live in the right ventricle of the heart, the majority reside in the pulmonary artery which is the vessel that carries blood from the right side of the heart to the lungs. Female worms can live for several years, during which time they release millions of immature worms, called microfilariae, into the animal’s blood stream. Microfilariae are so small they are sucked up by the mosquito as it takes a blood meal from your pet. The mosquito is an essential intermediate host for heartworms, meaning it 20
Delmarva Unleashed
Fall 2015
can only mature by spending time in a mosquito. Once in a mosquito for the required amount of time, the larva leaves the mosquito when it takes a blood meal from its next victim. Once the larva is in a dog, it travels around and finally takes up residence in the blood vessels. It takes six months for the heartworm to become completely mature and reproductively viable. Heartworms cause an inflammatory response inside the pulmonary artery. This restricts blood flow, causing the heart muscles to have to work harder. Eventually, the strain can be so great that the heart fails. Dogs with heartworms usually suffer from a soft cough. Those with heavy infestations are also intolerant to exercise, lose weight and have difficulty breathing. Cats with heartworm may cough, but they can also show some unexpected signs. In long-term infestations, they may vomit, breath hard and lose weight. In short-term infestations, cats may collapse, go blind, convulse or even die suddenly.
