As the temperatures begin to rise, you and your pets may spend more time outside. The mosquito population here in Central Virginia is also on the rise as the temperatures climb. Thus starts the beginning of heartworm season – as the weather becomes nicer, our pets and the pesky mosquitoes collide. To help promote awareness and education about this disease, the American Heartworm Society has declared April “Heartworm Awareness Month.” This week we will take the opportunity to discuss what exactly heartworm disease is, and why an ounce of prevention is worth a pound of cure. We see too many pets in area shelters with heartworm disease, so it is important to have your pets on heartworm prevention before having to encounter the costly undertaking of treatment that can be traumatic for the pet.
Heartworm disease is a serious and potentially fatal condition caused by parasitic worms, Dirofilaria immitis, living in the arteries of the lungs and heart of its host. The disease is transmitted by mosquitoes. While dogs are the definitive host for heartworms, cats and other species of mammals, including wolves, foxes, ferrets, sea lions and in rare instances, humans can be infected as well. The first published description of heartworms in dogs in the United States appeared in the 1840s and heartworm disease in cats was first described in the 1920s.
The disease cycle begins when the adult heartworms living in an infected host release their offspring, called microfilaria, into the bloodstream. Mosquitoes become infected by the microfilaria while biting and feeding from these infected animals. During the next 10-14 days, microfilaria mature to the infective larval stage within the mosquito. When the mosquito then bites another susceptible animal, the larvae are deposited onto the surface of the animal’s skin. They can then enter the new host through the fresh bite wound and migrate to the blood vessels. Inside the new host, it takes 6-9 months for the infective larvae to mature into adult heartworms, which reside in the heart, lungs and associated arteries. Once mature, heartworms may live up to 5-7 years in dogs and 2-3 years in cats.
Dogs may be infected by a few or up to several hundred heartworms. Cats are similarly infected although usually by only a few worms. Outdoor pets are at greatest risk of infection, especially in regions of the world with high mosquito populations. However, indoor pets can become infected by heartworms as mosquitoes can get into houses.
Heartworm infection has been diagnosed around the globe and in all 50 states. The highest infection rates in dogs in the United States are observed in temperate and tropical regions where mosquitoes flourish such as the Atlantic and Gulf Coasts and along the Mississippi River. However, urban areas in northern climates are also at risk due to mosquitoes surviving in “heat islands” produced by heat radiating from buildings and parking lots. Transportation of pets to different geographic regions contributes to the spread of heartworm disease across the country. The peak months for heartworm transmission are usually July and August.
Kate Hall, LVT, is the manager of veterinary services at the Richmond SPCA. To read the biographies of our regular bloggers, please click here. Before posting a comment, please review our comment guidelines. Please note that our comment policy requires a first and last name to be used as your screen name.