written by Dr. Nadine Cerny
Heartworm disease is a disease that we see – unfortunately – rather frequently in our patients at Carriacou Animal Hospital. As this severe and potentially fatal disease is easily preventable with a monthly medication, we’d like to raise awareness and give some background information with this article.
The disease is caused by a worm-like parasite called Dirofilaria immitis and it is transmitted to dogs – and occasionally to cats – by mosquitos (Culicidae).
Over the next 3 to 4 months the worms grow immensely in size. Adult female worms are about 30 cm long, the males are about 23 cm. Eventually they are ready to mate and the female gives birth to live young worms (microfilaria, larval stage 1; L1), which distribute in the dog’s vascular system. Now is the time, a mosquito gets infected again with young heartworm larvae, when it bites the dog and feeds on its blood. The young larvae need the mosquito as a host in order to evolve into the second and third larval stage. Once the larvae reached the third larval stage (L3), their life cycle is closed and they are ready to infect another dog.
Due to global warming, export/import of goods and traveling/moving with pets, the disease is distributed in other countries as well and occurs at least seasonally. Within the Caribbean, heartworm disease is highly endemic in mosquitos and dogs on all the islands. If your dog lives here or if you travel in this area with your dog without taking preventative actions, it will get bitten by mosquitos and therefore – very most likely – get infected with heartworm larvae.
Initially, the heartworm disease in dogs is often unnoticed by dog owners, as in the early stages of the disease, the dogs usually don’t show symptoms. The symptoms reflect the adult worm burden, the duration of the infection and the individual reaction of the dog to the parasite. In moderate to advanced stages of infection, the dog owner may notice symptoms like exercise intolerance, fatigue, coughing, shortness of breath, breathing noises and decrease in appetite. In very severe stages of the disease the dog may even cough up blood or worms.