Heartworm disease is a serious and potentially fatal disease in pets. It is caused by foot-long worms (heartworms) that live in the heart, lungs and associated blood vessels of affected pets causing severe lung disease, heart failure and damage to other organs in the body. Heartworm disease affects dogs, cats and ferrets, but heartworms also live in other mammal species including wolves, coyotes, foxes. This disease is transmitted by female mosquitoes. At least 70 species of mosquitoes can transmit heartworm disease.
In Nepal, canine heartworm is common in the Terai cities like Bhairahawa, Nepalgunj, Chitwan, Dharan and Biratnagar where the prevalence of mosquitoes is high. There is sporadic evidence of diagnosed canine heartworm in Kathmandu here at the Advanced Pet Hospital.
How is heartworm disease transmitted
Mosquitoes play an essential role in the heartworm life cycle. Adult female heartworms living in an infected dog, fox, coyote or wolf produce microscopic baby worms called microfilaria that circulate in the bloodstream. When a mosquito bites and takes a blood meal from an infected animal, it picks up these baby worms which develop and mature into “infective stage” larvae over a period of 10 to 14 days. When the infected mosquito bites another dog, cat or susceptible wild animal, the infective larvae are deposited onto the surface of the animal’s skin and enter the new host through the mosquito’s bite wound. Once inside a new host, it takes approximately six months for the larvae to mature into adult heartworms. Once mature, heartworms can live for 5-7 years in dogs and up to 2-3 years in cats. Because of the longevity of these worms, each mosquito season can lead to an increasing number of worms in an infected pet.
Signs of heartworm disease in dogs
In the early stages of the disease, many dogs show few symptoms or no symptoms at all. The longer the infection persists, the more likely symptoms will develop. Active dogs, dogs heavily infected with heartworms, or those with other health problems often show pronounced clinical signs.
Signs of heartworm disease may include a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite and weight loss. As heartworm disease progresses, pets may develop heart failure and the appearance of a swollen belly due to excess fluid in the abdomen. Dogs with large numbers of heartworms can develop a sudden blockage of blood flow within the heart leading to a life-threatening form of cardiovascular collapse. This is called caval syndrome and is marked by a sudden onset of laboured breathing, pale gums, and dark bloody or coffee-colored urine. Without prompt surgical removal of the heartworm blockage, few dogs survive.
Your pet’s risk for heartworm infection
Many factors must be considered even if heartworms do not seem to be a problem in your local area. Your community may have a greater incidence of heartworm disease than you realise or you may unknowingly travel with your pet to an area where heartworms are more common. Heartworm disease is also spreading to new regions of the country each year. Stray and neglected dogs and certain wildlife such as wolves and foxes can be carriers of heartworms. Mosquitoes blown great distances by the wind and the relocation of infected pets to previously uninfected areas also contribute to the spread of heartworm disease.
Heartworm disease is a serious, progressive disease. The earlier it is detected, the better the chances of the pet to recover. There are few if any early signs of disease when a dog or cat is infected with heartworms, so detecting their presence with a heartworm test administered by a veterinarian is important. The test requires just a small blood sample from your pet, and it works by detecting the presence of heartworm proteins. Some veterinarians process heartworm tests right in their hospitals while others send the samples to a diagnostic laboratory. In either case, results are obtained quickly. If your pet tests positive, further tests may be ordered.