The Vet Is In: HeartwormsMar 15th, 2009 | By Dr. Marvin Ordway | Category: Pets
Heartworm is a common parasite that is transmitted by mosquitoes and poses a major threat to your family pets. An ounce of prevention in this case is worth more than a pound of cure – it can save your dog’s or cat’s life.
Mosquitoes become infected by ingesting baby heartworms – called microfilaria – drawn from infected dogs, coyotes, foxes and other so-called “reservoir” hosts. Inside the mosquito, the microfilaria incubate for one to two weeks and are then ready to infect another mammal. When the mosquito takes a blood meal, the heartworm larva enter their new host, slowly migrating to the heart and pulmonary arteries where they mature.
The mature heartworms, each up to 12 inches long, may number in excess of 200 (think angel hair pasta). In their happy new home, nourished by a constant supply of
blood, the heartworms mate and release microfilaria into the host’s bloodstream. The host now becomes a reservoir, able to infect other mosquitoes.
While the heartworm and mosquitos are happy with this cycle, the dog,
cat, ferret, or other susceptible host becomes debilitated and may even die. The ill effects depend on the host’s size and response to the infection, and the number of worms. People can also become infected but are not natural hosts, so the larva typically get stopped in the lungs and die.
Cats, too, are not natural hosts, so heartworms don’t mature as easily as in dogs. However, even one worm has the potential to kill or severely debilitate a cat due to the severe pulmonary inflammation it provokes. Many cats with apparent asthma or chronic coughing are actually suffering from heartworm disease.
Dogs, considered a natural host, are more susceptible. Dogs can harbor as many as 250 worms in their heart and associated pulmonary vessels. The worms can live in this perfect environment for seven years and produce thousands of baby heartworms before dying. Imagine how hard the dog’s heart has to work to push blood past the worm mass.
Most dogs are asymptomatic until, bitten by numerous infected mosquitoes, their heartworm numbers increase. This results in inflammation, which causes arteries to thicken and constrict, reducing oxygenation. The dog suffers pulmonary hypertension, a chronic cough, exercise intolerance, and eventual heart failure. By the way, it’s a myth that long-haired dogs can’t get heartworm: mosquitoes bite them on the nose or face.
The antigen blood test, that detects proteins released by mature female heartworms, is the most common and accurate method of diagnosing heartworm in dogs. An X-ray, which helps determine the infection’s severity, will show characteristic changes in the shape of the heart and blood vessels. Currently, only Immiticide, a tamed arsenic drug, is approved for killing adult heartworms in dogs. Treatment is costly and not without risk.
In cats, heartworm is more difficult to diagnose. The small number of worms involved means there may not be enough antigen in the cat’s blood for detection; also, microfilaria are rarely released into the cat’s blood. There is no treatment for adult heartworm infection in cats. Immiticide is toxic to cats. Infected cats are treated symptomatically with anti-inflammatory drugs for one to three years until the worms eventually die. Unfortunately, many cats do not survive the infection.
The good news is that heartworm infection is easy and
inexpensive to prevent. Both Interceptor (milbemycin) and Heartguard (ivermectin) are
formulated into tasty once-a-month treats to prevent heartworm
infection. Dogs and cats that refuse to eat these monthly preventatives can be treated with once-monthly prescription topical “spot-on” products.
It is very important to give the heartworm preventative every 30 days, year-round. Most areas of California do not have a distinct mosquito season, and trying to guess when the season begins and ends will definitely put your pet at risk. An added benefit is that these drugs also prevent infection from many common intestinal worms that also can cause serious health problems in pets and people (roundworm larva, for example, can cause blindness in children).
Be safe: Treat your furry friends monthly to keep them healthy and protect your family from potential disease.
© 2009, Friends and Neighbors Magazine