Is heartworm on the rise?

Is heartworm on the rise?

I’ve heard more than a few Bay Area pet owners say that they don’t treat their pets with a monthly heartworm preventative because heartworm isn’t a big issue here — especially in San Francisco. We generally don’t have many mosquitoes buzzing about — the culprits responsible for transmitting the disease.

After Alice’s recent adverse reaction to Trifexis, I’ve been increasingly more wary of overmedicating my pooch, but recent reports seem to indicate that heartworm may be more prevalent, even here in the city, than we had previous thought.

heartwormsociety.org

According to a recent survey by the American Heartworm Society (AHS), heartworm-positive pets have been diagnosed in nearly every county and parish in every state in our country. The organization conducts the American Heartworm Incidence Survey every three years to track trends in heartworm incidence, using data from clinic heartworm testing and numbers of heartworm-positive dogs and cats. AHS gathered the 2010 data from more than 5,000 veterinary clinics across the country.

The infection rate in male dogs is as much as four times that of female dogs, and dogs housed outdoors are four to five times more likely to be infected than indoor dogs.

Treatment for heartworm infection is available, but is costly and requires strict supervision by both veterinarians and owners — and a month or more of cage confinement. The annual cost of prevention is roughly 10 percent of the cost of treatment. In addition, some heartworm medications treat other parasites as well.

The AHS recommends to both veterinarians and pet owners that pets be tested for heartworm each year and that dogs be put on heartworm prevention year-round. “Some owners, and even some veterinarians, question the necessity of following these recommendations, thinking that the cold or dry climate they live in makes such vigilance unnecessary,” says says veterinarian and AHS President Wallace Graham. “However, we can cite case after case of heartworm-positive pets living in areas assumed to be low-risk. It only takes one bite from an infected mosquito for a pet to acquire a heartworm infection.”

What is heartworm?

Heartworm disease is so named because the adult worms live in the right side of an animal’s heart. Heartworm is a mosquito-borne parasite that is transmitted when an infective mosquito is feeding. The infected larvae enter the dog through the hole that is created in the dog’s skin. Only a few of the many species of mosquitoes are significant vectors for hearworm. In Northern California, three species are thought to be the major carriers.

Where are dogs at the highest risk for contracting heartworm in California?

Dogs and outdoor cats at greatest risk of infection in California are those that live in the foothill plant climate zone of either the coast range or the Sierra Nevada mountain range. This includes areas with 65 cm of rainfall or more per year and elevations between 400 and 3000 feet. Next at risk are outdoor pets living in the upper Sacramento Valley along the Sacramento, Feather and American Rivers or their tributaries. This is followed by outdoor pets living in the intermediate valleys plant climate zone, which include much of the region between the mountains of the coast range. In these three areas, prevalence in dogs varies from 14 to 174 infected dogs per 1,000 examined or 1.4 to 17%. These figures are based upon prevalence data collected on over 75,000 dogs examined from 1983 through 1999 in Northern California. All were kept outdoors day, night, or both day and night without prophylactic treatment. At least risk of infection are pets in the coastal plant climate zone of the San Francisco Bay Area that are always kept indoors, with no travel out of that area. The Santa Cruz Mountains and Woodside are higher due to the increased population of coyotes in these regions which serve as a vector to transmit the disease.

Why is regular heartworm testing necessary?

A number of blood tests are available to diagnose heartworms. The most accurate is the heartwormantigen test, which identifies an antigen produced by the adult female heartworm. False negatives occur in dogs with early infections (before the appearance of mature worms), in light infections with fewer than five adult worms, and in infections in which only males are present. False positives are rare. If a dog is given heartworm prevention medication without proper testing, the medication could kill the pet. While heartworm medications are retroactive, meaning that they typically kill immature heartworm larvae that have infected a pet during the previous month, pets living for months without prevention medication could be infected with mature heartworms that require medication injected by the veterinarian to kill worms and prevent damage to the heart. No pet should be given heartworm medication without proper testing.

What are symptoms of heartworm?

In dogs, the signs of heartworm disease depend on the number of worms and the size of the animal. Pets with a mild infestation may remain asymptomatic. The typical early signs of heartworm infestation are lethargy, lack of appetite weight loss and a soft, deep cough. As the disease progresses these symptoms become more severe. *

What is the treatment for heartworm in dogs?

There are three stages of heartworm infection. The third stage is severe and may not be treatable. Blood testing and chest X-rays are needed to determine the stage of heartworm infection. The most common heartworm treatment for dogs is the injection of Immiticide, which will kill any adult heartworms that have taken up residence in your dog’s heart. The drug is injected in two sites in the hip area. The first few days after injection, your dog may be lethargic and may have trouble walking. The following four to six weeks are particularly stressful for the dog and owner as the dog must be prevented from playing, running or getting overly excited. The dead heartworms are expelled from the heart in small pieces. If a dog becomes too excited, his heart will pump harder and faster, which can cause the the dead heartworms to travel to the lungs. This can cause respiratory failure. The second stage of heartworm treatment is to kill the heartworm larvae in the dog’s bloodstream. At this point, your vet may allow you to increase your dog’s physical activity to light playing.

Is heartworm the same in cats as it is in dogs?

Diagnosis of heartworms in cats is often difficult and not always 100% reliable. There are several tests that your veterinarian may perform, but there are currently no approved methods to treat heartworm in cats. The available treatments are often dangerous as a single dead worm can cause a blockage of the pulmonary artery. Always discuss potential treatment options — and their risks — with your vet. If there are no clinical symptoms, your vet may decide not to treat your cat and wait for it to clear the parasite on her own. Heartworms live for 2 to 3 years in cats. If the cat is displaying symptoms, an anti-inflammatory may be used to lessen the reaction to the worm.

Can humans contract heartworm?

Yes, but not from your dog or cat. Heartworms cannot be spread animal-to-animal — they need a mosquito to complete their life cycle. Humans are not a natural host for heartworm, but there have been a few rare reports of human cases. In humans, the heartworm is usually found as a single worm in the lung versus the heart.

Posted By: Amelia Glynn (Email, Facebook) | June 15 2011 at 01:21 PM

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