ANIMAL BYTES: No Wiggle Room


By Stephanie Oba, DVM
(First published in The Rafu Shimpo on October 6, 2011)


A shortage of heartworm treatment medication for your pets exists nationwide. There is only one FDA-approved drug and its maker reports that a technical issue caused a supply disruption. Unfortunately, this means many animals will have to await medical treatment for heartworm until the supply returns.

What is heartworm?

Heartworm is a potentially fatal disease caused by a parasitic worm that lives in the bloodstream of dogs, cats and other species of mammals. It lives in the arteries of the lungs and occasionally enters the heart.

At first, it was easier to detect in the heart, hence the name heartworm. It is now known to infect the lung tissue first.

Shy is nine-month-old Pepper, a Catahoula leopard-Labrador mix rescue dog, who is available through Pups and Pals. (Courtesy of S. Oba)

What is its life cycle?

Adult female heartworms release their young, called microfilariae, into the animal’s bloodstream. Then a mosquito bites the animal and sucks the microfilariae into its body with the blood meal. Once inside the mosquito, the microfilariae mature into the larval form.

The infected mosquito then bites another animal and releases larvae through a bite wound. These larvae mature into adult worms in about six months.

The mosquito is a necessary vector, as the microfilariae can’t mature into adults without the mosquito host.

What are its symptoms?

In dogs and cats, there may be no signs of disease, especially early in the course of the infection. It may take months or years for the numbers of heartworms to accumulate and cause clinical symptoms.

In other words, recently infected pets may show no signs. When clinical symptoms do occur, you’ll notice a persistent cough, lethargy, difficulty exercising or fatigue after only moderate activity, symptoms mimicking heart failure or lung disease, vomiting, reduced appetite and weight loss. Sadly, in cats, there may be no signs other than sudden death.

How is it detected?

In an apparently healthy animal, heartworm is detected with routine screening blood tests. There are two commonly used blood tests. One looks for an antigen made by adult worms, the other for the microfilariae in the blood.

It can also be detected with an ultrasound or imaging of the heart and lungs, but this is usually seen in more advanced cases.

How is it treated?

In dogs, multiple doses of a drug that kills the adult worms are injected into the back muscles. The dog may need to be stabilized if there are signs of heart or lung disease present. Often, pets are hospitalized due to instability. Once they’re back home, you’re required to severely restrict their activity for four to six weeks after the last injection.

Many require cage confinement. Cats are much more difficult to treat. There is an ongoing debate whether or not to treat. Killing adult worms is likely to set off an inflammatory cascade that is potentially more dangerous to the cat than the actual worm. Currently, treatment is aimed at alleviating the symptoms until the worms die a natural death.

Is it preventable?

Yes, there are a wide variety of drugs available to prevent heartworm disease. It’s much easier, safer, and less expensive to have your pets on these preventatives. Currently, the one FDA-approved dog treatment is unavailable, so prevention is critical.

Preventatives come in the form of monthly pills, topical treatments and injections. You should check the heartworm status of your pet prior to starting the preventatives because a few of them can cause adverse reactions if your pet does have the disease.

Since the mosquito is needed to complete the heartworm life cycle, make sure your pet’s environment does not attract mosquitoes. Try to avoid letting them outdoors during the prime feeding times of dusk and dawn.

It’s very important to use preventatives now. They are your only line of defense at this time. Fortunately for SoCal residents, heartworm is not as common when compared to NoCal and the southeastern part of the U.S.


Stephanie Oba is a contributing writer and physician for animals in  Alhambra. Opinions expressed in this column are not necessarily those of The Rafu Shimpo.



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