Heartworm

If veterinarians are not promoting heartworm prevention to their clients, chances are their clients are not doing enough to protect their dogs and cats from the disease

For animal owners, springtime suggests an opportunity to spend more time outdoors with their pets. For your customers, it should signal an opportunity to reinforce the importance of a dependable heartworm program for their patients.

A large number of dogs, and an even greater percentage of cats, are not on heartworm prevention but should be, according to experts. In part, this is due to client misperceptions: Many pet owners do not realize that the disease is easily transferred by mosquitoes, while others believe that heartworm is easily “cured” by giving their pet a pill. At the same time, some vets fail to convey a sense of urgency about heartworm prevention to their clients. Before sales reps can sell their customers on the importance of heartworm prevention, they should help vets understand their clients’ complacency.

What is heartworm?
Heartworm infection is caused by worms (Dirofilaria immitis), which sometimes mature into 14-inch-long adults, according to the American Heartworm Society. Adult worms live in the right side of the heart and the arteries of the lungs, causing arterial damage and eventually heart failure. In extreme cases, the disease leads to organ damage as well, particularly liver and kidney.

The infection is spread from one animal to the next by mosquitoes, which become infected with microfilariae while taking a blood meal from another animal. The microfilariae mature to the infective larvae stage in the mosquito for the next 10 to 14 days. When the mosquito bites another animal, the infective larvae enter through the bite wound.

A number of animals, including dogs, cats, ferrets, coyotes, wolves and sea lions, may be infected with heartworm. Humans can be infected as well. However, the two largest reservoirs are untreated dogs and coyotes.

Generally, cats appear to be less susceptible to the disease, with fewer worms surviving into adulthood. When an infected mosquito bites a cat, it takes about eight months for the infective larvae to mature into adult worms, which may live for two or three years in the cat. In dogs, on the other hand, infective larvae take a little over six years to mature into adult worms, which live between five and seven years. While heartworm is more prevalent in regions more heavily infested with mosquitoes, the disease has been identified throughout the nation with the exception of Alaska.

Testing and treating
For both cats and dogs, clinical signs of heartworm disease often are not apparent in the early stages, since heartworms tend to accumulate gradually over a period of months or years, and after repeated mosquito bites, according to the American Heartworm Society. As the disease progresses, cats exhibit non-specific clinical signs, which mirror other feline diseases, including vomiting, gagging, difficult or rapid breathing, lethargy and weight loss. Untreated cases may result in acute death. Dogs exhibit such signs as mild, persistent coughing, reluctance to move or exercise, exhaustion following moderate exercise, reduced appetite and weight loss. Untreated cases lead to heart or lung failure, and fluid buildup in the abdomen.

Despite the danger, data indicate that about 40 percent of client-owned dogs have not been placed on heartworm prevention. Pet owners are often unaware that the disease is so easily transferred via mosquito bites. Sometimes they think they can save money each month by foregoing the preventive medicine, and then simply give their dog a pill if it is diagnosed with heartworm. Unfortunately, diagnosis and treatment are much more rigorous and expensive than administering a monthly tablet.

Diagnosing canine heartworm infection involves several steps:
• Recording an accurate patient history.
• Recognizing clinical symptoms.
• Administering several diagnostic procedures, including serological testing (for antigens and antibodies), microfilarial detection and differentiation, X-ray and angiography.

Treatment, which involves administering an organic arsenal compound, can be expensive. As the heartworms die, inflammation may occur in the dog, which must be hospitalized for a couple of nights and restrained in a crate for as long as a month or more.

Feline heartworm infection is more difficult to diagnose, and negative results do not always rule out an infection. In fact, an antigen test detects only adult female or dying male worms. Immature or male-only worm infections are rarely detected. The diagnostic plan for heartworm in cats may involve:
• Physical exam
• X-ray
• Echocardiograph
• Angiocardiograph
• CBC
• Serological testing (for antigens and antibodies)
• Microfilaria testing.

There is no approved treatment for feline heartworm infection. In some cases, cats are monitored with chest X-rays. Cats with radiographic or clinical evidence of lung disease may be given small, decreasing doses of prednisone. In severe cases, the animals require intravenous fluids, oxygen therapy, cage confinement, bronchodilators, cardiovascular drugs or antibiotics.

Prevention
For your customers and their patients, heartworm prevention is not only a practical solution, but a much gentler approach than permitting the disease to progress to the point where treatment is needed. But, unless veterinarians communicate the importance of a good preventive program, clients likely will not take this route.
Depending on the product, heartworm treatment should begin around the age of six weeks. Heartworm preventive products generally are administered to pets on the first day of each month. The dose may kill immature larvae. However, when the dog or cat ventures outdoors again, it may be bitten by a mosquito and reinfected with new larvae. If the pet does not receive the next dose of preventive medication on the first day of the next month, the new larvae have an opportunity to mature, and the disease may progress.

How to sell
When sales reps pay their vet customers a visit, they should not assume all practices are equally diligent about prescribing heartworm preventives. They should begin the sales process by discussing the clinic’s policy for addressing heartworm prevention. Some good probing questions for vets include the following:
• “Doctor, are your clients often leaving your practice without a prescription for a heartworm preventive?”
• “Do you recommend heartworm prevention, or do you stress it as a mandatory part of pet care?”
• “Does your front desk provide a prescription for clients as they check out?”

Often, veterinarians have great intentions of ensuring their patients are on a heartworm preventive, yet they do not realize how many clients leave their office without a prescription. As many as 500,000 dogs are infected with heartworm in this country, and hundreds of thousands become infected each year, according to some experts. A simple discussion can lead to healthier dogs and cats, more satisfied clients and a stronger bond of trust between doctor and client.

Editor’s note: Vet-Advantage would like to acknowledge the contribution of MERIAL Ltd. (Duluth, Ga.).