Pets column: Mosquitoes are out -- protect your pet

Mosquitoes are back! A recent walk with my dogs at dusk turned into a jog, as I was motivated to run to get away from pests. To me, mosquitoes are more than just annoying. Here at Animal Allies Humane Society we know that their presence is a remi...

Mosquitoes are back!

A recent walk with my dogs at dusk turned into a jog, as I was motivated to run to get away from pests. To me, mosquitoes are more than just annoying. Here at Animal Allies Humane Society we know that their presence is a reminder that it is time to break out the heartworm preventive medicine. Dr. Mary Wictor, our shelter veterinarian, said that last year we had roughly ten dogs who were diagnosed with heartworm disease and then treated

before adoption.

Heartworm disease, which is transmitted by mosquitoes, can be a serious problem for our pets. Dr. Wictor explains a bit more about the disease and how it can be treated and prevented. ~ Amy Miller

Heartworm Disease


By Mary Wictor, DVM

Mosquitoes can transmit a number of diseases. One, heartworm disease, is of particularly great concern for pet owners.

This serious and potentially fatal condition is caused by a parasitic worm and has been reported in all 50 states.

Heartworm disease is transmitted by mosquitoes. When a mosquito bites an infected animal, it may pick up a microfilaria, the parasite in its immature stage. Over the next 10-14 days, the microfilaria grows into a larva. When the mosquito bites another cat or dog, the larva passes to that animal. About six months later, the larva matures into an adult worm, which lives in the animal's heart.

If not treated, the heartworms will accumulate over months or years.

Heartworm can affect both cats and dogs, but each species suffers the disease differently. In dogs, signs vary according to the number of mature worms living in the heart, with heavily infected dogs showing signs such as a mild cough, lethargy, fatigue after moderate exercise, reduced appetite, and weight loss.

A cat's immune system, however, will destroy the adult worms over time. Symptoms affecting cats are caused by the inflammation that occurs in the lungs and airways as the parasites die. These signs are often mistaken for asthma or allergic bronchitis.

In both dogs and cats, clinical signs may not be recognized in the early stages of the disease, and recently infected animals may exhibit no signs


at all.

Heartworm is diagnosed with a blood test. In dogs, the test identifies a specific protein that is produced by the adult female heartworm. Because of the length of time it takes for the larva to mature, an infected dog will not test positive until approximately seven months after infection. The test for cats is also a blood test, but it detects antibodies to the parasite rather than the parasite itself. Thus, the test used for dogs is not reliable for cats. A positive test means the cat has been infected with heartworm at some point, not necessarily that there are currently adult worms present.

A pet that contracts heartworm disease can be treated. Treatment for dogs is designed in two parts. The first aims to keep any existing larvae from maturing into adult worms by giving the animal a preventive. Adult worms are then killed with a drug that is injected directly into the muscle. Depending on the severity of infection, the injections may be administered on an outpatient basis. When the dog returns home, exercise must be restricted to short leash walks during the recovery period (which can last from one to two months) to decrease the risk that dead worms will block blood flow through the lungs.

Some veterinarians may prescribe prednisone and an antibiotic before starting treatment to reduce potential side effects. Retesting to ensure that adult heartworms have been eliminated is recommended six months after adulticide treatment. Dogs that remain positive at that time should be considered for repeat treatment.

Because the sign of disease in cats is related to the death of adult worms, they are treated differently. Typically, a cat is placed on the preventive and some form of anti-inflammatory to reduce the reaction that occurs in the lungs. The adult worms are allowed to die on their own.

While heartworm disease may be treated once an animal is infected, the treatment can be costly and uncomfortable for your pet.

There are a number of options for heartworm prevention, the most common being monthly oral tablets and chewables. When giving these preventives, understand that the drug stops heartworm from maturing into an adult if your pet has been bitten by an infected mosquito in the previous month. Therefore, the final dose of preventive must be administered the month following the last possible exposure to mosquitoes.

To learn more about exposure, transmission, detection, treatment and preventive measures, please consult your veterinarian.


Amy Miller is the marketing and communications manager for Animal Allies Humane Society. She lives in Duluth with her husband and three adopted pets: dogs Maverick and Goose, and a cat named Buddy Love.

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