West Chester Veterinary Center
7330 Liberty Way, West Chester OH 45069 - Phone: 513-755-2273

treating heart worm disease dogAlthough nearly 100 % preventable, heartworm is a devastating disease with challenging treatment options. While states in the Gulf and Mississippi Valley are best known for their high levels of heartworm-positive dogs, other areas are showing increased incidences as well. One of these areas is the Upper Midwest, including Michigan, Illinois, Indiana and Ohio. What is contributing to this upward trend in Ohio? According to the American Heartworm Society, surveys of veterinarians noted that the number one reason for an increase in prevalence of heartworm disease was non-compliance by owners. Simply, owners are not giving their pet the monthly preventative year round. In areas where compliance increased, a downward trend in heartworm infection was noticed.

Download PDF - Heartworms with Cats

What is heartworm and why does it cause disease?

An adult heartworm is a long worm about a foot in length that lives in the pulmonary artery of dogs and cats (yes, cats can get heartworm, too!). The pulmonary artery takes blood from the heart to the lungs. Some dogs may only have a small worm burden, but others may have up to 100 worms living in the heart and pulmonary artery. Even a few worms can be very burdensome for the heart, for a number of reasons. The worms impeded blood flow through vessels, making the transfer of blood from the heart to the lungs less efficient. This causes the work load of the heart to increase. Eventually, dogs with heartworm disease will go into heart failure. The worms also damage the arteries in which they live. The immune system is stimulated to come and destroy the worm, but the worm is much too big for the immune system to get rid of. The chronic immune stimulation continues, however. As a result of this, the arteries become dilated and tortuous. This can be seen on a chest X-Ray. Aneurisms and emboli (abnormal clotting) are common sequelae.

heartworm transmitted by misquitoesHeartworms are transmitted by mosquitoes. Once there is an adult male and female present in the pulmonary artery, microfilaria (baby heartworms) are produced. These microfilaria are released into the blood system, in hopes of being picked up by another mosquito and transmitted to the next pet. Microfilaria can live in the circulatory system of a pet for several years. After an infected mosquito bites a pet, heartworm larvae are deposited into the pet’s skin. The heartworm larvae will live in the pet’s skin for approximately three months before making their way to the heart. Here is where heartworm preventative is important. Heartworm preventative kills the larvae at this stage, before the larvae make their way to the heart and before causing heart disease.

What happens if my pet tests positive for heartworms?

The most common type of heartworm testing in veterinary clinics is the canine antigen test. This test tests for very small amount of the adult female heartworm circulating in the blood. This means that, if positive, the dog has at least one adult female heartworm living in the pulmonary artery. The test does not define how many worms are present or how severe the disease is. In cats, if heartworm disease is suspected, it is very important to do an antibody test. Because cats are generally infected with lower numbers of heartworms, the antibody test may be negative. The antigen test measures the pet’s immune response to having the worms present in the body.
If we know that a pet has a heartworm infection, we will want to determine if the pet has clinical disease caused by the presence of the worms in the pulmonary artery. The next diagnostic steps include chest X Rays, ultrasound, and a microfilaria test. These tests help the veterinarian stage the disease and offer the safest treatment plan possible.

The treatment of heartworms

heart worm diseaseUndertaking the treatment of a heartworm positive dog or cat is a serious task and discussions with owners must be had regarding the possibility for sudden death resulting from treatment. After medication is given to kill adult heartworms (called an adulticide), the death of the heartworms can result in severe damage to the lung capillaries (small blood vessels in the lungs) and loss of blood to the air sacs (alveoli). The dying heartworms also cause intense lung tissue damage, which is directly related to the mass of dying heartworms and rate of breakdown. Some pets may have activation of platelets (clotting factors), causing severe thromboembolism of major pulmonary arteries. These pets may then suffer from acute respiratory distress. The most dangerous window for this is 2-3 weeks after the adulticide injection. This is why it is imperative to keep your pet quiet after his injection. Strict rest is important to decrease demand on the heart and facilitate healing of the lungs.

We are a local animal hospital you can trust for committed, compassionate and progressive care of your pets. We thank you for trusting West Chester Veterinary Center for your pet care service needs.

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