Many dog owners have heard about heartworm disease. This is a blood-borne parasitic infection spread by some mosquitoes. Domestic and wild dogs serve as the main reservoir for infection. Ferrets, cats and other animals can also be affected.
In certain parts of our country, mosquitoes carry this parasite. When this mosquito bites, it must inject some of its saliva to be able to ingest the blood of the bitten animal. If the mosquito is carrying the heartworm, it can then transmit it in its larval stage. The initial larval stage will then mature to the next stage in the skin in fewer than two weeks. From there, the new stage will migrate through the soft tissues and muscles to the chest area and molt into the final immature adult stage in around two months. They may then travel through the bloodstream to the vessels near the heart and produce microfilaria (baby heartworms) in 7 to 9 months from the time of the initial infection.
The main problem caused by adult heartworms in the vessels near the heart is the loss of blood supply to the lungs and decreased blood oxygenation. It has also been found that bacteria can be released from the heartworms every time they molt. The vessels in which the heartworms live become thickened and can become obstructed. Parts of the heartworms can also break free and cause damage in smaller blood vessels around the body.
Most dogs with low heartworm levels have no clinical signs and can show a normal physical exam. Some signs of infection include weight loss, tiring easily, coughing, and difficult and fast breathing. Heartworm disease can eventually cause a heart murmur and, if left untreated, cause death.
In our clinic, we diagnose the disease based on clinical signs along with chest X-rays and a heartworm-specific blood test. Treatment involves giving specific medication to kill the worms with close monitoring for problems from the heartworms dying off. Many pets are also on blood thinners to try to avoid clot formation around the body.
We give doxycycline to reduce the number of bacteria released from the heartworms. During treatment, pets normally should be confined and have restricted exercise for up to two months. Pets too weak for normal treatment are sometimes placed on medications meant for prevention, but which will help kill the baby heartworms so the disease doesn’t worsen.
Many preventative medications can be given to pets in heartworm areas to prevent a pet from developing adult heartworms. Some of these medications help repel or kill fleas as well. Maps of the geographic distribution of heartworm disease in the USA can be found on the American Heartworm Society website.
The good news is it appears our area does not have many mosquitoes carrying this parasite. If you have questions regarding heartworms, speak to your local veterinarian to check the incidence in the area. If your pet travels to a heartworm-prevalent area, use some medication to prevent a problem. Most preventative medications are used shortly after possible exposure since they kill the developing heartworms. Or simply have your pet tested. Enjoy your summer together!
Dr. Ron Resnick has been in practice for more than 32 years and previously operated two veterinary hospitals. He taught at Harvard University and graduated from Tufts University, considered the best veterinary school in the world. He operates an animal hospital in Simi Valley.
