Heartworms

Heartworm disease is a potentially serious problem in dogs in every geographic area in the United States. The
disease was initially prevalent in the southern coastal areas of the U.S., but due to the movement of dogs with the
human population, the disease has spread over most of the country. It is currently present in this area; however,
with proper preventive therapy, heartworm disease will not be a risk to your dog.
DESCRIPTION
Heartworm disease is caused by Dirofilaria immitis, a parasitic worm that lives as an adult in the right side of the
dog’s heart and large blood vessels leading to the lungs. Heartworms do most of the damage in the adult stage, at
which time the full grown male worms measure about six inches in length and the females can reach a length of
twelve inches.
DISEASE TRANSMISSION
Heartworms are transmitted from dog to dog by mosquitoes. There are three stages in the development of
heartworms in the dog.
1. The adult female, living in the right side of the heart and/or major vessels to the lungs, produces immature
worms called “microfilariae” that circulate in the blood stream. The microscopic microfilariae can live for up to
3 years.
2. When a mosquito bites an infected dog, it takes in blood containing microfilariae. The microfilariae mature in
the mosquito over a period of two weeks to become infective larvae.
3. The mosquito, carrying infective larvae, deposits them in other dogs during blood meals. Larvae develop over
3-6 months and migrate to the right heart. Within 6 months, the larvae develop into adult heartworms that are
responsible for the disease process in the heart and lungs. The adult heartworms can live up to 7 years. The
adults produce microfilariae, hence completing the life cycle.
CLINICAL SIGNS
Signs of heartworm disease may occur within 6 months of infection or may not appear at all depending the
number of adult worms that are present. In most cases, signs will begin within 1-2 years after infection. Typical signs include coughing, labored breathing, weakness, and tiring with exercise. Since the signs vary, the disease may be well advanced before the dog begins to show any problems, or signs may be mistaken for another problem. In advanced
stages, the heart and lungs can be severely damaged. Eventually, heart failure can occur and the dog can die from damage cause by heartworms unless appropriate treatment is instituted.
DIAGNOSIS
To identify heartworm infection, a blood sample is taken from your dog.
This test detects antigens from female worms and is very sensitive and accurate.

PREVENTION
The two preventive medications that are recommended by St. Francis 24 Hr. Animal Hospital are Heartgard  and Interceptor.  These products are intended to be given on a monthly basis and are highly effective in preventing heartworm disease if given as directed.

RECOMMENDATIONS
To control heartworms in the dog population and to provide your pet with the best possible protection against
heartworms, the following guideline are recommended:
1. All puppies should be started on preventive medication.
2. Your dog should be checked annually for heartworms with an antigen test particularly if there have been
breaks in the administration of preventive medication.
3. All dogs in our area should be on preventive medication year round.
4. Dog that shows signs of weakness, persistent coughing, breathing difficulty, or decreased ability to
exercise may have heartworms and should be tested.
5. If your dog is diagnosed with heartworms, it should be treated by a veterinarian to prevent permanent
damage to the heart and lungs.
6. Prevention is the best approach to heartworms. If preventive and monitoring programs are followed,
unnecessary treatment and permanent heart and lung damage can be avoided.
CATS
Heartworms can infect the cat but this is an uncommon problem in this area. Monthly preventative medication is
available but is not routinely recommended at St. Francis 24 Hr. Animal Hospital,  however, it is available for owners who decide preventive therapy is appropriate for their cat.