Heartworm and Tick-Borne Disease Testing

Annual testing for Heartworms and Tick-Borne disease is strongly recommended; based on the life cycle of the Heartworm parasite, the test is best performed early in the Spring.  The Idexx 4Dx test that we use tests for Heartworms (transmitted by mosquitos) and for exposure to Lyme Disease, Erlichia, and Anaplasma (the latter three diseases transmitted by ticks).  Although the number of tick-disease positive tests we see is low, studies show that the incidence of tick-related disease is increasing throughout the country.  In some dogs with limited likelihood of tick exposure, we may test only for Heartworms.  More information about Heartworm Disease and Tick-Borne Disease can be found below.
Heartworm Disease

Basic facts about Heartworm Disease:

Heartworms (scientific name -   Dirofilaria immitis) are long, thin worms which live in the right side of the heart.  These worms cause blockage and swelling of the chambers of the heart, gradually leading to the development of congestive heart failure.  Left untreated, Heartworm Disease will eventually kill a dog.

Heartworm Disease is a common problem in dogs in the Midwest, including our part of Ohio.  The disease is transmitted by mosquitoes; therefore, all dogs are at risk – it takes only one bite from a carrier mosquito to infect a dog.

From the time a dog is bitten by an infected mosquito, it takes approximately 6 to 7 months before the dog can show clinical signs of heartworm disease or be detected as positive by laboratory testing.  (This is why testing is not needed before starting heartworm preventative in puppies under 6 months of age).
The most common signs of heartworm disease are:  coughing, tiring easily with exercise, weight loss, loss of appetite, and occasionally a swollen abdomen.  However, most heartworm positive dogs are detected on routine screening tests and are not yet showing clinical signs at the time of diagnosis.

Many heartworm-infected infected dogs can be detected by a simple Filter Test done on a blood sample from the dog.  However, 20-30% of infected dogs may not show up positive on this test; these affected dogs are detected by what is called an Antigen Test (Occult Heartworm Test).  Because of the better sensitivity and accuracy of the Antigen Test, it is the primary test that we use here at Whetstone Animal Hospital. 

Can Heartworm Disease be treated??  Absolutely.  When your pet gets to that point, however, the problems are: 1) the dog is already infected with a parasite that can eventually be fatal; 2) the treatment is generally safe but is not without some risk, especially in dogs showing clinical signs; and 3) treatment is expensive, ranging from several hundred to several thousand dollars (depending on the size of the dog and their physical condition). 

Bottom line - preventing Heartworm Disease is safer and cheaper than treating it.

Heartworm is easily prevented by the year-round administration of a monthly preventative tablet (Heartgard Plus, Trifexis, Interceptor, Sentinel), in combination with annual blood testing. All dogs should be kept on a monthly heartworm tablet to prevent this deadly disease!

Tick-Borne Diseases

As noted above, the incidence of positive tests for Tick-Borne diseases here is low; however, we do see several positives each year.  In most cases, the positive test indicates prior exposure to the disease, and we see few clinically ill animals.  However, Lyme Disease, Erlichiosis, and Anaplasmosis all can cause significant and potentially fatal disease, with signs including anemia, joint swelling and lameness, neurologic signs, and kidney failure.  At this time, most of the dogs that we see test positive have traveled to areas where tick disease is prevalent (New England, Pennsylvania, etc.).  Dogs that are outside a lot (hunting dogs, farm dogs) are also at increased risk.

A positive test for one of the Tick-Borne diseases does not necessarily indicate that treatment is necessary; however, further evaluation of the dog is needed to help rule out early or low-grade disease.  Also, a positive test suggests that more intensive prevention against ticks is needed.