How do you detect canine heartworm disease

Canine heartworm disease is a clinical condition in dogs caused by the nematode parasite Dirofilaria immitis which resides within the dog’s heart. This disease is a serious veterinary problem having become widespread throughout the United States and tropics and is primarily associated with dogs. Canine heartworm can only be transmitted by the bite of mosquitoes. The Western Tree Hole Mosquito, Aedes sierrensis, is the most important vector (carrier) of canine heartworm in the San Francisco Bay Region.

Dogs are the most commonly infected mammals and are considered the preferred host of the heartworm. While the highest prevalence of heartworm infection is in areas with heavy mosquito populations, heartworm-infected animals can be found in all types of environments. The mobility of people and our four-legged companions as well as the widespread prevalence of mosquitoes make heartworm disease a health consideration no matter where you live.

Severe cases of dog heartworm result in general weakness, coughing and labored breathing. In advanced cases treatment is difficult and some dogs may die from cardiopulmonary failure. Visible symptoms do not occur in the early stages of the disease, although your veterinarian can diagnose and treat this disease. It is recommended that you check with your veterinarian about early detection and treatment.

Many people associate worms with feces, which is not the case for heartworms! This disease can only truly be diagnosed by a blood test that your veterinarian can perform. When adult heartworms are living in the dog’s heart, the females secrete a uterine antigen that can be detected by a special test, called an ELISA (Enzyme Linked Immunosorbant Assay). This can be done in the veterinary office and takes only about 10 minutes. The test is very specific. The only drawback is that a certain amount of antigen (and therefore, adult worms) must be in the blood for the test to detect it.

If my dog has a negative heartworm antigen test, does that guarantee he/she does not have heartworms? Unfortunately, no. It takes about 6 months from the time the mosquito bites the dog to the time the adult heartworms are secreting detectable antigen, which is what makes the test positive. For example, if a dog was infected three months ago, and is not kept on heartworm preventative, he/she can be infected with the disease, but will have a negative test result. Even if a dog has a negative heartworm test and is immediately started on heartworm preventative, he/she can still have a positive test up to 6 months later!

The L3 larvae which are injected into the dog’s blood by the mosquito will “swim around” for about 6 weeks. Then they develop into L4 larvae, which migrate to the heart and become adult heartworms, which secrete antigen that the ELISA heartworm test can detect. The preventatives used today are very effective at killing the L3, so if given once a month, your dog is protected (you are within that 6 week window of maturation to L4). However, after that 6 week length of time, the larvae are now L4, and the preventative is not very effective in killing that stage. You may not know this until your dog has a positive heartworm test a few months later!