Heartworm & Prevention

American Veterinary Medical Association
Encyclopedia of Canine Medical Veterinary Information

Post 1 of 2

Regarding the Treatment of Heartworm......

The new drug used is a lot safer and less toxic to the dog, than the former method, Caparsolate.  The problem with heartworms is, left untreated it can do irreprable damage to the heart itself.  Once the signs of coughing start, it is usually a good indication of more advanced infestation, and sometimes a sign of damage to the heart muscles.  We usually do a chest X-ray prior to the start of treatment to see if there is any enlargement of the heart, or fluid in the chest.  The X-ray we include as part of our standard price for treatment.  If we can get some specifics from the vet, I can give you more input into what exactly he means by "severe".  He may simply mean there are a large number of microfilarae (baby heartworms) present on the blood smear.  OR he could mean the dog is already showing signs of damage.  I had a Rottweilier who I rescued and successfully put thru treatment who is now doing wonderful.  She had a lot of worms circulating in her bloodstream, but no damage to the heart itself.  She is now 5 years old and doing well. :)

Regarding testing Procedures:

The blood test will tell you only if there is a circulating heartworm ANTIGEN in the blood. "Strong positive" simply means that the little dot on the test came in Fast, and Dark. The only other informational thing you can test for is Microfilarae (baby heartworms) You can do a direct smear on the blood and under a microscope you can actually see the worms in the blood.  This will tell you if they're in a reproductive stage.  We also use this test to confirm questionable results.  There is no way to tell by blood testing how advanced the heartworm disease is.  You can check liver and kidney function but the main diagnostic tool is physical exam and possibly chest Xrays.  Based on exam the vet should know the overall condition of the dog, rather any abnormal heart sounds were present and rather/how severe coughing is. The disease does get "graded" to level of severity.  Stage One being the best case scenario, on up to Stage 4 which is not able to be treated.

 Shanna Trautman, CatFaerie@worldnet.att.net

Post 2 of 2: Heartworm in Humans is Rare

( This from the July 1998 issue of Cornell University College of Veterinary Medicine's DogWatch newsletter, page 7.)

Heartworm in Humans: Rare and Getting Rarer

Humans can become infected with the canine heartworm, Dirofilaria immitis.  Although relatively rare, this infection can occur as the result of a bite from a mosquito carrying the microfilariae (immature worms), which the mosquito picked up when biting an infected dog.

Medscape, the on-line medical journal, recently published a report on a man with lung cancer who was discovered to be infected with the dog heartworm.  The worm was found during histological examination of the surgically removed lung tumor.  The authors of the report, J. Gregory Thomas, MD and colleagues from the University of South Florida College of Medicine in Tampa, point out that after a mosquito carrying the microfilariae bites a human, the worms mature in the subcutaneous tissue or within muscle.  The subadult worms then find their way into the lungs via the bloodstream.  Once in the lungs, the worms usually cause no symptoms, nor can their presence be readily diagnosed.  When they are found, it is usually during needle aspiration biopsy or surgical removal of suspected lung cancers.  Once removed, no additional treatment is necessary.

In an accompanying editorial, medical entomologist Jerome Goddard, PhD, of the Mississippi Dept. of Health in Jacson, points out, "Fortunately, humans are accidental hosts, and the larvae usually die."  He adds that dog heartworm infection of humans, rare in the first place, is probably decreasing, because nowadays we treat our dogs with heartworm preventative medications.

Thus, not only is heartworm prevention important for the health of our dogs, but for preventing humans from becoming infected with the parasite.