Canine heartworm (Dirofilaria immitis) is a life-threatening disease because, as the name implies, a worm up to 12 inches in length can invade and live inside the heart and major heart vessels. Heartworm is transmitted to dogs by a mosquito. Small immature worms called larvae survive inside the mosquito. When the mosquito bites a dog, the larvae are deposited under the skin of the dog. Over the course of 5-6 months, the larvae migrate to the canine heart and develop and grow along the way. Inside the heart, mature heartworms reproduce and make baby heartworms called microfilaria. These baby heartworm microfilaria circulate in the bloodstream. When a mosquito bites an infected dog it takes up the baby heartworms (to infect another dog) and thus completes the heartworm life cycle.
If a dog is infected with heartworm the main symptom is coughing and exercise intolerance. Heartworm infection can lead to heart failure and sudden death. Treatment is dangerous and expensive. It involves an arsenic-type medication. When the worms die they are carried in the bloodstream to the lungs where they can cause severe lung inflammation.
A simple blood test to check for heartworm infection is recommended at 5 months of age and older and every year or two thereafter, depending on whether the dog receives the preventive every month or not. Veterinary association guidelines recommend giving the heartworm preventive to all dogs, once a month, all year. Most of our staff members follow these guidelines with their own pets.
There are several brands of heartworm preventives on the market. Most are oral flavored tablets that dogs enjoy, given once a month. There is also a topical formulation that is applied to the skin. If a heartworm infected dog receives the preventive medication, the dog may have a bad reaction. Therefore, before a dog is put on the preventive, or if a dog misses more than 2 consecutive months of preventive, it is recommended to do a heartworm test. Many of the monthly heartworm preventives also protect against intestinal parasites, which inadvertently infect three to six million people and children every year. The preventives protect pets and people. Preventative medicine is the cornerstone to good medicine.
Veterinary association guidelines recommend that all pets should have a fecal test performed periodically to screen for intestinal parasites. Puppies and kittens commonly have intestinal parasites; the source of infection is usually from the mother (in- utero and from mother’s milk), and also from feces in their environment. Puppies and kittens should have at least two negative fecal results (false negative test results can occur because these parasites are sometimes shed infrequently). Adult animals should have a fecal exam at least once a year. Signs of intestinal parasite infection are loose stool, diarrhea, blood in stool, increased bowel movements, eating their own feces, vomiting and/or a distended abdomen. Some animals do not show any signs. Examples of intestinal parasites are roundworms, hookworms, tapeworms, whipworms, coccidia and giardia. Some of these parasites are potentially transmissible to people and children and other animals (it is primarily a fecal-oral route; sometimes transmission can occur through contact with skin). Common sense hygiene, like washing hands after cleaning up feces, is strongly recommended.
The American Veterinary Medical Association (AVMA), The American Animal Hospital Association (AAHA), The Center for Disease Control (CDC), veterinary infectious disease experts, and public health officials, all recommend fecal examination and strategic, prophylactic deworming and careful clean up of pet feces. For example, healthy puppies and kittens should be prophylactically dewormed several times. These vet guidelines also recommend adult dogs (and cats) should receive a monthly heartworm preventive, because not only do these products prevent heartworm disease, they will also kill and prevent several dangerous intestinal parasites.