Presence of the Parasite in Quebec Towns
In the last 5 years, the Association des médecins vétérinaires du Québec has been accumulating data provided by small animal veterinarians across the province concerning dogs that test positive for the heartworm parasite. This compilation of data, provided voluntarily by vets, and therefore most definitely under-estimated, reveals that positive cases of heartworm have been reported in 74 municipalities across Quebec. Among these are towns in which our own patients live: L’Île- Perrot, Notre-Dame-de-l’Île-Perrot, Vaudreuil-Dorion, Beaconsfield, St-Lazare, Kirkland, Les Coteaux, to name a few. Considering that the heartworm blood test is available for those privileged dogs who have access to veterinary care, and considering how many dogs within the territory of Quebec do not have access to veterinary care, those who do not receive prevention and who have never been tested for heartworm, it is safe to assume that the numbers of positive cases is much higher than the study reveals. Also, we have been living in close proximity to coyotes and foxes for several years, both species being carriers of the heartworm disease. One study from 1993 by Dr. Fortier confirmed that 10% of coyotes in the Monteregie were carriers of the disease. The sightings of coyotes near or in our communities have escalated at an incredible rate since this study was done, leading to the logical conclusion that the heartworm parasite is very present in Quebec. The French Bulldog of Dr. Gagnon and Dr. Lebeau was attacked this past winter by a pack of coyotes not far from their home.
Transmission of Heartworm and Symptoms of the Disease
Heartworm is a parasite known to exist in Quebec for 3 decades. The first cases were diagnosed in Hudson and St-Lazare in 1984. The round worm known as Dirofilaria Immitis is transmitted from an infected domestic dog or a wild canine (coyote, fox, wolf) to another via mosquito. The mosquito becomes carrier of microfilariae after biting an infested animal. He will then transmit the larvae while biting another host (dog, coyote, fox, wolf, cat, ferret). In order for the larva aspirated by the mosquito to infect another animal, they must mature for several days within the insect at a sufficiently elevated temperature. The duration of the incubation depends on the temperature. If the animal receiving the bite is protected by a monthly prevention during the highest risk season (June to November in Quebec), the animal in question will not develop the infection. If the animal bitten by a mosquito loaded with microfilariae is not protected for heartworm, these microfilariae will develop into adults and take up residence in the lung arteries and heart. The parasite load, meaning the number of worms present in relation to the size of the infested dog, will determine if the dog develops symptoms or not. If there are only a few worms, there could be no clinical symptoms and the animal serves as a reservoir for the parasite, silently spreading the disease to dogs, wild canines, and cats throughout the neighbourhood and neighbouring municipalities. It is important to be aware that mosquitos can cover a large distance between meals.
When the number of worms is too high, the infested animal will gradually begin to present certain symptoms. These include respiratory symptoms and/or general malaise including breathlessness, cough, fatigue, panting, weakness, and intolerance to exercise.
Heartworm Blood Test for Dogs
Every Spring, veterinarians remind their dog-owning clients of the importance of the heartworm blood test. This screening detects the presence of adult heart worms in our canine patients and verifies if the dog has been infected with the parasite the previous summer or before. It takes approximately 6 months from the time of the bite by a contaminated mosquito until the parasite can be detected in the bloodstream of the dog. The American Heartworm Society contends that early detection of the disease is essential in guaranteeing a successful outcome. They recommend regular testing, ideally every year, for all dogs that are exposed to mosquitos.
The testing for heartworm in cats and ferrets is much more complicated. For them, the diagnosis often requires a combination of tests, as well as X-rays and a thoracic ultrasound. These animals are atypical hosts, given that most microfilariae do not mature to the adult stage. The patient could suddenly become gravely ill from the heartworm disease, or could die abruptly without ever showing a single clinical symptom. Contrary to dogs, there is no homologated treatment for adult heartworms in cats and ferrets. However, there exist several preventive medications for cats and one approved topical treatment for ferrets.
Prevention of Heartworm and Intestinal Parasites
Regardless of the species, the prevention of heartworm is far easier and much less expensive than the treatment for a patient already infected.
Oral or topical monthly prevention from June to November plays a vital role in protecting dogs against heartworm disease. Minimising exposure to mosquito bites also lowers the risk of infection. For pets that travel to warm climates during the winter months, an extended prevention protocol supervised by a veterinarian is a must.
While protecting our companions against heartworm, we also provide an excellent, equally important monthly prevention for intestinal parasites. The preventive medications prescribed at the Ile Perrot Veterinary Hospital for heartworm are also excellent deworming treatments for intestinal round worms such as ascaris, hook worms and whip worms. It is not only puppies and kittens that are at risk for intestinal parasites. Adult dogs and cats that go outside in the yard, visit parks or forests are also at risk. The simple act of taking a walk in an environment contaminated with parasite eggs, then licking their paws (licking paws is a normal part of self-grooming in dogs and cats), offers the possibility of infection. Some dogs, who eat anything they find on their walk, will ingest the stool of another infected dog and thereby become infested.
Risks of Parasite Transmission to Humans
There have been very rare cases of people infected with heartworm. People can be accidental hosts of the Dirofilaria Immitis, which is not able to survive in the pulmonary vessels of humans. The parasite dies, causing an embolism that eventually becomes one or more pulmonary nodules. Diagnosis is often discovered by chance during a scan for another condition. The person is generally asymptomatic, but the discovery of a pulmonary tumour leads to pulmonary biopsies, which finally reveals a necrotic granuloma compatible with the heartworm parasite.
In the case of intestinal parasites, children and individuals who are immunosuppressed are the most at risk. The transmission is made by accidental ingestion of contaminated feces. The best prevention remains the monthly anti-parasitic dose for all companion animals that go outside and for all puppies and kittens. Good hygiene habits such as washing hands after handling pets and/or their excrement is also recommended. Regular pick-up of stool outside and cleaning of litter boxes are also effective. A once-per-year stool analysis of our pets’ stools by the veterinarian is equally essential.
Link
Man’s best friend: How humans can develop Dirofilaria immitis infections (2016/3/24)