Canine Heartworm Prevention and Testing
Canine heartworms, Dirofilaria immitis, are parasitic worms that pose a serious threat to dogs. These long, slender worms live in the pulmonary arteries (and, occasionally, within the heart) of dogs and can measure up to a foot in length. They can cause substantial damage to the lungs and heart.
Adult heartworms cause inflammation of the blood vessels in the lungs, resulting in respiratory issues and pulmonary hypertension. In some cases, this leads to weight loss, weakness, right-sided congestive heart failure, reduced quality of life, and even death.
The prevention of heartworms and early detection are crucial in managing heartworm disease.
Mosquitoes and the Heartworm Lifecycle
Mosquitos are vectors of heartworm disease. A vector is a carrier and transmitter of disease from an infected individual to a non-infected individual. Certain species of mosquito can ingest young heartworms, called microfilariae when they feed on an infected animal. Once inside the mosquito, the microfilariae develop into third-stage larvae (known as L3) over a few weeks, provided that the environmental conditions are conducive (ambient temperatures above 60oF- including night time temperatures). The larvae pass through the puncture wound the mosquito makes when it bites another animal.
The larvae grow under the skin of the newly infected animal over several weeks, progressing through additional larval stages. At a certain point, the larvae enter the bloodstream and float into the pulmonary arteries (the arteries carrying blood from the heart to the lungs). Here, they mature into adults. It takes about six to seven months for the larvae to reach adulthood. Adult heartworms mate, and then the females begin to release tiny larvae, the microfilariae, back into the bloodstream, continuing their lifecycle.
Prevention is Key
Preventing heartworms is much easier (especially for your dog) than having to treat an active heartworm infection.
Studies show that exposure to heartworm depends on factors such as:
- The presence of wild canine populations (foxes, coyotes, wolves) in the surrounding area can continue the spread of heartworm.
- Regional differences in climate and ecosystems (elevation, humidity, rainfall, temperature)
The Prevalence of Heartworms Around the World
Heartworms exist in many parts of the world, but the prevalence greatly varies. In warmer climates with higher mosquito populations, such as tropical and subtropical areas, the risk of heartworm transmission is higher. These areas make excellent habitats for mosquitoes and the development of heartworm larvae, so dogs living in or traveling to these regions are at a greater risk of heartworms. On the other hand, there are fewer heartworm infections in cooler or drier regions with smaller mosquito populations.
The travel, relocation, and presence of infected animals can allow heartworms to start infecting animals where they are less common. Climate change (and temperature increase) is also expanding mosquito ranges, creating longer active seasons and better environmental conditions for larvae.
Environmental Considerations
More recent recommendations for preventing heartworm infections advise reducing mosquito bites. This can be done by avoiding places with heavy mosquito populations, when possible, to reduce the chances of being bitten and contracting heartworms (for example, some studies have shown that indoor dogs in high-risk areas tend to have fewer infections than outdoor dogs). Avoid visiting permanent and semi-permanent (seasonal) bodies of water like lakes, streams, and floodplain areas with your dog, especially when large mosquito hatches are taking place (usually in warmer, humid weather). Check around your home for areas with standing water and eliminate containers or reservoirs that may be prime real estate for mosquito larvae.
Preventative Medications
Heartworm preventatives are prescribed by your veterinarian and come in oral, topical, and injectable forms. As mentioned before, preventing heartworms is much easier than treating them, and the American Heartworm Society recommends FDA-approved heartworm preventatives year-round. However, in Colorado, where the elevation is higher, humidity is lower, and our seasonal temperatures vary greatly making the “mosquito season” much shorter, our risk is really confined to the months June to November. Six months of heartworm preventatives (June to November) is the minimum recommendation for Colorado dogs. If you travel with your pet during the winter and shoulder seasons to parts of the country where risks are higher, then year-round prevention is recommended.
In areas where mosquitoes are endemic (native or regularly present), your dog can be infected if just one preventative dose is missed.
Detecting Heartworm Infection
Blood tests for heartworm infections are recommended yearly for all dogs over seven months. If you do not give preventatives regularly every month, or recently adopted a dog from a high endemic area then more frequent testing may be recommended. If your dog has tested positive for heartworms, your veterinarian will discuss the treatment options available. Treatment of a heartworm-positive dog infected with adult heartworms is a much more involved process. You do not want your dog to ever be heartworm-positive. Prevention is the key and is so easy.
Take Aways-
- Heartworm Disease is in Colorado
- All dogs should be tested (Heartworm antigen blood test) at 7 months of age and then annually. Additional testing may be recommended depending on exposure history.
- Heartworm preventatives (Oral, Topical, or Injectable) are available and are highly effective.
- Skipping even one dose during mosquito season can result in Heartworm disease. (Data reveals an average of 10% of doses are missed.)
- Prevention is much easier and cheaper than treating the disease.
Photo Source (HW Lifecyce): Veterinary Information Network Copyright 2024 Illustration by Tamara Reevs