What Is Heartworm Disease in Dogs?
Dirofilaria immitis is responsible for heartworm disease, affecting dogs, cats, ferrets, and other mammals. This sizable worm can grow over a foot long. It completes its developmental cycle over six to seven months, eventually settling in the heart and pulmonary arteries. Here, it can reside for many years. As these worms accumulate, the heart's capacity to circulate blood diminishes, potentially leading to heart failure.
Symptoms of Heartworm Disease in Dogs
The intensity of the infection corresponds with the exhibited symptoms, which are linked to the impacted organs, namely the heart and lungs. Common signs are:
- Persistent coughing
- Reduced stamina during physical activities
- Unexpected demise
Additionally, some dogs might display a decrease in weight, labored breathing, and unusually heavy panting. If not addressed, this can lead to right-sided heart malfunction and fluid accumulation in the abdominal region (ascites).
Causes of Heartworm Disease in Dogs
Mosquitoes are the primary agents responsible for spreading heartworm disease, meaning direct transmission between dogs isn't possible. When a mosquito feeds on a host carrying the disease, it ingests young heartworms known as microfilariae. Within the mosquito, these microfilariae transform through three larval stages, termed L1, L2, and L3.
Later, when this mosquito bites another dog, the L3 larvae get transferred onto the dog's skin. From there, it enters the dog's system, evolving into the L4 stage. Eventually, it progresses to the L5 stage, traveling through tissues and the bloodstream until it reaches the heart, where it matures into an adult. This progression typically spans around four months.
The mature female worms can reproduce when they reach approximately seven months old. They mate and give birth to new microfilariae. The diagnostic tests used in veterinary practices identify antigens (specific proteins found on the organism's surface) produced by mature female heartworms. This is why testing is typically initiated when the dog is around seven months old.
How Veterinarians Diagnose Heartworm Disease in Dogs
Dogs aged seven months and above should undergo heartworm testing at least once a year. If a preventative dose is missed, more frequent testing is recommended. The test, typically conducted in the clinic, necessitates a minor blood sample.
The predominant technique for detecting heartworm disease is through antigen-based tests. Antigens, specific proteins on an organism's surface, help ascertain the presence of that organism in a sample. Here, the detected antigens are from mature female heartworms. A positive result indicates an infection in the dog.
Alternative diagnostic methods encompass a blood smear or a modified Knott's test. These tests primarily detect circulating microfilariae and may need to be sent out for analysis.
After diagnosis, further examinations might be suggested by your vet to determine the infection's intensity and associated treatment risks. Such tests could involve chest X-rays, EKG, blood pressure measurements, evaluation of cardiac enzymes (like NT-proBNP), echocardiograms, standard blood tests, and urinalysis.
Dogs categorized under Class I have the least treatment risk, while those in Class IV are generally diagnosed with caval syndrome, indicating an extremely high worm load that hinders blood flow out of the heart. Such critical cases demand immediate worm surgical extraction, often performed by a specialist, to save the dog's life.
Treatment of Heartworm Disease in Dogs
After diagnosing your dog, the vet will likely guide you through the subsequent steps, encompassing treatment pathways, additional diagnostic tests, and the schedule for revisits.
It's crucial to limit your dog's physical activities. Exercise might elevate the risk of heartworms dislodging and forming clots in other body parts. Moreover, if your dog's bloodstream contains microfilariae, there's a chance mosquitoes could spread the disease after biting your dog, making it advisable to minimize outdoor exposure.
The veterinarian might recommend various medications, including:
- Steroids: To counteract inflammation induced by the worm.
- Antibiotics: Specifically, doxycycline, which eradicates Wolbachia, a mutualistic organism residing within the heartworm. Eliminating this symbiote renders the heartworm more vulnerable and curbs secondary inflammation.
- Heartworm preventive: To stop immature worms from maturing into adults and to cleanse the bloodstream of microfilariae.
About 60, 90, and 91 days post-diagnosis, your dog will receive an injection of melarsomine, an arsenic-derived compound. Aimed at eliminating mature heartworms, this treatment is typically injected deep into the muscle in the lower back. Given the discomfort associated with the injection, pain-relief medication will likely be provided during those appointments.
Prevention of Heartworm Disease in Dogs
Prioritizing prevention is the most effective way to care for your dog and safeguard against heartworm disease. Fortunately, there's a variety of heartworm preventatives available that are budget-friendly.
These preventatives come in diverse formats like tablets, topical applications, and even injections, offering protection ranging from a month to a year. Some products also combine flea and tick treatments, ensuring a broader protective spectrum for your canine companion.
These preventative measures primarily target and eliminate the L3 and L4 stages of heartworm larvae, with some also purging circulating microfilariae from the bloodstream.
When a dog tests positive for heartworms, it's crucial to consult your vet regarding the proper preventative to use during treatment. Only specific types are recommended to reduce the risk of added complications.
Engage in a discussion with your vet to pinpoint the ideal preventative tailored to your dog's needs and your financial capacity. While minimizing your dog's contact with mosquitoes is beneficial, in certain areas, achieving this entirely is challenging. Remember, it only takes a single infected mosquito to transmit heartworm disease.
Recovery and Management of Heartworm Disease in Dogs
Managing heartworm disease comes with its set of challenges and risks. Dogs subjected to the heartworm treatment may experience severe reactions such as anaphylactic shock, clot formation, and even sudden death. Additionally, there's a chance for an abscess to develop at the injection site of melarsomine, coupled with the emotional strain from prolonged activity limitations.
Moreover, the damage wrought by these worms to a dog's heart and lungs can lead to enduring health consequences. The scar tissue and inflammation left behind by the worms can impede blood flow through the heart and lungs, potentially resulting in right-sided heart failure, even if the treatment is successful.
The disease's severity heavily influences the prognosis. Detecting and addressing the disease early increases the chances of a favorable outcome. However, a prior bout with heartworm disease doesn't grant immunity, leaving dogs vulnerable to future infections. Hence, consistent prevention throughout the year remains vital for maintaining your dog's well-being.