Heartworm in dogs is a serious disease that can often go undetected. Most dogs who have a low number of heartworms show no clinical signs, but those with a high number of heartworms can develop symptoms. Symptoms of heartworm in dogs can include coughing, which is the most common sign and can be made worse by exercise. If you think your dog might have heartworm, it's important to get them checked out by a veterinarian as soon as possible. This article will explore some of the key symptoms of heartworm in dogs.
What is heartworm in dogs anyways?
Heartworm is a parasitic nematode called Dirofilaria immitis that is transmitted by mosquitoes. The larvae of the heartworm enter the dog through a mosquito bite and migrate to the heart and lungs, where they mature into adult worms. Adult heartworms can grow up to 12 inches long and live for five to seven years in the dog's body!
Heartworm disease in dogs is found in regions all over the world where there are mosquitoes that can act as hosts for the heartworm larvae, and where the temperatures are warm enough for those larvae to develop. In some areas, this only happens seasonally such as in the northern United States and Canada.
What is the lifecycle of the heartworm parasite?
The heartworm lifecycle starts when a mosquito bites an infected animal and ingests microfilariae, which are the larvae of the heartworm. The mosquito then passes on the microfilariae to other animals through its bites. Once inside a new host, the microfilariae mature into larvae and then travel through the bloodstream to the pulmonary arteries, where they mature into adult heartworms. This process requires temperatures to be above 57° F (14° C). The entire process takes about six months.
Adult heartworms can live for five to seven years in the dog's body and produce microfilariae, which can infect other animals through mosquito bites.
What are the symptoms of heartworm in dogs?
The symptoms of heartworm in dogs can vary depending on the number of worms present and the severity of the infestation. Most dogs who have a low number of heartworms show no clinical signs. However, dogs with a high number of heartworms or those that have a strong allergic reaction to adult worms or microfilariae can develop clinical symptoms.
Key clues that your dog may have heartworm include a cough that is worse with exercise, exercise intolerance, and syncope (fainting). These symptoms can occur three to six months after your dog is infected as the larvae reach the pulmonary arteries.
Other symptoms of heartworm disease in dogs include weight loss, lethargy, and anorexia. In severe cases, heartworm disease can lead to pulmonary thromboembolism (a blood clot in the lungs), right-sided congestive heart failure, and death.
How is heartworm in dogs diagnosed?
If you think your dog might have heartworm, the best thing to do is to take them to a veterinarian for testing. There are a few different tests that can be used to diagnose heartworm in dogs.
The heartworm antigen test is a commonly used and cost-effective test that looks for the presence of adult heartworm antigens in the dog's blood. This test can usually be done in your veterinarian's office and only takes a few minutes and is very accurate. It usually takes about 6-7 months for heartworms to mature and become detectable on either antigen or microfilaria tests. The heartworm antigen test checks for the presence of a protein that is most commonly found in the uteri of female worms and eggs. Therefore, the test can only detect female worms. Dogs may continue to test positive for this protein up to five months after successful treatment for heartworm infection.
The microfilariae test is another test that can be used to diagnose heartworm in dogs. This test looks for the presence of microfilariae, which are the larvae of the heartworm, in the dog's blood. This test is not as commonly used as the antigen test because it is less accurate and takes longer to get results if it is sent out to an outside laboratory.
Chest radiographs (x-rays) should also be performed to look for signs of heartworm disease in the major pulmonary arteries. In dogs with a heavy burden of heartworms, radiographs may show enlarged pulmonary arteries and densities within the lungs.
How is heartworm in dogs treated?
If your dog tests positive for heartworm, don't panic! There are treatment options available. Treatment options will vary depending on the severity of your dog's infection. The goals of treating heartworm are to improve the dog's clinical condition and eliminate all life stages of heartworm, including microfilaria, larvae, juveniles, and adults.
The treatment of choice for all classes of heartworm infestation is melarsomine (Immiticide®) which is given in three injections every 30 days. This drug is effective at eliminating adult heartworms but does not kill microfilariae. Additionally, melarsomine has a low margin of safety and can cause serious side effects, including death. For this reason, it is important that your dog be monitored closely by a veterinarian during treatment.
Other medications that your veterinarian may use include:
Doxycycline: Doxycycline suppresses microfilaria and prevents heartworm larvae from developing into adults. Dogs treated with doxycycline alongside an adulticide treatment have reduced complications.
Macrocytic lactones: A heartworm-positive dog is likely to have adult and juvenile heartworms. Melarsomine is not effective against juvenile worms, which can result in the worm not being cleared completely. Therefore, macrocytic lactones are used to kill juvenile heartworms.
Corticosteroids: Dogs that have a large number of heartworms or a severe allergic reaction to heartworm antigens may develop symptoms such as coughing and difficulty breathing. These symptoms can be alleviated with the use of corticosteroids.
What is the prognosis for dogs with heartworm?
The prognosis for dogs with heartworm is generally good if they are treated early and appropriately. However, untreated heartworm disease can be fatal. If you think your dog might have symptoms of heartworm, it is important to take them to a veterinarian as soon as possible for testing and treatment.
What are the early symptoms of heartworm in dogs?
The early symptoms of heartworm in dogs can be hard to spot. Many dogs show no symptoms at all in the early stages of heartworm infection. However, as the disease progresses, symptoms may develop. The first and earliest symptom of heartworm in dogs is a cough that is worsened by exercise.
Does heartworm disease in dogs cause fainting?
One of the important symptoms of heartworm in dogs is syncope or fainting. Syncope, or fainting, may occur in severely affected dogs during exercise or excitement. This is likely due to hypotension (low blood pressure), decreased vascular resistance (the vessels' ability to constrict), and vagal reflex.
What are the symptoms of heartworm in dogs with a low number of worms?
Dogs that have a low number of heartworms often show no clinical signs. However, some dogs may develop a mild cough or exercise intolerance.
What are the symptoms of heartworm in dogs with a high number of worms?
Dogs that have a high number of heartworms often develop symptoms such as pronounced and persistent coughing, difficulty breathing, and exercise intolerance. In more severe cases, dogs may also experience fainting or collapse, pale mucous membranes, weakness, elevated heart rate (tachycardia) and severe lethargy.
In conclusion, heartworm in dogs is a serious disease that can be fatal if left untreated. We discussed some of the key symptoms of heartworm in dogs and hopefully, this has given you a better understanding of the disease. Please visit the American Heartworm Society for additional information, as well. If you think your dog might have symptoms of heartworm, it is important to take them to a veterinarian as soon as possible for testing and treatment.