Heartworm in cats - Symptoms and treatment

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Heartworm disease or dirofilariosis can also affect cats, although less frequently and severely. It is a parasitic disease that can produce respiratory symptoms, but can also cause gastrointestinal or neurological symptoms. Although many cats will be asymptomatic and will overcome the disease, the existence of a single adult parasite in the vicinity of the heart of our cat can cause death, so it is a disease that must always be prevented by avoiding the bite of the transmitting mosquito..

¿You want to have more knowledge about the particularities of the feline heartworm? Keep reading this AnimalWised article to learn more about heartworm in cats, its symptoms and treatment..

You may also be interested in: Heartworm in dogs - Symptoms, treatment and prevention Index
  1. What is feline heartworm disease?
  2. Phases of feline heartworm
  3. Symptoms of heartworm disease in cats
  4. Diagnosis of feline heartworm disease
  5. Treatment of heartworm disease in cats
  6. Prevention of feline heartworm disease

What is feline heartworm?

Feline heartworm disease, or heartworm disease in cats, is a parasitic disease worldwide distribution caused by parasitic nematode Dirofilaria immitis and transmitted by a vector mosquito of the species Culex spp. It is a parasite that is located in the pulmonary artery or the right heart.

In the disease cycle, the mosquito bites the dog with microfilariae, which are the immature forms of the parasite, these develop into infectious larvae in the mosquito and the mosquito bites another dog or cat, transmitting the disease to them. The ideal climate is one with high humidity and good temperatures. In dogs, these larvae usually mature to adulthood, producing microfilariae and being a source of infection for mosquitoes, completing the cycle. However, in cats the larvae usually die before their progression to adulthood, they mature slowly and the feline's immune system can destroy them. However, even if there is only one adult parasitic worm, it can end the life of the feline.

Larval migrations, although infrequent, occur more in cats than in dogs, being found in body cavities, systemic arteries, subcutaneous nodules, and the central nervous system..

Phases of feline heartworm disease

The disease can be divided into two phases:

  • First phase: arrival of immature adult worms to the pulmonary artery between 3 and 6 months after infection. Macrophages in the area are stimulated, causing a vascular and parenchymal inflammatory response consisting of endoarteritis, vascular fibrosis, and hypertrophy of the pulmonary arteries. This response decreases as the parasites mature. Sometimes this phase can be mistaken for allergic bronchitis (asthma). It can cause sudden death or no symptoms, due to the suppression of the immune response, not appearing signs and tolerating the infection until the adult parasites begin to die, starting the second phase.
  • Second stage: the death and degeneration of the parasites causes an inflammation of the lung with thromboembolism, causing an acute respiratory distress syndrome. This can be caused by a single adult parasite.

Symptoms of heartworm disease in cats

Many cats tolerate parasitization without any clinical signs, others with transitory signs and others do present symptoms. If it occurs, the most frequent symptoms are respiratory, gastrointestinal and neurological symptoms can also appear. Thus, the symptoms of heartworm in cats are:

  • Dyspnea (respiratory distress).
  • Tachypnea (increased respiratory rate).
  • Intermittent cough.
  • Persistent vomiting not related to food.
  • Anorexy.
  • Weightloss.
  • Lethargy.
  • Right congestive heart failure with pleural effusion and jugular strain.
  • Hyperacute pulmonary thromboembolism syndrome (fever, cough, dyspnea, tachycardia, ataxia, collapse, seizures, hemoptysis, and sudden death).
  • Neurological signs due to migration of the larvae to the central nervous system, leading to seizures, apparent blindness, circling, ataxia, pupillary dilation, and hypersalivation.

Dirofilaria immitis harbors a bacterium of the genus Wolbachia, which may be related to pulmonary inflammatory reactions in the disease.

Diagnosis of feline heartworm disease

The most useful tests for the diagnosis of feline filariasis are serology, chest radiographs, and echocardiography. On physical examination of the cat, a systolic murmur may be found in the cardiac auscultation at the time when the parasites occupy the atrioventricular junction, interfering with the function of the tricuspid valve, tachycardia, heart murmur, gallop rhythm, lung crackles and reduced lung sounds if there is presence of pleural effusion. For its part, in the blood test Mild non-regenerative anemia, increased neutrophils, monocytes, and low platelets can be seen. With respect to serology, two serological tests are used:

  • ELISA to detect antigens, it has good specificity for confirmation, it better detects adult females of the parasite and if there is a higher parasite load. While it is ideal for the diagnosis of canine heartworm disease, in the case of cats this is not the case due to its lower sensitivity to rule out the disease, due to the higher prevalence of male infestations or low number of parasites..
  • Antibody detection test, They allow detecting that parasites have occurred in cats because it detects exposure to adult parasites, such as larvae regardless of their sex. Antibodies are detected 2 months after infection. Antibodies indicate infection by parasite larvae, but do not confirm that they are currently causing the disease.

In relation to the radiology, it can be useful to assess the severity of the disease and to monitor its evolution. The most common radiographic findings are:

  • Subtle enlargement of the main lobar arteries, especially on the right side.
  • Peripheral pulmonary arteries appear dilated and tortuous.
  • The left caudal pulmonary artery is enlarged 1.6 or more times the width of the ninth rib.
  • Focal or multifocal broncointerstitial lung pattern.
  • Radiographic signs of pulmonary thromboembolism: poorly defined, rounded or wedge lung areas with opacities that make it difficult to see the associated pulmonary blood vessels.

More than half of the affected cats present some alteration in the X-ray. With the completion of a echocardiography,Heartworms have been observed in 40-70% of infested cats. Parasites are seen mainly in the main or right lobar pulmonary artery, but the entire area should be observed for them.

Treatment of heartworm disease in cats

Treatment will vary depending on whether or not the cat has clinical signs:

  • In asymptomatic cats, Although the diagnosis by imaging or serology has shown that it is parasitized, antiparasitic treatment should not be established, since the cat may overcome the infection by itself. These cats should be monitored every few months with X-rays, antigen and antibody tests to see if the risk has passed if the result is negative. About 80% of asymptomatic cats heal spontaneously.
  • Conversely, if cats show pulmonary abnormalities evident in the x-ray or if there is a positive antigen or antibody test together with clinical signs, they should be treated with prednisolone at a dose of 2 mg / kg / 12 hours at the beginning, gradually decreasing to 0.5 mg / kg per day alternate for 2 weeks. Subsequently, the dose is reduced until it is withdrawn for another 2 weeks. If the clinical signs return, the treatment would be repeated periodically.

If cats present with acute respiratory distress syndrome, a shock treatment consisting of:

  • Intravenous corticosteroids.
  • Balanced electrolyte fluid therapy.
  • Oxygen administration.
  • Bronchodilators.

In cases of heart failure with pleural effusion, the fluid should be removed by thoracentesis and diuretics such as furosemide used, along with oxygen and rest..

The use of adulticidal treatment with ivermectin is not recommended because the death of adult parasites can produce anaphylaxis and pulmonary thromboembolism phenomena. They should be used when prednisolone is not effective in the regression of clinical signs. The use of the antibiotic doxycycline during the first month of infection, before treatment with the adulticide, can kill the bacteria and even lead to infertility in female heartworms..

The surgery can eliminate parasites. It is important that the extraction of the parasite is complete, since if they break, parasitic antigens are released that can lead to circulatory collapse, with a strong anaphylactic reaction and death of the feline.

Prevention of feline heartworm disease

They should be used preventive antiparasitics especially in those cats that live in a risk zone for the disease circulation. In cats that do not leave the house as well, since, although it is lower, the risk continues to exist.

This prevention should start one month before the beginning of the risk season, or two months before the end of this period in cats from two months of age. Ivermectin can be used orally or selamectin topically monthly, or the combination of fluralaner + moxidectin pipetted every three months..


Heartworm disease in cats has a reserved prognosis. Although most cats tolerate the infection well and heal spontaneously, in others it can be very devastating and even fatal. It should also be remembered that a single adult heartworm can end the life of our feline. For all this, prevention is the best way to avoid the disease.

This article is merely informative, at AnimalWised.com we do not have the power to prescribe veterinary treatments or make any type of diagnosis. We invite you to take your pet to the vet in the event that it presents any type of condition or discomfort.

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