Heartworm disease or dirofilariosis can also affect cats, although with less frequency and severity. 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 our cat's heart can cause death, so it is a disease that must always be prevented by avoiding the bite of the transmitting mosquito.
Do you want to know more about the particularities of feline heartworm disease? Keep reading this article on our site to learn more about heartworm in cats, its symptoms and treatment.
What is feline heartworm?
Feline heartworm disease, or heartworm disease in cats, is a worldwide parasitic disease caused byparasitic nematode Dirofilaria immitis and transmitted by a mosquito vector of the species Culex spp. It is a parasite that is located in the pulmonary artery or the right heart.
In the cycle of the disease, the mosquito bites the dog with microfilariae, which are the immature forms of the parasite, these develop into infective larvae in the mosquito and it bites another dog or a cat, transmitting the disease. The ideal climate is one with high humidity and good temperatures. In dogs, these larvae usually mature to the adult stage, producing microfilariae and being a source of infection for mosquitoes, completing the cycle. However, in cats, the larvae usually die before they progress to the adult stage, they mature slowly and the feline's immune system can destroy them. However, even if there is only one adult parasitic worm, it can kill the feline.
Larvae migrations, although infrequent, occur more in cats than in dogs, being found in body cavities, systemic arteries, subcutaneous nodules and the central nervous system.
Feline heartworm phases
The disease can be divided into two phases:
- First phase: arrival of immature adult worms in 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 endarteritis, vascular fibrosis, and hypertrophy of the pulmonary arteries. This response decreases as the parasites mature. Sometimes this phase can be confused with allergic bronchitis (asthma). It can cause sudden death or not present symptoms, due to the suppression of the immune response, with no signs appearing and tolerating the infection until the adult parasites begin to die, beginning the second phase.
- Second phase: the death and degeneration of the parasites causes inflammation of the lung with thromboembolism, causing an acute respiratory distress syndrome. This can be caused by a single adult heartworm.
Symptoms of heartworm disease in cats
Many cats tolerate parasitism without any clinical signs, others with transitory signs and others with symptoms. If it occurs, the most frequent symptoms are respiratory, gastrointestinal and neurological symptoms may also appear. Thus, the heartworm symptoms in cats are:
- Dyspnea (shortness of breath).
- Tachypnea (increased respiratory rate).
- Intermittent cough.
- Persistent vomiting not related to food.
- Anorexy.
- Weightloss.
- Lethargy.
- Right congestive heart failure with pleural effusion and jugular distention.
- 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, giving rise to seizures, apparent blindness, circling, ataxia, pupil dilation and hypersalivation.
Dirofilaria immitis harbors within it a bacterium of the Wolbachia genus, which may be related to pulmonary inflammatory reactions in the disease.
Feline Heartworm Diagnosis
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 can be found on cardiac auscultation at the time the parasites occupy the atrioventricular junction, interfering with valve function tricuspid pulse, tachycardia, heart murmur, gallop rhythm, lung crackles, and reduced lung sounds if pleural effusion is present. For its part, the blood analysis shows a mild non-regenerative anemia, increased neutrophils, monocytes and decreased platelets. Regarding serology, two serological tests are used:
- ELISA to detect antigens, has good specificity for confirmation, 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, in the case of cats it is not so due to its lower sensitivity to rule out the disease, due to the higher prevalence of infestations by males or low number of parasites.
- Antibody detection test, allow detecting that parasitization has occurred in cats because it detects exposure to adult parasites, such as larvae whatever your gender. Antibodies are detected from 2 months after infection. Antibodies indicate infection by parasite larvae, but do not confirm that they are actually causing the disease.
In relation to radiology, it can be useful to assess the severity of the disease and to monitor its evolution. The most frequent radiographic findings are:
- Subtly increased size of the main lobar arteries, especially on the right side.
- The peripheral pulmonary arteries appear dilated and tortuous.
- The left caudal pulmonary artery is enlarged to 1.6 or more times the width of the ninth rib.
- Focal or multifocal bronchointerstitial lung pattern.
- Radiographic signs of pulmonary embolism: ill-defined, rounded or wedge-shaped lung areas with opacities that make it difficult to see the associated pulmonary blood vessels.
More than half of affected cats show some abnormality on X-ray. With the performance of a echocardiography, heartworms have been observed in between 40 and 70% of infested cats. Parasites are seen primarily in the right main or 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 shows clinical signs:
- In asymptomatic cats, even if the diagnosis by imaging or serology has shown that it is parasitized, treatment should not be instituted antiparasitic, 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.
- On the contrary, if cats show pulmonary alterations evident on radiography or if there are positive antigen or antibody tests together with signs In clinical trials, they should be treated with prednisolone at a dose of 2 mg/kg/12 hours initially, tapering down to 0.5 mg/kg every other day for 2 weeks. Subsequently, the dose is reduced until withdrawn for another 2 weeks. If the clinical signs return, the treatment would be repeated periodically.
If cats have acute respiratory distress syndrome, they should be given a shock treatment consisting of:
- Intravenous corticosteroids.
- Fluid therapy with balanced electrolytes.
- Oxygen administration.
- Bronchodilators.
In cases where heart failure with pleural effusion has occurred, the fluid should be removed by thoracentesis and use of diuretics such as furosemide, along with oxygen and rest.
The use of adulticide treatment with ivermectin is not recommended because the death of adult parasites can cause anaphylaxis and thromboembolism pulmonary. They should be used when prednisolone is not effective in regressing 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.
surgery can kill parasites. It is important that the extraction of the parasite is complete, because 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
Preventive antiparasitics should be used especially in those cats that live in an area at risk of circulation of the disease. Also in cats that do not leave the house, since, although it is lower, the risk still exists.
This prevention should be started one month before the start of the risk season, or two months before the end of said period in cats over two months of age. Oral ivermectin or topical selamectin can be used monthly, or the combination of fluralaner + moxidectin pipetted every three months.
Forecast
Heartworm disease in cats has a guarded 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 these reasons, prevention is the best way to avoid the disease.
