Signalment: 4 YR FS DSH
History: “Layla” was an adult stray cat, wandering the neighborhood when she was taken in by her good hearted owner. For the first two years in her new home “Layla” was healthy and received regular veterinary care. Layla’s owner began to notice weight loss and then blood tinged urine outside the litter box. At that time, “Layla” also began hiding and avoiding all attention. “Layla” was taken to her regular veterinarian where her blood work revealed anemia. It was suspected that she had a blood borne parasite or an autoimmune disorder, immune mediated hemolytic anemia (IMHA). She was prescribed the antibiotic Doxycycline and a vitamin supplement. Her owner observed labored breathing and increasing lethargy the following morning, “Layla” was referred to the ER.
Exam: She presented depressed with fair pulses, pale mucus membranes and increased bronchovesicular sounds in dorsal lung fields.
Diagnostics: The CBC revealed anemia (Hct 14%) and thrombocytopenia (62 K/uL). Hyperbilirubinemia (0.8 mg/dL) and hyperglycemia (266 mg/dL) were noted on the chemistry analysis.
Treatment: “Layla” was placed in a supplemental O2 cage upon arrival. After the blood work was completed, “Layla” was blood typed and a compatible donor was found. She received a whole blood transfusion which increased her PCV from 14% to 24%.
“Layla” appeared to be improving and was more alert. Early that next morning she acutely became tachypneic (RR: 84 rpm) and depressed.
Further Diagnostics: Thoracic radiographs revealed markedly enlarged pulmonary arteries in comparison to the pulmonary veins, an enlarged caudal vena cava, a focal interstitial to alveolar infiltrate in the caudal lung lobe and an alveolar infiltrate in the right cranial ventral lung lobe.
Diagnosis: Caval Syndrome due to Heartworm disease
Discussion: Dogs are the natural host for heartworms. Because Cats are an atypical host, they do not develop a typical infection. Cats often become infected with a small number of heartworms (a low worm burden) and often have an occult infection (no circulating microfilaria). The worms live within the right atrium of the heart, the pulmonary vasculature and vena cava. There are varying degrees of damage to these structures, which are classified in the dog. Cats commonly develop pulmonary symptoms, often severe when due to pulmonary thromboembolism (PTE).
Diagnosis: These low numbers make it difficult to test cats for the presence of heartworms. Less than 20% of infected cats have patent (reproducing) infections. A number of tests are available, but all have their limitations. The antigen heartworm test only detects the presence of female worms, requiring an infection of several months with several adult worms. The filter test only checks for circulating microfilaria. The antibody test that will only detect a cat’s exposure to heartworm disease, that may have occurred at any point in its life. Often, a combination of tests is needed to make an accurate diagnosis, including thoracic radiographs and an echocardiogram.
Signs: Cats may not show any signs of infection. The most common symptoms are coughing or asthma and chronic vomiting. Anorexia, weight loss, lethargy, and exercise intolerance may also be seen. Unfortunately sudden death is the first sign in approximately 10% of cases. Because cats are not the natural host, the worms can have erratic migration, often to the brain, eyes, and other organs, causing signs to vary considerably.
Treatment: A number of preventative products are available by prescription. Most of these medications will also treat other conditions such as common intestinal parasites and even ear mites. Treatment of heartworm disease is problematic in cats. The adulticide treatment used in dogs’ causes severe adverse reactions in cats. There are currently no medications labeled for microfilaricide treatment in cats.
Treatment typically consists of a short term steroid to manage respiratory signs and starting one of the heartworm prevention medications. If the cat is dyspneic, supplemental O2, bronchodilators and cage rest are necessary. If the cat has developed heart failure due to the heartworm infection, appropriate CHF treatment should be instituted.
Prognosis: Good in mild to moderate heartworm infections.
Fair to guarded in severe cases.
Footnote: Due to “Layla’s” critical and deteriorating condition, her owner elected for humane euthanasia.
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