Detailed Explanation of the Symptoms and Prevention and Treatment Methods of Canine Heartworm Disease

This disease is a filarial disease caused by canine heartworm parasitizing the right ventricle and pulmonary artery of dogs (rarely in the thoracic cavity and bronchi), resulting in symptoms such as circulatory disturbance, difficulty breathing, and anemia. In addition to infecting dogs, cats and other wild carnivores can also be infected. This disease is widely distributed in China, and has been found from Shenyang in the north to Guangzhou in the south.

[Pathogen and its life cycle]

Canine heartworm (also known as dog heartworm) is yellow-white, slender, and thread-like. The male worm is 120-160 mm long, with a spirally curled tail; the female worm is 250-300 mm long. The larvae born alive are called microfilariae, which parasitize in the blood, with a body length of 307-322 micrometers, and have no sheath.

The completion of the life cycle of canine heartworm requires dog fleas, Anopheles mosquitoes, or Culex mosquitoes as intermediate hosts. Female worms parasitizing in the right ventricle produce freely moving microfilariae, which enter the blood. When fleas and mosquitoes suck blood, they ingest the microfilariae into their bodies, where they develop into infective larvae and enter the proboscis of the fleas and mosquitoes. When the fleas and mosquitoes suck blood, the larvae escape from the proboscis and penetrate into the skin of the final host, then circulate through the subcutaneous lymph or blood to the heart and large blood vessels.

[Key points for diagnosis]

(1) Clinical symptoms: The earliest symptom is a chronic cough, but without other symptoms of upper respiratory tract infection; it worsens during exercise, or the affected dog easily becomes fatigued during exercise. As the disease progresses, the affected dog develops hyperkinetic heartbeat, weak and intermittent pulse, and heart murmurs. Palpation of the liver area is painful, and the liver is enlarged. There is pleural and peritoneal effusion, and generalized edema. Difficulty breathing. In cases infected for a long time, pulmonary heart disease is very obvious. In the terminal stage, death occurs due to general weakness or collapse during exercise. Affected dogs often have nodular skin disease, characterized by pruritic and tendency-to-ulcerate multiple focal nodules. The skin nodules are pyogranulomatous inflammation centered on blood vessels, and microfilariae are commonly seen in the blood vessels around the pyogranuloma. X-ray photography shows dilation of the right ventricle and dilation of the aorta and pulmonary artery.

(2) Laboratory microscopic examination: A preliminary diagnosis can be made based on history investigation and clinical symptom observation, and the final diagnosis should be made by collecting peripheral blood at night for microscopic examination to find microfilariae.

[Prevention and treatment measures]

(1) Deworming: 1) Killing adult worms: use sodium thioarsenamide, at a dose of 2.2 mg/kg body weight, intravenous injection, twice a day, for two consecutive days. During intravenous injection, it should be injected slowly, and the medicinal liquid must not leak outside the blood vessel, so as to avoid causing tissue inflammation and necrosis. Or use dichlorophenarsine hydrochloride, at a dose of 2.5 mg/kg body weight, intravenous injection, once every 4-5 days; this drug has a strong deworming effect and low toxicity. 2) Killing microfilariae: use levamisole, at a dosage of 10 mg/kg body weight, orally, for 15 consecutive days; after the sixth day of treatment, test the blood, and when microfilariae can no longer be detected in the blood, stop treatment. Or use ivermectin (trade name Ivomec), at a dosage of 0.05-0.1 mg/kg body weight, once by intradermal injection. Or use fenthion, subcutaneous injection of 7% solution 0.2 mL per kg body weight, and repeat 1-2 times at an interval of 2 weeks if necessary. Symptomatic treatment should also be carried out according to the condition.

(2) Preventing and eliminating intermediate hosts: Preventing and eliminating fleas and mosquitoes is an important measure to prevent this disease. Drug prevention can also be used; the oral dosage of diethylcarbamazine (hetrazan) is 6.6 mg/kg body weight, and it should be used continuously during the season of mosquito and fly activity. For dogs positive for microfilariae, diethylcarbamazine is strictly prohibited; only after first using drugs to kill adult worms and microfilariae can diethylcarbamazine be started for prevention.