Symptoms & Diagnostic Methods of Canine Heartworm Disea

Canine heartworm disease is a condition caused by the parasitic worm Dirofilaria immitis, which resides in the right ventricle and pulmonary artery of dogs (the chest and bronchial tubes are less common). This parasitic infestation leads to circulatory disturbances, respiratory difficulties, anemia, and other symptoms. Beyond dogs, cats and other wild carnivores can also be infected. The disease is widely distributed in China, from the northern regions up to Shenyang and as far south as Guangzhou.

Section 1: Pathogen and Life Cycle

The heartworm is yellowishwhite and slender, belonging to the genus Dirofilaria. Male worms measure between 120 to 160 millimeters, while females can reach 250 to 300 millimeters in length, with their tails coiling into a spiral shape. The larvae, known as microfilariae, are born alive and parasitize the blood, measuring between 307 to 322 micrometers in length and lacking a sheath.

The life cycle of the heartworm requires intermediate hosts such as dog fleas, Culex mosquitoes, and Anopheles mosquitoes. Female worms in the right ventricle release microfilariae into the bloodstream. These microfilariae are then ingested by fleas and mosquitoes during their blood meals, developing into infective larvae. The larvae escape from the insect's proboscis and burrow into the skin of the final host, eventually entering the heart and major blood vessels through the subcutaneous tissue or bloodstream.

Section 2: Key Indicators for Diagnosis

In the early stages, clinical symptoms may include chronic coughing, without other upper respiratory infections, and these symptoms may worsen during exercise or lead to fatigue afterward. As the disease progresses, affected dogs may exhibit tachycardia, fine pulse, and multiple heart murmurs. Liver tenderness, liver enlargement, pleural and abdominal effusions, and generalized edema are common in chronic respiratory distress cases with pulmonary heart disease. Dogs may ultimately succumb to generalized weakness or ataxia. Dogs with the disease often suffer from nodular skin diseases characterized by itching and multifocal ulcers. Granulomatous dermatitis is primarily characterized by inflamed central nodules in the skin blood vessels, with microfilariae commonly found around the blood vessels. Imaging may show dilation of the right ventricle, aorta, and pulmonary artery.

A preliminary diagnosis can be made through a combination of medical history and clinical observations, followed by laboratory microscopic examination. The definitive diagnosis is confirmed by detecting microfilariae in the blood during a nighttime blood test.

Section 3: Preventive Measures

Parasiticide treatments include:

1. Sodium thiabendazole at a dose of 2 mg/kg body weight, administered intravenously twice daily for two days. The injection should be given slowly to prevent leakage outside the vein, which could cause tissue inflammation and necrosis. Alternatively, dichlorophenol at a dose of 2.5 mg/kg can be used, injected intravenously every 4 to 5 days; this product has strong anthelmintic activity with low toxicity.

2. Levamisole at a dose of 10 mg/kg body weight, taken orally for 15 consecutive days. A blood routine check is performed on the sixth day after treatment; treatment is discontinued when no heartworms are detected. Alternatively, ivermectin can be used, administered subcutaneously at a dose of 0.05 to 0.1 mg/kg body weight. This treatment should be repeated 1 to 2 times every two weeks. Symptomatic treatment should also be tailored to the individual case. For more information on canine heartworm disease, you can read this article, "Can Canine Heartworm Disease Be Cured?" to learn more.