How to Diagnose Avermectin Poisoning in Pigs

Avermectin is a natural fermentation product of Streptomyces avermitilis. It is a highly effective, broad-spectrum antiparasitic drug with strong killing effects against nematodes and mites in animals.

1. Causes

Incorrect dose calculation and blindly increasing the dose are the main causes of avermectin poisoning. Clinically, pigs are generally given a subcutaneous injection at a dose of 0.3 mg/kg body weight. Pigs have a strong tolerance to avermectin. Practice has shown that subcutaneous injection of avermectin at 5 times the dose daily for 5 consecutive days did not produce typical poisoning symptoms. On the sixth to eighth days, injection at 8 times the dose was given; typical poisoning symptoms appeared on the seventh day, and death occurred on the eighth day.

2. Clinical Symptoms and Lesions

In pigs with cumulative avermectin poisoning, the initial signs include an unsteady gait, paralysis of the tongue muscles, and the tip of the tongue protruding from the oral cavity. Subsequently, the pupils dilate, the eyelids become edematous, the whole body muscles become flaccid and weak, and the forelimbs drop to the ground. There is abdominal distension, involuntary trembling of the head, accelerated breathing, and weakened heart sounds. In severe poisoning, the animal is comatose, systemic reflexes are weakened or absent, and death finally occurs in a coma.

Necropsy reveals gastrointestinal bloating, urinary bladder paralysis with urine retention, pulmonary hemorrhage, pericardial effusion, cardiac edema, and splenomegaly. There is diffuse hemorrhage of the gastric mucosa, and the cecum is filled with a large amount of black feces, with petechial hemorrhage on the mucosa. There is hemorrhage of the dura mater, and hemorrhage of the pia mater and cerebral gyri.

3. Diagnosis

A diagnosis can be made based on the history of excessive avermectin use, combined with the onset symptoms and lesions.