Esophageal deformation of Gnathostoma spinigerum in ivermectin-treated rats, and anthelminthic efficacy

Ivermectin 2 mg/kg single dose reduced worm load by 83.3 % (75.0 – 91.7 %) for rats experimentally infected with 20 Gnathostoma spinigerum advanced third-stage larvae administered at week 1, with sacrifice at week 15 post-infection. Some larvae recovered from the muscles of treated rats were found to be grossly deformed in appearance. Morphological changes in the Gnathostoma larvae were clearly observed. The internal structures of the deformed larvae showed significant degeneration in the esophageal glandular tissues. The esophageal lumen branched irregularly and occupied a wider area in the center of the esophagus. The epithelial cells thickened along these branches. The esophageal gland ducts were completely destroyed. The excretory ability of the esophageal cell glands may be depressed, causing loss of function. It is suggested that ivermectin is effective against Gnathostoma larvae due to worm recovery reductions. The drug efficacy appears to generate by esophageal destruction of the worms.