Case report: Entamoeba invadens myositis in a common water monitor lizard (Varanus salvator)

Amoebiasis is one of the most common protozoal diseases of reptiles, but amoebic myositis has not been reported in any animal species. An 11-year-old, male common water monitor lizard (Varanus salvator) was found dead with several subacute ulcerated skin wounds. Gross examination revealed multiple discrete to coalescing, white-yellow to gray, caseous foci scattered in the skeletal muscles and liver. The mucosa of small intestine was thickened, red, and contained many variably sized, dark red ulcers, with depressed and hemorrhagic centers. Histopathologic examination revealed severe necrotizing and granulomatous myositis, hepatitis, and enteritis accompanied by large numbers of intralesional, 10-20-mm diameter, periodic acid-Schiff-positive, amoeboid protozoa. Gene sequence analysis of a 136-bp region of the 18S ribosomal RNA amplified by polymerase chain reaction revealed 98-100% similarity with Entamoeba invadens. Aside from intestinal and hepatic involvement, no other internal organs were affected. The muscular infection by E. invadens likely resulted from a combination of direct invasion of trophozoites via skin wounds and hematogenous spread.