Micronema deletrix in the kidney of a horse.

Although most members of the Rhabditoidea are free-living saprophagous nematodes, some are true parasites, whereas others are facultative parasites. The Rhabditidae, and the Cephalobidae in which Micronema spp. are found, are mainly of the facultative group (1). The various genera are differentiated primarily on the form and armature of the stoma and glottoid apparatus (1,2). Micronema deletrix has been found in lesions in horses (3-8) and humans (9-11), likely as the result of accidental infections. We discuss herein the occurrence of M. deletrix in the kidney of a horse in Alberta, Canada. The affected, unidentified horse was one of 145 killed during one day at a slaughter facility in Edmonton. Although most of these horses originated in Canada, 27 were known to have arrived from the United States. At inspection, personnel found that one kidney was enlarged, creamy white, and markedly fibrotic when sectioned. Other significant lesions were not found in the carcass and it passed inspection. Portions of the affected kidney were fixed in 10010 neutral buffered formalin and submitted to the Regional Veterinary Laboratory, Lethbridge. The fLxed tissue was trimmed, processed routinely, embedded in paraffin, cut at 4 utm, and stained by the hematoxylin and eosin (H & E) and Masson's trichrome methods. For identification, typical parasites were dissected from the fixed tissue, and cleared in lactophenol. A compound microscope and microprojector were used to measure these worms. On the basis of descriptions by Anderson and Bemrick (3), we identified the parasites as M. deletrix (Figure 1). All observed parasites were females; males or larvae were not found. Histologically, the lesions consisted of multiple confluent granulomas surrounding numerous nematodes that were found in the capsule, parenchyma, and within dilated tubules (Figure 2). Usually, both intact and degenerated parasites were surrounded by amorphous, intensely pink-staining exudate and a pleocellular population of epithelioid macrophages, and many lymphocytes and plasma cells intermixed with eosinophils, as well as interstitial fibrosis.