Identification of measles (cysticerci) and other larval cestodes (metacestodes) found in game carcasses

Posted on August 01, 2020

The Helminthology Laboratory of the Department of Veterinary Tropical Diseases renders a broad spectrum of diagnostic tests, among other the identification of measles (cysticerci) and other larval stages of tapeworms (metacestodes) of taeniids found in herbivore and omnivore game carcasses. Taeniid tapeworms follow, as the vast majority of tapeworms, an indirect life cycle with carnivores and humans acting as definitive hosts, carrying the adult stage (strobilar stage) in their small intestine. Measles (cysticerci) have the size of, approximately, a pea and cannot be distinguished macroscopically to species level. In most instances, measles found in herbivore and omnivore game carcasses during meat inspection, belong to taeniid species that do not have zoonotic implications. However, the measles of the beef tapeworm (Cysticercus bovis) and pork tapeworm (Cysticercus cellulosae) have, although rare, also been reported in the literature from herbivore and omnivore game carcasses, with the latter one posing a major threat to human health. The consumption of venison is becoming increasingly more popular, in light of greater consumer awareness of the wholesomeness of venison. To protect consumers, it is therefore important to identify particularly measles to species level. In order to identify measles, the invaginated head with the rostellar hooks is dissected and mounted on a slide and examined microscopically. Measles of the beef tapeworm uniquely do not possess neither a rostellum nor hooks, making identification a simple exercise. In the case of an ‘armed head’ further investigation is required which requires to establish the number, size and shape of the rostellar hooks and compare this information with published data obtained from the relevant taxonomic literature. In the 25 years the Helminthology Laboratory is offering this diagnostic test most measle specimens submitted have been identified as those of the non-zoonotic Taenia hyaenae and, to a lesser extent, Taenia crocutae which also has no zoonotic implications. The measles of the beef tapeworm and pork tapeworm have so far never been diagnosed. Apart from measles, other larval cestodes were identified in our laboratory as those of Taenia multiceps and Echinococcus granulosus s.l. Both species and particularly some species of the E. granulosus complex do have zoonotic implications. Lesions which can be erroneously interpreted as measles are the sarcocysts of the heteroxenous Sarcocystis species which are coccidean protozoal parasites. Sarcocysts are seen occasionally in specimens submitted to our laboratory.

Measles in a game carcass Rostellar hooks  
 Measles in a game carcass Rostellar hooks dissected and mounted from a larval tapeworm head  
Published by Linda Poggenpoel

Copyright © University of Pretoria 2020. All rights reserved.

FAQ's Email Us Virtual Campus Share Cookie Preferences