TAENIA (MULTICEPS) MULTICEPS

CAUSATIVE AGENT (CLASSIFICATION, morphology) Taenia multiceps formerly was classified in the genus Multiceps, which was defined by species with a coenurus rather than a cysticercus; however, metacestode stage later was dropped as a factor defining genus in ces- todes.

host range and distribution This spe­cies has a cosmopolitan distribution (Jones and Pybus 2001), including North America (Leiby and Dyer 1971), Europe (Sovgovia et al. 2001), the Middle East (Dalimi et al. 2006), and Africa (Minnaar et al. 2002). Definitive hosts include domestic and wild canids (Canis lupus, C. latrans, C. familiaris, C. mesomelas, Alopex lago­pus, Vulpes vulpes, Nyctereutes procyonoides) and occasionally felids (Puma concolor) (Jones and Pybus 2001). Intermediate hosts containing coenuri include a variety of bovids (Bos spp., Capra spp., Gazella subgutturosa, Hippotragus equinus, Ovis spp., Oryx gazella, Rupicapra spp., Saiga tartarica), camelids (Camelus spp.), cervids (Capreolus capreolus, Rangifer taran- dus), suids (Sus scrofa), and lagomorphs (Lepus americanus) (Jones and Pybus 2001).

life cycles and variations Taenia multi­ceps has a well-established sylvatic cycle involv­ing wild canids and wild herbivores, as well as a pastoral cycle in dogs and domestic livestock (Jones and Pybus 2001). Adult cestodes live in the small intestine of the definitive host. Eggs pass out with the feces and intermediate hosts ingest eggs on contaminated pasture and vege­tation. Among large mammals, coenuri invade the central nervous system, most often the cerebral hemispheres but also the spinal cord. In smaller mammals, the coenuri can invade the central nervous system or the subcutane­ous or intermuscular connective tissue. Canids acquire infection by preying or scavenging on infected hosts (Jones and Pybus 2001).

reservoirs and transmission Because the coenurus can lodge in the brain, this para­site can cause behavioral changes in intermedi­ate hosts such as chamois (Rupicapra rupicapra) and roe deer (Capreolus capreolus) that facilitate their ready susceptibility as prey for definitive hosts (Wetzel and Rieck 1972, Horning 1975). At one time, it also was believed that T. multi- ceps might retard color change in snowshoe hare (Lepus americanus), making this prey species more susceptible to predation and enhancing completion of the life cycle (Leiby and Dyer 1971). The parasite in question more likely was T. serialis (Boughton 1932, Jones and Pybus 2001); however, there are no known supporting field or laboratory findings to support this assertion.

CLINICAL EFFECTS AND IDENTIFICATION Oncospheres are carried by blood to the cen­tral nervous system; they then leave migratory tracts as they move through the nervous tissue. With heavy infections, animals can experience both meningitis and encephalitis (meningoen­cephalitis). The developing coenuri continue to grow and commonly cause a lack of motor coor­dination. Infected sheep may circle in a direc­tion opposite to the side of the brain in which the coenurus is lodged (Soulsby 1968). When the coenurus is lodged in the spinal column, paralysis of one or both hind limbs may occur (Soulsby 1968). This parasite can be fatal to chamois and roe deer (Wetzel and Rieck 1972, Horning 1975).

Adult worms can be numerous in definitive hosts. In intermediate hosts, clinical signs are suggestive, but not definitive, and diagnosis must be confirmed at necropsy; PCR-based restriction fragment techniques can be used to identify characteristic patterns of T. multiceps (Gasser and Chilton 1995).

population effects Although ongoing mortality among some wild cervid populations has been established (Wetzel and Rieck 1972, Horning 1975), there are no clearly established patterns of significant population impacts from this parasite in wildlife.

special problems Human cases of coenu­rosis caused by T. multiceps can occur. However, these are uncommon (Ing et al. 1998).

control and host immunity Population reduction of coyotes results in a lower mean abundance of T. multiceps (Henke et al. 2002). Niclosamide is effective against T. multiceps and other cestodes among infected wolves, foxes, jackals, hyenas, and dogs (Bekirov and Dzhumaev 1976). Anthelminthic drugs such as praziquantel have been used to success­fully treat larval stages of T. multiceps in sheep (Verster and Tustin 1982).

Most species of Taenia lend themselves well to effective vaccines (Lightowlers 1996). While there have been efforts to develop vaccines against T. multocida (Verster and Tustin 1987), none have yet been successful (Lightowlers et al. 2000).

Life Cycles Involving Hydatid Cysts

Only members of the genus Echinococcus pro­duce hydatid cysts in their intermediate hosts. All species of Echinococcus (Family Taeniidae) are very small in the adult form, with stro- bila up to 12 mm long and with only three to seven segments; all are parasites of the small intestine (Jones and Pybus 2001). Four species currently are recognized: E. multilocularis, E. granulosus, E. vogeli, and E. oligarthrus, with additional species proposed (Bowles et al. 1992, Thompson and McManus 2002) The hydatid for E. granulosus is a large single cyst with a thick outer, laminated, non-cellular layer and an inner, thin, nucleated germinal layer. The inner layer is a source of both protoscolices, as well as brood capsules within which protoscoli- ces are formed (Roberts and Janovy 2000).

In contrast to the large single cysts charac­teristic of E. granulosus, the E. multilocularis hydatid has a thin outer wall that grows and infiltrates processes into the surrounding host tissues like a cancer (Roberts and Janovy 2000). Because of this capacity to bud and metasta­size, this metacestode form is called an alveolar or multilocular (“many chambered”) hydatid (Roberts and Janovy 2000). The hydatids for E. vogeli and E. oligarthrus also are alveolar (Jones and Pybus 2001)

Definitive hosts rarely experience adverse effects from any of the Echinococcus spp., even with a large abundance of adult cestodes. The impacts of the larval forms will vary depending on where the hydatids develop in the intermedi­ate hosts.

Although well known as an important para­site of wildlife and domestic animals, there are many E. granulosus strains, often in the same region (Jones and Pybus 2001, Thompson and McManus 2002), and understandings about the taxonomic and ecological relation­ships of these strains still are very incomplete.

Consequently, our discussion on an example of a species with a hydatid will be focused on E. multilocularis, with brief summaries of E. granulosus, E. vogeli, and E. oligarthrus.