| Taenia | |
|---|---|
 | |
| Taenia saginata | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Platyhelminthes |
| Class: | Cestoda |
| Order: | Cyclophyllidea |
| Family: | Taeniidae |
| Genus: | Taenia Linnaeus,1758 |
| Type species | |
| Taenia solium | |
Taenia is the typegenus of theTaeniidae family oftapeworms (a type ofhelminth). It includes some importantparasites of livestock. Members of the genus are responsible fortaeniasis andcysticercosis inhumans, which are types ofhelminthiasis belonging to the group ofneglected tropical diseases. More than 100species are recorded. They aremorphologically characterized by a ribbon-like body composed of a series of segments calledproglottids; hence the nameTaenia (Greek ταίνια,tainia meaning ribbon, bandage, or stripe). The anterior end of the body is thescolex. Some members of the genusTaenia have an armed scolex (hooks and/or spines located in the "head" region); of the two major human parasites,Taenia saginata has an unarmed scolex, whileTaenia solium has an armed scolex.[1]
The proglottids have a centralovary, with avitellarium (yolk gland) posterior to it. As in allcyclophyllidcestodes, a genital pore occurs on the side of the proglottid. Eggs are released when the proglottid deteriorates, so auterine pore is unnecessary.
T. saginata is about 1,000–2,000 proglottids long with each gravid proglottid containing 100,000 eggs, whileT. solium contains about 1,000 proglottids with each gravid proglottid containing 60,000 eggs.[4]
Humans were previously thought to have acquiredTaenia species (T. solium,T. asiatica, andT. saginata) after the domestication of large mammals, although the omnivorous diet and foraging of early hominids suggest the contact between the ancestralTaenia was established prior to the rise of modern humans and advanced agriculture. Evidence suggests the domestication of animals by humans consequently introducedTaenia species to new intermediate hosts, cattle, and swine.[5]
Morphological and molecular data suggest that the divergence ofTaenia specialised human parasites has been directly associated with earlier hominids and prior to the existence of modernHomo sapiens. Direct predator-prey relationships between humans and the original definitive and intermediate hosts ofTaenia resulted in thishost switch. Ecological evidence showed that earlyhominids preyed heavily on one of the intermediate hosts, antelope, ofTaenia, thus resulting in earlier colonization by the parasite prior to mammalian domestication. The early hominids had anomnivorous diet; they were hunters and scavengers. The abundance of antelope in sub-Saharan Africa savannah in the Late Pliocene resulted in a vast food resource for hominids and other carnivorous animals such asfelids,canids, andhyaenids.[5] Hominids who hunted antelopes or scavenged killed antelopes bridged the beginning of a host-parasite relationship between hominids andTaenia. During this time, hominids may not have had the means of cooking their food. This would have greatly increased their chances of catching the cysticerci, as a result of eating uncooked meat. Also, transmission of the parasite may have been enhanced by directly consuming the definitive host. Parasitological data support the foraging of antelope byHomo species during the Late Pliocene and Pleistocene periods. This corresponds to the initial contact of the ancestralTaenia and specialize intoT. solium,T. saginata, andT. asiatica, thus resulting in colonization of the early hominids as definitive hosts.
Host switching forTaenia is most prevalent among carnivores and less prevalent among herbivores throughcospeciation. An excess of 50–60% ofTaenia colonization occurs among carnivores—hyaenids, felids, and hominids.[6] Acquisition of the parasite occurs more frequently among definitive hosts than among intermediate hosts.[6] Therefore, host switching likely could not have come from cattle and pigs. The establishment of cattle and pigs as intermediate host byTaenia species is consequently due to the synanthropic relationship with humans. During the past 8,000–10,000 years, the colonization of respectiveTaenia species from humans to cattle and to swine was established.[6] In contrast, the colonization of ancestralTaenia onto the early hominids was established 1.0–2.5 million years ago.[6] It clearly shows that the colonization of humanTaenia antedates the domestication of mammals.
