The body of an adult Raillietina is a typical tapeworm structure, composed ofa series of ribbon-like body segments, gradually enlarging from the anterior end towards the posterior. It is whitish in colour, highly elongated, dorso-ventrally flat, and entirely covered with a tegument. The entire body is divisible into 3 parts, namely the head region called scolex, followed by an unsegmented neck or growth region, and then by highly segmented body proper called strobila. The scolex is a bulbous knob-like structure bearing suckers and a rostellum, which are the organs of attachment to the host. A defining structure from those of other tapeworms is a single prominent rostellum surrounded by four suckers. Further, an important diagnostic character among the different species of the genus is the number and arrangement of hooks and spines on the scolex. The suckers are poorly developed, and completely devoid of special devices or spines. The scolex measures ~134 μ in diameter, and the hooks are 7-10 μ in length. Individual segments in the strobila are called 'proglottids' and are entirely covered with hair-like microtriches. These microtriches are the absorptive structures for feeding, and there are no digestive organs. As all other cestodes, they are hermaphrodite. A set of both male and female reproductive systems is present in each proglottid.
Life cycle
Raillietina require two different hosts for a complete life cycle. The definitive hosts are mostly wild and domestic birds, and sometimes humans. The intermediate hosts are insects, such as ants and beetles. Mature eggs are released from the avian host through feaces by detaching the last gravid proglottid. The number of egg cell in each egg capsule is an identifying feature of each species. Eggs develop into larval forms called oncospheres, which are ingested by ants, and enters the alimentary canal, from where they migrates into the abdominal cavity of the insect and develops into mature cysticercoids. A cysticercoid is an inflated sphere with distinct rostellar hooks, and each species has characteristic number and size of the hooks, which correspond to those of adult worms. Development of the juvenile stage in the intermediate host comprises 5 stages, namely oncosphere stage, lacuna stage, cystic cavity stage, scolex formation stage and cysticercoid stage, which is the ultimate infective form. When the insect with infective larvae is ingested by birds, the cysticercoid is released in host by the action of digestive juices. The rostellar hooks then become attached to the intestinal wall. New segments begin to form and within 3 weeks of ingestion of the host, a mature tapeworm develops. Therefore, the entire life-cycle can take 6 weeks for completion.
Infection is directly diagnosed by identifying proglottids in the faeces, or adult worms in the intestine upon autopsy. Broad-spectrum anthelmintics such as albendazole, fenbendazole, praziquantel, oxfendazole and niclosamide are all effective against the different species. The most effective control measure is disruption of the habitat of intermediate hosts near poultry farms.
