Morphology
A cestode ' s body is composed of three parts : the scolex , neck and strobila .
Scolex
The scolex ( head ) has attachment organs that consist of four suckers . Anterior to the suckers , located at the tip of the scolex , is the rostellum , a mobile attachment that protrudes outwards , allowing the tapeworm to anchor itself to the host ' s gut wall . Often , the rostellum is armed with hooks to facilitate attachment to the intestinal wall .
Neck
This is an unsegmented area behind the scolex where segments are formed . Treatment of tapeworms would need to eliminate both the scolex and the neck to be effective or the worm may regenerate [ 2 ] .
Strobila
The strobila consists of proglottids ( segments ). Each proglottid contains both male and female reproductive organs and is therefore hermaphroditic . The proglottids mature towards the end of the strobila , so the more caudal proglottids are gravid and contain eggs .
When mature segments are released , they usually disintegrate in the host ' s faeces , releasing individual eggs ( Taenia ) or egg packets ( Dipylidium ). Eggs can be identified under the microscope [ 2 ] , although Dipylidium proglottids can also be seen moving or contracting on faeces or around the perianal area .
Cestodes do not have a digestive tract and absorb nutrients directly through their protective tegument ( outer surface ) [ 3 ] . The tegument is covered with microtriches , which increase the surface area and play an active role in the absorption and secretion of nutrients [ 3 ] .
Life cycle
The common cestodes seen in veterinary practice all have an indirect life cycle , which means they need an IH to complete their life cycle ; some species can have more than one IH in their life cycle ( Figure 2 ). Eggs , once ingested by the IH , release invasive oncospheres into the gut . They migrate across the intestinal mucosa to tissues where they develop into larval cysts . These cysts are then ingested by the EH [ 4 ] , either accidentally or as part of predation .
When the EH ingests the IH , the larval cysts are released into the small intestine and develop into adults [ 2 ] . Adult cestodes can vary in size and do not usually cause clinical signs other than segments in faecal matter or around the host ' s anus .
The larval cyst stage , on the other hand , can cause disease when cysts develop in tissues such as the brain , liver or lungs , especially in longer-lived hosts , such as horses ( Figure 3 , page 57 ).
Intermediate host ingested
Adult worms in small intestine
Eggs ingested by an intermediate host , such as a small mammal for Taenia , or fleas or lice for Diphylidium
Life cycle of the cestode ( tapeworm ) in dogs
Eggs and end segments of adult worms pass in faeces
Figure 2 . The life cycle of the tapeworm in dogs .
56 Veterinary Nursing Journal