CESTODES (Also with notes on the few Acanthocephala reported from cats)

Wikis > CESTODES (Also with notes on the few Acanthocephala reported from cats)

 

CESTODES

(Also with notes on the few Acanthocephala reported from cats)

The cestodes or tapeworms comprise a large assemblage of parasites which as adults are found in the intestinal tract of vertebrates. Most typically, the tapeworms are acquired by the final host ingesting an intermediate host that contains a larval stage of the tapeworm. There are fourteen recognized orders of cestodes currently recognized (Khalil LF, Jones A, Bray RA. (eds) Key to the Cestode Parasites of Vertebrates. CAB International, Wallingford, UK, 751 pp). Most of these fourteen orders are found in sharks, rays, fish, reptiles, and birds, with only a few being found in mammals. The cat is a final host to only two Orders of these tapeworm parasites, the Pseudophyllidea and the Cyclophyllidea. Within the Pseudophyllidea are the two genera Diphyllobothrium and Spirometra. Within the Cyclophyllidea are the genera Mesocestoides of the Mesocestoidiidae, Dipylidium, Joyeuxiella, and Diplopylidium of the Dipylidiidae, and Taenia and Echinococcus of the Taeniidae. There have been rare reports of other cyclophillidean tapeworms in the cat, including Choanotaenia of the Dilepididae.

The body of adult tapeworms is characterized by a long ribbon-like body that is divided into segments containing the sexual organs and eggs. This collection of segments is called a strobila. Some tapeworms are very small and have strobila composed of only a few segments (e.g., Echinococcus) while some tapeworms become very long and have strobila composed of many segments (e.g., Diphyllobothrium). The head of the tapeworm is typically equipped with a hold-fast organ that is often termed a bothridia, bothria, or scolex. The holdfast may be armed with spines or tentacles, and may or may not have muscular suckers. The anterior of the scolex may also have a central anteriad portion, the rostellum, which may be equipped with hooks of various types. In some groups, the rostellum can be retracted. The segments of the body typically each bear both male and female reproductive organs and ultimately produce eggs that require fertilization. In some cases, the eggs are shed from the tapeworm’s segment while the segment is still attached to the strobila within the host (as with Diphyllobothrium and Spirometra), while in other cases, the segments become large sacks of eggs that are shed into the environment (as is the case with Dipylidium and Taenia). The eggs of tapeworms typically contain a larva that has six hooklets that are used for locomotion when ingested by the proper intermediate host. Some eggs are passed with the larva already developed (Taenia and Dipylidium) while others are passed in a state that requires additional development in the external environment (Spirometra). Some eggs have opercula, and some eggs do not.

With a group as large as the Cestoda, there are, of course, exceptions to almost every “typical” plan. Thus, three orders of tapeworms, the Gyrocotylidea, Amphilinidea, and Caryophyllidea, have no external segmentation. These three orders are parasites of fish and turtles. The larva in the egg of Amphilinidea and Gyrocotylidea has 10 hooks rather than 6 hooks. There is a tapeworm parasitic in wading birds, Dioecocestus in the Cyclophyllidea, that has separate male and female strobila. Also, even though almost all adult parasites are found in the intestine, there are exceptions, the Amphilinidea are found in the body cavities of their final hosts. One tapeworm of rodents and humans, Rodentolepisstraminea (syns., Hymenolepisnana and Vampirolepisnana), is capable of direct development in the vertebrate host.

The tapeworm parasites of cats have two major life-cycle types. In the first type, the Pseudophyllidea utilize an aquatic environment for the early stages of the life cycle. Thus, there is a swimming larval stage in the life cycle that infects aquatic invertebrates. Later in their life cycle, these Pseudophyllidean parasites utilize various vertebrate paratenic hosts such as fish, amphibians, reptiles, and mammals to facilitate the transfer of the larvae to the carnivorous final host. In the second life-cycle type, the Cyclophyllidea of cats utilize the terrestrial environment for the larval stages of the life cycle; thus. The larvae of Dipylidium are found in fleas, and the larvae of Joyeuxiella, and Diplopylidium are found in amphibia and reptiles. The larvae of Taenia and Echinococcus are found in mammalian hosts. The host in which the initial larval development of Mesocestoides occurs has not been found (it is presumed to be an invertebrate), but the later larval stages are found in vertebrates. In all cases, the cat becomes infected by the ingestion of a host that contains the larval stage of the parasite that grows to adulthood within its intestinal tract.

Cats can also serve as the intermediate host of certain tapeworms. Within the Pseudophyllidea, cats have been found to be infected with the larval stage of Spirometra, called a sparganum. Within the Cyclophyllidea, cats have been infected with larval stages of members of the Mesocestoidiidae and the Taeniidae. The larval stage of the Mesocestoidiidae is the tetrathryidum. The larval stage of the Taeniidae that has been found in cats in a coenurus of Taenia spp. that is parasitic as an adult in dogs.

Cats have been reported on occasion to be the final host of another phylum of parasites, the acanthocephala. There have been very few reports of acanthocephala in cats, and in almost all cases, the reports have been the results of necropsy results from surveys. Thus, the acanthocephala, did not seem to warrant a chapter of their own. They have no affinities with the tapeworms, and are placed here only for convenience.

Table 1. Tapeworms of the cat, how infected, and geographical distribution of the parasites.

Parasite

Larval stage ingested by cat

Host containing larval stage ingested by cat

Geographical distribution

PSEUDOPHYLLIDEA

Diphylobothriidae

Diphyllobothriumlatum

Plerocercoid

Fish

Northern Europe, Japan, Imported to Northern North America & Chile

Spirometraeuropaeerinaceae

Sparganum (Plerocercoid)

Amphibia, reptiles, rodents

Worldwide

Spirometramansonoides

Sparganum (Plerocercoid)

Amphibia, reptiles, rodents

Americas

CYCLOPHYLLIDEA

Mesocestoididae

Mesocestoideslineatus

Tetrathyridium

Amphibia, reptiles, rodents

Worldwide

Dipylidiidae

Dipylidiumcaninum

Cysticercoid

Flea larva

Worldwide

Diplopylidiumacanthotetra

Cysticercoid

Lizard

Southern Europe, Middle East

Diplopylidium nölleri

Cysticercoid

Lizard

Southern Europe, Middle East

Joyeuxiellapasqualei

Cysticercoid

Lizard

Southern Europe, Middle East, Asia

Joyeuxiella fuhrmanni

Cysticercoid

Lizard

Africa

Joyeuxiellaechinorhyncoides

Cysticercoid

Lizard

Africa

Dilepididae

Choanotaeniaatopa

Cysticercoid

Invertebrate

Kansas, USA

Taeniidae

Taeniataeniaeformis

Strobilocercus

Rodent

Worldwide

Echinococcusmultilocularis

Alveolar hydatid

Rodent

Holarctic

 

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