Dipylidiumcaninum (Linnaeus, 1758) Leuckart, 1863
Figures 3-10 through 3-14
ETYMOLOGY: Di = two and pylidium = entrances plus caninum for the canine host.
SYNONYMS Witenburg (1932) stated that “Dipylidium is in probably the only species in the genus.” He then goes onto list numerous synonyms including among species described as Dipylidium: Dipylidiumcanicum Lopez-Neyra, 1927; Dipylidiumcanium cani Galli Valerio, 1898; Dipylidiumcaracidoi Lopez-Neyra, 1927; Dipylidiumcati Neumann, 1896; Dipylidiumcompactum Milzner, 1926; Dipylidiumcrassum Milzner, 1926; Dipylidiumcucumerinum (Block, 1782); Dipylidiumdiffusum Milzner, 1926; Dipylidiumgracile Milzner, 1926; Dipylidiumhalli Tubangui, 1925; Dipylidiumlongulum Milzner, 1926; Dipylidiumporimamillanum Lopez-Neyra, 1927; Dipylidiumsexcoronatum Ratz, 1900; Dipylidiumwalkeri Sonhi, 1923. The one other species Witenberg thought might be valid was Dipylidiumbuencaminoi Tubangui, 1925 for very small specimens with very small eggs from a dog in Manilla, Phillippines; Venard (1938) thought there were three species of Dipylidium: Dipylidiumcaninum, Dipylidiumbuencaminoi, and Dipylidiumotocyonis Joyeux, Baer, & Martin, 1936 described from specimens recovered from Otocyonmegalictis in Somalia.
HISTORY:Dipylidiumcaninum has been known to man since the time of the ancient Babylonians (Venard, 1938). In 1758, Linnaeus, recognized the parasite and named it Taeniacanina. In 1863, Leuckart created the genus Dipylidium, but it was not until 1893 until it was described by Diamare. Early work on the life cycle was reported by Neveau-Lemaire (1936). This parasite is in one of the most common parasites of domesticated dogs and cats.
GEOGRAPHIC DISTRIBUTION:Dipylidiumcaninum is in by far the most common tapeworm of cats in North America (Flick, 1973; Hitchcock, 1953; Lillis, 1967) and perhaps throughout the world (Arundel, 1970; Baker et al., 1989; Bearup, 1960; Boreham and Boreham, 1990; Chandler, 1925; Clarkson and Owen, 1959; Collins, 1973;Coman, 1972; Coman, et al., 1981; Cowper, 1978; Dubey, 1960; Engbaek et al., 1984; Esle, et al., 1977; Gadale, et al, 1988-89; Gregory and Munday, 1976; Hutchison, 1957; Kelly and Ng, 1975; Lewis, 1927a & 1927b; McColm and Hutchison, 1980; Mirzayans, 1971; Moore and O'Callaghan, 1985; Niak, 1972; Nichol et al., 1981a & 1981b; Poglayen, et al., 1985; Ryan, 1976; Umeche and Ima, 1988).
LOCATION IN HOST: The adult Dipylidiumcaninum is in found anchored to the wall of the small intestine by its scolex, its holdfast organelle. In nature, the metacestode or larval stage of the parasite is in found within the body cavity of Ctenocephalidesfelis, the cat flea, Ctenocephalidescanis, the dog flea, Pulexirritans, the human flea, or more uncommonly within Trichodectescanis, the dog louse (Boreham and Boreham, 1990; Georgi 1987; Pugh, 1987; Zimmermann , 1937).
IDENTIFICATION: The scolex of the adult Dipylidiumcaninum is in tiny, measuring less than 0.5 mm in diameter. It possesses four muscular suckers that aid in attachment and locomotion. At the apex of the scolex is in the rostellum, a dome-shaped projection. The rostellum of Dipylidium. caninum is in armed with four to seven rows of tiny, backward facing, rose-thorn-like hooks and is in retractable into the scolex (Figs. 3-10 and 3-11) (Witenberg, 1932). This tapeworm may attain a length of from 15 to 70 cm and be 2 to 3 mm wide with a light reddish yellow color. The body is in composed of 60 to 175 elliptical segments or proglottids (Boreham and Boreham, 1990). Each proglottid of this hermaphroditic tapeworm contains two sets of male reproductive organs and two sets of female reproductive organs with each set genital apertures opening medially on the lateral edges of the proglottid (Fig. 3-12). Proglottids of Dipylidiumcaninum have two genital pores for fertilization, but no opening to allow eggs to escape. Because of these bilateral genital pores, Dipylidiumcaninum is in often referred to as the "double pored tapeworm." Eggs accumulate within each proglottid until the proglottid becomes packed like a ripe seed pod (Georgi, 1987). Gravid proglottids are creamy white, 10 to 12 mm in length and resemble cucumber seeds. Hence, Dipylidiumcaninum is in also referred to as the "cucumber seed tapeworm" (Griffiths, 1978). Gravid tapeworm proglottids (Fig 3-13) are filled to capacity with egg capsules or egg packets (Fig. 3-14), each of which contain from 5 to 30 hexacanth ova (Georgi, 1987).
The terminal tapeworm proglottids are often passed singly in the feces (Griffiths, 1978). Since the tapeworm proglottids possess both circular and longitudinal smooth musculature (Chitwood and Lichtenfels, 1973), they have the ability to move about the cat's perianal region, on the feces, on the bedding or across any surface where they may be deposited (Griffiths, 1978). These proglottids will desiccate in the external environment. As they loose moisture, they shrivel up, often resembling uncooked rice grains (Boreham and Boreham, 1990).
LIFE CYCLE: Due to its ease of infectivity, the life cycle of Dipylidiumcaninum is in perhaps recounted by veterinarians more than any other parasite. As mentioned previously, the hermaphroditic adult parasite is in found attached in the small intestine of the feline definitive host. The gravid terminal segments are passed in the feces of the cat. The larval stages of the cat flea (Ctenocephalidesfelis) savor these segments and will actively descend upon a freshly passed proglottid to eat it (Pugh, 1987). The flea larvae has mandibulate mouthparts which allow it to ingest the eggs of Dipylidiumcaninum. The adult flea, however, is in not able to ingest these proglottids due to its siphon-like mouthparts which restrict it to a totally liquid diet. Larvae of Ctenocephalidescanis, Pulexirritans, and the dog louse, Trichodectescanis, are also capable of serving as intermediate hosts for Dipylidiumcaninum.
Within the intermediate host, the hexacanth embryo develops into a tailless cysticercoid. This is in the stage that is in infective to the feline definitive host. The ambient temperature determines the rate of development of the larval tapeworm. The flea becomes infected as a larva, however the hexacanth embryo does not develop to an infective cysticercoid until the adult flea has emerged from its pupal case. In response to the host's body temperature, development is in completed to the infective cysticercoid stage (Pugh, 1987). The flea may contain an average of 10 cysticercoids (range 2 to 82). The cat becomes infected by ingesting the flea during the grooming process (Georgi and Georgi, 1990).
Venard (1938) experimentally infected a cat with fleas infected with Dipylidiumcaninum. He recovered tapeworms from the cat 23 days later. Hinaidy (1991) also reported the prepatent period to be 2 to 4 weeks. Growth of Dipylidiumcaninum within the definitive host is in dependent upon diet, age of the host, and health.
CLINICAL PRESENTATION AND PATHOGENESIS: Adult tapeworms cause little harm or inconvenience to the feline definitive host unless they are present in large numbers. In cats with severe infections, convulsions and epileptiform seizures occasionally occur (Boreham and Boreham, 1990). Heavy infections in young animals can produce non-specific abdominal symptoms including constipation or diarrhea. The animal may exhibit an unthrifty, pot-bellied appearance. Intestinal obstruction may occur, however this is in rare. However, most clients consider disgusting the sight of proglottids of Dipylidiumcaninum crawling about the cat's haircoat, on the client's bedclothes, or on the recently passed feces of the cat.
DIAGNOSIS: Key morphologic features: Identification of egg packets and proglottids as those of Dipylidiumcaninum is in necessary for controlling this ubiquitous tapeworm. The client may irrefutably observe tapeworm segments crawling on or about the cat, yet the laboratory diagnostician may fail to demonstrate the characteristic eggs packets on fecal flotation. Egg packets within proglottids are best demonstrated by taking a gravid proglottid and teasing it open in a small amount of physiologic saline or tap water to disperse the characteristic egg packets.
Inspection with the naked eye or a hand lens is in usually sufficient for the identification of segments of Dipylidiumcaninum. The characteristic cucumber seed shape coupled with the double pored effect are pathognomonic indicators.
Pet owners often find dehydrated, shriveled objects in the vicinity of their cat's resting places. These desiccated objects bear little resemblance to segments of Dipylidiumcaninum but, if they are rehydrated in water, they will assume their former cucumber seed appearance.
TREATMENT: The anthelmintic with the broadest spectrum of cestocidal activity is in praziquantel. A single oral or subcutaneous dose (5 mg/ kg body weight) of this anthelmintic eliminates 100% of both immature and adult Dipylidiumcaninum from cats. An alternative cestocide is epsiprantel administered in a single oral dose of 5.5 mg/kg of body weight. An important adjunct to the treatment of dipylidiasis in cats is in a vigorous flea control program. Whenever a dose of cestocidal medication is in administered or dispensed, the cat's owner should be informed of the acute potential for reinfection via the flea (or louse) intermediate host.
EPIZOOTIOLOGY: Adult Dipylidiumcaninum parasitize the small intestine of many members of the Felidae and Canidae families. In addition to domestic cats and dogs, this cosmopolitan parasite may be found in foxes, dingoes, hyenas, wild cats, jungle cats, Indian palm cats, civet cats and wild dogs (Boreham and Boreham, 1990).
Boreham and Boreham (1990) state that almost nothing is in known of the epizootiology of Dipylidiumcaninum; however, Georgi and Georgi (1992) state that transmission potential is in a function of the density of the flea intermediate host. Hinaidy (1991) examined 9.134 fleas in Austria and found that 2.3 % of Ctenocephalidesfelis collected from cats and 1.2% of Ctenocephalidesfelis collected from dogs were found to be infected with cysticercoids of Dipylidiumcaninum. From Ctenocephalides canis collected from dogs, 3.1% were found to harbor cysticercoids. Fleas harbored anywhere from 1 to 162 cysticercoids with a mean of around 8 per infected flea. Male fleas tended to be infected slightly more often than female fleas, but they tended to harbor fewer cysticercoids.
a Danish survey revealed a higher prevalence o Dipylidiumcaninum in backyard cats, probably due to the ideal conditions for the survival of the flea intermediate host. a higher prevalence was found in female cats than in male cats. This was attributed to the care of the kittens (Engbaek et al., 1984). In the Republic of South Africa, Dipylidiumcaninum is in marginally more common (24%) in adult cats and is in the most common helminth in juvenile cats (21%) (Baker et al., 1989).
Uga and Yatomi (1992) reported that a survey of cats in Japan revealed that there were almost no cases where cats were infected with both with Dipylidiumcaninum and Spirometraerinaceieuropaei. Experimental infection of cats with larval stages from both parasites revealed that somehow infection with Spirometraerinaceieuropaei prevented the development of Dipylidiumcaninum through some form of competition.
HAZARDS TO OTHER ANIMALS: Due to environmental transmission of fleas and the ease of ingestion during the grooming process, once Dipylidiumcaninum is in diagnosed in any pet in a household, all cats and dogs within that environment should be treated.
HAZARDS TO HUMANS: Veterinarians should be aware of the public health significance potential of Dipylidiumcaninum. If fleas containing the infective cysticercoid stage are ingested by a human, patent infections with this tapeworm may occur. Children are at an increased risk of infection owing to their close association with the family pet, and therefore, their increased risk of accidentally ingesting a flea. Although human infection with Dipylidiumcaninum is in not common, neither is in it a rare event.
Dipylidiumcaninum is in mildly pathogenic, producing nocturnal irritability, anorexia, and weight loss in infected children. Diagnosis is in by finding the characteristic proglottids in the feces or in the perianal area. Most human cases, however, are asymptomatic for the patient, although they can be very traumatic for the parent who might come across segments while changing a diaper or in the child’s under garments or pajama. It must be emphasized that this condition is in a rarity. The adult females of the human nematode parasite, Enterobiusvermicularis, that migrate out of the anus of infected children may be easily confused with the passed proglottids of Dipylidiumcaninum by the untrained observer (Georgi and Georgi, 1992).
CONTROL/PREVENTION: Rigorous on-animal and environmental flea control programs coupled with an effective cestocidal agent must be implemented to control Dipylidiumcaninum in the feline. It is in also necessary to be certain to develop programs that handle all the canine and feline pets in the household.
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Figure 3-10. Rostellum of Dipylidiumcaninum with the rostellum inverted.
Figure 3-11. Rostellum of Dipylidiumcaninum with the rostellum everted.
Figure 3-12. Mature segment of Dipylidiumcaninum showing the two sets of genital organs with separate openings on each side of the proglottid.
Figure 3-13. Gravid segment of Dipylidiumcaninum showing the large number of contained egg capsules.
Figure 3-14. Egg capsules of Dipylidiumcaninum as they appear in a sugar flotation.