Alariamarcianae (La Rue, 1917) Walton, 1949
(Figs. 2-4 to 2-7)
ETYMOLOGY:Alaria (winged - referring to the alate nature of the forebody) and marcianae for the specific name of the garter snake, Thamnophismarcianus, from which the mesocercarial stage was first recovered by La Rue (1917).
SYNONYMS:Cercaria marcianae La Rue, 1917; Agamodistomum marcianae (La Rue, 1917) Cort, 1918.
HISTORY: This species was first collected as a larval form, the mesocercaria, from the tissues of the garter snake and described as Cercariamarcianae. It was later demonstrated that the larval stage was present in frogs and that snakes may serve as paratenic hosts (Cort, 1918). The sporocyst and cercarial stages were described from naturally infected snails and the cercariae shown to be capable of developing in tadpoles by Cort and Brooks (1928). Cuckler (1941) recovered adult worms from cats fed mesocercariae from naturally infected frogs. Burrows and Lillis (1965) described the adult form for the first time from naturally infected cats.
GEOGRAPHIC DISTRIBUTION: North America.
LOCATION IN HOST: Small intestine.
PARASITE IDENTIFICATION: These are very small trematodes that are 1.2 to 1.6 mm long with a distinct forebody and hindbody (Figs 2-4 and 2-5). On each side of the small oral sucker are two anteriorly directed tentacles associated with pseudosuckers that are about 100 µm long. The oral sucker is about 100 µm wide. The forebody is concave ventrally and the lateral margins fold in and partially overlap the ventral surface of the body. The ventral sucker is about the same diameter as the oral sucker and is located in the middle of the forebody. The tribocytic organ is just posterior to the ventral sucker, and is approximate 150 to 200 µm wide and slightly more than twice as long as wide. The vitellaria are almost exclusively in the forebody. The sexual organs are located mainly in the hindbody. The posterior testis is bilobed with one lobe on each side of the body. the anterior testis appears only on one side of the body and is slightly smaller than a lobe of the posterior testis. The ovary is just anterior to the anterior testis.
The oval eggs are large, 110 to 127 µm long by 65 to 72 µm wide, operculate, and not embryonated when they leave the fluke (Fig. 2-6). When the eggs become embryonated after several weeks in fresh water, the miracidium has two dark eye spots (Fig. 2-7).
LIFE CYCLE: The life cycle of Alariamarcianae was initially elucidated by Johnson (1968) and then expanded by Shoop and Corkum (1982 & 1983). The eggs are passed in the feces of the final host in an undeveloped state. After development, the eggs contain miracidia that possess two pigmented eye spots. The miracidia then seek out a snail host of the genus Helisoma in which they develop into sporocysts. From the sporocysts are released longifurcous cercariae that possess both oral and ventral suckers, a pharynx, unpigmented eyespots, and well developed penetration glands. The cercariae penetrate and develop in tadpoles. The stage in the tadpole is termed a mesocercaria due to its resemblance to an enlarged cercarial body without the tail. Mesocercariae are capable of being passed between carnivorous paratenic hosts. When the mesocercaria is ingested by the final host, the mesocercariae typically migrate through the lungs where they develop through the metacercarial stage before returning to the intestine where they develop to adults. Eggs are produced in the feces of cats 19 days after infection. The work of Shoop and Corkum showed that it is possible for mesocercariae to be transmitted between mammalian paratenic hosts by transmammary transmission. Also, if queens become infected with mesocercariae while nursing they can pass the infection onto their offspring through the milk.
CLINICAL PRESENTATION AND PATHOGENESIS: There are no reports of Alariamarcianae causing clinical disease in cats. However, the migration through the lung could cause migrating tracts through the lung parenchyma.
TREATMENT: Probably praziquantel, but not reported.
EPIZOOTIOLOGY: Cats become infected by eating frogs, reptiles, or small mammals and birds that contain mesocercariae in their tissues. It is also possible for kittens to become infected through the milk of the queen. Other hosts of Alaria marcianae include the opossum, Didelphis virginiana, raccoon, Procyon lotor, striped skunk, Mephitis mephitis, spotted skunk, Spiglogale putrorius, red fox, Vulpes fulva, gray fox, Urocyon cinereoargeteus, and the dog.
HAZARD TO OTHER ANIMALS: None. Although other hosts are infected, the major means of infection is through the ingestion of the intermediate host which requires that the appropriate snail also be available.
HAZARD TO HUMANS: There have been reports of Alaria causing disease in humans. The first report was a single worm in the eye of a woman from Ontario, Canada (Shea et al., 1973); it was believed that the woman may have been infected by rubbing her eyes while cleaning frog legs for cooking. The second case was fatal (Fernandes et al., 1976; Freeman et al., 1976) and also occurred in Ontario. In this case, numerous mesocercariae were recovered from a patient who was suffering from severe respiratory distress who ultimately died. The mesocercariae in this case were identified as those of Alaria americana (= Alaria canis). It was never determined how the man became infected although it is suspected that he may have eaten raw or undercooked frog legs. The third case involved two intradermal swellings in the thigh and iliac crest of a man in Louisiana (Beaver et al., 1977). In this case, the mesocercaria has been stated to be similar if not identical to that of Alaria marcianae (Shoop and Corkum, 1981). It is believed that his man may have become infected by the ingestion of undercooked game, perhaps a raccoon.
CONTROL/PREVENTION: With cats that hunt, it will be very difficult to prevent infection with this parasite.
REFERENCES:
Beaver PC, Little MD, Tucker CF, Reed RJ. 1977. Mesocercaria in the skin of man in Louisiana. AM J Trop Med Hyg 26:422-426.
Cort WW. 1918. The excretory system of Agamodistomummarcianae (La Rue), the agamodistome stage of a fork-tailed cercaria. J Parasitol 4:130-134.
Cort WW, Brooks ST. 1928. Studies on the holostome cercariae form Douglas Lake Michigan. Tr Am Micr soc 47:179-221.
Cuckler AC. 1941. Morphological and biological studies on certain strigeid trematodes of mammals. PhD Thesis University of Minnesota, Minneapolis, Minn. 102 pages.
Fernandes BJ, Cooper JD, Cullen JB, Freeman RS, Ritchie AC, Scott AA, Stuart PF. 1976. System infection with Alariaamericana (Trematoda). CMA Journal 115:1111-1114.
Freeman RS, Stuyart PF, Cullen JB, Ritchie AS, Mildon A, Fernandes BJ, Bonin R. 1976. Fatal human infection with mesocercariae of the trematode Alariaamericana. Am J Trop Med Hyg 25:803-807.
Johnson AD. 1968. Life history of Alariamarcianae (La Rue, 1917) Walton, 1949 (Trematode: Diplostomatidae). J Parasitol 54:324-332.
La Rue GR. 1917. Two new larval trematodes from Thamnophismarciana and Thamnophiseques. Occa Papers Mus Zool Univ Michigan. 35:1-12.
Shea M, Maberley AL, Walters J, Freeman RS, Fallis AM. 1973. Intraretinal larval trematode. Tr Am Acad Ophth Otol. 77:784-791.
Shoop WL, Corkum KC. 1981. Epidemiology of Alariamarcianae mesocercariae in Louisiana. J Parasitol 67:928-931.
Shoop WL, corkum KC. 1982. Transmammary infection of newborn by larval trematodes. Science 223:1082-1083.
Shoop WL, corkum KC. 1983. Transmammary infection of paratenic and definitive hosts with Alariamarcianae (Trematodea) mesocercariae. J Parasitol. 69:731-735.
Figure 2-4. Alaria marcianae adult showing the alate tentacles associated with the pseudosucker on either side of the head and the division of the body into distinct forebody and hindbody sections.
Figure 2-5.Alaria marcianae adult showing how the alae are not always obvious on the anterior end. In the center of the body between the junctions of the fore and hind body can be observed the tribocytic organ.
Figure 2-6.Alaria marcianae egg as it appears when passed in the feces.
Figure 2-7.Alaria marcianae egg containing a developed miracidium with dark pigmented eyespots.