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The term amphiparatenic host was coined originally for hosts of Alaria marcianae that as adults are paratenic hosts, but as juveniles serve as definitive hosts. In this study the concept of amphiparatenesis is placed in a theoretical context, maternal transmission shown to be the basic mechanism, and the concept extended to include Toxocara canis, T. cati, T. pteropodis, Neoascaris vitulorum, Ancylostoma caninum, Uncinaria lucasi, various species of Strongyloides, Pharyngostomoides procyonis, and P. adenocephala. Alaria marcianae mesocercariae were used in a feline model to show that male and nonlactating female cats are definitive hosts, but lactating cats are primarily paratenic hosts. Inoculation of 1 female cat resulted in the infection of 21 of her offspring via the milk over the course of 5 litters and after a 3-yr period she still had viable larvae in her tissues. The ability of parasites to remain immature in amphiparatenic hosts is believed to be an adaptation on the part of the parasite to promote dissemination through maternal transmission and not the result of resistance, immunological or otherwise, on the part of the host. The amphiparatenic concept has important implications that include: the use of pregnant and lactating females as reservoirs of infection for the offspring; infection transmitted through a contagious transplacental or transmammary pathway; a parasite population structure in which adult worms are in greater abundance in neonate than adult hosts; and the effective control of parasites utilizing this strategy proving to be very difficult.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Notre Dame is collaborating with JSTOR to digitize, preserve and extend access to American Midland Naturalist.ABSTRACT: A total of 197 solitary sandpipers Tringa solitaria and 213 pectoral sandpipers Calidris melanotos were examined for trematodes from the hosts' tropical winter range in Ecuador, South America, during the autumn and spring migrations from Louisiana and South Dakota in the United States, and from the breeding grounds of the solitary sandpiper in Ontario, Canada. Of the 13 trematode species recorded, five were common to both hosts: Tanaisiafedtschenkoi, Cyclocoelum obscurum, Paramonostomum sp., Leucochloridium variae and Zonorchis microrchis. Of the remaining eight species, Cyclocoelum brasilianum, Plagiorchis maculosus, Stephanoprora denticulata and Eurytrema lubens occurred in solitary sandpipers while Cyclocoelum tringae, Plagiorchis elegans, Echinoparyphium speotyto and Echinoparyphium aconiatum were found only in pectoral sandpipers. Trematodes from the digestive tract were usually of low prevalence and intensity, whereas those from other sites were of higher prevalence and ubiquitous in geographical distribution. None of the collecting localities was the major source of trematode infection. Despite the hosts' different breeding ecology and feeding habits, their trematode faunas were similar.

Mesocercariae of Alaria marcianae were removed from snake paratenic hosts and fed to domestic cats. The cats were necropsied at specified intervals, the parasites recovered, and studied by SEM. During the prepulmonary phase of migration in cats, mesocercariae recovered from the stomach wall, abdominal cavity, diaphragm, liver, and heart underwent no tegumental modification compared to those fixed immediately after removal from the paratenic host. The mesocercaria resembled the body of an enlarged cercaria. The oral sucker was encircled by 14 or 15 rows of simple, posteriorly directed spines. Similar spines were also located along the margins of the venter and equatorially at the level of the acetabulum. This spinal pattern left two regions, one anterior and one posterior to the acetabulum, devoid of spines. Uniciliate papillae were found in a distinct pattern associated with the spined areas. In the pulmonary phase, the mesocercariae transformed into diplostomula. Earlike lappets on either side of the oral sucker developed with subsequent differentiation of microvilliform processes on their ventral sides. Body spines divided to give rise to three-pronged serrations. A depression on the venter between the acetabulum and posterior end of the body gave rise to the tribocytic organ. Stout, densely-clustered spines arose de novo on this organ. A rudimentary cylindrical hindbody gave the diplostomulum a distinct scoop-shaped appearance. Worms coughed up from the lungs and swallowed were later found in the duodenum. This postpulmonary phase of migration was a quick event and young worms in the duodenum were indistinguishable from those in the lungs. Within 4 days, the diplostomula in the duodenum matured to adulthood.(ABSTRACT TRUNCATED AT 250 WORDS)