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Longevity of Metacercariae of Fasciola hepatica on Pastures in the Upper Coastal Region of Texas and Its Relationship to Liver Fluke Control

1947; American Society of Parasitologists; Volume: 33; Issue: 1 Linguagem: Inglês

10.2307/3273618

1937-2345

O. W. Olsen,

Nematode management and characterization studies

In the coastal region of Texas the cercariae of Fasciola hepatica that emerge from the snail intermediate host, Stagnicola bulimoides techella (Hald.), during the winter and spring months, when water is present on the pastures, and attach to the grass at that time apparently, are destroyed by exposure to the summer heat and drought (Olsen, 1945). The unfavorable environmental conditions existing on the pastures during the summer and fall also inhibit snail activity, thus preventing reinfestation of the grass until the onset of the winter rains when the snails emerge from estivation in the soil (Olsen, 1944a). The period between the time when the pastures become free of infective cysts in the summer and the time when they become reinfested in the winter appears to be sufficiently long to allow the young flukes in the bodies of the cattle and sheep to complete their growth in the liver tissue and enter the bile ducts, where sexual maturity is attained (Olsen, 1945). Since young flukes migrating in the body cavity and through the liver parenchyma are not killed by carbon tetrachloride in sheep (Montgomerie, 1926) or goats (Shaw and Simms, 1927), or by hexachloroethane in sheep (Klobouk, 1927; Ganslmayer and Grmogek, 1941; Olsen, 1946) and cattle (Olsen, 1944b), it is important to ascertain if there is a time during the year when only the susceptible adult flukes are present in the livers. In the past, studies on the longevity of the metacercariae of the liver fluke were conducted, for the most part, under laboratory conditions. It is the purpose of this paper, however, to present the results of pasture experiments designed to determine (1) whether the pastures in the Gulf Coast region become free of metacercariae, (2) the periods that they are free of them, and (3) if such a period exists, whether it is sufficiently long to allow young flukes already in the bodies of the hosts to reach the bile ducts and attain maturity before reinfestation of the pastures occurs. Such information is basic to the development of a program of liver fluke control through medication.