Host Effects on the Migration of Nippostrongylus brasiliensis in a Thermal Gradient

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Nippostrongylus brasiliensis of a 17-day-old infection migrated more slowly than those of a 7-day infection in a thermal gradient. Worms, 17 days old, which were transplanted into an unexposed rat on day 7 migrated at the same rate as those of a 7-day infection. The migration rate of Nippostrongylus was faster during the night than the day. Reversal of the day-night light cycle for the host rats caused their worms to migrate faster during the day than those of rats on a normal day-night light cycle. McCue and Thorson (1964) and Thorson, Mueller, and McCue (1964) reported that parasitic stages of several phyla of helminths migrated toward higher temperatures in a thermal gradient until thermal damage and death occurred. With Nippostrongylus brasiliensis worms of older infections (18 days) migrated slower than those of a 7-day infection. It was suggested that this may be due to a host effect, presumably an immune response, or to senescence of the worms of the older infection. Preliminary observations also indicated that the response of the worms varied throughout a 24hr period with more rapid migrations occurring at night. This could also be interpreted as a host effect since the physiological and behavioral activity of rats is greatest during the night (Hemmingsen and Krarup, 1937; Browman, 1937). The experiments reported herein were designed to determine if in fact there was a host effect in older infections which caused slower migration in a thermal gradient and if the daily activity cycle of the host also influenced the migration rate of worms in a thermal gradient. MATERIALS AND METHODS The basic apparatus and methods described in McCue and Thorson (1964) were used. Male Wistar rats, 4 to 8 weeks old, were obtained from the Lobund Laboratory Conventional Animal ColReceived for publication 11 August 1964. * These studies were supported in part by a research grant (AI-03049) from NIAID, NIH, Public Health Service. t From work done by the senior author at the University of Notre Dame in partial fulfillment of the requirements for the Ph.D. degree. t Present address (R. E. T.): Department of Tropical Health, American University of Beirut, Beirut, Lebanon. ony, University of Notre Dame. Special experimental manipulations will be discussed in the following section.