Host-parasite relationships of Helminths in a coyote population from Southern Texas with particular reference to the dog hookworm
AuthorRadomski, Andrew Alan
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Prior to the development of proper management and effective control programs for coyotes (Canis latrans), general information regarding demographic data, particularly growth rates and mortality in the neonates, must be well understood. Chapter I reviews some of the current literature pertaining to natural mortality in coyotes and present control methods used on this predator. Chapter II examines certain facets of the question of whether or not a parasite can function as a mechanism to limit the population growth rate of its vertebrate host. This study was initiated to obtain additional information to support or refute the general hypothesis of coyote population regulation by hookworm disease. The specific objectives were to: (1) document the effects of hookworm infection (morbidity and mortality) on experimentally infected hand-reared coyote neonates; (2) determine if selective density-dependent pathogenicity of hookworm infection occurs in coyote neonates and, if so, obtain an estimate of hookworm densities required to cause clinical signs of morbidity and to cause mortality; and (3) determine if differential susceptibility exists among individuals within a litter. These objectives were accomplished by experimentally inoculated 51 captive handreared coyote neonates from a captive coyote population in Utah. The strain of infective strongyliform dog hookworm (Ancylostoma caninum) larvae was cultured from the feces of a free-ranging coyote captured in southern Texas. Twenty-eight coyote neonates, 3- to 4-wk-old, were inoculated at random with 0 (control), 250, 500 or 1,500 hookworm larvae/kg body weight to establish threshold levels of mortality. Mean weight gains and hematocrit values were recorded over a 30-day study period. An initial threshold level of 250 to 500 hookworm larvae/kg was estimated to cause 50% mortality (LD50) among neonates in Experiment I. Lesions in neonates included initial pneumonitis and pulmonary consolidation as a result of larval migration, with severe hemoglobinopathy and anemia associated with localization of hookworms in the small intestine over time. Differences in susceptibility among neonates within the same litter, as well as a more accurate estimate of hookworm larvae densities required to cause morbidity and mortality, were examined in Experiment II. Differential susceptibility was observed within litters administered the same dose of hookworm larvae. A threshold level of > 300 hookworm larvae/kg was determined to be the lethal number of hookworm larvae needed to cause mortality based upon 23 neonates in 7 different litters used in Experiment II. The absolute number of hookworms recovered in these experimental studies corresponded to the number of hookworms reported from naturally-infected free-ranging juvenile coyotes in southern Texas; suggesting that this infection could result in densitydependent pathogenicity in natural populations of this vertebrate host. Thus, hookworm can be considered as a potential factor in the regulation of coyote population growth rates in the in southern Texas. Chapter III examines the persistence and interrelatedness of a recurrent group of macroparasitic helminths from the small intestine in a free-ranging population of coyotes in southern Texas at 4-yr intervals (1979 to 1987), as well as across seasons (spring and fall 1979) and over a 1-yr period (fall 1986 and fall 1987). The study was designed to strengthen the data concerning the community ecology of the intestinal helminth species operating in this host population. The priori hypothesis was that a stable recurrent group of helminth species persists over time and that the respective Helminth species in this recurrent group are stable in terms of their frequency distributions and abundances. This hypothesis was addressed by examining the effects of the intrinsic factors of host sex and age on the population dynamics of a helminth community in coyotes from southern Texas. Eight species of helminths (Alaria marciana^r A. caninum. Mesocestoides lineatus. Qncicola canis. Physaloptera rara. Taenia multiceps, T. pisiformis. and Toxascaris leonina) composed the community occurring along the small intestinal gradient of coyotes in southern Texas. Computation of the Eager index and subsequent recurrent group analysis and rank correlations indicated the persistence of a small group of recurring species along with several affiliated species. These results provide information on the inter-relationships of these intestinal helminths that remain as a persistent recurrent group within coyotes in southern Texas and provides further documentation of the species that could most effect this coyote population (i.e., be an additive mortality factor in conjunction with hookworm to affect host population dynamics).