ENERGY RESTRICTION AND SEVERE ZINC-DEFICIENCY INFLUENCE GROWTH, SURVIVAL AND REPRODUCTION OF HELIGMOSOMOIDES-POLYGYRUS (NEMATODA) DURING PRIMARY AND CHALLENGE INFECTIONS IN MICE

The objectives of this study were (1) to determine the impact of sever e zinc deficiency on the establishment, growth, survival and reproduct ion of Heligmosomoides polygyrus in the laboratory mouse, during both primary and challenge infection protocols, and (2) to determine whethe r the observed effects resulted from zinc deficiency per se, or from t he accompanying energy restriction. Three diet groups were used: zinc- sufficient (Zn+: 60 mg zinc/kg diet), zinc-deficient (Zn-: 0.75 mg zin c/kg diet) and energy restricted (ER: 60 mg zinc/kg diet pair fed to Z n- mice). Neither Zn- nor ER influenced the establishment of the paras ite during a primary infection. However, both significantly influenced the early development of the parasite. The proportion of adult worms recovered 9 days post-infection (p.i.) was highest in Zn- mice, interm ediate in ER mice and lowest in Zn+ mice. Worms were also distributed more distally in the intestine of the Zn- mice and worm survival was h ighest in Zn- mice, intermediate in ER mice and lowest in Zn+ mice at both 4 and 5 weeks p.i. Although the length of female worms was reduce d in Zn- mice, neither per capita fecundity nor egg viability was affe cted by zinc deficiency. Energy restriction, on the other hand, signif icantly reduced worm fecundity at 5 weeks post-primary infection, but had no effect on egg viability. Zinc concentration of adult H. polygyr us was similar among dietary groups. The effects of zinc deficiency an d energy restriction were also investigated 4 and 5 weeks after a chal lenge infection. Whereas-strong host resistance was evident in Zn+ and ER mice, based on comparison of worm numbers between challenged mice and primary infection controls, no evidence of resistance was detected in Zn- mice. As in the primary infection,female worms were shorter in Zn- mice than in ER and Zn+ mice, and energy restriction but not zinc deficiency significantly affected per capita fecundity. However, in c ontrast to the primary infection, ER mice had elevated rather than red uced fecundity. This study demonstrates a complex interaction between H. polygyrus and zinc and energy restriction, and highlights the impor tance of controlling for reduced food intake in nutrition-infection st udies.