The relationship between worm population density, host survival and the growth of the third-stage larva of Amplicaecum robertsi Sprent & Mines, 1960, in the mouse

Abstract

Female mice survived longer than male mice when infected with 400 eggs but not when infected with 100 eggs of Amplicaecum robertsi.The larvae grew to greater lengths in young than in older mice; smaller worm burdens were also found in the older animals.The growth of the larva was associated with the total worm burden of the host. As the worm burdens, of 40-day-old female mice, increased up to 281 individuals the length of the larvae attained after 14 days decreased; when the larval population increased above this number the lengths of the worms also increased.These crowding effects are discussed in relation to competition for nutrients, immunological suppression of larval growth and to the ability of large larval populations to swamp the resistance mechanisms of the host. It is suggested that the increased growth of the larvae in large populations is due to their ability to break down the liver of the infected host more efficiently than small populations. However, this eventually leads to the deaths of the host through total liver breakdown.This work was done during the tenure of a Senior Research Fellowship from the Wool Research Board of Australia. My best thanks are due to Mr J. James for his assistance with the statistics, to Professor J. F. A. Sprent for his help and advice and to Mr C. Wilkinson for his assistance.