The significance of precocity in the transmission of the nematode parasites of vertebrates

Abstract

The significance of precocity in the transmission of heteroxenous parasitic nematodes is reviewed. Precocity of nematodes in intermediate hosts manifests itself in the following ways depending on the species: (i) the unusually large size of the infective larva; (ii) the advanced development of the genital primordium in the infective larva; (iii) development to the fourth stage in the intermediate host; and (iv) development to the subadult stage (early fifth stage) in the intermediate host. Precocity apparently accelerates gamete and egg production in the definitive host when the behaviour of intermediate and definitive hosts restricts transmission to confined limits of space and time. Examples of precocity are outlined and, whenever possible, related to the behaviour of definitive and intermediate hosts during transmission.