Trickle infections of Nippostrongylus brasiliensis in rats.

Abstract

Much of our knowledge of immune responses to gastrointestinal nematode infections stems from study of the rat/NippostrongyIus brasiliensis system. Most experimental infections of rats with N. brasiliensis consist of a single inoculation of many larvae resulting in the establishment of a worm population that is usually almost completely expelled within 2 weeks, leaving the host strongly resistant to challenge infections (Ogilvie and Jones 1971, Exp Parasitol 29:138-177). It has often been suggested that repeated inoculation with small numbers of larvae, called trickle infections, may more closely resemble naturally occurring infections. Despite the importance of this suggestion for the interpretation and understanding of immune and pathological processes during helminth infections, experimental investigation of the kinetics of trickle infections of N. brasiliensis is limited mainly to the work of Jenkins and Phillipson (Jenkins and Phillipson 1970, Parasitology 62:457-465; 1972a, Int J Parasitol 2:105-111; 1972b, Int J Parasitol 2:353-359; Jenkins 1972, Parasitology 65:547-550; 1973, Z Parasitenkd 41:73-82; 1974, Parasitology 68:13-17). They found that when rats were given a small number of larvae 5 times a week for 4-16 weeks, the worms which became established in the intestine persisted and continued egg production for many months. Following such trickle infections they recorded mean worm burdens of 150-250 or percentage takes of 50%-60%, which is the same as the percentage take at the peak of a primary infection (Ogilvie and Jones 1971, Exp Parasitol 29:138-177). On the basis of these results it is generally accepted that when infections of N. brasiliensis are acquired gradually, immune expulsion is impaired and a population of adapted worms continues producing eggs for several months. The present report describes two more experiments in which worm burdens and egg production were measured following trickle infections of N. brasiliensis. The rats used were of the same strain and sex as those routinely used by Jenkins and Phillipson. Outbred male Sprague-Dawley rats (purchased from Bantin and Kingman Ltd., UK) were housed in groups on sawdust, kept at about 18 ~ C with natural lighting and given food (Oxoid 41B, Herbert Styles Ltd., UK) and water ad lib. The methods of larval