Heligmosomoides polygyrus and Trypanosoma congolense infections in mice: effect of immunisation by abbreviated larval infection

Concurrent African trypanosome and gastrointestinal helminth infections are prevalent in subhumid savannah where they are endemic. However, acquired r esistance in animals varies with their responder status and exposure. As a guide to study in the definitive hosts, the effects of Trypanosoma congolen se infection on the development and maintenance of homologous Heligmosomoid es polygyrus resistance were investigated in outbred TO mice. These mice we re immunised by abbreviation of larval infection. Immune or naive mice were either infected with 500 infective larvae (L-3) of H. polygyrus and/or 10( 4) bloodstream forms of T. congolense or were not infected. The outcome of infection was monitored by routine parasitological and immunological techni ques for 30 days after the day of the T. congolense infection. Significantl y more immune mice concurrently infected with both parasites survived than did immune mice in which H. polygyrus was superimposed on a 10-day-old T. c ongolense infection. Although all the mice in this latter group died before the end of the experiment, larval immunisation prolonged their survival, r elative to similarly treated naive mice. The antibody titres to H. polygyru s in the sera of immune mice challenged with H. polygyrus alone were signif icantly higher than those of immune mice concurrently infected with both pa rasites but the levels of protection obtained were comparable. It is conclu ded that T. congolense may not completely block the strong acquired resista nce induced by abbreviated H. polygyrus larval infection in TO mice but is capable of interfering with protective responses, especially if the trypano some infection occurs prior to H. polygyrus challenge infection. (C) 1999 E lsevier Science B.V. All rights reserved.