The kinetics of repeated low-level infections of Nippostrongylus brasiliensis in the laboratory rat

The kinetics of low-level repeated infections of Nippostrongylus brasiliensis in the laboratory rat were studied.The administration of five infective larvae each weekday to the rats produced an infection which was cumulative over 16 weeks and which did not produce an acute host immune response.The repeated administration of 50 larvae/weekday produced a primary immune response after 14 days. This caused partial worm expulsion and the suppression of egg output but the resistance of these rats to reinfection was not as pronounced as that seen in classical laboratory infections where heavier but less frequent larval exposures are used. The secondary worms that established in these rats did not elicit an acute host immune response even when the worm burden was as high as 756 worms.It is suggested that the kinetics of this type of infection more closely approximate those found under natural conditions than do those of a ‘classical’ laboratory infection.We wish to thank Misses G. Merchant, L. Cleaver and J. Cobb for able technical assistance, and Dr B. M. Ogilvie (National Institute for Medical Research, Mill Hill, London) for her helpful comments and discussions.