SURVIVAL TO PATENCY OF LOW-LEVEL INFECTIONS WITH TRICHURIS-MURIS IN MICE CONCURRENTLY INFECTED WITH NEMATOSPIROIDES-DUBIUS

Large, single-pulse laboratory infections with T. muris are rejected by mice before patency, but low-level infections of < 20 worms survive for long periods. Data are presented to show that the threshold at which an effective immune response takes place is significantly higher in mice concurrently infected with N. dubius. In control CFLP mice trickle infections did not survive to maturity but in the slower responder C57 Bl10 mice egg production began on day 35 and continued for a further 7 wk, with some mature worms present at autopsy. Concurrent infection with N. dubius resulted in trickle infections, T. muris surving much better than in control mice, although these still showed some resistance to T. muris. Evidently, T. muris elicits concomitant immunity in the host. Thus, the first worms to establish survive to patency at which time they can no longer be removed by the host, but once the immunological threshold was exceeded incoming larvae are rejected by the host. Such a survival strategy would be very useful to T. muris in the wild.