Arrested development of Trichostrongylus colubriformis in experimentally infected rabbits.: Effect of decreasing photoperiod, low temperature and desiccation

Inhibited development of Trichostrongylus colubriformis was studied in rabbits. Experiments are described which show that in a recently isolated field strain of the nematode, the primary stimulus to the induction of inhibited development at the early third larval stage (EL3) in the host is exposure of infective larvae and hosts at decreasing photoperiod. Thus exposure of infective larvae and hosts to photoperiod decreasing daily by 5 min. for 4 weeks prior to their oral administration to rabbits resulted in a mean of 95.2 % of the established worm burden becoming inhibited at the EL3 stage. If only the L-3 stages were exposed to decreasing photoperiod prior to infection of rabbits, then the prevalence of inhibited EL3 stages amongst the worms established declined. Infective larvae subjected to periods of 4 weeks at 4degreesC and at the same time at decreasing photoperiod were able to induce arrested development in 90.6 % of the larvae. Storage of infective larvae at 4degreesC as well as storage Lit desiccation state for 4 weeks before being given as single infections to rabbits did not increase the proportion or worms subsequently found to be hypobiotic.