Immunization of rabbits with a midgut extract of the human body louse Pediculus humanus humanus: the effect of induced resistance on the louse population.

Resistance to human body lice, Pediculus humanus humanus L, induced by feeding on rabbits immunized with an extract of louse gut was studied. The mortality of lice fed on immunized rabbits was 73%, significantly higher than that of lice fed on control rabbits (52%) (P < 0.01). The proportion of dead nymphs and female lice with ruptured guts was significantly higher in lice fed on immunized rabbits (P < 0.01). The size of the bloodmeal was 35% greater in female lice fed on control rabbits than on immunized rabbits. Lice fed on immunized rabbits laid 40% less eggs than those fed on the controls, they also demonstrated a significant decrease in the number of eggs per female over time (P < 0.01). 86% of the eggs laid by lice fed on immunized animals hatched, compared with 92% hatching of eggs laid by the lice fed on control animals (P < 0.01). With the exception of the first bloodmeal the percentage of hatched eggs which were laid between any two bloodmeals was significantly smaller (P < 0.01) in the lice fed on immunized rabbits than in the control group. The first nymphal stage of lice fed on immunized rabbits took an average of 5.2 days to moult to the second stage, compared with 4 days for those fed on control rabbits.