Abstract:
This study was conducted to determine the effect of temperature and moisture stress on exsheathment
process and infectivity of the infective larvae of the parasitic nematode Haemonchus contortus. Laboratory
conditions were used in which infective (L 3 ) of H. contortus were either subjected to gradually increasing
temperatures, decreasing moisture or both. Post stress viability and exsheatment of L 3 was determined prior to
infection experiments. The viability of H. contortus after induction of anhydrobiosis declined significantly (p<0.05)
from 85 to 60% in about 60 days. The results showed significant (p<0.05) delay in exsheathment in stressed larvae
compared to unstressed larvae leading to low overall establishment (Infection). However, the proportion of the
immature in relation to the mature parasites (hypobiosis) was significantly (p<0.05) higher in stressed compared to
the unstressed L 3 . These results indicate that delayed exsheatment in stressed L 3 contributes to low infectivity in
ruminants.
