Following increasing calls for environmental safety over the past 2 decades, persistent pesticides are being replaced by more rapidly degradable products. However, even these pesticides can affect non-target species, and may be associated with slow growth and increased susceptibility to viral and
bacterial infections. In this study, juvenile white shrimp Litopenaeus vannamei (also named Penaeus vannamei) were challenged by
intramuscular injection with Vibrio parahaemolyticus after 4 d prior exposure to
methyl parathion in feed pellets at 0.080 microg g(-1). The bacterial injection control group consisted of shrimp fed pellets containing the
methyl parathion-carrier
solvent acetonitrile. Three additional control groups comprised 2 sterile saline-injection groups fed pellets containing
methyl parathion or
acetonitrile prior to injection, and 1 uninjected group fed normal pellets. Cumulative mortalities were recorded on the 4th and 8th days, and the presence of histological lesions was recorded on the 8th day. Cumulative mortalities were significantly higher in the group exposed to
methyl parathion and bacteria on Day 8. Histological lesions, typical of
vibriosis, were significantly associated with the injection of V. parahaemolyticus. The study provides strong experimental evidence that prior exposure to
methyl parathion can increase the severity of
Vibrio infections.