IMMUNOPATHOLOGY OF 8-WEEK-OLD RING-NECKED PHEASANTS (PHASIANUS-COLCHICUS) EXPOSED TO MALATHION

In addition to their acute neurotoxic effects, some organophosphorus c ompounds have been shown to have immunotoxic properties. Alterations i n the immune system may lead to chronic morbidity and/or mortality tha t is not readily apparent at the time of initial exposure. Because it often inhabits land that is intensely farmed, the ring-necked pheasant (Phasianus colchicus) may be a suitable biomonitor of agroecosystems, especially those used in the production of corn. We examined immunopa thologic effects of a widely used organophosphate insecticide, malathi on, on 8-week-old, cage-reared ring-necked pheasants 3 d after a singl e oral dose. No differences were seen in hematologic parameters, body weight, or weight of the bursa of Fabricius. Birds given a high dose o f malathion (230 mg/kg) displayed significant decreases in absolute an d relative thymic and splenic weights (p less than or equal to 0.05). Significant changes were also seen in thymic and splenic histomorphome try (p less than or equal to 0.05). The high-dose group and, in some c ases, the low-dose group (92 mg/kg) displayed significant histologic l esions. These findings indicate that a single dose of malathion, at th e LD50 level (230 mg/kg) and occasionally at 40% of the LD50 level (92 mg/kg), is capable of inducing quantitative and qualitative changes i n the lymphoid organs of the ring-necked pheasant that may affect immu ne function.