Studies on Leucocytozoonosis of Turkeys, with Notes on Schizogony, Transmission, and Control of Leucocytozoon smithi

Abstract

In turkeys, Leucocytozoon smithi causes anorexia, droopiness, incoordination, and occasionally convulsions that end in death. The acute stage usually lasts 2-3 days, after which the birds die or start to recover. Necropsy reveals emaciation, dehydration, congestion, and enlargement of the spleen and other organs. Recovered birds may carry the organism in their blood. The only intermediate host known is the simuliid, or blackfly, which ingests the gametocytes of L. smithi while feeding on the blood of carrier birds. Infected flies transmit the parasite to susceptible turkeys while ingesting blood. While investigating an outbreak of leucocytozoonosis at the Cypress Woods Plantation in 1953, the writer discovered for the first time that the turkey gnat fly, Simulium slossonae, was capable of transmitting the disease under experimental conditions. Other investigators have confirmed this finding, and it is believed that this species of fly is the chief vector of the disease in southeastern South Carolina. The fly feeds readily on turkeys and was observed to be very active about sunrise. S. congareenarum was also observed to feed on turkeys, but attempts failed to transmit the disease experimentally. The asexual or schizogonous development of the parasite has been studied in smears and sections of domestic turkeys infected experimentally and naturally. Spleen, heart, intestinal, brain, kidney, and liver tissues were examined microscopically, and schizonts were seen only in liver tissue. These have been designated as hepatic schizonts. The megaloschizont stage, present in L. simondi of ducks, was not observed. Fairly well graded series of stages in the development of the schizont have been observed. Bodies resembling very early stages in schizogony were observed in birds necropsied 3 days post-inoculation. The earliest schizogonous stage recognized as such was seen in the liver of a bird necropsied 6 days after injection of infected blackfly suspension. Fully-formed gametocytes appeared in the blood of infected turkeys about 13 days after infection. The hepatic schizont apparently causes little or no alteration of the host cell. The parasite ultimately fills the entire hepatic cell with merozoites, which escape by rupturing the cell wall. Control of leucocytozoonosis in turkeys is largely a matter of controlling the Simulium fly, which lives in and along streams.