Biomphalaria glabrata (Gastropoda): effect of urethane on the morphology and function of hemocytes, and on susceptibility to Schistosoma mansoni (Trematoda)

Urethane (ethyl carbamate) anesthesia of Biomphalaria glabrata resulted in several rapid changes to the snail's blood picture. At 2 hr postexposure (PE) to the drug, there was an elevation in the prevalence of acid phosphatase (APase)-positive hemocytes, a significant increase in the number of APase granules per cell, a three fold increase in circulating blood cell number, and a decrease in the percentage of hemocytes expressing a cell subpopulation-specific surface membrane epitope (BGH₁). However, urethane had little effect on erythrophagocytosis by host hemocytes. All of the observed changes returned to control levels by 12 hr PE to the drug. Blood cells cultured with various concentrations of the anesthetic in vitro did not exhibit any alterations in the parameters described above. Since circulating hemocytes represent the primary effector component involved in internal defense reactions, the effect of urethane-induced changes in the composition of circulating blood cells on susceptibility to a larval trematode, Schistosoma mansoni, was examined. Such changes had no apparent effect on host susceptibility since the rate of infection for urethane-exposed snails (88.2%) was the same as for nonurethane-treated B. glabrata (82.4%). However, the effects of urethane-induced changes in hemocyte number and composition on other invading organisms is not known. Therefore, it is suggested that such alterations should be considered when internal defense reactions are studied in snails exposed to this drug and other commonly used anesthetics.