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(19-34) Effects of agricultural pesticides on the immune system of Rana pipiens and on their resistance to parasite infection. Christin, Marie-Soleil1, Brousseau, Pauline*,1, Gendron, Andrée2, Marcogliese, David2, Cyr, Daniel1, Ruby, Sylvia3, Fournier, Michel1, 1 Human Health Research Center,INRS-Institut Armand-Frappier, Pointe-Claire, Québec2 St. Lawrence Centre, Environnement Canada, Montréal, Québec3 Concordia University, Montréal, Québec ABSTRACT- In the last 30 years, population's size of many amphibian species has experienced a decline throughout the world. Many of these declines have been clearly linked to habitat degradation but in a number of recent cases, infectious diseases appear to be the proximal cause of the die-offs. One hypothesis proposed to explain these disease outbreaks involves contaminant-induced immunosuppression that might lead to an increase in the vulnerability of amphibians to various pathogens. Indeed, some chemicals of environmental concern are already known to alter the immune system of different organisms. Since amphibians are frequently exposed to agricultural pesticides, it is possible that these pollutants could also affect their immune system. In this study, we found that a mixture of pesticides, similar to what is found in the environment, could alter the lymphocytes proliferation in the Rana pipiens frogs. Moreover, an exposition to the pesticide subsequently reduced the resistance of frogs to Rhabdias ranae, a common Rana nematode. In animals exposed to high concentrations of pesticides, an increase in the migration and the maturation of the parasite larvae was observed. Therefore, the pesticides used could decrease certain immunological responses against parasites since after an exposure, the animals could no longer respond adequately to pathogen challenge. Finally, pesticides and parasites may have a synergistic effect on the immune system since suppression in the phagocytic activity could only measured after infection with Rhabdias ranae and exposition to pesticides. This suggests that the immunosuppression caused by parasites and pesticides may be cumulative. Taken together, these results suggest that agricultural pesticides, at concentration to which amphibian are exposed in the wild, can have an effect on the immune system of Rana pipiens and subsequently diminish their resistance against pathogens. Key words: Pesticides, Immunotoxicology, Amphibian, Parasite infection |
