The influence of Encephalitozoon cuniculi on neural tissue responses to implanted biomaterials in the rabbit

Laboratory rabbits are commonly used for testing the tissue response of neural device biomaterials. Rabbits of many colonies in the U.S. are infected by the intracellular microsporidian parasite, Encephalitozoon cuniculi, with rates of infection ranging from 15 to 76% (1). Several authors have suggested that infection by this parasite may alter immune system response and experimental results. We report that infection by E. cuniculi made the interpretation of results more difficult and altered the animals' responsiveness to implanted platinum wires coated with various polymers such as glow discharge methane, Parylene C, or polyimide. Edema, neuronal and glial reaction, and inflammatory responses to the coated wires were quantitated at four sites in each animal. Inconsistency of response in all measured parameters was found, both between animals and between sites in infected animals. Infected animals showed the greatest variability, primarily in the degree of inflammatory reaction. Parylene C was found to induce the most severe inflammatory reaction, an unexpected finding. No consistent reaction to any of the coating materials was found in this study. We believe that this variability in response was primarily due to infection by E. cuniculi. Our results suggest that rabbits should not be used for tissue compatibility testing of neural device biomaterials until the animals are free of E. cuniculi infestation as demonstrated by serologic screening.