Attempts to differentiate elaphostrongyline larvae (Nematoda : Protostrongylidae) using guinea pigs (Cavia porcellus) as alternate hosts / by Lana M. Bresele

First-and third-stage larvae of Parelaphostrongylus tenuis, P. andersoni \nand Elaphostrongylus cervi could not be distinguished morphometrically. Third-stage \nlarvae of P. tenuis did develop into recognizable adults in \nexperimentally-infected guinea pigs, but P. andersoni and E. cervi did not. At \npresent, elaphostrongyline larvae found in the feces of cervids in eastern \nNorth America are most likely to be either P. tenuis or P. andersoni-, this \nstudy confirms that the experimental infection of guinea pigs will allow this \ndistinction to be made. Because E. cervi is currently believed to be restricted \nto Newfoundland, its third-stage larvae are distinguished by geographic origin. \nAs many as 22 migrating P. tenuis larvae were recovered from outside the \ncentral nervous system (CNS) of each of seven guinea pigs necropsied between \n1 and 27 days post-infection (DPI); all resembled third-stage larvae digested \nfrom snails and used for infections. From one to six developing P. tenuis \nlarvae were recovered from the CNS of each of fourteen infected guinea pigs. \nThese included third-stage larvae, longer than reported in published literature, \nwhich were recovered as early as 9 DPI and as late as 20 DPI in the CNS. \nFourth-stage larvae were recovered between 18 and 47 DPI, and fifth-stage \nlarvae between 20 and 61 DPI; these stages were only found in the CNS. The \nmorphology of the buccal capsule and the tail distinguished the third-, fourth and \nfifth- stage larvae. Descriptions and dimensions of third- and fourth-stage \nP. tenuis larvae recovered from the CNS are provided for the first time. \nLesions found in the stomach wall, mesentery and liver of guinea pigs \ninfected with P. tenuis suggest that third-stage larvae migrate through the \nabdominal cavity towards the CNS. Similar lesions found in guinea pigs infected with P. andersoni and E. cervi suggest that larvae of these species \nfollow a similar route. However, P. andersoni apparently failed to reach the \nmusculature of any of six experimentally-infected guinea pigs. Similarly, E. \ncervi was not recovered from the CNS or musculature of any of six \nexperimentally-infected guinea pigs. \nAdministration of dexamethasone appears to have been ineffective in \nsuppressing the immune response of guinea pigs to infection with these \nelaphostrongylines. The mean number of P. tenuis larvae recovered from the \nCNS of guinea pigs given dexamethasone was not significantly different from \nthat recovered from guinea pigs given saline. Treatment with dexamethasone \nallowed neither P. andersoni nor E. cervi larvae to establish in guinea pigs.

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