Epidemiological Aspects of the Infection With Oswaldocruzia Filiformis (Goeze, 1782), Travassos, 1917 (Nematoda: Trichostrongylidae) in the Common Toad (Bufo Bufo L., 1785) in the Netherlands

Abstract

Twenty-eight males and fifteen females of B. bufo were collected before and after spawning and in November 1979 at a fieldstation for examination for the presence of O. filiformis. From this fieldstation another sample of the adult toad population was collected in the same spring and placed in an outdoor enclosure (experimental plot). The fluctuation of the parasitic stages in these hosts (twenty-three males, thirty-one females) was observed monthly from May till September/October. The availability of infective larvae of O. filiformis was investigated each month in the experimental plot by using wormfree Rana temporaria as tracers from May till November. Tracers were also used to registrate survival of preparasitic stages following the winters of 1979 and 1980. All parasitic stages overwintered in the toads and resumed their development after spawning of the host. In the experimental plot this development resulted in a first wave of adult parasites in B. bufo during May/June. They caused a midsummer-increase of infective larvae on the ground resulting in significant values in tracers in June and in the toads in June and July. It is suggested that these larvae result in a second wave of adults from the end of August on. From that moment increasing numbers of fifth stage larvae and adults were observed in toads, the increase being significant for adult female parasites. During the summer a significant decrease in available numbers of infective larvae on the ground was seen in the results from the tracers, but the chances for infection considerably increased in late summer and autumn. After both winters tracers became infected, but it is suggested that survival capacity of preparasitic stages is probably low. Under natural circumstances no infection of B. bufo up to the end of May was observed. No significant differences in the intensity of the infection between males and females of both host species, or first and second year of life tracers were found. Instead of 0-20 parasites per animal, as seen in toads in the fieldstation, intensities of 100-200 parasites in both host species were seen most frequently in the experimental plot. Traces became infected earlier than toads, in which new infections were not observed until June. Under outdoor conditions the prepatent period of O. filiformis in R. temporaria apparently takes more than one month.