Seasonal Fluctuation, Localisation and Inhibition of Development of Parasitic Stages of Oswaldocruzia Filiformis (Goeze, 1782) Travassos, 1917 (Nematoda: Trichostrongylidae) in Bufo Bufo L, 1785 Under Natural and Experimental Conditions in the Netherlands

Abstract

Fourty males and thirtytwo females of B. bufo were collected before and after spawning at two field stations for examination for the presence of O. filiformis. From one of these places another fifty males and twenty females of B. bufo were collected and placed in outdoor enclosures. The seasonal fluctuation of developmental stages of O. filiformis was followed from March 1978 till March 1979. The infection percentage with O. filiformis is almost 100%. The intensity of the infection varied from 0-102 helminths; in the field 10-20 parasites were frequently found as opposed to 20-30 in the experimental plots. There was no correlation between the intensity of the infection and the length of the host; not could a clear difference be demonstrated in intensity of infection between males and females of B. bufo. Early parasitic stages of O. filiformis are localised in the mucosa of the stomach and must be collected by digestion of this organ in a pepsin-HCl solution. Later on the parasite migrates to the upper intestine. Overwintering hosts harbour different parasitic developmental stages of O. filiformis. During hibernation the development is interrupted and the parasite burden does not change. Resumption of development is not correlated with the spawning activity of the host but seems to be dependent on the rise of temperature in spring. During this development older adult worms and possibly a part of L4 and L5 stages are lost with the faeces. In the experimental plots the infection in May-July was small. The level of infection was lowest in early August. From the middle of August on the infection increases and reaches a maximum in November. The length distribution of the early larval stages in the stomach shows a bimodal size distribution in autumn, winter and spring, indicating that O. filiformis is inhibited in the host B. bufo in a specific stage of development. The seasonal fluctuation of the developmental stages of O. filiformis, the inhibition of development and some facts of the life cycle are discussed.