A study of the life-cycle of the important buffalo parasite Toxocara Vitulorum to provide a basis for control procedures

• University of Paradeniya, Sri Lanka

Development of effective control procedures for Toxocara vitulorum depends on an improved understanding of its life cycle. In the humid tropics, especially in Southern Asia, the parasite is the major cause of mortality in buffalo calves, of which it commonly kills 25-30%, and up to 80% in some years. Since the countries it infests together contain about 80 million buffaloes, its control would greatly increase the supply of draught animals.
Shortage of draught power has become a constraint on crop production in many developing countries, where this high mortality and poor reproductive performance have both contributed to falling buffalo populations. Subsistence farmers depend on the animals for cultivation, for some fertiliser and for fuel, milk and meat. In Sri Lanka where the project will be carried out, rehabilitation of ancient irrigation schemes and establishment of new schemes have further increased the demand for buffaloes.
At present, much of the parasite's complex life cycle remains unknown, and knowledge of the host-parasite relations also has many gaps and discrepancies. Research is needed to fill those gaps, to establish vulnerable points in the life cycle so that scientists can formulate control procedures appropriate for village farmers. Research findings will be applicable to Asia, Africa and South America.
A new technique for radiolabelling worm parasites, developed at CSIRO Armidale, now makes it possible to study the life cycle in detail. Recent work there has investigated sheep parasites, especially Haemonchus contortus, using 75Se and 14C and has added to our knowledge of interactions between worm populations and of the mechanisms controlling acquired resistance in the host.
The research in Sri Lanka will broaden Australian experience with the radiolabelling technique, and elucidate the T. vitulorum life cycle.
Investigations of the life cycle will involve four coordinated approaches. Firstly, field studies in villages will examine the duration and level of infectivity of maternal milk, and the relation betwwn that level and the age of the cow. Secondly, joint field and laboratory studies will probe the interaction between the parasite's life cycle and the host's reproductive cycle, especially hormone changes associated with the migration of larvae in the cow and their transfer to the calf. Thirdly, parasite-free environmentsboth field station and pen facilitieswil be used to study the source and timing of transfer of larvae to the calf. In the fourth approach, the work with radiolabelled larvae will begin by establishing the best mehtod of attaching the radiolabel to the parasite. The scientists can then determine: the dynamics of the possible pathways of calf infection (in utero, by larvae from milk and/or by infective eggs); the dynamics and route(s) of larval migration within the cow; the histology of the host-parasite interface during larval migration; the site and state of arrested larvae; and the reaction of the host cow against arrested larvae and its effect on them.
Some of the studies on eggs and larvae, especially those on radiolabelling, will be undertaken at CSIRO's Armidale laboratories. However, most research will be centred at the University of Peradeniya, where the Faculty of Veterinary Medicine and Animal Science has made substantial contributions, and the Nuclear Medicine Unit of the Medical School will collaborate in the ratiation measurements. Both the United Kingdom Overseas Development Administration, through the University of Cambridge, and the International Atomic Energy Agency already have support programs in progress or planned at the University, and will be linked to this project. In addition, the Sri Lanka Department of Animal Production and Health will participate, providing equipment, facilities, and field stations. The Department will disseminate recommendations for control of T.vitulorum arising from the project.