The invited participants were all actively engaged in the control of ECF or its vector within Africa. Initially, attention was given to a number of trials where ECF immunization (particularly by infection and treatment) was being implemented under different conditions and in different situations. The situations covered a wide spectrum of different field programs and approaches, indicating the complexities of ECF control by immunization, but at the same time emphasizing the needs, where possible, for a common approach to data collection, processing and analysis.
The first trial discussed was one in Kenya where 80 ECF-immunized Boran steers and 80 non-immunized controls were exposed to field challenge. Each of the groups was subdivided into four parallel groups which were submitted to different tick control procedures. The comparative productivity of the groups is being compared and an economic assessment of the various management systems will be made.
An alternative approach to infection and treatment immunization was described; this involves the use of extended tetracycline antibiotic cover to protect cattle during early field challenge. While it was recognized that this method is only of value where there is consistently high challenge, its advantages are that virtually no back-up or professional services are required, it is easy to apply, and cover may also be provided against other tickborne diseases.
Two large-scale extension trials in Theileria parva lawrencei enzootic areas of Kenya were considered. In the first trial, 400 Boran heifers were immunized with a locally derived composite stabilate, followed by treatment with either long-acting tetracycline (day 0) or parvaquone (day 8 after stabilate). Immunized cattle were maintained under different tick control procedures for a year. Production parameters were measured and disease incidence recorded. Immunized cattle were successfully maintained under high T p lawrencei challenge, but the incidence of other tickborne diseases, notably anaplasmosis, increased as the dipping intervals were extended. There were no significant differences between parvaquone or tetracycline-treated cattle in mortality or general disease incidence. The second large-scale trial was conducted in an area with both traditional pastoralist and ranch management systems. Initial baseline data on disease epidemiology was obtained and cattle were subsequently immunized with two locally-derived stabilates using a range of treatment regimes. The efficiency and costs of the different systems were compared. Excellent protection was obtained and productivity achieved for ranch cattle under different levels of acaricide cover, but performance of cattle under traditional management was less satisfactory due to massive tick and disease challenge, and management problems.
The programme in Malawi, using a mixture of defined T parva stocks (Muguga cocktail) to immunize cattle against ECF, has unfortunately been curtailed due to the completion of the joint National/FAO/DANIDA project. It is hoped that ECF immunization in this country will soon be revived. In the meantime it is encouraging to note that over 620 cattle have been immunized, distributed to smallholder farmers and are being followed-up in the field. The need to maintain the impetus of this work in Malawi is very important.
The Muguga cocktail has been used for immunization of cattle in Zambia, but the effects of immunization cannot yet be judged because of the low and irregular challenge that has been experienced on exposure of cattle in the field.
The performance of cattle under different levels of tick (Rhipicephalus appendiculatus or Amblyomma hebraeum) infestation has been examined in experimental and field situations in areas of Kenya, Zambia and Zimbabwe, where effects of disease have been controlled or eliminated so that the performance parameters which have been measured reflect primarily the effect of the ticks themselves. Data on tick feeding, cattle weight gain and performance have been collected. These studies will provide data on the effects of tick infestation in different cattle systems so that economically and ecologically acceptable methods of tick control can be formulated.
