A. Nambota
Central Veterinary Research Institute
P.O. Box 33980
Lusaka, Zambia
Tick-borne diseases, particularly theileriosis, pose a serious threat to the development of the cattle industry in Zambia. The first recorded case of theileriosis was in the Nakonde area of Northern Province in 1922. According to the annual reports of the Veterinary Department of Zambia, no cases of the disease were diagnosed within the country from 1928 to 1945. In 1946 theileriosis was diagnosed in Mbala District, Northern Province, and in 1947 in Chipata District, Eastern Province. Since 1947 theileriosis has spread within the Northern and Eastern provinces, throughout much of which it is now established enzootically. In 1977/78 a malignant form of theileriosis was detected in the Hufwa area of Monze District, in Southern Province. It is fairly certain that prior to this time Southern Province was free of the disease. The disease has since then become endemic in this region, which is an important cattle-raising area containing 900000 head, which is approximately 45% of the national herd.
In Zambia theileriosis manifests itself in the form of Corridor disease, caused by Theileria parva lawrencei, and East Coast fever, caused by T. p. parva Corridor disease appears mostly in Central, Lusaka and Southern provinces. East Coast fever is found in the Northern and Eastern provinces of the country, where high rainfall is common. The current cattle population of Zambia is 2.6 million, out of which 1259000 are at risk to theileriosis.
Despite concerted efforts by the government to control theileriosis, it is becoming obvious that control of this killer disease at economically accepted levels will be difficult to achieve. Considering the problems with current control methods - such as the rising costs of acaricides and antitheilerial drugs, the long distances to many dip-tanks, which discourage farmers from regular dipping, and resistance to acaricides by ticks - it became necessary to look for alternative methods of controlling theileriosis.
In view of the above the government of Zambia, with the help of the Food and Agriculture Organization of the United Nations, embarked on a theileriosis immunization programme in 1985 in the Southern Province. This project was designed to assess the following:
a) the protection provided to groups of cattle immunized using the "Muguga cocktail" against laboratory challenge with three field isolates and exposure to natural field challengeb) the "Muguga cocktail" protection for traditionally managed cattle against natural theileriosis challenge in Northeast Choma in the Southern Province, where the disease is endemic
The results of laboratory challenge and field exposure have been very successful. The (b) phase was equally successful and the data are being analysed. In this immunization programme a total of 1184 cattle 4-15 months old were eartagged and 950 of these were immunized by the infection-and-treatment method, 834 with the Muguga cocktail and 116 with T. parva (Mandali), a local isolate. Both groups were treated simultaneously with 20 mg/kg of long-acting oxytetracycline. Two hundred and thirty-four cattle served as ear-tagged controls in addition to the untagged non-immunized cattle in the area. The ear-tagged cattle were divided into two groups, group A consisting of 200 immunized and 200 control cattle and group B consisting of 750 immunized and 34 control cattle for convenience of monitoring. Group A cattle were monitored for haematocrit and serology, liveweight changes and tick control and survival; group B was monitored only for survival and serology. Forty-five cattle of the 834 Muguga cocktail immunes died between September 1986 and March 1988. Fifteen of the 45 died of theileriosis; this seems to have been due to either underdosing with long-acting oxytetracycline or overdosing with Theileria sporozoites. These cattle died in late February and early March 1987. Only one of the 116 T. parva (Mandali) immunized cattle died of theileriosis. From September 1986 to March 1988, 100 of the 234 ear-tagged control cattle died. Between December 1986 and March 1988, a total of 465 cattle died in the trial area. At least 92% of the post-mortem examinations confirmed theileriosis as the cause of death. An additional 286 cattle were treated for theileriosis during the same period from these herds.
The following problems were encountered in this project.
a) The application of immunization was slowed down considerably by the lack of suitable crushpens. These delays lead to loss in viability of the stabilates, wastage of materials and uncertainty about the success of immunization.b) Accurately estimating the weights of animals was a problem in some cases and at times resulted in either underdosing or overdosing with the long-acting oxytetracyclines.
c) Although farmers were advised to bring cattle for inspection on specific days after the immunization, several failed to do so.
d) The immunization was organized so that farmers whose cattle had been ear-tagged on a previous occasion would bring the animals on a given day at a pre-arranged time. Unfortunately, on a number of occasions farmers did not gather all the animals to be immunized, causing a waste of time and stabilates.
e) There was a great demand for immunization of adult animals, which caused difficulty: the design for this phase of the project deliberately discouraged immunizing adults because it was difficult to get proper histories of these animals and the project resources did not cater for these cattle.
These trials have demonstrated clearly that in the Southern Province, immunization against Corridor disease by infection and treatment using the Muguga cocktail and a local isolate, T. parva (Mandali), can be carried out successfully. Furthermore, immunization against theileriosis would mean dipping animals less frequently. We therefore believe that in tick-borne-disease endemic areas if cattle are immunized against theileriosis when they are young and relatively resistant to other tick-borne diseases, dipping intervals can be safely increased. This would allow limited tick-parasite challenge without the fear of lethal theileriosis breaking through. This is desirable as limited tick/parasite challenge also provides a biologically stable situation where immunity to ticks and tick-borne diseases is continually reinforced.
