F.L. Musisi, J.C. Quiroga, B. Ngulube and G.K. Kanhai
Central Veterinary Laboratory
P.O. Box 527
Lilongwe, Malawi
East Coast fever (ECF), a Theileria parva infection in cattle, is a major cause of cattle mortality in Malawi. Moodie (1987) reported that 66% of each year's calf crop was lost before the calves reach two years of age. Most of these losses were attributed to ECF, which is widespread in the central and northern regions of Malawi. In addition, Radley (1981) observed that ECF caused a reduction in productivity and was also costly because of the money and time spent on tick control.
Project RAF/67/077, conducted at the former East African Veterinary Research Organisation, in Muguga, Kenya, demonstrated that a combination of three Theileria stocks, T. p. parva (Muguga), T. p. parva (Kiambu 5) and T. p. lawrencei (Serengeti transformed) protected cattle against a variety of T. parva parasites isolated from different parts of East Africa, with only a few breakthroughs observed. Cross-immunity experiments were conducted between the East African stocks and isolates from Malawi under project GCP/MLW/018/DEN between 1980 and 1985. On the basis of the findings, the Malawi Government authorized field immunizations against ECF in the central region, using the East African stocks as the base vaccine, but added the proviso that monitoring of the immunized cattle be continued to look for potential breakthrough strains.
In 1986 and 1987 ECF immunization field trials were conducted in Karonga District, in the northern region, to assess the protection afforded by the East African Theileria stocks. The first trial was at Kayuni in 1986, but the results were inconclusive because most of the cattle died of other tick-borne diseases. A second trial was conducted in the same district, at Kasoba, a cattle market where many cases of ECF had been reported. This report records the findings during the exposure of ECF-immunized cattle at Kasoba.
MATERIALS AND METHODS
Cattle. The cattle used in the experiment were Friesian-Malawi Zebu cross-breds approximately 2 years old, which had been raised in the southern region on farms where strict tick control is practiced and where active ECF cases have not been observed. These cattle were transported to the laboratory and maintained under a strict tick control regime. Prior to immunization, they were found to be serologically negative to T. parva schizont antigen using the indirect immunofluorescent antibody test. They were dewormed and vaccinated against blackquarter. During the trial the cattle were monitored for enlargement of lymph nodes, the presence of parasites in lymph node biopsies, the development of fever, serological responses to T. parva antigen and survival. The tick numbers on the head and ears were counted.
Stabilates. The following Theileria stocks were pooled to provide the immunizing material: T. p. parva (Muguga), T. p. parva (Kiambu 5) and T. p. lawrencei (Serengeti transformed).
Drug. Long-acting oxytetracycline (Terramycin LA, Pfizer, UK) was administered intramuscularly at 20 mg/kg bodyweight shortly before the inoculation of the stabilates, during the immunization process at the Central Veterinary Laboratory, Lilongwe.
Other Vaccines. Twenty ECF-immunized and 15 non-immunized control cattle were immunized against anaplasmosis, babesiosis and heartwater using Anaplasma centrale, Babesia bigemina, B. bovis and Cowdria ruminatium vaccines obtained from the Onderstepoort Veterinary Laboratory, South Africa.
Ticks. Clean Rhipicephalus appendiculatus nymphs reared at the Central Veterinary Laboratory were applied to reacting control cattle with schizonts in attempts to pick up the field Theileria at Kasoba.
RESULTS
The cattle were grazed communally with the local cattle in the area but were kraaled separately in the evening. The cattle were in good condition at the start of the trial but because the grazing was poor and became progressively worse, their diet had to be supplemented with maize bran and mineral blocks.
A generalized lymph node enlargement, which persisted throughout the trial period, was first detected after ten days in the field. The development of fever within the ECF-immune and ECF-naive groups of cattle is summarized in Figure 1. The generalized lymph node enlargement was followed by a fever, which was most prominent in the control group from days 21 to 34 of the exposure; the fever in the immunized group was very mild.
Detection of Theileria schizonts also coincided with the generalized lymph node enlargement. The percentages of animals in which schizonts could be detected in the control and immunized groups during the trial are shown in Figure 2. More than 70% of the cattle in the immune group had detectable schizonts between days 12 and 19, compared to 60% in the control group. The percentage of cattle with schizonts in the immune group dropped to 31% between days 20 and 27, while it rose to 80% in the control group in the same period. No schizonts could be detected in the immune group after day 27, while schizonts were detected in the control group up to the end of the trial.
Figure 1. The development of fever in Theileria parva immunized and control cattle following exposure to natural disease challenge at Kasoba, Malawi.
Babesia parasites were detected in both the immune and control groups on days 30 and 3 1, and all cattle were treated with imidocarb dipropionate.
Twelve of the 15 animals in the control group died during the trial, compared to 3 of the 19 in the ECF-immune group. The mean number of days to death for the control group was 28.5, compared to 33 in the immune group. The causes of death in the control group were as follows: 9 to ECF, 1 to a combination of heartwater and ECF, 1 to heartwater and 1 to B. bovis. The causes of death in the ECF immures were as follows: 2 to babesiosis and 1 to a combination of heartwater and babesiosis.
The common findings on gross post-mortem examination in the control group were widespread haemorrhages in the lungs, gastro-intestinal tract, kidneys, myocardium, urinary bladder, gallbladder and spleen. Splenomegaly, hepatomegaly and oedema in the lungs were evident in all cases. The brain was congested and oedematous. In the immune group, jaundice and haemorrhages were the most outstanding abnormalities in two of the three carcases while the third had only minor haemorrhaging along the coronary vessels.
The mean tick counts for the control and immune groups during the trial are shown in Figure 3. The general trend for both groups was similar: there was a rapid build-up in tick numbers in the first two weeks, reaching a peak within the next two weeks, followed by a rapid decline to about half the maximum mean tick counts. The minor differences observed between the groups were not significant.
Figure 2. The percentage of Theileria parva immunized and control cattle with detectable schizonts following exposure to natural disease challenge at Kasoba, Malawi.
A total of 915 adult R. appendiculatus, resulting from clean nymphae applied to the control cattle during the trial, were harvested in the laboratory. These have since been used in laboratory cross-immunity studies.
DISCUSSION
Although Theileria schizonts and fever were observed in the immunized group, none of these cattle died of ECF during the trial; 9 out of the 15 control cattle died of ECF. It was concluded that the immunization was successful and that the Theileria stocks used provided protection against the local Theileria parasites in the area during the trial period.
Figure 3. The mean number of ticks counted on Theileria parva immunized and control cattle during exposure at Kasoba, Malawi.
The immunization against babesiosis and heartwater was not satisfactory, as evidenced by deaths due to these diseases in both the immune and control groups of cattle. It is not known whether this apparent breakdown in the immunity was due to a failure of the immunization or the existence of entirely different immunogenic strains. It is possible that the poor grazing and generally harsh environmental conditions for these cattle accustomed to stall feeding may have contributed to and exacerbated the situation.
ACKNOWLEDGEMENTS
We thank Messrs F.G. Munkhondya and K. Chamambala and Ms. F. Mtileni for their technical assistance. Further thanks go to Dr. F.B.D. Jere, former Divisonal Veterinary Officer, Karonga ADD, for the logistical support given during the trial. This work was funded by the Malawi Government and the Food and Agriculture Organization of the United Nations Technical Cooperation Programme.
REFERENCES
Moodie, P.A. (1977). Theileriosis in Malawi. In: Henson, J.B. and Campbell, M., eds. Theileriosis: Report of a Workshop Held in Nairobi, Kenya, 7-9 December 1976. Ottawa: The International Development Research Centre, pp. 25-27.
Radley, D.E. (1981). Infection and treatment method of immunization against theileriosis. In: Irvin, A.D., Cunningham, M.P. and Young, A.S., eds. Advances in the Control of Theileriosis: Proceedings of an International Conference Held at the international Laboratory for Research on Animal Diseases, Nairobi, 9-13 February 1981. The Hague: Martinus Nijhoff, pp. 227-237.
