T.S. Kavishe
Ministry of Agriculture and Livestock Development
P.O. Box 9152
Dar-es-Salaam, Tanzania
East Coast fever (ECF) has been recorded in Tanzania since the beginning of the century, but its history among traditional herdsmen is much older. Local shorthorn Zebu cattle have a natural resistance to the disease and have shown a population growth rate of about 1% per year without any specific tick control measures. If improved cattle are introduced, however, tick control methods must be used to prevent serious losses. Rhipicephalus appendiculatus is widely distributed in Tanzania (Figure 1) and ECF coincides with its distribution. The government has an established livestock improvement programme that uses livestock multiplying units and artificial insemination to increase the numbers of high-producing dairy and beef cattle and to upgrade the local Zebu stock. In addition, local and cross-bred cattle are being used as draught animals on a wider scale. The cattle population of Tanzania is estimated at 12.5 million, with an improved herd of 200000 dairy and 100000 beef cattle.
Annual veterinary reports provide figures for disease diagnosis, treatments, recoveries and deaths. These figures are compiled from data returned mainly by auxiliary veterinary personnel, in most cases from the traditional farming sector. These personnel have very limited equipment and almost no access to laboratory diagnosis. Disease reporting from the commercial sector is more accurate because of better trained personnel and some laboratory support in that sector. Nonetheless, the cases reported still represent only a small proportion of the total. The reported cases of tick-borne diseases and trypanosomiasis in 1986 are presented in Table 1. Tick-borne infections are considered as a group in Table 1 because diagnosis and treatments of these infections are based on similar clinical signs and because mixed infections often occur. Similarly, figures for trypanosomiasis are included because the clinical signs and treatments for trypanosomiasis overlap with those of tick-borne infections, and once again, because mixed infections are common.
CONTROL OF EAST COAST FEVER
The official Tanzanian policy for control of ECF and other tick-borne diseases is tick control. This policy has evolved from one of compulsory free dipping in the late sixties and early seventies to the introduction of a dipping fee in the 1980s. This has led to a drop in the number of immersions from 56 million per year in 1972 to 18 million in 1986. Approximately one-third of the 1900 dips in the country are non-functional. Tick-borne disease infections have been increasing, but the rise has not been proportional to the decline in immersions. Thus, due to the high cost of acaricides, their environmental damage and the difficulties in maintaining strict acaricidal control, control methods involving strategic dipping and enzootic stability of cattle to tick-borne infections should now be considered. Such methods would fit in well with an immunization programme for very susceptible herds.
Table 1. Reported cases of tick-borne diseases and trypanosomiasis in cattle in Tanzania, 1986
|
|
Number of cases |
Number treated |
Number cured |
Number dead |
|
East Coast fever |
83,961 |
71,284 |
64,339 |
19,562 |
|
Anaplasmosis |
57,997 |
51,419 |
48,509 |
9,484 |
|
Babesiosis |
19,355 |
17,456 |
16,798 |
2,557 |
|
Heartwater |
11,685 |
11,151 |
8,979 |
2,706 |
|
Total tick-borne diseases |
172,998 |
151,310 |
138,625 |
34,309 |
|
Trypanosomiasis |
23,592 |
- |
- |
9,148 |
TREATMENT OF EAST COAST FEVER
Several treatment regimes for ECF/tick-borne infections have been used in Tanzania, including the following:
a) oxytetracycline hydrochloride 10% at a dose rate of 1 ml/10 kg for five days
b) parvaquone (Clexon, Wellcome) at a dose rate of 10 mg/kg repeated after 48 hours
c) halofuginone (Terit, Hoechst) at a dose rate of 1.2 mg/kg repeated after 48 hours
d) a combination of halofuginone and oxytetracycline at the prescribed dose rates
e) a combination of parvaquone and oxytetracycline at the prescribed dose rates
Recoveries from combinations of the above treatments are difficult to attribute to a single compound. Before halofuginone and parvaquone became available, recoveries from ECF using tetracycline alone were about 30%. Using combinations, field observations have shown recovery rates of 56% for halofuginone and 55% for parvaquone.
The cost of the new antitheilerial drugs is prohibitive. Moreover, milk from treated animals must be withheld for 14 days after the treatment and treated animals cannot be slaughtered for human consumption for 28 days. Bearing these disadvantages in mind, the case for control by immunization is attractive.
OTHER CONTROL OPTIONS
While tick control and chemotherapy for ECF have their role in the control of tick-borne infections, zero grazing cattle is another effective control method. Few, if any, infected ticks can reach a susceptible animal that does not graze. Of course, not many cattle can be kept in this manner without a heavy capital investment. Immunizing zero-grazed animals against tick-borne infections would probably give these animals near-complete protection against these diseases.
CONCLUSION
Immunization against ECF is desirable. Once cattle are immmunized, it is expected that a low ECF challenge will be maintained. This, together with the considerable economic saving, justifies relaxation of the tick control programmes. When tick control is relaxed, however, other theilerioses and tick-borne infections will appear if they have not been included in the immunization programme. Of particular concern is T. mutans, which is reported to have caused problems when treatment of ECF was directed only at T. parva using halofuginone or parvaquone.
Disease control will be made more effective by making available basic diagnostic facilities, by making more complete records of disease occurrences and by disseminating information about disease situations more thoroughly. Unfortunately, what we have now is a collection of epidemiological information and assumptions from work done long ago, some as far back as 1967. Therefore, along with instituting an immunization programme, there should be a determined attempt to rehabilitate diagnostic services (which is being addressed) and, concerning tick-borne diseases particularly, the information on tick ecology should be updated. Serological surveys should be conducted to determine the distribution of theileriosis more accurately. Immunization programmes should be incorporated into the management of all improved commercial dairy and beef herds, as well as draft oxen in areas that can sustain R. appendiculatus.
