K. M. Biwi¹, A. R. Rabia¹ and T. T. Dolan²
1. Ministry of Agriculture, Livestock and Natural Resources, P.O. Box 159, Zanzibar, Tanzania
2. International Laboratory for Research on Animal Diseases (ILRAD), P.O. Box 30709, Nairobi, Kenya
Introduction
Development of stabilate
Trials conducted
Degrees of immunity
Protection against ECF in other areas of Unguja
ECF challenge to immunised cattle
Other experiences gained
Future prospects
Conclusion
References
|
Summary Concern about the introduction of the T. parva strain unknown in Zanzibar by using the Muguga cocktail for immunisation against East Coast fever led the Government to request ILRAD to develop a vaccine stabilate using T. parva strains found in Unguja and Pemba. Tests by researchers finally came up with the Zanzibar South stabilate and the Pemba Mnarani stabilate for immunisation against ECF in Unguja and Pemba, respectively. Trials carried out in Unguja showed that the Zanzibar South stabilate protected cattle against ECF after immunisation. Field immunisation, which started in 1990, has been well accepted by smallholder farmers. Five hundred Bos taurus cattle and their crosses have been immunised and the work is still in progress. However, further work on immunisation against other tick-borne diseases, particularly babesiosis, needs to be undertaken. Trials in Pemba which have lagged behind need to be completed so that field immunization in Pemba can start as soon as possible. Experience gained so far indicates that immunisation against ECF coupled with strategic dipping is crucial for the development of small holder dairy industry in Zanzibar. |
Zanzibar comprises two main islands, Unguja and Pemba, situated in the Indian Ocean off the coast of East Africa. The islands have a total area of 2332 km² (Unguja 1464 km², Pemba 868 km²). Currently the human population is estimated around 650,000 and is growing at 2.7% per annum.
Unguja and Pemba have an equatorial type climate which is hot and humid with a bimodal rainfall pattern. Unguja receives an average annual rainfall of 1575 mm, while Pemba receives 2083 mm. The mean maximum temperatures for Unguja and Pemba are 33.5° and 32.1° Celsius, respectively, while the minimum temperatures are 18.9° and 21.3° Celsius, respectively.
According to the 1978 livestock census, the cattle population was 61,140, of which slightly more than half were in Pemba. The population of sheep, goats and donkeys was 418, 17,700 and 670, respectively. Currently, it is estimated that there are 75,000 cattle of which 4-5% are Jersey, Friesian and crosses of these breeds with the local zebu breed. The rest of the cattle are indigenous East African Shorthorned Zebu.
The climate in Zanzibar is ideal for ticks. Surveys conducted by Newson (1976), Tatchell (1976) and Irvin (1984) showed predominance of the following tick species:
· Rhipicephalus appendiculatus - vector of ECF
· Rhipicephalus evertsi - not an important vector
· Amblyomma variegatum - vector of heartwater
· Boophilus microplus - vector of babesiosis and anaplasmosis.
There is evidence that East Coast fever (ECF), caused by Theileria parva, is the major fatal disease in cattle in Zanzibar and that exotic and crossbred cattle are more susceptible to it than is the indigenous zebu. A survey conducted by Juma and Shambwana (1985) showed that 31% of crossbred cattle died of ECF between one and two years old age, compared with 10% of the indigenous zebu. An epidemiological survey carried out by Rushigajiki (1990) confirmed the importance of ECF. Out of 3027 blood samples from cattle in Unguja, 30% were found to contain Theileria. Infection rate was up to 100% in some localities, particularly those with higher rainfall.
Traditionally, ECF has been controlled through tick control using dipping or spraying with acaricides. However, acaricides are increasingly expensive and environmentally hazardous. Recently, Parvaquone Clexon (Coopers) has become an important drug for treatment of the disease and immunisation is being applied more widely.
This paper discusses ECF immunisation in Zanzibar, its historical background, approaches, experiences so far gained and future prospects for its use.
In the early 1980s, although much publicity had already been given to the use of a combination of three East African stocks of the Muguga cocktail for immunisation against ECF, Zanzibar was concerned by its introduction. The principle concern focused on the possibility of introducing strains of T. parva unknown in Zanzibar.
It was therefore decided that assistance should be sought to develop vaccines using the T. parva strains common in Unguja and Pemba, with assistance from the International Laboratory for Research on Animal Diseases (ILRAD).
Missions to Zanzibar by Irvin (1984) and Irvin and Morzaria (1985) and the subsequent isolation and characterisation of the indigenous T. parva strains from Unguja and Pemba by Morzaria et al (1986) developed what are known as Zanzibar South and Pemba Mnarani stabilates. These stabilates were found to be protective against T. parva strains in Unguja and Pemba, respectively, and were recommended for use in immunisation. The stabilates stored at ILRAD were made available when necessary in Unguja and Pemba for immunisation.
Immunisation trials commenced in 1986 and ended in 1990 when field immunisation started. In these trials the objectives were to:
· test immunity against T. parva as measured by serological means obtained using the indirect Fluorescence Antibody Test (FAT) (Burridge and Kimber, 1972) before and after infection with the stabilate· test whether T. parva Zanzibar South stabilate protected against ECF in other areas of Unguja
· compare the protection against theileriosis of recently immunised cattle with the immunity of surviving cattle from previous trials.
Table 1 shows the results of serological tests before immunisation (day 0), 28 days after immunisation and 63 days after exposure to tick challenge.
Table 1. Mean serological results: T. parva antibody titres.
|
Group |
0 days |
28 days |
63 days |
|
i immunised |
0 |
3400 |
2440 |
|
ii immunized |
0 |
3400 |
5000 |
|
iii immunized |
0 |
3175 |
2714 |
|
iv immunised |
0 |
2600 |
3000 |
|
v control |
0 |
0 |
0 |
|
vi control |
0 |
0 |
0 |
Source: Rabia (1989)
In this trial, which involved 30 calves aged between four and nine months divided into six groups, the results showed very high antibody titres as a result of T. parva immunisation. The value at which an animal was considered to have contracted the disease or become immune was 1:200. At day 0, all the groups showed no antibody titre for T. parva which meant that none of the animals had contracted the disease. At day 28, animals in groups i to iv showed titres significantly higher than those in control groups v and vi. The higher titres were still maintained at day 63 after exposure to tick challenge. The high antibody titre values indicated a high degree of immunity when the animals were infected with the Zanzibar South stabilate.
Immunised cattle were exposed to ECF at Tunguu, Kipange, Kizimbani and Kitumba. These areas represented a good cross-section of the whole island of Unguja in terms of cattle keeping, climate and vegetation.
According to Rabia (1987; 1988; 1989), calves immunised in those areas with the Zanzibar South stabilate and exposed to tick challenge showed effective protection against theileriosis.
Results from trial 3 reported by Rabia (1988) showed that immunised animals had no clinical signs when challenged by ticks during exposure. Only transient pyrexia was evident in three of the animals in these groups. Similarly, freshly immunised cattle evinced mild ECF reactions while the control groups had severe ECF responses and one animal died of ECF. This indicated that both previously and freshly immunised cattle were well protected. These results are shown in Table 2.
Table 2. ECF reactions in trial 3: Unguja ECF immunisation.
|
Group |
Identity of animal |
Days to schizont |
Duration schizont of (days) |
Day to pyrexia |
Duration of pyrexia |
Cause of death (days) |
|
1 | ||||||
|
Immunised |
CB5 |
30 |
2 |
- |
- |
- |
|
|
CB9 |
25 |
3 |
- |
- |
- |
|
|
CB11 |
- |
- |
- |
- |
- |
|
|
CB12 |
- |
- |
22 |
5 |
- |
|
|
CB15 |
- |
- |
18 |
1 |
- |
|
|
CB16 |
- |
- |
- |
- |
- |
|
|
CB17 |
- |
- |
32 |
1 |
- |
|
|
CB20 |
- |
- |
17 |
1 |
- |
|
|
CB21 |
- |
- |
- |
- |
- |
|
|
CB22 |
- |
- |
- |
- |
- |
|
|
CB23 |
- |
- |
58 |
1 |
- |
|
|
CB24 |
- |
- |
15 |
2 |
- |
|
2 | ||||||
|
T. mutants | ||||||
|
Control |
CB7 |
28 |
11 |
29 |
9 |
ECF(38) |
|
|
CB8 |
43 |
2 |
44 |
1 |
- |
|
|
CB13 |
- |
- |
15 |
8 |
- |
|
|
CB14 |
- |
- |
- |
- |
- |
|
|
CB18 |
- |
- |
- |
- |
- |
Source: Rabia (1988).
Immunisation against ECF proved effective in these trials and field immunisation was started in 1990. Acceptance by farmers was good, with about 500 pure-bred Jerseys, Friesians and their crosses having been immunised. However, the trials have shown that when immunisation against ECF has been completed other tick-borne diseases are being detected and are a cause for concern. The most significant tick-borne disease to surface is babesiosis.
Experience gained has also shown that anaemia and low packed cell volume (PVC) can be a problem in cattle immunised against T. parva. Other researchers (Uilenberg, 1984; Morzaria, 1988) have reported anaemia and parasitaemia during exposure of ECF immunised cattle. The anaemia syndrome has been associated with high T. mutans parasitaemia (Rabia, 1989). Poor nutrition has also been associated with the anaemia syndrome and parasitaemia (Biwi, 1991). From this experience, it has been recommended that only well-nourished cattle should be immunised, with further studies being conducted on the possible pathogenicity of T. mutans.
The age at which calves should be immunised is still in debate. While Rabia (1991) recommended six months of age as being optimal, this was in conflict with studies by de Boorder (1989) who recommended immunisation of much younger calves, at between one and two months of age. Immunisation at a later age appears to be more practical where zero-grazing is practiced and early contact with ticks can be controlled. This situation is not possible in natural grazing. On the other hand, passive immunity from the mother may interfere with immunisation at a very early age; in addition, the calf may not be able to develop an effective immune response because of its immaturity.
Field ECF immunisation has so far been successful (Dolan, 1992). Five hundred pure and crossbred cattle have been vaccinated. Farmer acceptance is very high and the work is progressing very well in Unguja.
During the trials, farmers were assured of compensation if their calves died due to ECF immunisation. This has since been waived during field immunisation as farmers accepted the risk without promise of compensation from the Government. Towards the end 1992, farmers will start to pay for the tetracycline used during immunisation as a measure to begin cost recovery for ECF immunisation.
As stated earlier, acaricides are becoming increasingly expensive and are proving hazardous to the environment. Hence, is now geared to the combined use of strategic dipping and immunisation.
The surfacing of other tick-borne disease problems, particularly babesiosis, may overshadow the usefulness of ECF immunisation. However, the problem is being further studied and contacts with the Regional Centre for Immunisation Against Tickborne Diseases in Malawi have been made for possible supply of babesia vaccine when the fear of introducing Enzootic Bovine Leukosis has been cleared by the Zanzibar Government.
In Pemba, earlier trials on ECF immunisation using Pemba Mnarani stabilate showed poor safety (Crees, 1989), the trials being associated with the death of many calves.
Subsequent trials by de Boorder (1989) also did not produce results that would recommend commencement of field immunisation in Pemba. Dr Rabia and a United Nations Volunteer, Dr Rushigajiki, are now conducting ECF immunisation trials. These trials will include similar studies to those carried out in Unguja plus work on the immunisation of calves at young ages. Field immunisation is expected to commence after these studies.
Ticks thrive in the Zanzibar climate. In areas where there has been little use of acaricides to control ticks a kind of enzootic stability between tick-borne diseases and indigenous (Bos indicus) cattle has been achieved, but high mortalities have subsequently been experienced with the Bos taurus cattle and their crosses.
ECF immunisation and strategic dipping appears to be feasible and important for the development of smallholder dairying. However, immunisation against other tick-borne diseases, particularly babesiosis, may have to be incorporated in the Zanzibar immunisation programme.
ECF immunisation trials have just started in the sister island of Pemba. This work should be hastened so that full field immunisation can be commenced as soon as possible.
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