E.J. Flach,* I.A. Shambwana,* T.T. Dolan,+ A. Kassim,* H. Pedersen,* M. Glass* and S.P. Morzaria+
*Department of Livestock Development
Ministry of Agriculture
P.O. Box 159
Zanzibar, Tanzania
+ International Laboratory for Research on Animal Diseases
P.O. Box 30709
Nairobi, Kenya
Immunization against Theileria parva on Unguja Island, Zanzibar, has been undertaken jointly by the Department of Livestock Development, Zanzibar, the International Laboratory for Research on Animal Diseases, the Livestock Development Project of the Food and Agriculture Organization of the United Nations and the Overseas Development Administration, U.K. Two stabilates were prepared from ticks collected from sites in the north and south of Unguja Island and characterized at the International Laboratory for Research on Animal Diseases (Morzaria, Irvin and Dolan, 1986). The stabilate, designated Zanzibar South (stabilate 2914), was found to be the more pathogenic of the two stabilates and it protected against challenge with the Zanzibar North stock. The stabilate was effective at a 1:10 dilution when Used in infection-and-treatment immunization of cattle with two treatments of long-acting oxytetracycline (Terramycin LA, Pfizer) at 20 mg/kg on days 0 and 4.
In October 1986 an immunization trial (trial 1) was carried out on Unguja using the Zanzibar South stock (stabilate 2914). Twenty-two Bos taurus calves were immunized and exposed to natural challenge together with 11 unimmunized controls. The calves were exposed at Kizimbani (Central Unguja), Tunguu (Southern Unguja) and again at Kizimbani over a three-month period. All 33 animals reacted to East Coast fever (ECF) at least once and 5 unimmunized cattle died of uncomplicated ECF. None of the immunized animals died of uncomplicated ECF. Three other controls and 8 immunized animals died of a complicated syndrome involving severe anaemia, which affected most of the trial animals. Low numbers of T. parva schizonts could be found in necropsied animals, but in addition, T. mutans was detected in all anaemic animals and Anaplasma marginale, Babesia bigemina and possibly B. bovis in some. Other complications were a very high tick challenge at Tunguu (head counts of up to 200-250 ticks), turning sickness (one animal) and heartwater (one animal).
Sixteen survivors from trial 1 were re-exposed in the second trial (August-December 1987), together with twelve Bos taurus calves, six of which were immunized with the other six being controls. They were exposed at Kipange (northern Unguja) for 20 days and encountered a heavy tick challenge of 60-100 adult R. appendiculatus. The ECF reactions are summarized in Table 1. The unimmunized control animals had earlier and more severe reactions than the newly immunized cattle. Six survivors from trial 1 reacted and one died of ECF. Two major complications, heartwater and anaemia, were encountered. Heartwater killed six animals, five of which were survivors from trial 1, and anaemia affected the new calves, with marked falls in packed cell volume (to 8%). There was an association between the degree of anaemia and the mean T. mutans piroplasm parasitaemia, which suggested that concurrent T. mutans and T. parva infections were the main causes of anaemia. However, B. bigemina and B. bovis were detected in some of the animals, despite prophylactic treatment with imidocarb diproprionate (Imizol, Wellcome). One animal had A. marginale.
Table 1. Unguja ECF immunization trial 2: exposure reactions
|
Group |
Number of animals |
Mean number of days to: |
Cause of death |
|||
|
Schizonts |
Fever |
Piroplasms |
Death |
|||
|
Immunized |
6 |
21.3(6) |
21.7 (6) |
21.3 (6) |
40.0 (2) |
1 ECF plus anaemia, A. marginale and T. mutans |
|
Unimmunized controls |
6 |
19.4 (5) |
20.3 (6) |
20.5 (6) |
26.3 (3) |
3 ECF |
|
Survivors |
16 |
24,5 (6) |
23.4(14) |
25.4(11) |
27.9 (7) |
1 ECF |
|
Trial 1 |
|
|
|
|
|
5 heartwater |
Numbers in parentheses: number of animals.
In the third trial, 5 survivors from trial 2 and 17 cross-bred (Jersy × local Zebu) calves on loan from smallholder farmers were exposed for 5 weeks at Tungau (the second exposure site in trial 1). Ten of these cross-bred calves had antibodies to T. parva despite farmers, efforts to apply acaricide weekly. Twelve animals, including four which were serologically negative, were immunized. The immunization was well tolerated except for one calf, which had a moderate reaction and was treated with parvaquone (Clexon, Wellcome). The tick challenge at Tunguu was low (body counts of 6-10 adult R. appendiculatus). Theileria parva schizonts were detected in only four animals, two controls and two newly immunized calves. One of the controls died of ECF.
During these trials 40 animals were immunized with the Zanzibar South stabilate; there was only one adverse reaction. Susceptible control cattle had earlier and more severe ECF reactions when exposed to field challenge (Table 2). However, there have been many deaths in both immunized and control groups associated with other tick-borne diseases. During these trials Cowdria ruminantium and B. bovis were confirmed on the island. The anaemic syndrome, affecting particularly the cattle in the first trial, was in part attributed to T. mutans and these cattle appeared to be immune to this syndrome on subsequent exposure. It is clear that ECF can be controlled by immunization but that immunization must be part of an integrated strategy of tick and tick-borne disease control. In pursuing this aim of controlling tick-borne disease through immunization of calves born in the artificial insemination scheme, Ministry of Livestock Development officials wish to adopt ECF immunization together with immunization against heartwater and T. mutans, using locally isolated parasites.
Table 2. Summary of Unguja ECF immunization trials
|
Group |
No. of animals |
Mean number of days to: |
Cause of death |
|||||
|
Schizonts |
Fever |
Piroplasms |
Death |
ECF with |
Other |
|||
|
ECF |
other |
|||||||
|
Immunized |
40 |
27.8 (22) |
27.7 (27) |
27.3 (31) |
40.3 (5) |
1 |
2 |
15 |
|
Controls |
22 |
25.2(15) |
24.8(17) |
25.6(16) |
30.4(9) |
9 |
2 |
3 |
Numbers in parentheses: number of animals.
ACKNOWLEDGEMENTS
E.J. Flach was supported by a Post-Graduate Award Training Scheme grant from the Overseas Development Administration, U.K. H. Pedersen and M. Glass were staff members of the Food and Agriculture Organization of the United Nations Project.
REFERENCE
Morzaria, S.P., Irvin, A.D. and Dolan, T.T. (1986). Immunization against East Coast fever: isolation and characterisation of Theileria parva stocks from Unguja and Pemba for use in infection and treatment. ILRAD Technical Report. Nairobi: International Laboratory for Research on Animal
