livestock/wildlife ecozone of Northern Tanzania

Aim: Tsetse-transmitted animal and human trypanosomosis is considered to be one of the major constraints to improved livestock and agricultural production in sub-Saharan Africa. A cross sectional survey to determine the prevalence of trypanosomosis and identifying trypanosome species infecting cattle was conducted in Makuyuni division, Arusha region of northern Tanzania, an area where livestock and wildlife graze together. Materials and methods: A total of 239 indigenous Tanzania short horn zebu cattle at four different villages, and of different ages and sex, were randomly selected and sampled. Field examination of Giemsa stained thick and thin blood smears was undertaken. Results: The overall prevalence of slides positive for bovine trypanosomosis was 5% (95% [confidence interval], CI = 2.68.6). The prevalence was significantly higher in Mswaki juu village (7%) and lower in Ortukai (3%). Of the positive cattle, 8/12 (66.6%) had infections with T. vivax and 4/12 (33.3%) T. congolense. No cases of T. brucei were detected. Animals with poor (13.7%) body score were significantly associated with high prevalence of trypanosomes infection than animals with good (2.7%) score. Prevalence of trypanosomes infections was significantly higher in males (8.42%) than in females (2.47%) and increased markedly in cattle aged >4.5 years, with no significant difference among the age group. Conclusion: Because of the risk of trypanosomosis in the Mswaki juu, a locality which is close to a wildlife Reserve; integrated tsetse and trypanosomosis control strategies need to be improved and enforced.


Introduction
and human trypanosomosis is the vector-tsetse fly distributions [3].The main field vectors for Tsetse-transmitted animal and human trypanotransmission of trypanosomosis includes the seven somosis is considered to be one of the major species of Glossina, namely G. morsitans, G. constraints to improved livestock and agricultural pallidipes, G. longipennis, G. brevipalpis, G. austeni, production in sub-Saharan Africa (SSA) [1].While G. swynertonni and G. fuscipes [3].Past records of the tsetse-borne trypanosomosis is excluding some prevalence of the disease in Tanzania concentrated 13,127,000 ha of agriculturally suitable land for mostly in tsetse endemic areas and there is a paucity of livestock and wildlife grazing in Tanzania; 11 million information for areas that were considered to have head of cattle, 7 million small ruminants, nearly 4 lower densities of flies as in the Maasai plains/steppes million people and 2 million wildlife animal species or wildlife livestock ecosystem or interface areas are at the risk of contracting trypanosomosis at any one [4,5].Evidence of human specific trypanosomes time [2], though these figures many vary over years.
species, namely T. brucei rhodesiense, have been The most important tsetse-borne diseases in demonstrated in livestock/ wildlife ecosystem areas Tanzania include bovine and human trypanosomosis [5][6][7].For example, tsetse surveys carried out on the caused by the four major species of salvarian areas adjacent to the Tarangire National Park revealed trypanosomes namely, T. congolense, T. vivax and T.
apparently high tsetse densities of G. swynnertoni and brucei brucei and T. brucei rhodesiense.One of the G. pallidipes, the main vectors for T. brucei major factors influencing the transmission of animal rhodesiense [8].However reports on the situation of study.The smallest administrative units (villages) and wildlife and domestic animal trypanosomosis are farms were selected by stratified random sampling largely unknown.Given the situation of animal method.First, all villages were classified according to trypanosomosis and the importance of domestic and wards.Two villages from each of the two wards were wild animals as reservoirs for T. brucei rhodesiense then selected using random numbers to give a total of 4 [6,9], a survey was carried out on villages adjacent to villages.All villages were eligible for selection.In the Tarangire National park so as to form a basis for second stage, through collaboration with division justifying the planned implementation of the livestock field officer, a list of all household owning integrated tsetse and trypanosomosis control measures cattle (subsequently referred to as farms) was on the area [10].
compiled and ten from each village selected, using The objective of this parasitologal survey was random numbers, to give a total of 40 farms.therefore, (i) to estimate the prevalence of bovine The prevalence of trypanosomes infections has trypanosomosis, (ii) identify the trypanosome species not known a priori then 30% prevalence and 5% involved, and (iii) assess the relationship between tolerable error were assumed when determining the trypanosomes prevalence and some risk factors desired size of cattle to be sampled.The sample size responsible for maintenance and transmitting the (239) was determined according to the method disease in the study area.
described by Thrusfield [11].The age of the selected animals was determined by dentition and categorized

Materials and Methods
as follows: immature, 1.5-2.5 years old; mature, >2.5-Study area: The study was conducted in four villages 4.5 years old; and older >4.5 years old.Selected belonging to Makuyuni division, Monduli district, animals were restrained in a kraal or boma using sisal Arusha region.The division is located 80 km South ropes and nose rings.Thin blood was drawn from ear vein using a sharp hypodermic needle.A drop of blood West of Arusha town.The criterion for selection of the was taken near one end of the clean glass slide and Makuyuni division was the high densities of cattle and another slide used to prepare the blood smear.the close proximity to the 2 major wildlife parks, Prepared blood smears were air-dried, labelled along namely Tarangire to the south and Lake Manyara to the with collection of animal bio-data, i.e. sex, body north.Geographically, Makuyuni division lies at 0 0 condition score (BCS) at a time of visit, categorized as latitude 03 34'04" South and 036 05'01" East.The area 'poor' or 'good'.is semi-arid with annual average rainfall of 600-700 mm and an elevation of 1200 m above sea level.The Parasitological examination: The dried blood vegetation is mainly Acacia cammiphora bushland, smears were fixed in absolute methyl alcohol for 5 min wooded savanna with short grass.The rains are and allowed to dry.The dry smears were placed in a normally concentrated in two seasons: from the end of glass staining jar containing working 10% Giemsa March to May, and the end of October to December.stain solution for 20 min.Subsequently the smears 0 Mean temperature ranges from 15 to 30 C. were taken out and washed with phosphate buffer Administratively, Makuyuni division is composed of 2 solution (PBS) to remove excess stain.The slides were wards and 8 villages.The study was carried out from allowed to dry in air and then examined by microscope October to November 2006.
under oil immersion with a magnification of 100x objective lens [12].Ten microscopic fields in each Cattle husbandry system: The study animals were smear were examined in order to establish whether the indigenous breeds of cattle, Tanzania short horn zebu smear was positive or negative.Species identification (TSHZ) reared under extensive husbandry which was confirmed by morphological examination of allows free grazing, usually mixed with livestock from trypanosomes on Giemsa stained thin blood smear as other villages and wildlife.The animals are housed at described by Murray et al., [13].night in bomas or kraals constructed from thorny tree branches to protect them from thieves and predators.Ethical consideration: During the survey visits, the The breeding system used is natural mating, with bulls interviewers introduced themselves and explained the running freely with females all year round.No objectives and methodology of the study to all cattle supplementary feeding is given.
owners or their representative.Verbal consent was then sought from all the interviewees before

Study animal selection and sampling strategy:
To increase the geographical extent of the study, the proceeding.Approval and clearance for the study was two wards of Makuyuni division were included in the obtained from the District Veterinary office.

Statistical analysis: Data collected from each study
The prevalence of trypanosomosis varied among animal and laboratory analyses were coded into sampling villages.Highly significant difference was appropriate variables and entered in Epi-info (version observed between Mswaki juu and Ortukai, whereas 6.04d, CDC, Atlanta, USA).Biostatistical analysis no significant difference was observed between was performed using Epi-info (version 6.04, CDC, Mswaki juu and Makuyuni.With respect to body Atlanta, USA).The point prevalence (%) was condition score, prevalence was significantly higher in calculated for all data as the number of infected animals with poor score than good score (13.7% vs. individuals divided by the number of individuals 2.7%).The difference in trypanosomes infections sampled x 100.Categorical data were analyzed by among the different age categories was not significant.2 using Chi-square (÷ ) test of independence.In all the However, the highest proportion of positives animals analyses, a value of p < 0.05 was considered significant.
was observed at age group > 4.5 years old.

Results Discussion
Results of Giemsa stained blood smear Microscopic examination of blood smears was examination in cattle are given in Table -1.Out of the used in the present study because of its simplicity and total 239 cattle examined, trypanosomes were easy handling, even in a developing country, in detected in 12 (5%; 95%Confidence interval [CI] = addition to lacks of the equipments needed for ELISA 2.6-8.6)animals.Trypanosome infection was found in and PCR in its rural districts.Magona et al., [14] all surveyed villages.Overall, T. vivax was the reported 78% sensitivity and 27% specificity when predominant species identified (8/12; 66.6%) compared to gold standard tests, i.e.ELISA and PCR.followed by T. congolense (4/12; 33.

3%). T. brucei
The results of the study revealed that T. vivax is the most prevalent trypanosomes specie in the study was not detected in this survey.Significant factors population that constituted 66%, followed by T. influencing prevalence of trypanosome infection are congolense (33%).given in Table-2.A significantly higher prevalence of The overall prevalence of trypanosomes trypanosomes infection was recorded in males infections recorded in the present study (5%) was compared to females.,15] and in Mtwara region, southern appearing to be more resistant to trypanosomosis than Tanzania [16] but slightly higher to the 1.3% recorded older animals [23].Similar patterns, though based on in mixed crossbred and indigenous TSHZ in the same serology, have been observed in earlier studies in region, Morogroro [17].However, the low prevalence Burkina Faso [28] and Ghana [29] involving rate could be perhaps due to the limited number (10) of trypanotolerant cattle.microscopic fields examined and the use of less The differences in trypanosomosis prevalence sensitive diagnostic tool (thin blood smear) in this across ages are probably influenced by livestock study.
management systems used in such areas [30].The relevant data from western Africa, East and However, further research is required to elucidate the central Africa, and from other environments similar to role of management systems and the interaction those found in Tanzania, also indicate bovine between age and the different livestock management systems on the trypanosomes infection in different trypanosomosis is prevalent and wide spread among cattle ages and breeds.cattle populations.For examples in other buffy coat Consistent to other studies on bovine trypanoand thin blood smear-based investigations, prevalences somosis, males were found to be more prone to of 8.4%, 1.6%, 14.6%, 20.4%, 13.5% and 36% have trypanosomes infection and susceptible to been reported in Nigeria, Chad, Cameroon, Ethiopia, trypanosomosis than females [31].In agreement to Zambia and Mozambique respectively [16,18,19,20, this study, a similar report in Ethiopia [32] indicated 21,22].The apparent geographical variation in that the exposure rate and the proportion of prevalences may reflect differences in the levels of cattle trypanosomes parasite positive were higher among management system, regular use of trypanosome males than females.This may reflect the lowered chemoprophylaxis, breeds, resistance to parasite and immunity developed in animals following exposure to distribution and challenges by fly vectors [23,24,25].
parasite [33,34].Some studies have shown that Two trypanosomes species, T .congolenseand animals infected with T.vivax develop immunity more T.vivax were identified in this study, with the latter readily than T. congolense infected [35].Also there is consistently being more common than T. congolense.evidence that T. vivax is less virulent and consequently This is the first report of trypanosomes infections in cattle develop tolerance to T. vivax more easily than T. cattle in the study area.It was also evident that the congolense.The present study revealed a lower prevalence of trypanosomes was higher in Mswaki prevalence of T. congolense from the study villages, juu, a village which share border with Tarangire which might be due to the lowered development of National Park, than other surveyed villages.The immunity in the cattle following exposure to this differences observed in trypanosomes infections parasite [27].In agreement with this hypothesis, between the four villages, which are approximately animals with poor body score were at a higher risk of 15-20 km apart, may be attributed to differences in the trypanosomosis than their in good health looking tsetse challenges or cattle management practices.counterparts.

Potential haematophagous insect vector other than
In this study, no attempt was made to undertake tsetse flies, including mechanical insect vectors such detailed investigations such as packed cell volume as Stomoxy spp., Tabanus spp.and Haematopota spp., (PCV) profiles and entomological surveys, to are also abundant in this livestock-wildlife interface determine the level of anemia, challenges and species zone, and the presence of game animals such antelopes of fly vectors present in the study area.Furthermore, and other ungulates are generally accepted to be the detailed investigation of other potential risk factors i.e. reservoir hosts of T.vivax from which the infections cattle/ wild animal density and contact, vector and are transmitted to domestic ruminants [26].
parasite control regime and their association with In the present study, there was no significant trypanosomes infections were not undertaken.difference between the prevalence of trypanosomes Resources constraints affecting logistics and infections recorded between animal age groups, laboratory capacity were the main reason.However, supporting the observations made elsewhere [17,27].
information from previous entomological survey in Although the prevalence among animal category of the areas close to the surveyed villages has shown >4.5 years were observed to be higher when compared substantial flies and other biting flies such as Tabanus to age group 1.5 to 4.5 years, one hypothesis that can and Stomoxys spp.A further study to disclose the be advanced is perhaps this trend simply reflects the

Table - 1
. Prevalence of trypanosome infections and species of trypanosomes identified in cattle

Table - 2
[23]alysis of the association of various factors with prevalence of trypanosome infection in cattle much lower than the corresponding values reported, number of 'exposure years' as young stock age[23].for indigenous TSHZ of similar age range in Some studies have shown young Boran calves generally Morogoro [5 Cis = confidence intervals, =chi-square test, P = level of significance, BCS = body condition score 2 ÷