| Livestock Research for Rural Development 24 (8) 2012 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
A cross-sectional study was conducted with the aim of determining the prevalence of bovine Trypanosomosis and assessing possible Host-related risk factors in some selected area of Amhara region, Northwest Ethiopia, from October 2011 to March 2012.
Blood samples collected from 384 randomly selected cattle of different age groups and both sexes were screened for Trypanosomosis using the Buffy coat method. The PCV value of each animal was also measured using haematocrit reader. The overall prevalence of Trypanosomosis was found to be 2.10% and Trypanosoma vivax was the only specie identified. The dominant prevalence was observed in Amarit (4.30%) followed by Addis Amba (1.70%), however, there are no positive cases detected in and around Merawi peasant associations. Prevalence was slightly higher in females (2.50%) than males (1.70%). Both age groups were infected with trypanosome and the prevalence rate was higher in adult (2.5) than young (0.9) cattle and in good (3.6%) than in poor body condition animals (0.0%) (P>0.05).The trypanosome infection significantly influences the PCV and with mean PCV of parasitaemic and aparasitaemic animals being 21% and 28.54% respectively (p<0.05). Although the presents study revealed a low prevalence in the study area; nevertheless, a vigorous disease mitigation strategies is warranted owing to the economic implication of the disease.
Key words: age, pcv, sex, T. vivax, trypanosome
Animal Trypanosomosis is an important livestock disease in Africa which is considered as a threat to the ongoing effort on poverty alleviation in the continent (Wint et al 2010). It is a serious disease in domestic livestock that causes a significant negative impact in food production and economic growth in many parts of the world (Taylor et al 2007), particularly in sub-Saharan Africa (Cecchi et al 2008).
In Ethiopia, unlike human Trypanosomosis which is distributed in South-western administrative region in distribution, animal Trypanosmosis is among of the most important diseases limiting livestock productivity and agricultural development due to its high prevalence in the most arable and fertile land of South West and North West part of the country following the greater river basins of Abay, Omo, Ghibe and Baro, which has a high potential for agricultural development (Shimels et al 2005). Over 6 million heads of cattle and equivalent number of other livestock species are at risk of contracting the diseases. More than 20,000 heads die per annum, and annual loss attributed to the diseases is estimated to be over US$236 million, whereas loss due to reduce meat, milk and draft power is not applicable to this figure (OAU 2002).
The most important Trypanosoma species affecting cattle in Ethiopia are Trypanosoma congolense, Trypanosoma vivax and Trypanosoma brucei in cattle, sheep and goats. Camels are affected by Trypansosoma evansi which is common species in camel rearing areas of the country while equines mainly horses are affected by Tryranosoma equiperdum in some highland parts of the country (Abebe 2005).
The tsetse flies are widely distributed in the western southern and south western low lands and river valleys and 15% of the land believed to be suitable for livestock production is affected by one or more of the following species of tsetse flies; Glossina morsitans sub morsitans, G. paulidipes, G. tachinoides, G. fuscipes fuscipes and G. longipennis (Abebe, 2005). Apart from cyclical transmission of Trypanosomosis by Glossina species, mechanical transmission is a potential threat to livestock productivity in some parts of Ethiopia (Abebe and Jobre 1996). Trypanasoma vivax infection can be transmitted mechanically by several tabanide and large number of biting flies (Chernet et al 2006). Biting flies have been reported as the major cause of T. vivax infection in three highland districts bordering Lake Tana (Sinshaw et al 2006).
Although Trypanosomosis may be found almost in all parts of the Amhara National Regional State, the problem is much more severe in most areas of East Gojjam, West Gojjam and Awi administrative zones. In West part of Amhara Regional State bordering the Abay river, one of the North Western tsetse belt areas of Ethiopia, tsetse transmitted Trypanosomosis is becoming a serious threat for livestock production and agricultural activity (Shemelis et al 2005).
The Amhara Bureau of Agriculture and Rural Development has already prepared a control strategy for three years. Applying control program of tsetse and Trypanosomosis regionally, evaluating the effectiveness of the control program and identifying the challenges of the control strategy were the main objectives of the control programme. In line with this, assessment of bovine Trypanosomosis after completion of control measures is an important step to measure the effectiveness of control strategy in Mecha worda. Therefore, this study aims to determine the prevalence of bovine Trypanosomosis and to identify the major bovine infesting Trypanosoma in Mecha Woreda of west Amhara region bordering the Blue Nile River.
A study was conducted in three peasant associations (PAS) in Mecha Woreda of west Gojjam zone in Amhara Regional State, North West Ethiopia located about 525 km North West of Addis Ababa and 34 km south east of Bahir Dar the capital city of Amhara region. In Mecha Woreda the climatic condition alternate between along summer rain fall (June- September) and winter dry season (December- March) with mean annual rain fall of 1200-2000 ml. The mean temperature is between 24-27oC and altitude ranges from 1800 to 2500 m.a.s.l. The study area is located at latitude 10o 30o N and longitude 37o29o E. The land is covered by different vegetation types such as Savanna grassland, forest reverine and bush lands. Agriculture is the main economic sector in the study area employing nearly 100% of labor force. The main agricultural activities currently practiced include irrigation (modern and traditional) and mixed farming. The major agricultural products seasonally harvested include sorghum, maize, Teff, Wheat, linseed and other legume groups. In this Woreda there are 192, 556 cattle, 148 971 ovine, 23, 106 equine and 204, 181 poultry (MWARDO 2011).
The study was carried out on 384 indigenous zebu cattle of all age groups of both sexes in three selected Peasant Associations (PAs), which are managed under mixed farming system.
A cross-sectional study was conducted to establish the prevalence of bovine Trypanosomosis in Mecha woreda from October 2011 to March 2012. Since there was no previous survey conducted in the study area the sample size was determined based on the expected prevalence rate of 20% and absolute desired precision of 5% at confidence level of 95%, and the sample size was determined to be 384 based on formula given by Thrusfield (2005). Three PAs were selected purposively. In each PAs the studied cattle were herded together during the day time, hence with the assumption of 5-15 cattle in one herd, animals from the PAs were then systematically selected from the herd and Simple random sampling technique was used to select animals from the herd. During sampling, age, sex, address and body condition of the animals were recorded. Body condition for each cattle was estimated based on Nicholson and Butterworth scores (1986) with scale ranging from 1 (emaciated) to 5 (obese). The age of the animals was grouped as young (between 1 and 3 years) and adults (>= 3 years) according to the classification used by Bitew (2011).
Thin Blood Smear: A small drop of blood from a micro-hematocrit capillary tube was applied to a clean slide and spread by using another clean slide at an angle of 45°. The smear was air dried and then fixed for 2 minutes in methyl alcohol. The thin smear was flooded with Giemsa stain (1:10 solution) for 30 minutes. Excess stain was drained and washed by using distilled water. Then it was allowed to dry by standing up right on the rack and examined under the microscope (x100) oil immersion objective lens (OIE 2008).
Packed Cell Volume (PCV) Determination: Blood samples were obtained by puncturing the marginal ear vein with a lancet and collected directly into a pair of heparinised capillary tubes. The tubes were then sealed at one end with crystal seal. The capillary tubes were placed in micro-hematocrit centrifuge and were allowed to centrifuge at 12,000 revolutions per minute (rpm) for 5 minutes. After centrifugation, the capillary tubes were placed in a haematocrit reader. The length of the packed red blood cells column is expressed as a percentage of the total volume of blood. Animals with PCV less than 24% were considered to be anaemic (OIE 2008).
Buffy Coat Technique: Heparinised microhaematocrit capillary tubes, containing blood samples were centrifuged for 5 min at 12,000 rpm. After the centrifugation, trypanosomes were usually found in or just above the buffy coat layer. The capillary tube was cut using a diamond tipped pen 1 mm below the buffy coat to include the upper most layers of the red blood cells and 3 mm above to include the plasma. The content of the capillary tube was expressed onto a glass slide, and covered with cover slip. The slide was examined under x40 objective and x10 eye piece for movement of parasite (Paris et al 1982). Trypanosome species were identified according to their morphological descriptions on Giemsa stained blood film as well as movement in wet film preparations provided by (Radostitis et al 2007).
Animal and laboratory data were stored in Ms-Excel, and later exported to SPSS software version 20 for analysis. The prevalence of trypanosome infection was calculated as the number of positive slide animals as examined by Giemsa stain of thin blood film and buffy coat method divided by the total number of animals examined at the particular time (Thrusfield, 2005). Pearson’s chi-square (χ2) was carried out to determine the association of the explanatory variables (sex, age, body condition and PAs) with the prevalence of trypanosome infection and two sample student t-test was used to compare mean PCV of infected and non-infected animals, using SPSS version 20 software. P-value < 0.05 was considered significant in all analysis.
Out of the total of 384 cattle examined, 8 were positive for Trypanosomosis hence the overall prevalence rate of the study area was 2.10 %. All of the infection in this study was found to be due to Trypanosoma vivax. The prevalence rate in this study was considered to be low when compared with earlier reports from other parts of Ethiopia. This result was in close agreement with the finding of Abebayehu et al (2011) who reported a prevalence of 2.66% Trypanosomosis from Western Tigray, Northern Ethiopia. However, the result of the present study was contrary to the finding of Tesfaheywet and Abraham (2012) who reported a prevalence of 14.2% in Arbaminch due to T.vivax. Prevalence of Trypanosomosis ranging from 4.0%-9.60% due to T. vivax in highland district areas bordering Lake Tana was also documented (Sinshaw et al 2006). The ongoing application of Trypanosomosis control program in the study woreda and also the absence of tsetse flies in the current study area could have contributed for the lower prevalence. Furthermore, density fly population is another determinant factor for occurrence of Trypanosomosis, where fly population increases after the short and long rainy seasons, this lies from April to June and September to November. However, this study was conducted in November to April which is in the dry periods, hence lower fly population and consequently lower prevalence of Trypanosomosis. In support of this, Sinshaw et al (2006) revealed that reproduction and development of biting flies is best suited to the climatic conditions prevalent during the heavy rainy seasons.
Looking in to the distribution of trypanosomiasis in the peasant associations (PAs) (Table 1), the prevalence of Trypanosomosis was significantly high in Amarit followed by that of Addis Amba (p =0.048), but there wasn’t any positive cases detected in and around Merawi. The high prevalence rate observed in Amarit could be explained by the location of this PA where, it is quite closer to Wotet Abay River and expansion of Koga irrigations than other PAs which may be suitable habitat for biting flies.
|
Table 1: Prevalence of bovine Trypanosomosis in the selected peasant associations |
||||
|
Area |
Total examined |
No. positives (%) |
Prevalence (%) |
χ2 (p-value) |
|
Amarit |
140 |
6(75) |
4.30 |
6.069(0.048) |
|
Adis Amba |
120 |
2(25) |
1.70 |
|
|
Around Merawi |
124 |
0(0) |
0.0 |
|
|
Total |
384 |
8 |
2.10 |
|
In the present study, the rate of infection was compared among the various categories of age, sex and body condition (Table 2). Accordingly, there was no significant difference in the prevalence of Trypanosomosis in female animals compared to male animals (p=0.581). This result is in agreement with what was reported previously in the country (Adane and Gezahegne 2007; Abebayehu et al 2011) and this might be due to the fact that both sexes have virtually similar exposure to biting flies in grazing areas.
Similarly when the prevalence of Trypanosomosis was computed for the two age categories in this study, the infection rate in adult cattle was twice greater than the young ones (Table 2). This finding was in line with previous report of Tesfaheywet and Abraham (2012). Rowland et al (1995) in Ghibe valley indicated that suckling calves are not allowed to go out with their dams until they are weaned off. Young animals are also naturally protected to some extent by maternal antibodies (Fimmen et al 1999). This could result in low prevalence of trypanosome in the youngs.
The prevalence of Trypanosomosis under different body condition groups is indicated in Table 2. The infection rate animlas with poor body condition was slightly higher than in animals with medium body condition, but good body condition cattle were apparasitaemic for bovine Trypanosomosis. In contrast, 35.2% of apparasitaemic cattle were with poor body condition and this indicates that other factors such as diseases, nutritional factors as well as management system may have contributed for the poor body condition of cattle (Smith 2009). The absence of trypanosome infection in the good body condition animals might be related to that well-nourished animals have good level of immunity and are in a better position to resist infection, moreover there is a very rare possibility of re-establishment of infection in animals with good body condition.
|
Table 2: Prevalence of bovine Trypanosomosis based on host related risk factors |
||||
|
Host related factors |
No. Examined |
No. Positive (%) |
Prevalence (%) |
χ2 (P-value) |
|
Sex |
|
|
|
|
|
Male |
181 |
3(37.5) |
1.7 |
0.304(0.581) |
|
Female |
203 |
5(62.5) |
2.5 |
|
|
Age |
|
|
|
|
|
Young |
105 |
1(12.5) |
0.9 |
0.906(0.341) |
|
Adult |
279 |
7(87.5) |
2.5 |
|
|
Body Condition |
|
|
|
|
|
Poor |
140 |
5(62.5) |
3.6 |
4.385(0.112) |
|
Medium |
116 |
3(37.5) |
2.6 |
|
|
Good |
128 |
0(0.0) |
0.0 |
|
The packed cell volume (PCV) of aparasitemic animals falls in the range of 17.0-47% while in parasitemic cattle the PCV was in the range of 17- 25%. The overall mean PCV of the examined animals was 28.38±0.37 %. The mean PCV of parasitemic animals were significantly lower than that of the aparasitemic ones (p=0.000) (Table 3). This finding was in consent with what was reported by Haile (1996), Cherinet et al (2006), Abebayehu et al (2011), and Tesfaheywet and Abraham (2012).
Furthermore, from the total of 384 examined animals, 109 (28.4%) were anaemic having PCV < 24.0%. On the other hand among 376 non-parasitized animals 172(37.7%) had PCV < 24. The prevalence of parasitemic animals which were anemic (4.6%) was higher compared to the parasitemic animals which were not anemic (normal) (p<0.05) (Table 4). Taking the PCV value 24 to 46% as normal for zebu cattle (Blood and Radostits 2007), 62.5% of the parasitaemic and 27.66% the aparasitaemic animals have registered PCV values less than 24%. PCV values have been demonstrated to be a good indicator of trypanosomal infection (Marcoty et al 2008). The aparasitaemic cattle with PCV <24% in this study could be due to the low sensitivity of buffy coat method in chronic cases of Trypanosomosis (Picozzi et al 2002) or it might suggest that even though anaemia is characteristics of Trypanosomosis, other factors such as poor nutrition and the effect of other blood feeding parasites which ultimately cause reduction of PCV.
|
Table 3: Mean PCV value of parasitaemic and aparasitaemic animals |
|||||
|
Infection status |
No. animals |
Mean PCV |
SEM |
t-test |
p-value |
|
Pasitaemic |
8 |
21.00 |
1.16 |
6.158 |
0.000 |
|
Aparasitaemic |
376 |
28.54 |
0.38 |
|
|
|
Total/Average |
384 |
28.38 |
0.37 |
|
|
|
Table 4: Prevalence of bovine Trypanosomosis based on PCV value |
||||
|
PCV |
Total Examined |
No. Infected (%) |
Prevalence (%) |
χ2 (P-value) |
|
Anaemic (PCV<24) |
109 |
5(62.5) |
4.6 |
4.670(0.031) |
|
Normal (PCV>24) |
275 |
3(37.5) |
2.6 |
|
|
Total |
384 |
8(100) |
2.10 |
|
In general, the prevalence of trypanosome infection in the study area was low (2.10%) and all of these infections were due to Trypanosoma vivax. This low prevalence demonstrated the effectiveness of the ongoing application of control strategies in the study area. Although, low prevalence of bovine Trypanosomosis was demonstrated in the study area, the potential impact of T. vivax infection on production and productivity of cattle shall not be undermined and serious attention and further application of effective control strategies is warranted.
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Received 2 July 2012; Accepted 19 July 2012; Published 1 August 2012