Research Article, J Vet Sci Med Diagn Vol: 11 Issue: 8
Prevalence of Bovine Trypanosomosis, Infection Rate of Trypanosomes in Glossina pallidipes and Apparent Density of the Vectors in Two Districts of Gamo Zone, Southern Ethiopia
Department of Medical Sciences, Addis Ababa University, Addis Ababa, Ethiopia
*Corresponding Author: Yakob Bekele
Department of Medical Sciences,
Addis Ababa University,
Email: [email protected]
Received date: 22 May, 2022, Manuscript No. JVSMD-22-64567; Editor assigned date: 25 May, 2022, PreQC No. JVSMD-22-64567 (PQ); Reviewed date: 08 June, 2022, QC No. JVSMD-22-64567; Revised date: 21 July, 2022, Manuscript No. JVSMD-22-64567 (R); Published date: 28 July, 2022, DOI: 10.4172/2325-9590.100035.
Citation: Bekele Y, (2022) Prevalence of Bovine Trypanosomosis, Infection Rate of Trypanosomes in Glossina pallidipes and Apparent Density of the Vectors in Two Districts of Gamo Zone, Southern Ethiopia. J Vet Sci Med Diagn 11:8.
A cross sectional study were conducted from November 2020 to April 2021 in two districts of Gamo Zone, southern Ethiopia to determine the prevalence of bovine trypanosomosis, infection rate of trypanosome in G. pallidipes, and its vector density. Blood samples were collected from 384 randomly selected cattle and examined using conventional parasitological and hematological techniques. The overall prevalence of bovine trypanosome infection recorded in the study area was 20 (5.2%). Most of the infections were due to Trypanosoma congolense 10 (2.6%) followed by Trypanosoma vivax 8 (2.08%) and 2 (0.52%) by T. brucei. This study showed statistically significant association (p24%) value was found to be infected by trypanosomes. among the total 167 (43.38%) anemic cattle, 149 (38.7%) were aparasitaemic. In an attempt to determine tsetse fly population density, flies were trapped using baited stationary NGU traps. A total of 1943 flies were captured during the study period; out of these, 1210 were Glossina pallidipes and the remaining were biting flies, namely Tabanus and Stomoxy with score of 718 and 15 respectively. The overall apparent density of tsetse and biting fly recorded in the study area was 10.08 fly/trap/day and 6.11 fly/trap/day respectively. The tsetse fly dissection study revealed the overall infection rate of 32 (8.33%) trypanosomes in G. pallidipes. Among the tsetse flies captured 5 (3.5%) were male and 27 (11.2%) were female. The prevalence of trypanosome infection rate was significantly higher (χ2=6.98; P=0.008) in female flies than in male flies. The high infection rate of trypanosome in the tsetse fly and its vector density indicated that, trypanosomiasis remained as the main constraint for livestock production and agriculture in the study area. Therefore, strategic and community based vector and trypanosomiasis control and preventive measures should be taken.
Keywords: G. pallidipes; Infection rate; Trypanosomosis; Tsetse fly dissection; Vector density
African Animal Trypanosomosis (AAT) is among the well-known constraints to livestock production in the continent of Africa as it causes a serious and often fatal disease of livestock mainly in rural poor community and rightfully considered as a root cause of poverty and food insecurity in the Africa . It is the most serious disease of cattle which causes great socioeconomic losses in Africa. Its socioeconomic impact is reflected on direct losses due to mortality, morbidity, and reduction in milk and meat production, abortion and stillbirth .
In Ethiopia trypanosomosis is one 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 flowing the greater river basins or Abay, Omo, Ghibe and Baro with a high potential for agricultural development. It is a serious constraint to agricultural activity and livestock production in extensive areas of tsetse infested law lands. Tsetse-borne trypanosomosis is excluding some 180,000 to 200,000 km2 of agriculturally suitable lands of the west and south west of the country. As a result of the trypanosomosis threat, a large proportion of the livestock population is found in the highlands that are assumed to be tsetse free .
Tsetse flies in Ethiopia are confined to the South Western and North Western regions between longitude 33 and 38E and latitude 5 and 12? N. They infest areas which together amount to 220,000 km2. Tsetse infested areas lie in the lowlands. Currently five species of Glossina (G. m. submoristans, G. pallidipes, G. tachinoides, G. f.fuscipes and G. longipennis) were recorded from Ethiopia and except G. longipennis, all of them are widespread and significant economic importance . In most low land areas, especially the south west was highly infested with tsetse fly .
The most important trypanosome species affecting livestock in Ethiopia are T. congolense, T. vivax, T. brucei, in cattle, sheep and goat, T. evansi in camel, and T. equiperdum in horse . In Giemsa stained blood smears, the species are distinguished by their size, shape, location and size of kinetoplast, position of nucleus and the attachment and length of flagellum. Trypanosomes move actively and progress by movement of the undulating membrane and the free flagellum when present. Trypanosomes are characteristically leaf like in shape; they have single flagellum and attached to the organism by undulating membrane .
Tsetse flies (Glossina species) are the primary vectors of animal and human trypanosomosis and hurt livestock production, human health and agricultural development. These flies, after feeding on an infected host, usually remain infective for the rest of their lives. Studying of infection rate in tsetse flies is essential to obtain a reasonable indication about the risk of trypanosomosis in domestic livestock and a useful parameter to design a strategy for disease control. In Ethiopia, little studies were carried out regarding trypanosome infection rate in tsetse fly and also little studies were performed in the current study area. Tsetse transmitted animal trypanosomosis still remain as one of the largest causes of livestock production losses in Gamo zone.
Therefore; the objectives of the study were:
• To determine the prevalence of bovine trypanosomosis in the study area.
• To determine the infection rate of trypanosomes in G. pallidipes, and to indicate the risk of trypanosomosisin the study area.
• To determine apparent densities,distribution and species of tsetse fly in the study area.
• To identify the species of trypanosomes in the cattle and in the tsetse fly in the study area.
Materials and Methods
The study were conducted from November 2020 up to April 2021 at selected kebeles in Arba Minch zuria woreda and mirab abaya woreda of Gamo Zone which was located in the Southern rift valley of Ethiopia, in between 5° 57’N latitude and 37° 32’E longitude. The altitude ranges from 1200-3125 meter above sea level (m.a.s.l.) with mean annual rainfall ranging from 750 to 930 mm and mean annual temperature ranging from 14°C-32°C. The vegetation is dominantly occupied by Woody Grass Land (WGL) especially along the sides of grazing area and drainage lines and there is a height gallery of forest along the rivers. Acacia species are the most common woody vegetation in the area. This area is considered as the major tsetse infested area, where G. pallidipes and tabanus biting flies are abundant. The cattle populations in the area are more of indigenous and they are kept under traditional extensive husbandry system with communal herding. The area has a sub-humid climate with a moderately hot temperature (Figure 1) .
Figure 1: Administrative map of GamoGofa Zone and its Woredas; SNNPR; Ethiopia
The study animals were indigenous zebu cattle managed under smallholder mixed crop-livestock farming system, the animals are kept under traditional extensive husbandry system.
A cross sectional study was conducted from November, 2020 to April, 2021 to determine the prevalence of bovine trypanosomosis, infection rate of trypanosome in G. pallidipes and apparent density of the flies. The study animals were selected by using simple random sampling method based on their age, sex and body condition into account. The selected cattle were categorized according to their body condition good, medium and poor based on the appearance of short ribs, dorsal spines and tail head. The body condition was characterized good, medium and poor according to Nicholson and Butterworth .
Sample size determination and sampling method
The simple random sampling technique was used to determine prevalence of bovine trypanosomosis, infection rate trypanosome of in G. pallidipes and apparent density of the flies. The sample size can be determined based on the study type and sampling method for investigation, 95% confidence interval, 5% desired absolute precision and 50% average prevalence and 384 cattle were sampled by the following formula.
Therefore, N=1.962(0.5) (1-0.5)/(0.5)2
N=384, Where, N=required sample size, Pexp=expected prevalence, d=desired level of precision (usually 0.05).
Determination of packed cell volume: Blood samples were obtained by puncturing marginal ear vein with lancet and collected directly in to a capillary tube. The capillary tubes were placed in haematocrit centrifuge with sealed end positioned outward. The tube was loaded symmetrically to ensuring good balance after screwing the rotators cover and closing the centrifuge lid, the specimens were allowed to centrifuge at 12,000 revolutions per minute for 5 minutes. Tubes were then placed in a haematocrit and readings were expressed as a percentage of packed cells to the total volume of whole blood. Animals with PCV<24% were considered to be anemic .
Buffy coat technique: Blood sample was collected from an ear vein using heparinized haematocrit capillary tube. A haematocrit tube filled with a whole blood sample up to ¾ of its length and the end was sealed with crystal sealant. The tube was centrifuged at 12000 revolutions per minute for five minutes. After centrifugation Trypanosome 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 uppermost layers of the red blood cells and 3 mm above to include the plasma. The content of capillary tube was expressed on to slide, homogenized on to clean slide and covered with cover slip. The slide was examined under x40 objective x10 eyepiece for the movement of the parasites .
Thin blood smear: Drop of blood from a haematocrit capillary tube applied to clean slide and spread by using another clean side at angle of 450, air dried and fixed for 2 minutes in methyl alcohol, then immersed in Giemsa stain (1:10 solution) for 50 minutes drained and washed of excess distilled water, allowed to dry by standing up right on the rack and was examined under microscope with oil immersion objective lens . In Giemsa stained smears the species were distinguished by their size, shape, location and size of the kinetoplast, position .
Entomological survey: A total of 40 monoconical standard traps were deployed in the study area for tsetse fly trapping. All traps were baited uniformly with octenol (1-oct-3-nel), acetone and three weeks old cow urine . All odours were placed on the ground about 30 cm upwind of the trap. The poles of traps were greased to prevent fly predators, mainly ants. Traps were stayed at the site of deployment for a period of 72 hrs before collection. Trap deployment sites were selected to represent all vegetation type/habitat that could be related to fly multiplication, behavior, feeding, and other related aspects. After 72 hrs of deployment, the catchments of each trap were sorted by fly species and then counted. The apparent density of the tsetse fly was calculated as the number of tsetse catch/trap/day . The flies were collected from the trap and before dissecting them the number of each sex of tsetse flies were recorded. Tsetse flies were identified as male or female by examining the posterior end of the abdomen. The male fly has a lump on the ventral side of the abdomen (hypophgeum) at the posterior end but not in the female flies.
Dissection of tsetse flies and microscopic examination: Before starting to dissect tsetse flies, the species of each fly were differentiated and recorded on data record sheet. In Glossina pallidipes the last two tarsal segments of the hind leg has dark color, all tarsal segments of the front leg had pale color, while in G. fuscipes fuscipes, most of the tarsal segments of the hind leg had dark color and the general color of the abdomen was very dark on the dorsal side. Tsetse flies were identified as male or female by examining the posterior end of the abdomen. The male fly has a lump on the ventral side of the abdomen (hypopygium) at the posterior end but not in the female flies . Wings were removed from the flies. Then the legs of the flies were removed. The dissections were carried out as described by the FAO Training manual for tsetse control personnel. The freshly killed tsetse flies were dissected under a dissecting microscope by using 0.9% saline solution. The proboscis, midgut and salivary glands were examined.
Data analysis and management: Raw data were entered into a microsoft excel spreadsheet and descriptive statistics were used to summarize the data. STATA version 14.2 statistical software programs were used to analyze the data. The point prevalence was calculated for all data as the number of infected individuals divided by the number of individuals examined and multiplied by 100. The association between the prevalence of trypanosome infection and risk factors were assessed by chi-square test (χ2).The test result was considered significant when the calculated p-value was less than 0.05 at 95% confidence interval.
A total of 384 blood sample from cattle were examined to determine the prevalence of bovine trypanosomiasis. Among these, 20 (5.2%) of the animals were found infected with trypanosomes. Of the total positive animals, 10 (2.6%), 8 (2.08%) and 2 (0.52%) were infected with T. congolense, T. vivax and T. brucei respectively. The prevalence of trypanosomes on the basis of species of trypanosome showed statistically significant difference (p<0.05) (Table 1). The prevalence of trypanosome infection in different peasant association was 6.1%, 6%, 5.5%, 3.8% and 3.4% in Gantakanchama, shara, ugayehu, faragosa and fura respectively. The highest prevalence of trypanosome infection was found in Gantakanchama and lowest was in fura. There was no statistically significant variation in trypanosome infection rate among the five study sites (p>0.05).
Table 1: Prevalence of bovine trypanosomosis on the basis of trypanosome species.
The prevalence of trypanosome infection according to sex categories was 15 (6.33%) in female and 5 (3.9%) male cattle (Table 2) but there was no statistically significant difference (p>0.05). Prevalence of trypanosomosis varied among age groups (Table 2) and he highest prevalence was observed in old cattle aged x>7 years t (5.6%). Where X-represent age in terms of years. The prevalence of bovine trypanosomosis on the basis of body condition score graded as good, medium, poor, and was found to be 5.21%, 5.56%, and 5.84%respectively (Table 2). Statistically, there is no significant difference between different body conditioned animals (P <0.05).
Table 2: Prevalence of bovine trypanosomiasis.
Out of 384 examined animals, 20 of them were positive for trypanosome infection and the mean PCV value of positive animals was 18.45 ± 3.4 % with an interval of 16.86 ± 3.4% (Lower boundary) to 20.04 ± 3.4% (upper boundary) and in the remaining 365 animals the parasite of disease was not detected. The mean PCV value of trypanosome negative animals was 24.89 ± 4.81% with an interval of 24.39% lower limit and 25.38 ± 4.81% higher limits. In current finding, the overall mean PCV value was 24.55 ± 4.96% with 24.06-25.05 class intervals. Statistically there is significant association in between trypanosome infection and anemic status of the animals. X2= 18.67, p=0.000 (Table 3).
Table 3: Mean PCV values and status of anemia.
A total of 1943 flies were caught at the time of the study; out of these 1210 belong to tsetse fly of the genus Glossina and the remaining was shared by other genera (biting flies), namely Tabanus and Stomoxy with score of 718 and 15 respectively. Only one tsetse species has been identified, Glossina pallidipes at study site. The overall apparent density of tsetse and biting fly obtained in the study area was 10.08 fly/trap/day and 6.11 fly/trap/day respectively. Therefore, the overall apparent density of tsetse fly at five different PAs level was found 5.76%, 12.52%, 21.03%, 0% and 1.25% Gantakanchama, shara, Ugayehu, Fura and Faragosa respectively (Table 4).
Table 4: Apparent density of tsetse flies trapped from the study area.
Infection rate of trypanosome in G. pallidipes
A total of 384 tsetse flies were dissected to determine the infection rates of trypanosomes in the Glossina pallidipes. Out of them, a total of 241 female and 143 male flies were dissected and 32 of them were positive for trypanosome infection. The overall infection rate of rypanosome 27 (11. 2%).in female and also 5 (3.5%) in male G. pallidipes were recorded. The infection rate of trypanosome on the t basis trypanosome species detected was found to be 3.65% by T. congolense, 2.86% by T. vivax, and 1.82% by T. brucei. Trypanosome parasites were identified in the proboscis, salivary glands and midgut of the tsetse fly. More trypanosome infections were observed in female tsetsefly (Table 5). The infection rate was significantly different with variation in sex (X2=6.98, P=0.008).
Table 5: Shows infection rate of trypanosome in G. pallidipes.
The overall prevalence of bovine trypanosomosis in the present study revealed that from a total of 384 randomly selected cattle in study area, 20 (5.2%) of them were positive for trypanosome infection. This result is slightly lower than previous reports 5.43% in Dodessa by Bekele, et al. , 6.3% in kindokoysha by Adale and yasine, et al. , 6.9% in chena by Alemayehu, et al. , 8.5% in western wollega by tasew and dugma, et al. , 18.5% in arbaminch by Terzu, 21.25% in bambasi by yalew and fantahun and 27.5% in Arba Minch by Zacharias and Tesfahiwet. In contrary, Girma, et al. , Wale and Ermiyas and Dawit, et al. reported lower findings than the current study [22,23]. The reason for variable reports wasagro ecological difference of the study areas, seananal variation of the study periods, control measures of tsetse fly and trypanosomosis by national tsetse fly and trypanosomosis investigation and control center and the use prophylactics and curable treatment by the owners of the animal were included.
In the current study different species of trypanosome was detected among them the majority of the infection was due to T. congolense. Trypanosome species prevalence data from other tsetse infested regions of Ethiopia indicates that T. congolense is the most prevalent species in cattle. The higher proportion of T. congolence infection in study area was in line with reports of Wale and Ermias and Zelalem et al. . And this prevalence of T. congolense infection in cattle may be due to high number of serological variation of T. congelencse as compared with T. vivax and the development of better immune response to T. vivax by infected animal . The ratio of T. Congolese, T. vivax and T. brucei was 5: 4:1 indicating high Trypanosome infection was due to T. Congolese in current study.
During the present study period, the prevalence of bovine trypanosomosis was assessed between sexes of animals and among 20 trypanosome positive animals; 15 (6.33%) of them were female animals and 5 (3.9%) of them were male animals. This result agrees with previous results of Dawit, et al., Adane, Daya and Abebe Tefera, but statistically, there is no significance difference. The possible suggestion for an increase of prevalence in females in this study could be that female animals are used for milking purposes, travel long distances to an area of tsetse challenge for grazing thus, stressed by tsetse flies and by other biting flies and because of shortage of feed, female animals in study area were allowed to graze together with males. As a result, the risk of contracting trypanosomosis is high. In contrast reported that males had a significant higher prevalence of trypanosomosis than females.
The present study showed the prevalence of bovine trypanosomosis in three categories of age 5.6%, 5.26% and 4.79% in old (x>7), adult (2
This study also revealed that there is strong association between the body condition of cattle and trypanosome infection. The occurrence of infection was 5.21%, 5.56% and 5.84% in cattle with good, medium and poor body conditions, respectively. Thus, the majority of the infected animals manifest poor body conditions because of the effect of the disease. The finding agrees with the reports of earlier studies in Ethiopia. Bekele and Nasir , Ali and Bitew and mulatu, et al [27,28]. However, poor body condition could also be the consequence of other pathogens and nutritional stress .
As result shown in current study, the prevalence of bovine trypanosomosis was not significantly different in between peasant association of the study area. Prevalence of trypanosomosisi in the basis peasant association was 7 (6.1%) in Gantakanchama, 6 (5.5%) in Ugayehu, 3 (6%) in shara, 2 (3.4%) in Fura, 2 (3.8%) in faragosa. High prevalence of trypanosomosis was recorded in Gantakanchamakebelle and the lowest was in furakebelles. The reason for less prevalence in fura may be due to controlled animal movements between PA’s, presence of favorable environment, moisture and vegetation for replication of vectors.
The mean PCV value for all examined animals was 24.55 ± 4.96 SE. However, the mean PCV value of trypanosome positive animals was significantly lower (18.45 ± 3.4 SE) than that of negative animals (24.89 ± 4.81 SE). This finding is aligned with previous studies done by Ali and Bitew and Rowlands, et al. . The overall incidence of anemia was 43.38% in the research area and the presence of anemia was higher in trypanosome positive animals than negative animals. This is due to the contribution of trypanosomosis for causing anemia in infected animals. This finding agreed with previous reports by Tewelde in western Ethiopia and Desta in upper Dedesa valley of Ethiopia. Among the anemic animals 38.7% of them were negative to trypanosome infection . This is because the observed anemia can be caused by other means such as blood sucking gastrointestinal parasites and malnutrition . However, 4.75% of the cattle with normal PCV (≥ 24%) value was also found infected by trypanosome and this result is in line with Garoma report from East Wollega Zone. This might happen due to the ability of trypanosome positive animal to maintain their PCV value and technical errors of diagnosis methods used .
The overall apparent density of tsetse and biting fly obtained in the study area was 10.08 and 6.11 fly/trap/days respectively. The overall apparent density of tsetse fly was found to be higher than that of biting fly during the study period. The apparent density tsetse flies in terms of peasant association 21.03F/T/D, 12.52F/T/D, 5.76F/T/D, 1.2F/T/D, 0F/T/D was recorded in ugayehu, shara, Gantakanchama, Faragosa,and fura respectively. The apparent density of fly obtained from current study is slightly lower than that of Teka, et al. report (14.97F/T/D). The reason for decreased fly density may be the presence of considerable suppression of fly’s population by the use of insecticide impregnated targets and insecticide treated livestock undertaken in the area by national tsetse and trypanosome investigation and control center.
During present study, a total of 384 G. pallidipes were dissected to determine the infection rate trypanosome in the fly. Among them 32 flies were positive for trypanosome infection having 8.33% of overall infection rate in the study area. In terms trypanosome species detected, 3.65% of T. congolense, 2.86% of T. vivax and 1.82% of T.brucei was recorded. The current result revealed that T. congolensewas most prevalent species identified in the tsetse fly. According to Bitew, et al., Adams et al., Desta et al., T. vivax were reported in high prevalence which disagrees with current study. More trypanosome infections were observed in female tsetse with an infection rate of 11.2% while 3.5% infection rate was found in male flies [34,35]. There was significant difference in the proportion of tsetse infected with trypanosomes between male and female flies (χ2=2.01; P=0.00). The reason for a higher infection rate in females might be due to their better life expectancy as suggested by Jordan . The lower infection rate found in male flies can be explained by the low average age of traped male flies (20 days or less). The presence of high number females might result in high population density which is indicative for future high infection rate. Similar results have been reported by Dseta et al., Msangi, Leak and Mohammed and Dairri which showed that in unbiased sample, female would comprise between 70 to 80% of the mean population .
M. anisopliae significantly demonstrate high level of efficacy in the control of larval stage of C. quinquefasciatus, as 95% of larval mortality was reported at higher conidia/ml concentration of 1 x 1010. Likewise other lower concentration demonstrates relatively good larvicidal activity even at 24 hour of larval exposure. Therefore in a near future entomopathogenic can favourably compete and even replace conventional synthetic insecticide.
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