Dejene, Dawit: Seroprevalence and associated risk factors of foot and mouth disease in selected Woredas of West Omo Zone, SouthWest Ethiopia
ABSTRACT
Aim and Background:
Foot and mouth disease (FMD) is a prioritized transboundary animal disease, endemic in Ethiopia, and it has a high impact on cattle production and trade nationally and internationally.
Methods:
To ascertain the sero-prevalence and identify the exposure factors connected to a seropositive FMD in cattle, a cross-sectional study was conducted in three weredas of the West Omo Zone from January to February 2022. Multistage sampling was used to take one study wereda based on agroecology from the highland, midland, and lowland of the zone. Selection of cattle herd and blood samples from cattle were taken by using a simple random method. The Statistical Package for Social Science Version 25 was used to analyze the pertinent data once it had been entered and coded into Microsoft Excel.
Results:
The study area’s FMD seroprevalence for individual cattle and at the herd level was 5.3% with a 95% confidence interval (3.51%–7.99%) and 77.78% (n=9), respectively. The high herd level recorded during the current study was evidence that the disease has spread throughout the zone. Multinomial logistic regression analysis showed the age of the animal and study wereda are significantly(p < 0.05) associated with the sero-prevalence of FMD in this study. High cattle movement to big markets and long exposure of old cattle to the disease may contribute to the significant association of the disease with these risk factors.
Conclusion:
This study showed that herd-level FMD seropositivity is high, necessitating the identification of specific FMD serotypes and the commencement of appropriate FMD prevention and control strategies in the zone.
KEYWORDS Foot and mouth disease; age; sex; cattle; sero-prevalence; West Omo zone
Introduction
The foot-and-mouth disease virus (FMDV), which causes foot and mouth disease (FMD) in cloven-hooved domestic and wild animals, is a highly contagious, transboundary animal disease and has caused a high economic impact on livestock production. It can cause a high number of deaths among young animals and production losses in adults and is the single most limiting constraint to the international trade of live animals and animal products [ 1, 2]. FMDV has a single strand of positive-sense ribonucleic acid (RNA) with a very low molecular weight between 7.2 and 8.4 kb and belongs to the member of the genus Aphtho virus in the family Picornaviridae. Its basic and tiny structure, which is 25–30 nm in diameter, speeds up the virus’s airborne transmission, enabling it to travel across vast distances in a relatively short time by matching the characteristics of the wind’s speed and direction. Since the viral RNA-dependent RNA polymerase is incapable of proofreading, it has a high mutation rate, leading to seven immunologically unique serotypes [O, A, C, Southern African Territories (SATs) 1, SAT 2, SAT 3, and Asia 1] and numerous and diverse mutations [ 3, 4]. FMD is endemic in Ethiopia and five of the seven FMD serotypes have been identified from outbreak cases in different regions of the country, which exacerbates the socioeconomic problems in farming [ 5]. Serotypes O and C of FMD were isolated in Ethiopia for the first time in 1957 [ 6, 7]. The identification of serotypes A and SAT 2 did take place in 1969 and 1989, respectively [ 7, 8]. From an outbreak sample obtained from Mizan teferi, South West Ethiopia Region bordering Kenya, Serotype O, East African four topotypes, and SAT 1 FMD virus were identified in 2005 and 2007, respectively [ 5]. According to regular reports of outbreaks all around the country, the frequency of FMD in Ethiopia appears to have increased since 1990 [ 9]. FMD remains largely uncontrolled as prevention of the disease is rarely performed in the country, except for a few dairy herds containing exotic animals and infrequent ring vaccination for suppressing outbreaks in mixed farming and pastoral production systems [ 10]. To fulfill the high demand for animal protein from an expanding population, to guarantee adequate food supply, and to overcome the limit of export markets for animals and animal products, Ethiopia should control and eliminate FMD. Strengthening active and passive surveillance systems and increasing knowledge of the disease’s economic and social effects among decision-makers for the government-ups are required to start the prevention, control, and elimination of the disease from the nation. Although a few sero-prevalence studies have been conducted in different parts of Ethiopia, the prevalence and spread of the disease in the West Omo zone of southwestern Ethiopia are not well understood. West Omo zone has a large number of cattle population and many farmers lose their livelihood by rearing of it for utilizing their products, as source of income by selling them and also use oxen’s for ploughing purpose for crop production. Therefore, the objectives of this study were to determine the seroprevalence of FMD virus antibody and exposure factors linked to the seropositivity of the disease in the West Omo zone of southwestern Ethiopia.
The study area
A cross-sectional study of FMD was conducted from January to February, 2022 in three weredas of the West Omo zone, Part of the South West Ethiopia Regional State. West Omo zone is found at a distance of about 684 km at its zonal town Jemu from southwest of Addis Ababa, the capital of Ethiopia. It is bordered by the Kaffa zone in the North, the Debub Omo zone in the North East direction, the Gambella region and Bench Sheko zone in the South West, and the South Sudan Republic in the South direction. West Omo zone is organized into seven weredas; they are Meinit-Goldya, Meinit-Shasha, Maji, Gorigesha, Gachit, Bero, and Surma woredas ( Fig. 1). The livestock population of the West Omo zone is cattle 2,052,162; sheep’s 611,031; goats 641,794; poultry 1,067,601; and equines 50,423 (West Omo Zone Agricultural Department, 2022, personal communication).
Study design
A cross-sectional study design was applied to determine the sero-prevalence of FMD in cattle and associated risk factors of the disease in the study zone.
Study population
All indigenous breeds of cattle aged 6 months and above kept under an extensive husbandry system for which the cattle graze at a communal grazing area were randomly selected from the study weredas.
Sampling technique and sample size determination
Multistage sampling techniques were employed in this study to sample representative animals in the study area. The total woredas in the West Omo zone will be stratified into three agro-ecological categories highland, midland, and lowland. One woreda will be selected randomly from each agro-ecology (strata). From each woreda, a minimum of 10% of kebeles will be selected randomly to ensure all kebeles in a woreda have the same probability of being selected. For this study, a group of cattle grazing on communal land was considered as a herd. Sampling of individual cattle will be done by simple random sampling. As no previous study was conducted on sero-prevalence of FMD in cattle found in the West Omo zone, the present study has considered 50% expected prevalence, 95% confidence level, and 5% absolute precision or marginal error. Based on these assumptions, the total number of animals to be included in the study was determined using the Thrusfield formula [ 11]: where n= required sample size, d= desired absolute precision, and Pexp=expected prevalence (50%). Based on the formula, the total sample size was computed to be 384 cattle to be selected from these weredas. Proportionally, a total of 135, 128, and 132 blood samples were collected from Gorigesha, Meenit Shasha, and Meenit Goldiya, respectively, based on the density of the cattle population in the wereda.
Methodology
An average of 8–10 ml whole blood was drawn from the jugular vein of each 395 cattle into labeled plain vacutainer test tubes using 21-gauge needles. Sera were separated from the blood into labeled cryogenic vials. The serum was placed into a portable fridge until its delivery to the laboratory for investigation. In the laboratory, all serum samples were stored at −20°C as to achieve very good preservation before serological analysis. During the serological investigation, the required serum sample and the kit should be placed at room temperature for 30 minutes to liquidize the serum. After 30 minutes a 50 µl serum sample was dispatched to each well of a 96 uncoated microplate, only left 4 wells considering the control wells. According to the manufacturer’s recommendation, we take the required sample volume and control by using a multichannel pipette to the coated microplate.
Questionnaire survey
Semi-structured questionnaires were administered to selected cattle owners following verbal consent on the study’s need. For each animal sampled, questionnaire data concerning age, sex, body condition, and agro-ecology were collected to analyze the impact of these variables on the occurrence of the disease.
Description and Principle of FMD competitive enzyme linked immune sorbent assay (C-ELISA). (ID. Vet, France): - The assay is designed to detect specific antibodies against the nonstructural protein of the FMD virus by C-ELISA. Microwells are coated with the non-structural protein of the FMD virus. Samples to be tested and the controls are added to the microwells. Anti-NSP antibodies, if present, form an antigen-antibody complex that masks the virus epitopes. An anti-NSP horseradish peroxidase (HRP) conjugate is added to the wells. It fixes to the remaining free epitopes, forming an antigen-conjugate-HRP-complex. The excess conjugate is removed by washing, and the substrate solution is added. The resulting quantity coloration depends on the specific antibodies present in the sample to be tested. In the presence of antibodies, no coloration appears while in the absence of antibodies, a blue solution appears which becomes yellow after the addition of the stop solution. To quantify the result for identification of negative and positive samples, the microplate is read at 450 nanometers by spectrophotometer. Sample presenting a competition percentage of less than or equal to 50% are considered positive, while greater than 50% are considered negative
Data management and analysis
Relevant data were organized, coded, and entered into a Microsoft Excel sheet. Organized data were transferred to Statistical Package for Social Science Version 25. Descriptive and logistic regression analyses were employed during data analysis. Descriptive statistics was used to determine the prevalence of the disease and other frequencies. Univariable logistic regression analysis for the proportions was carried out to reduce the non-important hypothesized risk factors with p=0.25. The multicollinearity of risk factors was checked. This was further tested by multivariable logistic regression analysis for the conclusion with a probability predictive limit of less than 5% ( p < 0.05). The odds ratio (OR) was used to associate the statistical strength of FMD seropositivity with different potential risk factors. Model fitness was assessed using the Hosmer-Lemeshow goodness of test ( p-value >0.05). Mendeley desktop was used as a reference manager for citation and reference [ 12].
Result
Descriptive statistics were employed to calculate the prevalence and percentages of associated factors (age, sex, and study wereda) with respect to the test results, as summarized in Table 1. The total number of animals sampled was 395 (248 females and 147 males). Table 1.FMD sero surveillance result at West Omo zone by study wereda.
| Study wereda |
FMD c -ELISA RESULT |
Grand Total |
Sero prevalence (%) (95%CI) |
| Negative |
Positive |
| Gorigesha |
133 |
2 |
135 |
1.48 (0.41–5.24) |
| Meenit Goldiya |
121 |
11 |
132 |
8.33 (4.72–14.31) |
| Meenit Shasha |
120 |
8 |
128 |
6.25 (3.2–11.85) |
| Grand total |
374 |
21 |
395 |
5.3% (3.5–7.99). |
FMD=foot and mouth disease, b. c-ELISA=Competitive Enzyme linked immunosorbent assay, c. CI=confidence interval.
Among 395 sera samples, 21 have tested positive for FMD, with an overall prevalence of 5.3% and a 95% confidence interval (3.5%–7.99%). The finding of the study was described by the age and sex of cattle and by the study weredas as shown in Figure 2, Table 1, and Figure 3 below
Figure 1.
Figure 2.
Sero positivity of FMD by sex category. 
Figure 3.
Seropositivity of FMD by age category. 
The herd-level seroprevalence at the communal grazing area (village) is 77.78% ( n=9), as shown in Table 2 below. Table 2.Seroprevalence of FMD at herd level.
| Communal grazing (Herd level) |
Number of examined |
Sero positive |
Sero-prevalence rate% |
| Maka |
66 |
1 |
1.6 |
| Baka |
12 |
0 |
0 |
| Shewajibabu |
58 |
1 |
1.8 |
| Baas |
72 |
2 |
2.8 |
| Jemu |
55 |
6 |
10.9 |
| Bera |
40 |
7 |
17.5 |
| Biyagelich |
26 |
2 |
7.7 |
| Chebera |
34 |
2 |
5.9 |
| Shariya |
32 |
0 |
0 |
| Total |
395 |
21 |
5.4% |
To assess the impact of associated factors on the disease occurrence, binary and multinomial logistic regressions were computed. Accordingly using 95% CI and p < 0.05, the unadjusted OR was computed using binary logistic regression separately for each factor (Sex, age, wereda, and body condition) to estimate the magnitude each factor could pose on the disease ( Table 3). Similarly, the adjusted odds ratio (AOR) was also computed simultaneously to determine the real magnitude (without compounding effect) of the factors one on the disease ( Table 4). Table 3.Univariable logistic regression analysis of potential risk factors of FMD in the study area.
| Variable |
Category |
Total Sampled examined |
Number of positive |
COR (95%CI) |
p-value |
| Age |
<3.5 years |
125 |
1 |
|
0.033 |
| 3.5–6 years |
133 |
7 |
6.9 (0.84–56.8) |
| >6 years |
137 |
13 |
13 (1.7–100.9) |
| Sex |
Male |
147 |
7 |
|
0.706 |
| Female |
248 |
14 |
1.19 (0.47–3.03) |
| Body condition |
Emaciated |
83 |
5 |
|
0.907 |
| Good |
206 |
10 |
0.796 (0.26–2.4) |
| Fair |
106 |
6 |
0.936 (0.27–3.2) |
| Study wereda |
Gorigesha |
135 |
2 |
0.069 |
| Meenit Shasha |
128 |
8 |
4.43 (0.92–21.28) |
| Meenit Goldiya |
132 |
11 |
6.04 (1.3–27.8) |
COR=crude odd ratio, b. CI=Confidence interval.
Table 4.Multinomial logistic regression analysis of potential risk factors of FMD in the study area.
| Variable |
Category |
Total sampled examined |
Number of positive |
AOR (95%CI) |
p-value |
| Age |
<3.5 years |
125 |
1 |
|
0.000 |
| 3.5–6 years |
133 |
7 |
1.8 (0.68–4.7) |
0.237 |
| >6 years |
137 |
13 |
13.76 (1.76–107.3) |
0.012 |
| Study wereda |
Gorigesha |
135 |
2 |
|
|
| Meenit Shasha |
128 |
8 |
1.43 (0.54–3.75) |
0.466 |
| Meenit Goldiya |
132 |
11 |
6.5 (1.4–30.3) |
0.017 |
AOR=adjusted odd ratio, b. CI=confidence interval
Discussion
The present study revealed that FMD is a significant disease in the West Omo zone, Southwestern Ethiopia, with a seroprevalence of 5.3% ( n=395) at the individual cattle level. The result recorded in this study shows the disease is endemic in the zone, which signals the economic significance of the diseases in the area has been high as it causes high production losses gained from the cattle, mortality, and indirectly induces the reduction of crop production as all farmers in the study area rely upon plowing solely by ox. This FMD seroprevalence study results at animals agreed with the seroprevalence of 4.8% and 5% found in western Oromia and in Bale Zone, Oromia regional state [ 13, 14], and a little higher than seroprevalence documented as 3.4% in Northern Amhara, Ethiopia [ 15]. However, lesser seropositivity was found in the current study when compared to the findings of Sahle et al. [ 16], who reported a seroprevalence of 21.% in the Borena pastoral system, and Rufael et al. [ 17], who reported a seroprevalence of 26.5% in Gamo zone, South Ethiopia, respectively. Among the sampled herd, by taking the communal grazing and watering point at the village level as a herd, the highest prevalence was observed in Bera and Jemu kebele at 17.5% and 10.9%, respectively, and the lowest in Shariya and maka kebele as no seropositive sample found. This difference is probably due to the location of Jemu and Bani villages being near the district’s town, where the farmer brought their cattle for better veterinary service at the wereda clinic and movement of cattle to the town for marketing, and these factors may enhance the transmission of the disease in these herds. The results of this study show that FMD seropositivity in cattle herds is higher than average (77.78%), indicating the need for effective methods for preventing and controlling the disease in the zone. The herd level FMD seroprevalence result is similar to FMD herd level sero-prevalence reported in west Shoa by Shurbe et al. [ 18] at 74.7%; however, this sero-prevalence result is much higher than the result found by Megersa et al. [ 10] in southern Ethiopia and Hussain et al. [ 19]’s study in Oman with seroprevalence of 48.1% and 55.2%, respectively. A logistic regression was used to determine the associated risk factors of age, sex, body condition score, and study wereda on the likelihood of FMD antibody detection in cattle. The age of the animals and study district were noticed to have a statistically significant association (p < 0.05) with the seropositivity of FMD; whereas, the sex and body condition score of the animals are not associated (p > 0.05).
The present study revealed that the seroprevalence of FMD in cattle was significantly associated (OR=6.5 (95% CI: 1.4–30.3) within the study weredas. At the wereda level, a higher prevalence was observed in Meenit Goldiya 8.33% (95% CI 4.72–14.31) and Meenit Shasha 6.25% (95% CI: 3.2–11.85) than in Gorigesha wereda 1.48 (95% CI: 0.41–5.24). This probably relates to the difference in livestock movement due to the livestock market. According to the questionnaire survey in Meinit Shasha and Meinit Goldiya, there is a large livestock market in which animals come from many adjacent weredas and other neighboring zones. Therefore, this condition may facilitate contact between different animals and people from different localities and spread the disease to other healthy cattle. According to Abunna et al. [ 20] and Rufael et al. [ 17], the movement of cattle for marketing in most parts of Ethiopia is by trekking to the main town, and movement of cattle for searching of grazing areas and watering points in the dry season of the year in pastoral area suits for the dissemination of FMD virus and occurrence of FMD outbreak. In the present study, the age of the animals was significantly ( p < 0.05) associated with FMD seropositivity in cattle. Older animals exceeding the age of six had a 14-fold (OR=13.76 (95%1.76–107.3) higher FMD seroprevalence than their younger counterparts. High FMD seropositivity of older cattle recorded in this study might be due to the existence of long periods of increased exposure to disease risk factors, and also, in the study area, young animals have been kept separately in the homestead area until cessation of lactation time. Additionally, calves obtained maternal immunity acquired passively from their dam to prevent FMD infection. In addition to the findings of this study, studies done in other regions of Ethiopia also revealed that older cattle had higher seropositivity rates than their younger counterparts [ 17, 18, 21, 22]. However, in contradiction with the above findings, Gelaye et al. [ 23], and Bahiru and Assefa [ 15]in the Bench Maji zone and in Northern Amhara, Ethiopia, reported that the age of the animals is not associated with the seropositivity of FMD prevalence, respectively.
Conclusion and Recommendation
The present study found the seroprevalence prevalence of FMD in the West Omo zone is 5.3% and 77.78%, at the individual cattle and herd level, respectively, indicating its high economic significance for the livelihood of the cattle-producing community. Among the hypothesized risk factors considering, the age of the animals and study weredas were noticed to have a statistically significant association (p < 0.05) with the sero positivity of FMD. The result revealed that FMD occurred in many parts of the zones, triggering further study, especially for identifying the circulating FMD sero types to set up for scheduled prevention and control strategy in the zone.
Acknowledgments
The authors would like to thank Mizan Regional Veterinary Laboratory Center for allocating the budget for the research work. Furthermore, they want to extend their thanks to Meenit goldiya, Meenit Shasha, and Gorigesha Weredas Office of Agriculture’s animal health officer for their valuable assistance during the sample collection.
Conflict of interest
No conflict of interest regarding the publication of this manuscript.
References
1. Chen J, Wang J, Wang M, Liang R, Lu Y, Zhang Q, et al. Retrospect and risk analysis of foot-and-mouth disease in China based on integrated surveillance and spatial analysis tools. Front Vet Sci 2020; 6:511.
2. Kandeil A, El-Shesheny R, Kayali G, Moatasim Y, Bagato O, Darwish M, et al. Characterization of the recent outbreak of foot-and-mouth disease virus serotype SAT2 in Egypt. Arch Virol 2013; 158:619–27.
3. Doel CMFA, Gloster J, Valarcher JF. Airborne transmission of foot-and-mouth disease in pigs: evaluation and optimisation of instrumentation and techniques. Vet J 2009; 179(2):219–24.
4. Konig GA, Cottam EM, Upadhyaya S, Gloster J, Mansley LM, Haydon DT, et al. Sequence data and evidence of possible airborne spread in the 2001 foot-and-mouth disease epidemic in the UK. Vet Rec 2009; 165(14):410.
5. Ayelet G, Mahapatra M, Gelaye E, Egziabher BG, Rufeal T, Sahle M, et al. Genetic characterization of foot-and-mouth disease viruses, Ethiopia, 1981-2007. Emerg Infect Dis 2009; 15(9):1409–17.
6. Martel JL. Foot and mouth disease in Ethiopia: distribution of foot and mouth disease virus serotypes. Rev Elev Med Vet Pays Trop 1974; 27(2):169–75.
7. Martel JL. Comparative serological study of principal strains of foot-and-mouth disease virus isolated in Ethiopia from 1969 to 1974 [French]. Rev Elev Med Vet Pays Trop 1975; 28(3):287–95.
8. Roeder PL, Abraham G, Mebratu GY, Kitching RP. Foot-and-mouth disease in Ethiopia from 1988 to 1991. Trop Anim Health Prod 1994; 26(3):163–7.
9. Asfaw W, Sintaro T. The status of FMD in Ethiopia, a growing concern. Ethiop Vet Epi News Lett 2000; 1:1–5.
10. Megersa B, Beyene B, Abunna F, Regassa A, Amenu K, Rufael T. Risk factors for foot and mouth disease seroprevalence in indigenous cattle in Southern Ethiopia: the effect of production system. Trop Anim Health Prod 2009; 41:891–8.
11. Thrusfield M. Veterinary epidemiology. 3rd edition, Blackwell Science Ltd., Oxford, UK, pp 46–74, 2007.
12. Manis K. How to use Mendeley desktop (successfully). Res Berlin Ger. 2020.
13. Gelana M, Mersha T, Mideksa T, Abera H. Sero-prevalence study on foot and mouth disease in selected districts of Western Oromia. J Pharm Altern Med 2016; 13:15–8.
14. Duguma M, Jibril Y, Issa A, Hunde A. Sero-prevalence of foot and mouth disease of cattle in Bale Zone, Oromiya regional state, Ethiopia. Glob Vet 2013; 11(1):59–64.
16. Sahle M. An epidemiological study on the genetic relationships of foot and mouth disease viruses in east Africa. University of Pretoria, Pretoria, South Africa, 2004.
17. Rufael T, Catley A, Bogale A, Sahle M, Shiferaw Y. Foot and mouth disease in the Borana pastoral system, southern Ethiopia and implications for livelihoods and international trade. Trop Anim Health Prod 2008; 40:29–38.
18. Shurbe M, Simeon B, Seyoum W, Muluneh A, Tora E, Abayneh E. Seroprevalence and associated risk factors for foot and mouth disease virus seropositivity in cattle in selected districts of Gamo zone, Southern Ethiopia. Front Vet Sci 2022; 9(August):931643.
19. Hussain MH, Body MHH, Al-Subhi AHA, Al-Senaidi NYA, Eltahir HA, Mansoor MK, et al. Seroepidemiology of foot and mouth disease (FMD) virus non-structural protein (NSP) antibodies in the livestock of Oman. Acta Trop 2019; 199:105106.
20. Abunna F, Fikru S, Rufael T. Sero-prevalence of foot and mouth disease (FMD) at dire dawa and its surroundings, Eastern Ethiopia. Glob Vet 2013; 11(5):575–8.
21. Dubie T, Negash W. Seroprevalence of bovine foot and mouth disease (FMD) and its associated risk factors in selected districts of Afar region, Ethiopia. Vet Med Sci 2021; 7(5):1678–87.
22. Gelana M. Seroprevalence study on foot and mouth disease in selected districts of western Oromia. J Pharm Altern Med 2016; 13:15–8.
23. Gelaye E, Ayelet G, Abera T, Asmare K. Seroprevalence of foot and mouth disease in Bench Maji zone,Southwestern Ethiopia. J Vet Med Anim Heal [Internet] 2009; 1(1):5–010. Available via http://www.academicjournals.org/JVMAH
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