Discussion
The present study revealed that FMD is a significant disease in the study districts with a seroprevalence of 19.8% (n= 76/384). The current study finding indicated that the overall seroprevalence of FMDV at individual animal level was 19.8% in the study areas, which is in close agreement with the previous seroprevalence records of 21% in the Borana pastoral area (Rufael et al ., 2008), 21% in Borana zone and Guji zone (OIE & FAO, 2013), 21% in kellema Wollega Zone (Fanta et at ., 2014), 21 % in Borna pastoral area (Tesfaye, 2006). In contrast to the current study finding, lower seroprevalence of FMD was previously reported as mentioned below; 13% in selected districts of western Ethiopia (Tolosa et al ., 2015), 10.88% in selected district of eastern showa zone, Oromia regional state (Dinaol et al ., 2016), 12.05% in the Bench Maji zone, Southern Ethiopia (Gelaye et al ., 2009), 8.8% in South Omo Zone (Molla et al ., 2010), 9.5% from indigenous cattle in southern Ethiopia (Megersa et al ., 2009), 5.53% on quarantined bulls for export at Nazareth and Dire Dawa stations (Bedru, 2006) and 4.8% in selected districts of western, Oromia (Milkessa et al ., 2016). These relative lower seroprevalence of FMD in comparison to the current study might attributed to diagnostic tests employed, the sampling method, study population and sites, the geographic structure and timing of infection, the pastoral production system, which is characterized by a high level of herd mobility in search of pasture and water, intermingling of animals at watering points, large herd sizes and frequent contact with the livestock of neighboring countries through cross-border contact as well as contact of livestock with FMD virus reservoirs’ of wildlife such as buffalo, wild pigs, kudu and warthog and other factors (Gelayeet al ., 2009; Megersa et al ., 2009). On the other hand, relatively higher seroprevalence was previously reported in comparison to our study from Borna pastoral and agro-pastoral area with 23% (Berecha et al ., 2011), in Borena and Guji Zones with 24.6 % (Mekonnen et al., 2011), in west Shewa zone, North Shewa zone and Addis Ababa with 30.8% (Beksisa, 2017), 32.7% in Guji zone of Oromia region and 30 % in Yeka district of the city of Addis Ababa as well as eastern zone of Tigray with 41.5% (Ayelet et al., 2012) and 28.3% seropositivity in Akaki-kality sub-city (Nigussie et al ., 2011). A study finding from neighboring Sudan also revealed that following an active occurrence of the disease, the seroprevalence of FMD was reported with 79% in cattle (OIE, 2012). Moreover, according to Hafez et al . (2014), FMD seropositivity was reported in Saudi Arabia with 53% seroprevalence and Namatovu et al. ( 2015) as well reported 77% in infected cattle in Uganda. This seropositivity variation could be resulted from differences in individual animal breed, immune status, interaction of cattle with other animals and production system as well as differences in geographical area or the way sampling was conducted based on the existence of recent outbreak cases, sample size, methodology, regular contact with ungulate wildlife (Gelayeet al ., 2009).
The overall herd level seroprevalence in this study was 56.9% (N=41/72). This finding was in line with the findings of Tesfaye (2006), who reported the seroprevalence rate of 59 % in Borna pastoral area, Berecha et al ., (2011), who reported 58.6% in Borna pastoral and agro pastoral area. The highest herd level seroprevalence (85%) recorded in Dubti as compared to Asayita (48.13%) and Chifra (44%); this might be due to the fact that, Dubti is centers for cattle markets and have high population of small ruminant. This suggests that small ruminants have an important role in the epidemiology of FMD as they can serve as potential carriers and transmitters of the disease (Jenbereet al ., 2011) and (Mohamud et al ., 2011).
Among the risk factors considered in the current study age, herd size, district and contact with ungulate wild life were found to be statistically significant (P<0.05) in multivariate logistic regression. In this study, the prevalence of FMD in adult age group was higher than in young group and this age specific seropositivitity of FMD was statistically non-significant. Thus, Adult cattle were 2.97 times more likely to have a chance of contracting FMD than young cattle. This statistically significant higher seroprevalence of FMDV in old and adult animals than young cattle in this current study finding was in accordance with earlier studies of Tolosa et al . (2015) who reported that adult cattle were 2.7 times more likely to have the chance of develop disease than young cattle in western Ethiopia, Berechaet al . (2011) in Borna pastoral and agro-pastoral area, Mollaet al . (2010) in south Omo zone and Megersa et al. ( 2009) in Gamogofa and Sidama zones, Chepkwony et al . (2012) in Awbere and Babille districts of Jijiga zone. Age association with FMD seroprevalence was also in close agreement with the previous study of (Olabode et al ., 2013). The possible justification for age association with FMD seroprevalence could be due to adult cattle have acquired the infection through frequent exposure over time to multiple serotypes of the virus and could get access to mix with other herds at communal pasture land and market places. Furthermore, it might be due to persistence of antibodies against FMDV for extended periods of time (Sangare, 2005). Relatively low seroprevalence in animal groups below 2 years old might be indicative of the existence of passive maternal immunity and low frequency of exposure (Jenbere et al ., 2011; Mohamoud et al ., 2011). In our study areas, young animals were often managed separately at around homestead so that young’s have low frequency of exposure to the virus and they could also prevailing passive maternal immunity can give them protection against the disease. On the contrary, our study result contradicted with Esayas et al . (2009) and Gelaye et al . (2009), who documented no significant association between seropositivity of FMD and age of cattle in Bench Maji zone of southern Ethiopia.
In the current study, seroprevalence of FMD was also significantly influenced by herd size, which means seroprevalence of antibodies against FMDV increased with increasing herd size. In our study result, those animals from medium herd size and large herd size were 2.49 and 6.05 times more likely to develop the disease as compared to those animals from small herd size respectively by keeping the other factors constant. Our research finding was in agreement with Tolosa et al . (2015), Gelaye et al. (2009), Bayissa et al . (2011), Berecha et al . (2011), who reported that they have positive relationship between FMD seroprevalence and herd size. This direct association might be an indication of contagious nature of the disease and mode of transmission, which is attributed to crowding of animals that can facilitate frequency of direct contact and hence enhances chances of transmission.
In our study finding, statistically significant association was found between study districts and FMD seroprevalence of 35.05% (n=34/97), 14.29% (n=20/140) and 14.97% (n=22/147) in Dubti, Chifra and Asayita district respectively. Thus, cattle found in Dubti district were 2.49 times more likely to develop the disease as compared with those cattle found in Asayita district. Our study finding is in close agreement with previous reports of Milkessa et al . (2016), who reports the significant variation of Horro (8.2%) and Gobu-sayo (0.8%) districts of western Oromia regional state and Molla et al . (2010). This might be due to differences in the movement and distribution of livestock, the level of contact between herds and ungulate wildlife and the grazing type in each administrative structure. (Ekboir, 1999) also suggested that movements of infected animals are by far the most important dissemination and transmission means for FMDV. Again Paulet al . (1996) in northern Thiland and Bronsvoort et al . (2004) in Cameroon observed the influence of cattle movement and keeping animals at homestead in the incidence of FMD.
Cattle that contact regularly with ungulate wild life were 8.97 times more likely to develop the disease as compared to cattle having no contact with wild life by keeping other factors constant. This study finding was in agreement with previous studies of Tolosa et al . (2015) in western Ethiopia and Molla et al . (2010) in South Omo zone who reported that cattle that regularly contact with ungulate wildlife were 3.3 times more likely to develop the disease than cattle having no contact with wild life. According to Bronvoort et al . (2008) contact between ungulate wildlife and livestock at watering points and grazing areas is the main risk factor for FMDV circulation and it is a challenge for disease control in East Africa (Lazarus, 2012). Although Statistical analysis using the chi-square test and uni-variable logistic regression showed that contact with animals from different peasant association/herds appeared to have a significant effect on seropositivity, multivariable logistic regression showed that contact animals to other herds/peasant association had no statistically significant relationship with the seropositivity of the animals (p>0.05). It was a confounding factor in the relationship between seropositivity and contact with herds/PAs. However, this result contradict with Tolosa et al . (2015), who reported the herds were 3.4 times more likely to be seropositive for FMD than herds that did not have a history of contact with other herds. The difference from the present study might be because of unequal involvement of differently contact animal groups in our sampling where majority of our study animals were animals that regularly contact with other herds/PAs due to accessibility.