Sero-prevalence and associated risk factors of small ruminant’s brucellosis in the Yabello and Elweye districts of Borana zone, Southern Ethiopia

Abstract

AbstractSection Methods

A cross-sectional study was carried out to determine the Seroprevalence and associated risk factors of small ruminant’s brucellosis in Borana Zone of Yabello and Elweye districts from November, 2024 to June, 2025. Different sampling methods were used to select the study districts, Peasant associations (PA), villages, householders and individual study animals. A questionnaire survey was administered to animal owners (pastoralists) from whose animal’s blood sample was collected.

AbstractSection Results

Out of 541 sera collected, 13 of them were seropositive for Brucella with an overall animal seroprevalence of 2.40%. Rose Bengal Plate test (RBPT) was used to screen the samples and Complement Fixation test (CFT) was employed on RBPT positives for confirmation. The study also revealed flock level seroprevalence of 14.29%. A statistically significant difference was observed between small ruminants with previous history of abortion and those without history of abortion (p = 0.002, OR = 7.88 with 95% CI: 2.20–28.23%). Similarly, Seropositivity for Brucella infection was significantly higher in small ruminants with more than three parities compared to those with zero or between one and three parities (p = 0.04, OR = 5.92; 95% CI: 1.07–32.58%). Regarding the knowledge of the interviewed pastoralists about brucellosis, more than 90% of them didn’t have any awareness about the zoonotic nature of brucellosis, control and prevention measures and had contacts with aborted fetuses and retained fetal membrane.

AbstractSection Conclusion and recommendations

The finding confirms that the disease is circulating within the small ruminant population of the study areas and significant gaps in awareness and preventive practices among pastoralists. It is advisable to implement comprehensive control and prevention strategies aimed at reducing the incidence and impact of the disease and undertake community sensitization on public importance of the disease.

Introduction

Ethiopia, a sub-Saharan African country, is home to the world’s largest small ruminant population, with an estimated 42.9 million sheep and 52.5 million goats, collectively representing approximately 4% of the global and 10% of Africa’s total small ruminant population [1]. Besides sustaining livelihoods, especially among pastoral communities as a key source of income and food, small ruminants serve as major export commodities and make a significant contribution to Ethiopia’s national economy. Although Ethiopia has a larger small ruminant population than most African countries, it has not fully realized sector’s potential benefits due to various challenges, including diseases [2]. Among these, brucellosis is a significant infectious disease that hinders sheep and goat production in the country [3].

Brucellosis leads to significant economic losses in Ethiopia’s small ruminant sector by causing breeding inefficiencies, abortion, loss of lambs and kids, reduced production of wool, meat, and milk, and by limiting access to international markets for live animals and their products [4]. Although eradicated in many developed countries, brucellosis remains a major public and animal health concern in many developing nations where livestock serve as a key source of food and income [5]. The disease is caused by Brucella, a gram negative, facultative intracellular bacterium capable of infecting various animal species and humans. While Brucella species exhibit a preference for certain hosts, they are not strictly host specific and are classified based on phenotypic traits, antigenic properties, and host association. In sheep and goats, Brucella melitensis (biovars 1–3) is the primary causative agent [4].

Brucellosis is clinically marked by abortion and retained fetal membrane in cows, and orchitis and epididymitis in bulls [6]. The main sources of infection for human are direct contact with aborted fetuses, fetal membranes, vaginal discharges, and consumption of unpasteurized milk from infected animals. Transmission in cattle primarily occurs through direct contact with aborting animals or their aborted fetuses [7]. The diseases causes significant economic losses in livestock by leading to reproductive failures such as infertility, loss of offspring, delayed estrus, decreased meat and milk production, increased culling rates, and trade restrictions on livestock and their products [8].

The prevalence of brucellosis notably high in low income countries, posing serious animal and public health challenges. This is largely due to limited public health awareness, inadequate veterinary services, insufficient diagnostic capacity, and the absence of effective control strategies [9]. In Ethiopia, various studies have reported differing prevalence rates of small ruminant brucellosis: 1.23% in the Somali region [10], 1.76% in Central Ethiopia [11], 3.50% in the Tigray region [12], and 4.80% in the Afar region. These findings reflect differences in the diseases epidemiological patterns across different agro-ecological zones

In spite of the aforementioned prevailing situation and the presence of a number of problems due to Brucellosis in small ruminants, there is dearth of well documented information on the occurrence of the disease in small ruminants of Yabello and Elweye districts, Borana zone, Southern Ethiopia. Therefore, the aim of this research was to investigate the sero-prevalence and associated risk factors of small ruminant’s brucellosis in the Yabello and Elweye districts.

Materials and methods

Description of the study area

The study was conducted from November, 2024 to June, 2025 to determine the seroprevalence and assess associated risk factors of small ruminants Brucellosis in Yabello and Elweye districts of Borana zone, Oromia region, southern Ethiopia (Fig. 1). Borana is bordered by West Guji in the North, Kenya in the South, the Guji zone and Somali regional state in the East and the Southern nation’s region in the West. It is geographically located at 3 °30′ N to 5 °25′ N latitude and 36 °40′ E to 39 °45′ E longitude. Yabelo town, located on the way to Moyale-Kenya, is the administrative seat of the Borana zone. Yabello and Elweye districts are located at a distance of 565 and 595 Kms respectively from Addis Ababa, Capital city of the Ethiopia.

Fig. 1

Map of the study area

The goat and sheep population of Yabello district respectively were 101,604 and 51,626 while 90,120 of goat and 72,330 of sheep population were found in Elweye district. From Yabello district; Dharrito, Dambi, Dambala Ambachana and Did Yabello kebele’s were selected for the study while from Elweye district; Ade Galcheti, Elweye Golba, Hiddi Alle and Sarite kebele’s were included. The majority of the communities of the area are practicing a pastoral farming system where most of their income is based on livestock rearing while some of them were following mixed farming. Farming practice is a very recent activity in the area introduced by the government to diversify means of generating additional income for the family.

Study populations and their management

The target study population includes apparently healthy local breeds of domestic small ruminants that were kept under extensive management system.

Study design

A cross-sectional study was carried out supported with a semi-structured questionnaire survey to collect data on associated risk factors: age, sex, Number of gestation, history of abortion, species, and district. The questionnaire was prepared in English language and translated to Afaan Oromoo, the local language used by the community, by veterinarians of the area who are fluent both in Afaan Oromoo and English.

Sampling method and sample size determination

The study areas at zone and district level were selected purposively based on the scarcity of the disease information and its risk factors. The study kebeles (Peasant associations (PAs)) were selected conveniently based on the infrastructure and security issues. Those herds that are reared in close proximity of each other (housed in consecutive barns and graze on the same field) were grouped together and considered as one herd although owned by different farmers [13]. From the list provided, animal owners were selected randomly and study animals were included by simple random sampling method.

Sample size determination was calculated using established formula, Thrusfield [14] based on previously reported seroprevalences of 6.10 and 8.78% for sheep and goats, respectively in the Yabello district Teshome et al. [15]. Based on the availability of laboratory kits and the size of the small ruminant population in the study areas, samples size was increased to 541 with 164 sheep and 377 goats sampled for the present study. For the questionnaire, interviews were conducted with 63 pastoralists whose animals were sampled for the study.

Blood sample and data collection

Approximately 5–7 mL of blood sample was collected from the jugular vein of each animal using vacutainer tubes. Each sample from each animal was labeled by using codes describing their age, sex, species, Number of gestation and history of abortion. The blood sample was kept overnight at room temperature to allow clotting. At the next morning, clearly separated serum of approximately 2 ml was decanted to the cryovials to which identification was recorded. Then, the obtained sera’s were stored at − 20 °C at Yabello Regional Veterinary Laboratory until transported to Animal Health Institute, and laboratory analysis was performed.

A questionnaire was designed to collect information on factors that are believed to influence the spread and prevalence of Brucella infection. A questionnaire survey with open and closed ended questions was used among the owners from whose animals sample was taken. The study population was grouped into two age groups as young (< 2 years) and adult (≥ 2) years. Number of gestation was grouped as: zero gestation, 1–3 gestation and > 3 gestation [16].

Serological tests

The laboratory analysis was performed at Ethiopian Animal Health Institute (AHI), an accredited and referral laboratory. The rose Bengal plate test was employed as a screening test and the complement fixation test was used as a confirmatory test in accordance with procedures described within the World Organization for Animal Health Manual. Samples on the RBT were considered positive if visible agglutination was observed. Samples were considered positive on the CF test if 75% fixation of complement occurred at a 1:5 dilution or if 50% fixation of complement occurred at a dilution of at least 1:10.

Data management and analysis

All field and laboratory data were entered into spreadsheets for analyses. Logistic expression analysis was used to compare relationships between the outcome variable and different explanatory variables. Risk factors with P < 0.25 in the univariable logistic regression analysis were included in the multivariable logistic regression model, with significant associations determined at P < 0.05.

Results

Overall sero-prevalence

In the current study, a total of 541 serum samples were collected from small ruminants, comprising 377 goats and 164 sheep, to investigate the seroprevalence of brucellosis. The initial screening of all samples was conducted using the Rose Bengal Plate Test (RBPT). Samples that yielded positive results in the RBPT were subsequently subjected to the Complement Fixation Test (CFT), a confirmatory diagnostic method. In this study, all RBPT-positive samples were also confirmed positive by CFT. The overall seroprevalence of brucellosis among the sampled population was found to be 2.40%, with a 95% confidence interval ranging from 1.41% to 4.07%. At species level, a sero-prevalence of 3.18% (12 out of 377) and 0.61% (1 out of 164) was recorded in goats and sheep, respectively. When analyzed at flock level, the prevalence of brucellosis was recorded at 14.29% (9/63), with a 95% CI: 7.70% to 24.97%. The selected risk factors were filtered by univariate logistic regression analysis and all except sex (p > 0.25) were subjected to multivariate logistic regression analysis (Table 1).

Table 1 Output of univariate logistic regression analysis of predictor variables

Potential risk factors

According to multivariate logistic regression analysis, statistically significant difference was observed between small ruminants with history of abortion and those without history of abortion (p = 0.002, odds ratio = 7.88, 95% CI = 2.20% − 28.23%), (Table 2). The final multivariable logistic regression model (Table 2) showed that animals with gestation of > 3 were more likely to be exposed to Brucella infection than those animals with zero and 1–3 gestations (p = 0.04, OR = 5.92, 95% CI = 1.07–32.58). But, there was insignificant difference between different sex groups, district and species of animals. Age was removed by the analytic software because of the effect of colleaniarity.

Table 2 Output of multivariate logistic regression analysis of filtered variables

So, number of gestation and previous history of abortion were considered as potential risk factors for the occurrence of brucellosis in small ruminants (Table 2).

Questionnaire survey

In the present study, a total of 63 small ruminant flocks were included for sample collection and analysis. Demographic analysis of the respondents showed that the majority were female, accounting for 60.32%, while the remaining 39.68% were male. A significant knowledge gap was evident, as 80.95% of the respondents had no understanding of the causes or modes of transmission of brucellosis. When asked specifically about the zoonotic aspect of the disease and its ability to be transmitted from animals to humans, even a larger proportion, 90.48%, indicated they had no awareness of this risk.

Regarding hygiene practices, about 60.32% of the participants reported that they practiced hand washing after handling animals following parturition. However, 39.68% of respondents did not recognize the importance of hand hygiene in this context, suggesting continued vulnerability to infection due to poor preventive practices (Table 3).

Table 3 Awareness of the respondents about brucellosis

Discussion

The present study was conducted on 541 small ruminants of Yabello and Elweye districts of Borana zone. Rose Bengal Plate Test (RBPT) was used for initial screening and RBPT seropositive sera samples were re-tested by Complement Fixation Test (CFT) for confirmation. The study revealed an overall seroprevalence of brucellosis of 2.40%, with 13 out of the 541 small ruminant serum samples testing positive for the disease.

A comparable findings were obtained by Muhidin et al. [16], Mohammed et al. [17], Bezabih and Bulto [18], Addis [19], Tsegay et al. [11]. and Teklu et al. [20], who reported seropositivity of 2.97% in Berbere district of Bale zone, 2.70% in Selected Export Abattoirs of Addis Ababa, 2.25% in Werer Agricultural Research Centre of Afar region, 1.56% in Yabello district of Borana zone, 1.76% in Debre Ziet and Modjo export abattoirs of Ethiopia and 3.5% in Southern Zone of Tigray, respectively.

In contrast, it is lower than the previous reports of seroprevalence of brucellosis in small ruminant reported in different areas of Ethiopia including 12.35% reported in Afar region by Tegegn et al. [21], 9.6% in Yabello pastoral Area by Yohannes et al. [22]., 6.50% in Chiro and Burka Dhintu districts of West Hararghe by Wubay et al. [23]., 6.40% in Korahey zone of Somali regional state by Hussen et al. [10], 8% in Borana zone by Edao et al. [24]., 5.80% in Karnataka (India’s Southern province) by Natesan et al. [25]. and 9.11% in Dire Dawa by Negash et al. [26]. The lower prevalence observed in this study may be attributed to the intense heat and scorching sun, which likely reduce the survival of the bacterium under such high-temperature conditions [27].

However, the prevalence of small ruminant brucellosis in the current study is higher than previous reports done in various areas of Ethiopia, with 0.2% in West Hararghe Zone by Geletu et al. [28]., 0.7% around Kombolcha by Ferede et al. [29]., and 1.5% in South Wollo Zone by Yesuf et al. [30]. The lower prevalence reported in previous studies may be linked to mixed farming systems, where only a small number of animals are kept separately, reducing the odds of disease transmission [31]. In contrast, the higher prevalence observed in this study could be associated with pastoral production systems, where households tend to cluster with their herds in camps. The diversity of livestock species kept as a coping strategy for livelihood odds, combined with large herd sizes, leads to increased animal aggregation and interaction at villages, grazing areas, and water points, conditions that favor disease spread. Additionally, the frequent migration of pastoral herds raises the likelihood of contact with potentially infected herds in neighboring regions [32]. Large herd sizes further heighten exposure odds, especially after abortion events, when shared feeding and watering sites can facilitate can facilitate the transmission of Brucella organisms [7].

The variation in brucellosis prevalence reported across different regions of Ethiopia may be influenced by multiple factors, including differences in testing methods, animal age, sex, pregnancy status, geographic location, management practices, presence of other reproductive diseases, herd size, and sample size, all of which can contribute to these observed disparities [33]. The current study area is predominantly pastoral, with communities practicing seasonal migration in search of water and grazing resources for their livestock. This movement often leads to high animal concentrations in critical locations, such as watering points, which facilitates the spread of disease. Additionally, drought and prolonged dry seasons, common in pastoral regions, cause significant stress in animals, making them more susceptible to infections [34]. The combination of migratory pastoral practices, communal grazing, and limited access to veterinary and public health services contributes to the persistence and endemic nature of small ruminant brucellosis in these areas [31].

Brucella seropositivity was significantly associated with small ruminants having previous history of abortion (p = 0.002, odds ratio = 7.87 (95% CI: 2.20–28.23%)). This may be described by the higher concentration of erythritol (2R, 3 S)-butane-1,2,3,4- tetraol, a naturally occurring sugar alcohol produced by the developing fetus, which supports the multiplication of Brucella. The presence of erythritol in the placenta promotes bacterial growth, leading to degeneration and necrosis of the cotyledons and resulting in abortion, typically during the later stages of gestation [35]. This finding was in agreement with the results of Muhidin et al. [16]., Teshome et al. [15]. and Edao et al. [24]. works who reported a statistically significant difference in Brucella seropositivity between small ruminants with history of abortion and without abortion history.

Similarly, multivariable logistic regression revealed a statistically significant difference in seropositivity of Brucella between different number of gestations of small ruminants with higher seropositivity in > 3 gestation animals compared to (1–3) and zero gestations group (p = 0.04, odds ratio = 5.92 (95% CI: 1.07–32.58%)). This finding is in consistent with the findings of Ashagrie et al. [36]., Asmare et al. [37]., Muhidin et al. [16]. and Edao et al. [24]. This is likely because the prevalence of brucellosis tends to increase with repeated exposure to parturition and the physiological stresses associated with pregnancy [38, 39].

The current finding showed that, adult sheep and goats were by far more likely to become seropositive for brucellosis than animals in the young age category with no statistically significant difference. Similar results have been reported previously by Natesan et al. [25]., Hussen et al. [10]., and Edao et al. [24]. This may be explained by the fact that, although animals can become infected with Brucella at a young age, the bacteria often remain localized in regional lymph nodes without triggering antibody production until the animals reach sexual maturity. At that stage, the production of sex hormones and erythritol promotes the growth and multiplication of Brucella species, leading to a detectable immune response [40].

In the present study, though the seropositivity of Brucella was higher in female than male small ruminants, there was no significant difference observed between different sex groups (p = 0.32, odds ratio = 0.35 (95% CI: 0.05–2.74)). Some studies have indicated that male animals often exhibit a limited serological response, with infected males frequently showing no detectable reaction or producing low antibody titers [36]. Additionally, males are considered less susceptible to Brucella infection due to their lower levels of erythritol, a carbon 4-sugar that promotes the growth and multiplication of Brucella organisms [11, 41]. This observation aligns with the findings reported by Muhidin et al. [16]. and Alhussain et al. [42].

At a species level, the odds of Brucella seropositivity was five times more likely common in caprine than ovine species with no significant difference between the groups (p = 0.13, odds ratio = 5.07 (95% CI: 0.63–40.92)). The higher prevalence of brucellosis in goats compared to sheep may be partly attributed to the greater susceptibility of goats to Brucella infection. Unlike goats, sheep tend excrete Brucella organisms for a shorter duration, which reduces the likelihood of disease transmission within sheep flocks [43]. Similar findings were reported by Ashenafi et al. [44]., Teshale et al. [43] and Bekele et al. [45]. While Brucella species are known to show host preference, B.melitensis primarily affects goats. Furthermore, goats tend to shed Brucella in larger quantities and for longer periods than sheep, thereby increasing the odds of disease spread within goat herds [46].

According to multivariate logistic regression, the occurrence of brucellosis was almost two times higher in Elweye than yabello district, but statistically no significant difference was recorded. This is in agreement with the finding of Wubay et al. [23] who reported statistically insignificant difference between study areas on the occurrence of brucellosis in small ruminants.

The current work also assessed the status of brucellosis at the flock level and showed a flock level prevalence of 14.29% which is comparable to flock level seroprevalence report of 14.14% [47], 16% [24], 15% [48], 13.60% [49] and 19.9% [50]. However, the present result is higher than the reports of previous studies in different parts of Ethiopia in which a flock level prevalence ranging from 1.5 to 4.9% were reported [51, 52, 53 and 54]. The contrasting findings may be attributed to differences in the overall individual animal level prevalence or the size of the studied flocks. The higher prevalence observed in extensive smallholder production systems could be explained by the unrestricted movement of animals and their frequent congregation at shared grazing areas and watering points, which facilitates the transmission of brucellosis either through direct contact between animals or exposure to contaminated environments [32, 55, 56].

The assessment of disease prevention practices among the surveyed pastoralists revealed significant gaps in the use of protective measures during high-risk animal handling activities. Specifically, only 10% of the respondents reported using personal protective equipment (PPE), such as gloves or other barriers, when coming into contact with aborted fetuses or retained fetal membranes. In contrast, an overwhelming majority, over 90%, admitted to handling such materials without any form of protective gear, thereby increasing their vulnerability to infection. Furthermore, knowledge and awareness regarding the zoonotic nature of brucellosis were found to be severely lacking. Around 94% of the respondents believed that brucellosis affects only animals, with no understanding of its potential to infect humans. This misconception significantly reduces the likelihood of implementing effective preventive behaviors. Knowledge about the disease and preventive flock management practices have previously been identified as the most important factors needed for minimizing the disease odds in animals [56].

Additionally, the study found that 94% of the participants had direct physical contact with aborted materials and retained fetal membranes during livestock care. This combination of high-odds of exposure and poor awareness underscores the urgent need for targeted education programs and training on safe animal handling practices and the importance of using PPE to protect both human and animal health. Moreover, findings from the questionnaire survey showed that a large proportion of the pastoralist community (88.89%) reported to consume raw milk. This traditional practice poses a significant public health concern, as it increases the likelihood of exposure to and transmission of various pathogens, including Brucella species and other milk borne infectious agents.

As a limitation of the study, CFT, the laboratory test method used, may fail to detect low levels of antibodies or antigens, especially in early or chronic stages of infection. The test is unable to differentiate between antibody classes and may also miss early-phase infections where IgM was predominant. The absence of culture and molecular diagnostic techniques in this study could be regarded as a limitation, as these methods provide more definitive identification of Brucella species and allow confirmation of active infection, which serological tests alone cannot fully achieve.

Conclusion and recommendations

The findings of the current study indicate the presence of brucellosis among small ruminants. The likelihood of small ruminants testing seropositive for Brucella infection was found to be significantly associated with animals that had a previous history of abortion and those with more than three parities. Goats exhibited a higher infection rate compared to sheep, suggesting species-specific susceptibility or differing exposure risks. Additionally, the study revealed significant gaps in awareness and preventive practices among pastoralists, including limited knowledge about the zoonotic nature of brucellosis.

Based on the above conclusion, the following recommendations are forwarded:

• Implement comprehensive control and prevention strategies aimed at reducing the incidence and impact of the disease.

• Implement community-based education programs to raise awareness about the causes, transmission routes, and zoonotic potential of brucellosis.

• It is advisable to undertake a broader research involving a larger scale study and reservoir species to gain deeper practical insights into the disease.