Prevalence and associated risk factors of Bovine Fasciolosis in smallholder dairy Cattle in and around Dire Dawa, Eastern Ethiopia

Introduction

What economic burden does bovine fasciolosis impose on smallholder dairy farmers in sub-Saharan Africa, and how effectively are current control measures mitigating this parasitic challenge? Fasciolosis, caused by trematodes of the genus Fasciola, remains one of the most economically important parasitic diseases of ruminants worldwide, with an estimated 600 million animals infected globally and annual losses exceeding 3.2 billion USD [1] . The disease is caused primarily by two species: Fasciola hepatica, which predominates in temperate and highland regions, and Fasciola gigantica, which is more common in tropical lowland areas [2] . In regions where both species coexist, mixed infections and hybrid forms have been documented, complicating diagnosis and control efforts [3] . Bovine fasciolosis manifests through chronic hepatic damage, resulting in reduced weight gain, decreased milk production, impaired reproductive performance, and liver condemnation at slaughter [4] . In smallholder dairy systems, where cattle represent critical livelihood assets, the economic impact of fasciolosis is disproportionately severe, often reducing household income by 8-15% annually [5] . The epidemiology of fasciolosis is intimately linked to the ecology of its intermediate hosts, freshwater snails of the family Lymnaeidae, whose populations are in turn governed by rainfall patterns, temperature, soil moisture, and the availability of suitable aquatic habitats [6] .

Ethiopia, with the largest livestock population in Africa, bears a substantial fasciolosis burden. Previous investigations across various agro-ecological zones have reported prevalence rates ranging from 11.5% to 87.2%, depending on the region, season, and diagnostic method employed [7] . Highland areas with adequate moisture and cooler temperatures tend to exhibit higher prevalence than arid lowland zones [8] . However, the eastern lowland regions of the country, including the Dire Dawa administrative area, have received comparatively limited epidemiological attention despite supporting significant smallholder dairy populations [9] . Smallholder dairy farming around Dire Dawa has expanded substantially in recent years as part of national dairy development initiatives, yet veterinary service coverage remains inadequate, and parasitological data to guide evidence-based control strategies are scarce [10] . Understanding the prevalence and risk factor landscape in these emerging dairy corridors is essential for designing costeffective intervention programs. Therefore, this research was undertaken to determine the prevalence of bovine fasciolosis and identify the associated risk factors among smallholder dairy cattle in and around Dire Dawa, eastern Ethiopia.

Material and Methods

Material

The research was conducted from October 2022 to September 2023 in and around Dire Dawa city administration, located in eastern Ethiopia at approximately 9°36'N latitude and 41°52'E longitude, with an altitude ranging from 950 to 2,260 meters above sea level. The area experiences a bimodal rainfall pattern, with mean annual rainfall of 604 mm and average temperatures between 19.7°C and 34.6°C. Four sub-districts (Gendekore, Legehare, Wahil, and Melka Jebdu) were purposively selected based on the concentration of smallholder dairy farms and accessibility. A total of 384 cattle were sampled from 96 smallholder dairy farms using systematic random selection, with an average of four animals per farm. The sample size was determined using the formula for estimating proportions with an expected prevalence of 50%, a 95% confidence interval, and a 5% absolute precision. Ethical clearance was obtained from the Dire Dawa Institute of Agricultural Sciences Institutional Research Ethics Committee (Protocol No. DDIAS/IREC/2022/047). All animal handling procedures adhered to institutional guidelines for the humane treatment of research animals.

Methods: Fresh faecal samples (approximately 10 g each) were collected directly from the rectum of each animal into clean, labeled universal bottles containing 10% formalin and transported in an ice box to the Parasitology Laboratory of the Dire Dawa Institute of Agricultural Sciences within six hours of collection. Faecal examination was performed using the standard sedimentation technique as described by Hendrix and Robinson (2006). Briefly, approximately 3 g of faecal material was mixed with tap water, sieved through a 150-μm mesh, and allowed to sediment for three minutes. The supernatant was discarded, and the process was repeated until the supernatant became clear. The sediment was transferred to a glass slide, stained with methylene blue, covered with a coverslip, and examined under a light microscope at 10× and 40× magnification for the presence of Fasciola eggs. Positive samples were further processed using the Flukefinder diagnostic kit (Flukefinder, Richard A. Foreyt, USA) to improve egg recovery rates and facilitate species differentiation. Fasciola species were identified based on egg morphometry: F. hepatica eggs measured 130-150 μm × 63-90 μm, while F. gigantica eggs measured 156-197 μm × 90-104 μm, following the criteria established by Periago et al. (2008). Samples containing eggs of both size ranges were classified as mixed infections. A structured questionnaire was administered to farm owners to collect data on potential risk factors, including animal age, sex, breed, body condition score (BCS; scored on a 1-5 scale following Nicholson and Butterworth, 1986), management system, grazing area type, water source, deworming history, and farm location. Data were entered into Microsoft Excel 2019 and analyzed using STATA version 17.0. Prevalence was calculated as the number of positive samples divided by the total number examined. Univariable logistic regression was performed for each potential risk factor, and variables with p<0.25 were entered into a multivariable logistic regression model using backward stepwise elimination. Statistical significance was set at p<0.05. Odds ratios with 95% confidence intervals were computed to quantify the strength of associations.

Results

Of the 384 cattle examined, 117 (30.5%; 95% CI: 25.9-35.1) were positive for Fasciola eggs by the standard sedimentation technique. Among the positive samples, Fasciola hepatica was identified in 61 (52.3%) animals, Fasciola gigantica in 41 (34.8%), and mixed infections in 15 (12.9%). The prevalence varied significantly across the four sub-districts, ranging from 22.9% in Melka Jebdu to 39.6% in Gendekore (χ² = 8.74; p = 0.033). Age-stratified analysis revealed a statistically significant association between age group and fasciolosis prevalence (χ² = 14.82; p = 0.002). The highest prevalence was recorded in cattle aged 5-7 years (41.6%), followed by those older than 7 years (28.9%), 2-4 years (32.4%), and animals younger than 2 years (18.7%). The decline in prevalence among the oldest age category may reflect acquired partial immunity following repeated exposure or survivorship bias in the sampled population. The multivariable logistic regression model identified four variables as independent predictors of bovine fasciolosis. Cattle aged 5-7 years had 3.42 times higher odds of infection compared to those younger than 2 years (p<0.001). Animals with poor body condition were 2.91 times more likely to be infected than those in good condition (p = 0.001). Grazing on marshy pastures conferred the highest risk, with an odds ratio of 4.17 (p<0.001). Cattle without anthelmintic treatment history had 2.68 times greater odds of infection (p = 0.003). Species identification among the 117 positive samples revealed that Fasciola hepatica was the predominant species (52.3%), followed by Fasciola gigantica (34.8%) and mixed infections (12.9%). The co-occurrence of both species reflects the transitional agro-ecological characteristics of the Dire Dawa area, which spans altitudes from lowland to midland zones, providing suitable habitats for both Lymnaea truncatula and Lymnaea natalensis, the respective intermediate hosts of F. hepatica and F. gigantica. in the Somali region of Ethiopia [11] . The prevalence observed in the current investigation was, however, lower than the 45.6-62.8% reported from highland areas of central and western Ethiopia [7] , which is consistent with the generally lower fasciolosis burden expected in semi-arid lowland environments where intermediate snail host habitats are less abundant [12] . The predominance of Fasciola hepatica (52.3%) over Fasciola gigantica (34.8%) among positive cases was somewhat unexpected given the predominantly lowland topography of Dire Dawa. However, the sampled area spans a considerable altitudinal range (950-2,260 m), and the higher elevation subdistricts, particularly Gendekore and Wahil, provide environmental conditions conducive to the survival of Lymnaea truncatula [13] . The 12.9% mixed infection rate is consistent with findings from other transitional zones in East Africa, where overlapping habitats of both snail species facilitate co-transmission of both Fasciola species [3] . The significant association between increasing age and fasciolosis prevalence, particularly the peak at 5-7 years, reflects the cumulative nature of exposure in grazing animals. Older cattle have longer exposure duration to contaminated pastures and water sources, thereby accumulating greater parasite burdens over time [14] . The apparent decline in prevalence among cattle older than 7 years may indicate the development of partial acquired immunity, as has been documented in chronically exposed populations, or may reflect selective removal of heavily infected animals from herds [15] . Poor body condition emerged as a significant risk factor (OR = 2.91), consistent with the well-documented bidirectional relationship between fasciolosis and nutritional status. Fasciola infection directly impairs hepatic function, reduces feed conversion efficiency, and decreases appetite, leading to progressive body condition deterioration [16] . Conversely, cattle in poor nutritional condition may have compromised immune responses, rendering them more susceptible to parasite establishment and proliferation [17] .

The strong association between marshy grazing areas and bovine fasciolosis (OR = 4.17) underscores the fundamental role of intermediate snail host ecology in the transmission dynamics of the parasite. Marshy areas with slow-moving or stagnant water provide optimal habitats for Lymnaea species, where cercariae encyst on herbage as metacercariae, the infective stage for definitive hosts [6] . This finding emphasizes the practical importance of restricting cattle access to known snail habitats as a key component of integrated fasciolosis control programs [18] . The protective effect of anthelmintic treatment history (OR = 2.68 for untreated cattle) highlights the continued relevance of strategic chemotherapy in fasciolosis control. However, the relatively high prevalence even among treated animals (19.3%) suggests that treatment coverage, timing, and drug quality may be suboptimal in the research area. Similar concerns regarding anthelmintic efficacy and treatment adherence have been raised in other smallholder livestock systems across sub-Saharan Africa [19] .

Epidemiological Significance

The epidemiological findings from this research carry important implications for livestock health policy in eastern Ethiopia. The identification of modifiable risk factors, particularly grazing management practices and deworming protocols, provides actionable entry points for intervention design. The co-existence of both Fasciola species within the research area necessitates diagnostic approaches capable of species differentiation, as this influences treatment selection and pasture management recommendations. Furthermore, the spatial clustering of high-prevalence areas around marshy landscapes suggests that geographic information systembased risk mapping could substantially improve the targeting efficiency of control programs in the region.

Limitations and Future Directions

Acknowledgement

AcknowledgementsThis research was financially supported by the Dire Dawa Institute of Agricultural Sciences Research. The authors acknowledge the Parasitology Laboratory of the Dire Dawa Institute of Agricultural Sciences for providing diagnostic facilities and technical support. The contributions of field veterinary technicians who assisted in sample collection and questionnaire administration are gratefully recognized.

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