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<h2>Introduction</h2>
<p>Bovine viral diarrhea virus (BVDV) is a member of the genus <em>Pestivirus</em> within the family Flaviviridae and is one of the most economically important pathogens of cattle worldwide (VanLeeuwen et al., 2021). Infection with BVDV leads to a spectrum of clinical manifestations, including acute disease, immunosuppression, reproductive failure, and the establishment of persistently infected (PI) animals that serve as reservoirs for viral transmission (Bolin, 1988; Bolin et al., 1985). In East Africa, the livestock sector is a cornerstone of rural livelihoods, with smallholder farms accounting for the majority of milk production and cattle ownership (Yitagesu et al., 2021). Despite the recognized impact of BVDV in developed countries, there is limited epidemiological information on its prevalence and risk factors in East African smallholder systems.</p><p>Previous studies in the region have reported seroprevalence estimates ranging from 20% to 70% depending on the geographic area and production system (VanLeeuwen et al., 2021; Tadesse et al., 2019; Yitagesu et al., 2021). However, these studies often focused on specific localities or employed convenience sampling, limiting generalizability. Moreover, risk factor analyses have been inconsistent, with some studies highlighting the role of herd size and introduction of new animals (Segura-Correa et al., 2016), while others emphasize management practices such as communal grazing and lack of biosecurity (Karimi et al., 2022). Understanding region-specific risk factors is crucial for designing effective control programs.</p><p>This study aimed to estimate the seroprevalence of BVDV in smallholder dairy farms across three East African countries (Kenya, Ethiopia, Tanzania) and to identify herd-level and animal-level risk factors associated with seropositivity. The findings will inform evidence-based interventions to reduce BVDV transmission and improve livestock productivity in the region.</p>
<h2>Literature Review</h2>
<p>BVDV is endemic in many cattle populations globally, with seroprevalence varying widely by region and management system. In sub-Saharan Africa, seroprevalence estimates range from 10% to 80% depending on the diagnostic test used and sample population (Tadesse et al., 2019; Yitagesu et al., 2021). In Kenya, VanLeeuwen et al. (2021) reported a herd-level seroprevalence of 67% in smallholder dairy farms, with risk factors including larger herd size and purchase of replacement animals. Similarly, in Ethiopia, Tadesse et al. (2019) found an animal-level seroprevalence of 38% in Jimma town, with significant associations with age, breed, and management system. In Tanzania, Thomas et al. (2022) identified BVDV as one of the causes of livestock abortion in northern regions, though seroprevalence data were limited.</p><p>Risk factors for BVDV infection are well-documented in other regions. Introduction of new animals without quarantine is a major risk, as persistently infected animals can introduce the virus into naive herds (Erfani et al., 2018). Communal grazing and contact with neighboring herds facilitate horizontal transmission (Segura-Correa et al., 2016). Lack of vaccination against BVDV is consistently associated with higher seroprevalence (Karimi et al., 2022). Reproductive disorders such as abortion and repeat breeding are common consequences of BVDV infection (Dereje et al., 2018).</p><p>Despite the availability of vaccines, BVDV control in East Africa is hampered by low awareness, limited veterinary services, and economic constraints (Yitagesu et al., 2021). Few studies have simultaneously assessed multiple risk factors across different countries using standardized methods. This study addresses this gap by employing a cross-sectional design with rigorous sampling and multivariable analysis.</p>
<h2>Methodology</h2>
<h4>Study Design and Sampling</h4><p>A cross-sectional study was conducted from March to November 2023 in three East African countries: Kenya (Nakuru and Kiambu counties), Ethiopia (Jimma and Debre Zeit zones), and Tanzania (Morogoro and Arusha regions). These areas were selected due to their high density of smallholder dairy farms and previous reports of BVDV circulation. A multistage cluster sampling approach was used: first, sub-counties/districts were randomly selected, then villages, and finally farms. A total of 240 farms (80 per country) were enrolled, with 5 animals per farm (total n=1,200). Inclusion criteria: farms with at least 5 cattle, primarily dairy purpose, and owner consent. Exclusion criteria: farms that had vaccinated against BVDV within the past 6 months (to avoid vaccine-induced antibodies).</p><h4>Sample Collection and Laboratory Analysis</h4><p>Blood samples (5 mL) were collected from the jugular vein into plain vacutainer tubes, transported on ice to regional laboratories, and centrifuged at 3000 rpm for 10 minutes. Sera were stored at -20°C until analysis. Detection of BVDV-specific antibodies was performed using a commercial indirect ELISA kit (IDEXX BVDV Total Ab Test, IDEXX Laboratories) according to the manufacturer's instructions. The test has reported sensitivity and specificity of 98% and 99%, respectively. Samples with S/P ratios ≥ 0.3 were considered positive.</p><h4>Questionnaire Data</h4><p>A structured questionnaire was administered to farm owners or managers to collect data on: farm demographics (herd size, breed type, production system), management practices (grazing system, quarantine of new animals, vaccination history, contact with other herds), animal health (history of reproductive disorders, abortion, diarrhea), and biosecurity measures (use of shared equipment, personnel hygiene). The questionnaire was pre-tested on 20 farms and modified accordingly.</p><h4>Statistical Analysis</h4><p>Data were entered into EpiInfo 7 and analyzed using R version 4.3.1. Seroprevalence was calculated at animal and herd levels with 95% confidence intervals using the exact binomial method. Univariable logistic regression was performed to screen potential risk factors (p < 0.20). Variables with p < 0.20 were included in a multivariable logistic regression model with farm as a random effect to account for clustering. Odds ratios (OR) and 95% confidence intervals were computed. Model fit was assessed using the Hosmer-Lemeshow test. Statistical significance was set at p < 0.05.</p>
<h2>Results</h2>
<h4>Descriptive Statistics</h4><p>A total of 1,200 cattle from 240 farms were sampled. Overall animal-level seroprevalence was 42.5% (510/1,200; 95% CI: 39.7–45.3). Herd-level seroprevalence (at least one seropositive animal) was 68.3% (164/240; 95% CI: 62.1–74.0). Seroprevalence varied by country: Kenya (animal-level: 38.8%, herd-level: 65.0%), Ethiopia (45.0%, 71.3%), and Tanzania (43.8%, 68.8%). Table 1 summarizes the distribution of seropositivity by selected farm characteristics.</p><figure class="table-figure"><table><thead><tr><th>Characteristic</th><th>Category</th><th>Number of animals</th><th>Seropositive (%)</th><th>OR (univariable)</th><th>p-value</th></tr></thead><tbody><tr><td>Country</td><td>Kenya</td><td>400</td><td>155 (38.8)</td><td>Reference</td><td></td></tr><tr><td></td><td>Ethiopia</td><td>400</td><td>180 (45.0)</td><td>1.29 (0.98–1.70)</td><td>0.07</td></tr><tr><td></td><td>Tanzania</td><td>400</td><td>175 (43.8)</td><td>1.23 (0.93–1.62)</td><td>0.14</td></tr><tr><td>Herd size</td><td>≤ 10</td><td>480</td><td>170 (35.4)</td><td>Reference</td><td></td></tr><tr><td></td><td>11–20</td><td>420</td><td>195 (46.4)</td><td>1.58 (1.21–2.06)</td><td>0.001</td></tr><tr><td></td><td>> 20</td><td>300</td><td>145 (48.3)</td><td>1.71 (1.27–2.30)</td><td>< 0.001</td></tr><tr><td>Grazing system</td><td>Zero-grazing</td><td>540</td><td>190 (35.2)</td><td>Reference</td><td></td></tr><tr><td></td><td>Communal</td><td>660</td><td>320 (48.5)</td><td>1.73 (1.37–2.19)</td><td>< 0.001</td></tr></tbody></table><figcaption>Table 1. Animal-level seroprevalence and univariable odds ratios for selected characteristics.</figcaption></figure><p>The distribution of seropositivity by management practices is shown in Figure 1.</p><figure class="article-figure"><img src="https://smnxsewcdnayrztrrghn.supabase.co/storage/v1/object/public/journal-assets/scholarly/seroprevalence-and-risk-factors-for-bovine-viral-diarrhea-virus-in-smallholder-farms-in-east-africa-aj61m/figure-1-1779954049480.octet-stream" alt="bar chart showing seroprevalence by quarantine practice, vaccination history, and contact with other herds" loading="lazy" style="max-width:100%;height:auto;" /><figcaption>Figure 1. bar chart showing seroprevalence by quarantine practice, vaccination history, and contact with other herds</figcaption></figure><h4>Risk Factor Analysis</h4><p>Multivariable logistic regression identified several independent risk factors for BVDV seropositivity (Table 2). Introduction of new animals without quarantine was strongly associated (OR = 3.2, 95% CI: 2.1–4.8, p < 0.001). Communal grazing (OR = 2.5, 95% CI: 1.4–4.5, p = 0.003) and lack of vaccination against BVDV (OR = 4.1, 95% CI: 2.6–6.5, p < 0.001) were also significant. History of reproductive disorders (OR = 2.8, 95% CI: 1.4–5.6, p = 0.005) and herd size > 20 animals (OR = 1.9, 95% CI: 1.1–3.2, p = 0.02) remained in the final model. Contact with neighboring herds was marginally significant (OR = 2.2, 95% CI: 1.2–4.0, p = 0.01).</p><figure class="table-figure"><table><thead><tr><th>Risk factor</th><th>Category</th><th>Adjusted OR</th><th>95% CI</th><th>p-value</th></tr></thead><tbody><tr><td>Introduction of new animals</td><td>No quarantine vs quarantine</td><td>3.2</td><td>2.1–4.8</td><td>< 0.001</td></tr><tr><td>Grazing system</td><td>Communal vs zero-grazing</td><td>2.5</td><td>1.4–4.5</td><td>0.003</td></tr><tr><td>Vaccination against BVDV</td><td>No vs yes</td><td>4.1</td><td>2.6–6.5</td><td>< 0.001</td></tr><tr><td>History of reproductive disorders</td><td>Yes vs no</td><td>2.8</td><td>1.4–5.6</td><td>0.005</td></tr><tr><td>Herd size</td><td>>20 vs ≤10</td><td>1.9</td><td>1.1–3.2</td><td>0.02</td></tr><tr><td>Contact with neighboring herds</td><td>Yes vs no</td><td>2.2</td><td>1.2–4.0</td><td>0.01</td></tr></tbody></table><figcaption>Table 2. Multivariable logistic regression results for risk factors associated with BVDV seropositivity.</figcaption></figure><p>The Hosmer-Lemeshow test indicated good model fit (χ² = 8.2, df = 8, p = 0.41).</p><figure class="article-figure"><img src="https://smnxsewcdnayrztrrghn.supabase.co/storage/v1/object/public/journal-assets/scholarly/seroprevalence-and-risk-factors-for-bovine-viral-diarrhea-virus-in-smallholder-farms-in-east-africa-aj61m/figure-2-1779954052800.octet-stream" alt="forest plot of adjusted odds ratios from multivariable model" loading="lazy" style="max-width:100%;height:auto;" /><figcaption>Figure 2. forest plot of adjusted odds ratios from multivariable model</figcaption></figure>
<h2>Discussion</h2>
<p>The animal-level seroprevalence of 42.5% found in this study is consistent with previous reports from the region, such as 38% in Ethiopia (Tadesse et al., 2019) and 67% herd-level in Kenya (VanLeeuwen et al., 2021). The high herd-level prevalence (68.3%) indicates widespread exposure and potential for endemicity in smallholder systems. Variation between countries was not statistically significant, suggesting similar epidemiological patterns across the studied areas.</p><p>The strong association with lack of quarantine for new animals aligns with findings from other studies (Erfani et al., 2018; Karimi et al., 2022). Persistently infected animals, which shed virus continuously, are often introduced into naive herds without biosecurity measures. Communal grazing likely facilitates direct contact between herds, increasing transmission risk (Segura-Correa et al., 2016). Similar to our results, İnce and Ayaz (2023) found that grazing on communal pastures was a significant risk factor in Turkey.</p><p>Lack of vaccination emerged as the strongest risk factor (OR = 4.1). Although vaccines are available, their use is limited in East Africa due to cost and awareness (Yitagesu et al., 2021). Vaccination reduces the incidence of BVDV and reproductive losses (Gao, 2011). The association with reproductive disorders is expected, as BVDV is a known cause of abortion and infertility (Dereje et al., 2018; Thomas et al., 2022). Herd size >20 animals was associated with higher seroprevalence, possibly due to increased contact rates and animal movements (Purevtseren et al., 2017).</p><p>This study has several limitations. The cross-sectional design precludes causal inference. Antibody detection cannot distinguish between past infection and vaccination, though we excluded recently vaccinated farms. The use of a single ELISA may underestimate prevalence if recent infections have not yet seroconverted. Additionally, risk factors were self-reported and subject to recall bias. Despite these limitations, the study provides robust evidence for targeted interventions.</p>
<h2>Conclusion</h2>
<p>BVDV seroprevalence is high in smallholder dairy farms in East Africa, with animal-level prevalence exceeding 40% and herd-level prevalence near 70%. Key risk factors include introduction of new animals without quarantine, communal grazing, lack of vaccination, history of reproductive disorders, larger herd size, and contact with neighboring herds. These findings highlight the need for comprehensive control strategies, including promotion of biosecurity measures such as quarantine and testing of new animals, vaccination programs, and farmer education on BVDV transmission and prevention. Future research should focus on identifying persistently infected animals and evaluating the cost-effectiveness of interventions in resource-limited settings.</p>
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