Risk-based serological survey of bluetongue and the first evidence of bluetongue virus serotype 26 circulation in Tunisia

Seroprevalence and risk factors of bluetongue virus infection in sheep and goats in West Gondar zone, Northwest Ethiopia

Introduction

Bluetongue is a non-contagious arthropod-borne viral disease that affects ruminants. No investigations have yet been conducted to ascertain the seroprevalence and associated risk factors of bluetongue in Northwest Ethiopia. It is essential to determine the seroprevalence and correlated risk elements to formulate an effective strategy for preventing and surveillance of the disease.

Methods

A cross-sectional study was carried out between February 2023 and May 2023 to determine the seroprevalence and risk factors associated with Bluetongue virus (BTV) in sheep and goats in the selected districts of West Gondar zone. A multistage cluster sampling technique was employed, with zones and districts purposively selected, and kebeles within these districts chosen through simple random sampling. Villages were treated as clusters. A total of 444 blood specimens were collected from the sheep and goats and subsequently tested for BTV antibodies using a commercially available competitive enzyme-linked immunosorbent assay kit. A mixed-effects logistic regression was employed to evaluate the relationship between Bluetongue virus seropositivity and potential risk factors.

Results

The overall seroprevalence rate at the individual animal level was 84.5% (95% CI: 81.09-87.82). The seroprevalence in sheep and goats was 83.8% (257/308) and 86.8% (118/136), respectively. Species and age were significant risk factors for BTV seropositivity in the study area (p < 0.05). Adult and older sheep and goats exhibited 3.49 (95% CI: 1.90-6.41) and 25.95 (95% CI: 9.45-71.28) times higher seroprevalence with the bluetongue virus in comparison to their younger counterparts, respectively.

Discussion

In conclusion, the current findings showed that BTV is highly prevalent. The specific circulating BTV serotypes and the temporal pattern of Bluetongue in the study area remain unknown, necessitating further investigation.

Seroprevalence and risk factors of bluetongue virus in domestic cattle, sheep, goats and camels in Africa: a systematic review and meta-analysis

Bluetongue (BT) is a vector-borne disease affecting wild and domestic ruminants in many parts of the world. Although bluetongue virus (BTV) is widespread in ungulates in Africa, available epidemiological information on BT in this continent is limited. This systematic review and meta-analysis aimed to estimate the seroprevalence of BTV and summarize information on associated risk factors in domestic ruminants and camels in Africa. Systematic searches were conducted from the inception of the database to November 2022 on PubMed/MEDLINE, ScienceDirect, Web of Science, and Google/Google Scholar. Forty-four eligible publications were identified, published in the range from 1973 to 2020, and statistically analyzed. The pooled overall seroprevalence of BTV was 45.02% (95% confidence interval [CI]: 36.00-54.00%). The pooled seroprevalence was 49.70% (95% CI: 34.50-65.00%) in cattle, 47.00% (95% CI: 29.90-64.50%) in goats, 40.80% (95% CI: 19.60-63.90%) in camels, and 36.30% (95% CI: 29.00-44.90%) in sheep. The pooled seroprevalence decreased after 1990 and increased again after 2010. The highest pooled overall seroprevalence was found in the southeastern region, and the highest pooled overall seroprevalence was obtained by Competitive Enzyme-Linked Immunosorbent Assay. Finally, the seroprevalence in females (53.30%, 95% CI: 34.80-71.00%) was significantly higher than in males (28.10%, 95% CI: 17.40-40.30%) (p < 0.05). We showed that antibodies against BTV were common in African ruminants and camels. Monitoring the seroprevalence of BTV, as well as systematic and continuous surveillance of the Culicoides population, are encouraged to prevent and control the spread of BT.

Exposure to Arboviruses in Cattle: Seroprevalence of Rift Valley Fever, Bluetongue, and Epizootic Hemorrhagic Disease Viruses and Risk Factors in Baringo County, Kenya

Rift Valley fever virus (RVFV) causes disease outbreaks in livestock and humans; however, its inter-epidemic circulation is poorly understood, similar to other arboviruses affecting cattle such as bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV). Serum samples were collected in Baringo County, Kenya from 400 cattle, accompanied by a risk factor questionnaire. Serological tests were then conducted to determine the exposure of cattle to RVFV, BTV, and EHDV. RVFV, BTV, and EHDV IgG seroprevalence rates were 15.5%, 91.5%, and 91%, respectively. Seropositivity for RVFV, BTV, and EHDV was significantly higher in adult cattle, as well as in females for RVFV. Cattle with herd owners aged between 30-39 years were less likely to be seropositive for RVFV compared to those with owners over the age of 60 years. High seroprevalence of BTV and EHDV in cattle indicates significant exposure and the subclinical circulation of these viruses, presenting a risk of outbreaks to sheep and naïve cattle. Moreover, the detection of RVFV-seropositive young cattle born after the last reported outbreak suggests inter-epidemic circulation of the virus. Overall, monitoring these arboviruses in cattle is crucial in understanding their distribution and seroprevalence during inter-epidemic periods.

Estimation of the economic impact of a bluetongue serotype 4 outbreak in Tunisia

Introduction

Since 1999, Tunisia has experienced multiple occurrences of Bluetongue (BT) outbreaks, leading to numerous reported cases of infection and mortality in flocks. The re-emergence of the disease in 2020 caused substantial economic losses in cattle, attributed to the incursion of serotype BTV-4.

Methods

To evaluate the economic impact of the recent BT episode, we conducted a retrospective study on outbreaks that occurred in Tunisia between August and November 2020, focusing on the impact at the owner's level and its effects on both small ruminants and cattle. A total of 234 ruminant farms (sheep, cattle, and mixed) were randomly selected across Tunisian governorates and included in the study to estimate both the direct and indirect costs of these outbreaks.

Results

Total costs were calculated as the sum of losses and expenditures resulting from the BT outbreaks. At the animal level, total losses were estimated to range between 116.280 and 207.086 TND for one infected ewe (€33.721 and 60.055). For one lactating cow, costs varied between 2,590.724 and 3,171.107 TND (€751.310 and 919.621). In cattle, exposure to BTV led to a daily unit milk yield decrease of 12.50 to 14.66 L over an average period of 5 months. Diseased sheep experienced weight loss ranging between 4 and 10 kg during the BT outbreaks. The total mean cost of the 2020 BT outbreak in Tunisian investigated farms was estimated at 1,935 million TND (million €561.15) (range: 1,489 and 2,474 million TND; 431.81 and million €717.46). The most influential costs of the total BT outbreaks were the decrease in milk yield, mortality, and veterinary treatment.

Discussion

This study gives valuable insights on the economic impact of the incursion of a new serotype of BT in a naive population in Tunisia. Considering the substantial costs incurred, it is imperative that this disease receives increased attention from stakeholders, including animal owners, veterinary services, practitioners, and decision-makers.

Retrospective Phylodynamic and Phylogeographic Analysis of the Bluetongue Virus in Tunisia

Bluetongue virus (BTV) is an arbovirus considered as a major threat for the global livestock economy. Since 1999, Tunisia has experienced several incursions of BTV, during which numerous cases of infection and mortality have been reported. However, the geographical origin and epidemiological characteristics of these incursions remained unclear. To understand the evolutionary history of BTV emergence in Tunisia, we extracted from Genbank the segment 6 sequences of 7 BTV strains isolated in Tunisia during the period 2000 to 2017 and blasted them to obtain a final dataset of 67 sequences. We subjected the dataset to a Bayesian phylogeography framework inferring geographical origin and serotype as phylodynamic models. Our results suggest that BTV-2 was first introduced in Tunisia in the 1960s and that since 1990s, the country has witnessed the emergence of other typical and atypical BTV serotypes notably BTV-1, BTV-3 and BTV-Y. The reported serotypes have a diverse geographical origin and have been transmitted to Tunisia from countries in the Mediterranean Basin. Interserotype reassortments have been identified among BTV-1, BTV-2 and BTV-Y. This study has provided new insights on the temporal and geographical origin of BTV in Tunisia, suggesting the contribution of animal trade and environment conditions in virus spread.

Epidemiology of bluetongue virus infection among small ruminants in Turkey: Seroprevalence and associated risk factors

Bluetongue (BT) is an endemic disease of small ruminants in Turkey, and it has substantial socio-economic impact at national level. To reduce this impact, vaccination has been used for the control of BT but sporadic outbreaks have been reported. Although sheep and goat farming plays an important role in rural communities, little is known about the BT epidemiological situation in small ruminants in Turkey. Therefore, this study aimed to estimate the seroprevalence of the bluetongue virus (BTV) and to identify the potential risk factors associated with BTV seropositivity in small ruminants. This study was conducted in the Antalya Province in the Mediterranean region of Turkey, from June 2018 to June 2019. A total of 1026 blood samples, from clinically healthy goats (n = 517) and sheep (n = 509), obtained from randomly selected unvaccinated flocks (n = 100) were tested for BTV anti-VP7 antibodies by using a competitive enzyme linked immunosorbent assay test. A questionnaire was administered to the flock owners to obtain data related to sampled flocks and animals. At the animal level, the true prevalence of BTV antibodies was 74.2% (n = 651/1026, 95% CI = 70.7-77.7) with 85.3% (n = 370/509, 95% CI = 80.6-89.9) seropositive sheep and 63.3% (n = 281/517, 95% CI = 58.2-68.4) seropositive goats. The true flock-level seroprevalence of BTV was higher in goats (100.0%, 95% CI = 92.8-100.0) than in sheep (98.8%, 95% CI = 86.6-100.0). The intra-flock seroprevalence within seropositive flocks varied between 36.4% and 100%, with a mean value of 85.5% and 61.9% in sheep and goat flocks, respectively. The logistic regression model revealed that odds of seropositivity for sheep were significantly higher in female animals (OR: 1.8, 95% CI = 1.1-2.9), animals older than 24 months old (OR: 5.8, 95% CI = 3.1-10.8), Pirlak breed (OR: 3.3, 95% CI = 1.1-10.0) and Merino breed (OR: 4.9, 95% CI = 1.6-14.9), whereas for goats, it was higher in female animals (OR: 1.7, 95% CI = 1.0-2.6), animals older than 24 months old (OR: 4.2, 95% CI = 2.7-6.6) and Hair breed (OR: 5.6, 95% CI = 2.8-10.9). The use of insecticides was identified as a protective factor. The present study revealed that BTV infection is widespread in sheep and goats in the Antalya Province. It is recommended to implement biosecurity measures in flocks and use insecticides to mitigate the spread of infection and contact between hosts and vectors.