Bluetongue disease in small ruminants in south western Ethiopia: cross-sectional sero-epidemiological study

Bluetongue virus infection in cattle: serosurvey and its associated risk factors

Bluetongue virus (BTV) is a vector-borne virus that primarily affects sheep. However, the disease is usually asymptomatic in cattle without obvious clinical signs related to BTV infection. Although there is evidence of BTV antibodies through serology in Egypt, it is still unknown whether Egyptian cattle have ever been exposed to the virus in the north or south of the country. The study's aims were to determine the seroprevalence of BTV and evaluate the potential risk factors for BTV infection in cattle in Egypt. We used a competitive ELISA to screen 690 healthy cattle for BTV-specific immunoglobulin G (IgG) antibodies in four governorates in Egypt. A total seroprevalence of BTV antibodies in examined cattle was 51.47%, 95%CI: 48.01-55.45. The odds of BTV seropositivity were higher in Aswan (OR=1.30, 95%CI: 0.71-2.36), females (OR=3.29, 95%CI: 1.87-5.79), and elder cattle >8 years (OR=12.91, 95%CI: 6.63-25.13). Moreover, cattle contacted with other animals (OR=1.40, 95%CI: 0.94-2.10), with history of abortion (OR=4.88, 95%CI: 3.14-7.59), and those living with presence of insects (OR=12.34, 95%CI: 8-19.30) were more likely to be infected with bluetongue (BT). To effectively predict and respond to a potential BTV outbreak in Egypt, surveillance for BTV infection should be expanded to cover other susceptible ruminants and the range of the insect vectors.

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.

Serological evidence of bluetongue virus and associated factors in small ruminants of Bangladesh

Bluetongue (BT) is an infectious, vector-borne viral disease of animals having a substantial economic impact and it is endemic in the bordering states of the Indian subcontinent. Livestock enters frequently from India into Bangladesh without any screening. Hence, this study aimed to estimate the seroprevalence of Bluetongue virus (BTV) and associated risk factors in small ruminants of Bangladesh. We conducted a cross-sectional study in the Dhaka, Chattogram, and Faridpur districts of Bangladesh between 2017 and 2018. The team collected 333 serum samples from 123 goats and 210 sheep and tested them for the presence of antibodies against BTV using a competitive enzyme linked immunosorbent assay (c-ELISA). A mixed multivariable logistic regression model was built to identify risk factors. Sample collection location was included as a random effect and husbandry and demographic variables as fixed effects to identify the potential risk factors. The BTV seroprevalence was found to be 55.3% (n = 184; 95% CI: 49.74-60.68). In the mixed-effect logistic regression analysis, animal species (AOR: 4.69; 95% CI: 2.49-8.82; p = 0.001) and vector control measurement (AOR: 9.01; 95% CI: 4.01-20.00; p = 0.0001) were significantly associated with BTV seropositivity. However, no significant association was found in multivariable mixed-effect logistic regression for the variables age, body condition score (BCS), vaccination against PPR (p > 0.05). The study found evidence of high seroprevalence of BTV in both sheep and goats in different districts of Bangladesh, indicating natural exposure of the virus and the animals can serve as a potential threat for other animals. Further research is needed to isolate and identify the circulating virus serotype(s) of BTV in Bangladesh as well as longitudinal studies for epidemiological investigations to formulate sound control programs and to enhance the awareness about the possible impacts of this disease on the livelihood of the people.

Serological and molecular prevalence study of bluetongue virus in small domestic ruminants in Morocco

Bluetongue is an arthropod-borne viral disease transmitted by Culicoides biting midges, affecting domestic and wild ruminants. The current study aims to assess the seroprevalence of the bluetongue virus (BTV) and confirm its active circulation among sheep and goats populations in Morocco, as well as study the risk factors associated with BTV infection. To this end, a total of 1651 samples were randomly collected from 1376 sheep and 275 goats in eight (out of 12) regions of the country between March 2018 and July 2021.These samples were primarily tested using competitive ELISA (c-ELISA). Subsequently, 65% of c-ELISA positives (n = 452) were analyzed by real-time reverse transcription-polymerase chain reaction (RT-qPCR). The results revealed an overall BTV seroprevalence in small ruminants in Morocco of 41.7%, including 42.6% in sheep and 37.5% in goats. The RT-qPCR results showed that the overall BTV viropositivity rate was 46.7%, including 48.1% in sheep and 41.8% in goats. These viro-serological rates varied significantly by age, sex, and breed of the tested animals, husbandry method, season, and geographic origin. This indicates that these parameters constitute risk factors for BTV transmission routes in Morocco. The findings also indicate that goats play a role as reservoirs in maintaining the BTV in Morocco. It appears from this study that bluetongue is endemic in Morocco. The environmental and climate conditions as well as the husbandry methods adopted in the country are particularly favorable for the virus transmission throughout the country.

Seroprevalence of Bluetongue Virus Antibodies in Ovine in Maji District of West Omo Zone, Southwest Ethiopia

BACKGROUND

Bluetongue (BT) disease is an arthropod-transmitted viral disease of domestic and wild ruminant species caused by Bluetongue virus (BTV). It is of most importance in sheep and endemic primarily in the tropical and subtropical regions where vectors (Culicoides species) are present.

MATERIALS AND METHODS

A cross-sectional study was conducted in July-November 2019 to examine the seroprevalence of BTV infection in ovine in Maji district of West Omo zone. Serum samples were examined for the presence of specific antibodies of BTV using competitive enzyme-linked immunosorbent assay (c-ELISA) test. The collected data was coded and analyzed using STATA version 13 software. Associations between sero-prevalence and its risk factors were tested in a Chi-square analysis and with a P<0.05 were considered as statistically significant.

RESULTS

The individual animal prevalence was revealed as 39.23% (153/390). Herd size prevalence was: small size herd (37.42%; 61/163), medium size herd (32.35%; 55/170), and large size herd (64.91%; 37/57). Species-based prevalence showed ovine (38.00%; 141/371) and caprine (63.15%; 12/19). Age-based prevalence revealed adult (39.26%; 150/382) and young (37.5%; 3/8). The cumulative sex prevalence for both ovine and caprine was male (37.95%; 52/137) and female (39.92%; 101/253).

CONCLUSION

The current prevalence of BTV antibodies in the area was found to be high. Lack of application of bluetongue disease control mechanisms like vaccination for the animals is a key factors for the high prevalence of the disease in the areas besides the existence of the vectors.

Insight on Bluetongue virus transmission in small ruminants in Senegal

Bluetongue (BT) is an infectious, arthropod-borne viral disease of domestic and wild ruminants. The disease causes animal mortality, production decrease and commercial limits for herds. Despite the active circulation of the disease in the world, few studies have been carried out in Senegal. The objective of this study was to assess the current prevalence of BT in small ruminants and the serotypes circulating in Senegal. A cross-sectional study was conducted in the fourteen regions of Senegal. After the sampling campaign, sera collected in sheep and goats herds were screened for the presence of Bluetongue virus (BTV) specific antibodies using c-Elisa. The whole blood of seropositive animals was further analyzed by RT-qPCR and positive samples were typed to identify BTV serotypes. Analysis of several risk factors such as age, sex and species of animals was performed using logistic regression. The overall seroprevalence of BTV in Senegal was 72.6% (95% CI: 70.3-74.9%) with 75.9% (95% CI: 72.2-79.5%) in goat and 70.6% (95% CI: 67.5-73.6%) in sheep. Female (prevalence=77.1%) and adult (prevalence=80%) animals showed the highest seropositivity to BTV compared respectively to male (55.7%, p=6.133e-09) and young (49.4%, p < 2.2e-16). The RT-qPCR results showed the presence of BT viral genome in 359 small ruminants. The results obtained from serological and genotyping studies showed an active spread of the Bluetongue virus in domestic ruminants and phylogenetic analysis showed that the BTV-2 is one of the circulating serotypes in Senegal. This study allows having baseline information for controlling Bluetongue in Senegal.

Modeling the spatial distribution of Culicoides species (Diptera: Ceratopogonidae) as vectors of animal diseases in Ethiopia

Culicoides biting midges (Diptera: Ceratopogonidae) are the major vectors of bluetongue, Schmallenberg, and African horse sickness viruses. This study was conducted to survey Culicoides species in different parts of Ethiopia and to develop habitat suitability for the major Culicoides species in Ethiopia. Culicoides traps were set in different parts of the country from December 2018 to April 2021 using UV light Onderstepoort traps and the collected Culicoides were sorted to species level. To develop the species distribution model for the two predominant Culicoides species, namely Culicoides imicola and C. kingi, an ensemble modeling technique was used with the Biomod2 package of R software. KAPPA True skill statistics (TSS) and ROC curve were used to evaluate the accuracy of species distribution models. In the ensemble modeling, models which score TSS values greater than 0.8 were considered. Negative binomialregression models were used to evaluate the relationship between C. imicola and C. kingi catch and various environmental and climatic factors. During the study period, a total of 9148 Culicoides were collected from 66 trapping sites. Of the total 9148, 8576 of them belongs to seven species and the remaining 572 Culicoides were unidentified. The predominant species was C. imicola (52.8%), followed by C. kingi (23.6%). The abundance of these two species was highly influenced by the agro-ecological zone of the capture sites and the proximity of the capture sites to livestock farms. Climatic variables such as mean annual minimum and maximum temperature and mean annual rainfall were found to influence the catch of C. imicola at the different study sites. The ensemble model performed very well for both species with KAPPA (0.9), TSS (0.98), and ROC (0.999) for C. imicola and KAPPA (0.889), TSS (0.999), and ROC (0.999) for C. kingi. Culicoides imicola has a larger suitability range compared to C. kingi. The Great Rift Valley in Ethiopia, the southern and eastern parts of the country, and the areas along the Blue Nile and Lake Tana basins in northern Ethiopia were particularly suitable for C. imicola. High suitability for C. kingi was found in central Ethiopia and the Southern Nations, Nationalities and Peoples Region (SNNPR). The habitat suitability model developed here could help researchers better understand where the above vector-borne diseases are likely to occur and target surveillance to high-risk areas.

Prospective cohort study reveals unexpected aetiologies of livestock abortion in northern Tanzania

Livestock abortion is an important cause of productivity losses worldwide and many infectious causes of abortion are zoonotic pathogens that impact on human health. Little is known about the relative importance of infectious causes of livestock abortion in Africa, including in subsistence farming communities that are critically dependent on livestock for food, income, and wellbeing. We conducted a prospective cohort study of livestock abortion, supported by cross-sectional serosurveillance, to determine aetiologies of livestock abortions in livestock in Tanzania. This approach generated several important findings including detection of a Rift Valley fever virus outbreak in cattle; high prevalence of C. burnetii infection in livestock; and the first report of Neospora caninum, Toxoplasma gondii, and pestiviruses associated with livestock abortion in Tanzania. Our approach provides a model for abortion surveillance in resource-limited settings. Our findings add substantially to current knowledge in sub-Saharan Africa, providing important evidence from which to prioritise disease interventions.

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

BACKGROUND

Bluetongue (BT), a vector-borne disease of wild and domestic ruminants, is responsible for severe economic losses in flocks. To reduce this impact, a surveillance and control plan was implemented in Tunisia. However, the epidemiological situation of BT remains incompletely understood, especially for the circulating serotypes.

OBJECTIVE

The aim of this survey was to determine the seroprevalence, to identify the circulating serotypes and to identify the associated risk factors for bluetongue virus (BTV) circulation in Tunisia using risk-based sampling (RBS).

METHODS

A total of 3314 blood samples were randomly collected from 67 sectors using risk-based sampling and screened by competitive enzyme-linked immunosorbent assays (c-ELISAs). Out of the 1330 positive samples, 200 samples were analysed by serum neutralization test (SNT) to identify circulating BTV serotypes.

RESULTS

Of 3314 sera, 1330 were c-ELISA-positive (40.1%) for antibodies against the BTV structural protein VP7. The result of SNT showed the presence of BTV-1, BTV-2, BTV-3, BTV-4 and, for the first time in Tunisia, BTV-26. The logistic regression model revealed that older animals had nearly two times the odds of being infected with BTV compared to younger animals. Flocks with a history of BT were almost 1.5 times more likely to be at risk for contracting BTV infection. The flock size, housing indoors and intensive production system were significant protective factors.

CONCLUSIONS

High seroprevalence of BTV among sheep was highlighted in Tunisia. The neutralization test showed the presence of the following BTV serotypes: BTV-1, BTV-2, BTV-3, BTV-4 and, for the first time in Tunisia, BTV-26. Age, production system and flock size were important variables associated with BTV infection in sheep. This finding is crucial, as it will allow the adjustment of the BT control programme in Tunisia.

Prioritizing smallholder animal health needs in East Africa, West Africa, and South Asia using three approaches: Literature review, expert workshops, and practitioner surveys

Managing the health needs of livestock contributes to reducing poverty and improving the livelihoods of smallholder and pastoralist livestock keepers globally. Animal health practitioners, producers, policymakers, and researchers all must prioritize how to mobilize limited resources. This study employed three approaches to prioritize animal health needs in East and West Africa and South Asia to identify diseases and syndromes that impact livestock keepers. The approaches were a) systematic literature review, b) a series of expert workshops, and c) a practitioner survey of veterinarians and para-veterinary professionals. The top constraints that emerged from all three approaches include endo/ ectoparasites, foot and mouth disease, brucellosis, peste des petits ruminants, Newcastle disease, and avian influenza. Expert workshops additionally identified contagious caprine pleuropneumonia, contagious bovine pleuropneumonia, mastitis, and reproductive disorders as constraints not emphasized in the literature review. Practitioner survey results additionally identified nutrition as a constraint for smallholder dairy and pastoralist small ruminant production. Experts attending the workshops agreed most constraints can be managed using existing veterinary technologies and best husbandry practices, which supports a shift away from focusing on individual diseases and new technologies towards addressing systemic challenges that limit access to veterinary services and inputs. Few research studies focused on incidence/ prevalence of disease and impact, suggesting better incorporation of socio-economic impact measures in future research would better represent the interests of livestock keepers.

Global emergence and evolutionary dynamics of bluetongue virus

Bluetongue virus (BTV) epidemics are responsible for worldwide economic losses of up to US$ 3 billion. Understanding the global evolutionary epidemiology of BTV is critical in designing intervention programs. Here we employed phylodynamic models to quantify the evolutionary characteristics, spatiotemporal origins, and multi-host transmission dynamics of BTV across the globe. We inferred that goats are the ancestral hosts for BTV but are less likely to be important for cross-species transmission, sheep and cattle continue to be important for the transmission and maintenance of infection between other species. Our models pointed to China and India, countries with the highest population of goats, as the likely ancestral country for BTV emergence and dispersal worldwide over 1000 years ago. However, the increased diversification and dispersal of BTV coincided with the initiation of transcontinental livestock trade after the 1850s. Our analysis uncovered important epidemiological aspects of BTV that may guide future molecular surveillance of BTV.

Serological Investigations of Bluetongue Virus (BTV) among Sheep and Goats in Kassala State, Eastern Sudan

Bluetongue (BT) is an infectious, noncontagious, vector-borne viral disease of wild and domestic ruminants. BTV is a member of the Orbivirus genus of the family Reoviridae. The present study aimed to investigate the seroprevalence of BTV in sheep and goats in Kassala State, Sudan. It also aimed to determine risk factors associated with BTV infection. The study was carried out by a structured questionnaire survey, and a total of 809 serum samples were collected from sheep (n = 459) and goats (n = 350) from 9 different localities in Kassala state. These samples were analyzed using a competitive enzyme-linked immunosorbent assay (cELISA) for the detection of BTV antibodies. The overall seroprevalence of BTV was 91.2% (738/809). In goats, the prevalence of BTV antibodies was comparatively higher (100%) than in sheep (84.5%). The prevalence differed between localities and was the highest in the center section of Kassala and Western Kassala (100%). Animals aged 6–11 months were highly infected (93.9%) compared to 1-year-old (85.5%). Caprine species was more likely to be infected (100%) than ovine (84.5%), and females were highly infected (92.8%) than males (85.5%). BTV infections were higher in the winter season (91.4%). Risk factors that showed significant associations with cELISA positivity included locality and sex (p ≤ 0.003) and species and age (p ≤ 0.000). Factors significantly associated with cELISA positivity in multivariate analysis were localities, species, age, and sex. BTV infection is prevalent in sheep and goat populations in Kassala state.

Bluetongue Virus Nonstructural Protein 3 Orchestrates Virus Maturation and Drives Non-Lytic Egress via Two Polybasic Motifs

Bluetongue virus (BTV) is an arthropod-borne virus that infects domestic and wild ruminants. The virion is a non-enveloped double-layered particle with an outer capsid that encloses a core containing the segmented double-stranded RNA genome. Although BTV is canonically released by cell lysis, it also exits non-lytically. In infected cells, the BTV nonstructural glycoprotein 3 (NS3) is found to be associated with host membranes and traffics from the endoplasmic reticulum through the Golgi apparatus to the plasma membrane. This suggests a role for NS3 in BTV particle maturation and non-lytic egress. However, the mechanism by which NS3 coordinates these events has not yet been elucidated. Here, we identified two polybasic motifs (PMB1/PMB2), consistent with the membrane binding. Using site-directed mutagenesis, confocal and electron microscopy, and flow cytometry, we demonstrated that PBM1 and PBM2 mutant viruses retained NS3 either in the Golgi apparatus or in the endoplasmic reticulum, suggesting a distinct role for each motif. Mutation of PBM2 motif decreased NS3 export to the cell surface and virus production. However, both mutant viruses produced predominantly inner core particles that remained close to their site of assembly. Together, our data demonstrates that correct trafficking of the NS3 protein is required for virus maturation and release.