Seroepidemiology of bluetongue disease in small ruminants of north-east of Iran

Potential roles of Culicoides spp. (Culicoides imicola, Culicoides oxystoma) as biological vectors of bluetongue virus in Yuanyang of Yunnan, P. R. China

Introduction

Culicoides plays a crucial role as an insect vector in the field of veterinary medicine. The transmission of significant viruses such as bluetongue virus (BTV) and African horse sickness virus (AHSV) by this insect poses a substantial threat, leading to the development of severe diseases in domestic animals. This study aimed to explore the Culicoides species, identify their blood-meal sources, and assess the presence of BTV and AHSV carried by Culicoides in Yuanyang County, Yunnan Province. The aim was to gain insights into the potential vectors of these two viruses and elucidate their potential roles in the transmission of pathogens.

Methods

The midges were collected from cattle (Bos indicus), pig (Sus scrofa), and goat (Capra hircus) pens in Yuanyang County, Yunnan Province in June 2020. Initial identification of midges was conducted through morphological characteristics, followed by molecular identification using the cytochrome C oxidase subunit I (COI) gene. The determination of Culicoides blood-meal sources was accomplished using specific primers targeting the cytochrome b (Cyt b) gene from potential hosts. BTV and AHSV RNA were identified in Culicoides pools through the application of reverse transcriptase PCR and quantitative real-time PCR. Nucleotide homology and phylogenetic analysis were performed using MegAlign (DNAStar) and Mega 6.0 software.

Results

A total of 6,300 Culicoides, consisting of C. oxystoma, C. arakawai, C. imicola, and C. innoxius, were collected from cattle, pigs, and goat pens. The engorgement rates for these species were 30.2%, 54.6%, 75%, and 66.7%, respectively. In the cattle pen, the prevailing species is C. oxystoma (100%). In the pig pen, C. arakawai dominates (70%), with C. oxystoma following at 30%. In the goat pen, C. imicola holds the majority (45.45%), trailed by C. oxystoma (25%), C. innoxius (20.45%), and C. arakawai (9.09%). These Culicoides species were identified as feeding on cattle, pigs, goats, chickens (Gallus gallus), and humans (Homo sapiens). The positivity rates for BTV were 20.00% and 11.54% in blood-fed specimens of C. imicola and C. oxystoma, respectively. Conversely, the positivity rates for BTV in non-blood-fed specimens were 0.00% and 6.67% for C. imicola and C. oxystoma, respectively. BTV was not detected in C. arakawai and C. innoxius. The specimens (YY86) from C. imicola that tested positive for BTV had the closest genetic relationship to YTS-4 isolated from Mangshi, Yunnan Province in 1996. All test results for the nucleic acid of AHSV were negative.

Conclusion

The study reveals variations in the species distribution, community composition, blood sucking rate, and blood-feeding sources of Culicoides across different habitats. Notably, C. imicola and C. oxystoma emerge as potential vectors for the transmission of BTV in local animals. Accordingly, this investigation provides crucial insights that can serve as a valuable reference for the prevention and control of BTV in local animals, particularly from the perspective of vector management.

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.

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.

Prevalence and risk factors of bluetongue virus infection in sheep and goats in China: A systematic review and meta-analysis

Bluetongue is a viral disease transmitted by the bite of bloodsucking insects, which mainly occurs in sheep, goats, and cattle. Bluetongue is characterized by fever, leukopenia, and severe catarrhal inflammation of the oral and gastrointestinal mucosa. The present study aimed to evaluate and analyze the prevalence of bluetongue and its associated risk factors in sheep and goats in China. We collected 59 publications from 1988 to 2019 through searches at ScienceDirect, PubMed, the Chongqing VIP Chinese journal database, Wanfang database, and Chinese Web of knowledge. In these studies, a total of 123,982 sheep and goats across 7 regions of China were investigated, and the pooled prevalence of bluetongue in sheep and goats was 18.6%, as assessed using serological methods. The prevalence of bluetongue in Southern China was 30.3%, which was significantly higher than that in Northeastern China (4.7%). The prevalence of bluetongue between sheep (12.9%) and goats (28.1%) was significantly different (P < 0.05). Detection methods subgroup analysis showed that the prevalence of bluetongue was significantly higher (P < 0.05) in the others group (43.8%) than in the agar immunodiffusion (15.9%) and enzyme-linked immunosorbent assay groups (20.5%). In addition, different geographical factors (latitude range, longitude range, altitude range, average precipitation, and average temperature) could affect the prevalence. Our results suggested that bluetongue is widespread in sheep and goats, and sheep and goats in contact with insect media, such as Culicoides, or in a warm and humid environment, could have an increased prevalence of bluetongue disease. Animal disease prevention and control departments should focus on continuous monitoring of the bluetongue epidemic in sheep and goats to prevent and control outbreaks.

Seroprevalence and Risk Factors of the Bluetongue Virus in Cattle in China From 1988 to 2019: A Comprehensive Literature Review and Meta-Analysis

Background: Bluetongue caused by the bluetongue virus (BTV) is a non-contagious and an insect-borne disease mainly affecting domestic and wild ruminants. Bluetongue in cattle is associated with vesicular lesions, weight loss, low milk production, and low reproductive capacity. It should not be ignored as it is associated with large economic losses to the livestock breeding industry in China. Although many studies have investigated bluetongue virus infection in cattle, no nationwide study on the prevalence of bluetongue virus infection in cattle from China has yet been conducted. This meta-analysis aimed to evaluate the seroprevalence and risk factors for bluetongue in cattle. Results: We collected 50 publications from 1988 to 2019 through PubMed, ScienceDirect, Chinese Web of Knowledge (CNKI), VIP Chinese journal database, and Wanfang database. A total of the pooled bluetongue seroprevalence of 12.2% (5,332/87,472) in cattle was tested. The point estimate of bluetongue collected from 2001 to 2011 was 22.5% (95% CI: 1.2-58.9), which was higher than after 2012 (9.9%, 95% CI: 3.3-19.4). The analysis of the feeding model subgroup revealed that the seroprevalence of bluetongue was significantly higher (P < 0.05) among free-range cattle (22.5%; 95% CI: 7.7-42.3) than among cattle from intensive farming systems (1.8%; 95% CI: 0.0-6.7). The seroprevalence of bluetongue in different species showed significant variation (P < 0.05), with the highest seroprevalence of 39.8% (95% CI: 18.7-63.0) in buffalo and the lowest seroprevalence of 4.3% (95% CI: 1.2-9.0) in yak. In the zoogeographical division subgroup, the seroprevalence of bluetongue correlated positively within a certain range with the species distribution of Culicoides. Conclusion: Our findings suggested that bluetongue was prevalent in cattle in China. In addition, the contact with sheep, other ruminants, or transmission media such as Culicoides may increase the seroprevalence of bluetongue disease in cattle. It is necessary to carry out continuous monitoring of the bluetongue seroprevalence. Moreover, comprehensive and improved strategies and measures should be implemented to prevent and control the spread of bluetongue.

Large-scale seroprevalence and risk factors associated with Bluetongue virus in Iran

Bluetongue virus (BTV) remains as an economically major concern in the world. Seroprevalence and potential risk factors of BTV were assessed in a cross-sectional study at both the herd and animal levels in Iran. A total of 73 Epidemiologic Units (E.Unit), defined as a herd, flock or village including animals with equal chance of exposure to infectious agents, were randomly selected. Serum samples from all animals (n = 34,575) within the E.Units were collected and tested for BTV sero-group antibodies by using commercially competitive ELISA test. Using cluster analysis, 90.41 % (95 %, CI: 80.85 %-95.47 %) of the E.Units and 56.13 % (95 % CI: 55.61 %-56.66 %) of the tested animals were detected seropositive against BTV. A seroprevalence rate of 57.59 % (95 % CI: 48.01 %-66.63 %), 65.65 % (95 % CI: 59.10 %-73.74 %) and 27.63 % (95 % CI: 14.40 %-46.43 %) was estimated for sheep, goats and cattle, respectively. At E.Unit (herd) level, density was identified as a great risk factor for the infection (r² = 0.891; P = 0.000), and particularly density of cattle significantly correlated with BTV infection within the E.Units (r² = 0.247; P = 0.019). Using multilevel logistic regression, adjusted odds ratios (ORs) were estimated at individual level. A significantly less risk of BTV infection was evaluated for cattle than for sheep (OR = 0.42, 95 % CI: 0.38-0.47, P < 0.001), while no significant difference was observed between sheep and goat (OR = 1.03, 95 % CI: 0.97-1.10, P = 0.345). Animals over 2 years and between 6 months and 2 years expressed 2.22 (OR = 2.22, 95 % CI: 1.96-2.52, P < 0.001) and 2.18 (OR = 2.18, 95 % CI: 1.92-2.49, P < 0.001) times higher chance for the infection than animals under 6 months. Males were at significantly less risk of the infection than females (OR=0.68, 95 % CI: 0.63-0.74, P < 0.001). Animals kept in industrial farming systems displayed 0.46 (OR=0.46, 95 % CI: 032-0.66, P < 0.001) times less chance than animals kept in traditional farming system for BTV, while animals lived in semi-industrial farming system were found to be at 2.97 (OR=2.97, 95 % CI: 2.41-3.66, P < 0.001) times higher chance for BTV than animals lived in traditional farming system. Furthermore, seropositive animals exhibited a high amount of antibodies against BTV (s) suggesting that viral exposure may have frequently occurred during their lifetimes. This large - scale study yielded information on epidemiology of BTV in Iran that is prerequisite for further research, and also for evaluation of any cost-benefit control measure to be established in an enzootic zone of the virus.

Sero-epidemiology of bluetongue virus (BTV) infection in sheep and goats of Khyber Pakhtunkhwa province of Pakistan

Bluetongue virus (BTV) infection is an emerging hazard in small ruminants having socio-economic impacts on animals and associated people. The current study was aimed to estimate the sero-prevalence and associated risk factors in sheep and goat from Khyber Pakhtunkhwa (KP) province of Pakistan. Three distinct zones (northern, central and southern) with four districts (Mansehra, Abbottabad, Swabi, and Kohat) with a higher population of small ruminants were selected. A total of n = 408 sera originating from sheep (n = 212) and goats (n = 196) were randomly collected for detection of BTV group specific antibodies through competitive ELISA (c-ELISA). Univariable and multiple logistic regressions were applied to assess the potential risk factors associated with the occurrence of this disease. Results showed an overall prevalence of 50.00% (CI = 44.17-54.83) of BTV in both sheep and goats with a significant difference (p < 0.05) among different districts. The prevalence of BTV in sheep was found higher (56.60%, CI = 49.6-63.4) than goats (42.86%, CI = 35.8-50.1). The risk factors identified based on chi-square test were; 1-2 year of animals, herd size and location in sheep while, milking status, ticks infestation, location and herd size for goats (p < 0.05). On the basis of univariable analysis, 1-2 year of animals, and location for sheep while, ticks infestation and location for goats (OR > 1). Multiple logistic regressions conferred only herd size and location as potential risk factors (OR > 1) for BTV in sheep and goats. The study concluded higher prevalence of BTV in sheep than the goats, the risk factors were significantly associated with the occurrence of disease, and together ascertaining the needs to design appropriate disease management and control strategies in sheep and goats.

The development of a real-time reverse transcription-polymerase chain reaction (rRT-PCR) assay using TaqMan technology for the pan detection of bluetongue virus (BTV)

Bluetongue virus (BTV) is an infectious, non-contagious viral disease of domestic and wild ruminants that is transmitted by adult females of certain Culicoides species. Since 2006, several serotypes including BTV-1, 2, 4, 6, 8, 9 and 16, have spread from the Mediterranean basin into Northern Europe for the first time. BTV-8 in particular, caused a major epidemic in northern Europe. As a result, it is evident that most European countries are at risk of BTV infection. The objective of this study was to develop and validate a real-time reverse transcriptase-polymerase chain reaction (rRT-PCR) assay based on TaqMan technology for the detection of representative strains of all BTV serotypes. Primers and probes were based on genome segment 10 of the virus, the NS3 gene. The assay was tested for sensitivity, and specificity. The analytical sensitivity of the rRT-PCR assay was 200 copies of RNA per reaction. The assay did not amplify the closely related orbivirus epizootic hemorrhagic disease virus (EHDV) but successfully detected all BTV reference strains including clinical samples from animals experimentally infected with BTV-8. This real time RT-PCR assay offers a sensitive, specific and rapid alternative assay for the pan detection of BTV that could be used as part of a panel of diagnostic assays for the detection of all serotypes of BTV.