Isolation of Bluetongue Virus Serotype 1 from Culicoides vector Captured in Livestock Farms and Sequence Analysis of the Viral Genome Segment-2

Host-seeking and exophilic-endophilic activities of Culicoides spp. (Diptera: Ceratopogonidae) with notes on two trapping methods

Host-seeking behavior of Culicoides species was examined from 2018 to 2019 in West Bengal, India, which elucidated diel activity, feeding success, attack rate, biting rate, and preferential landing of adult Culicoides on the cattle. A comparative assessment was done between the light trap and the aspirator. The host-seeking experiment involved a substantial timeframe of 297 h of catch collections over 27 nights. The number of adult Culicoides captured in the light trap was 1.3 times higher than the aspirator collections. The species in light trap catch were Culicoides oxystoma Kieffer Culicoides peregrinus Kieffer, and Culicoides fulvus Sen and Das Gupta (Diptera: Ceratopogonidae). However, only C. oxystoma and C. peregrinus were collected using the aspirator. The findings related to feeding success, attack rate, and biting rate carried significant implications for the vectorial potential of C. oxystoma and C. peregrinus. The light trap data suggest that Culicoides species displayed crepuscular behavior, while the aspirator collections peaked 1 h before sunrise, between 04:00 and 05:00 h, and gradually declined. A separate study evaluated the exophily and endophily of Culicoides in 2016 at Memari in West Bengal. To delve into the indoor-outdoor activity, 264 trap collections were made in 4 combinations: Light trap operated in the presence and absence of cattle, placed outdoors and indoors. The study revealed that the outdoor prevalence of midges was 14 times higher than the indoor. There was a 6-time increase in the prevalence of adult Culicoides in the presence of cattle, indicating a preference for outdoor locations for feeding.

Elucidating the life history parameters of Culicoides oxystoma (Diptera: Ceratopogonidae) under varied substrate compositions and temperatures

A comprehensive study was conducted on the life history parameters of an important vector Culicoides oxystoma Kieffer (Diptera: Ceratopogonidae), to standardize potential rearing procedures. Data on life history traits and rearing conditions are crucial for establishing laboratory colony and conducting vector competence-based studies utilizing specimens with a known rearing history. Six different substrate compositions were used to rear the larvae: S1: habitat mud containing cattle manure + nutrient broth + yeast, S2: yeast, S3: habitat mud containing cattle manure + nutrient broth, S4: nutrient broth, S5: sterile (habitat mud consisting cattle manure + nutrient broth + yeast) and S6: tap water. Gravid females preferred ovipositing on beds moistened with tap water compared to distilled water. Egg hatching recorded minimal (3%) in the sterile substrate (S5), hinting at the role of live microbial load. Progression of larval instars got disrupted at 1st instars in S5 and S6. Larval survival and adult emergence were the highest in S1 and the lowest in S4, indicating that S1 is highly effective in the rearing of this species. The life cycle parameters and duration between transitional stages were evaluated at 15 °C, 20 °C, 26 °C, 30 °C, and 35 °C using rearing substrate S1. The highest larval survival (>70%) and adult emergence (69%) were achieved at 26 °C. The duration from egg to adult was 16 to 20 d at 35 °C, 18 to 24 d at 26 °C, but up to 36 d at 15 °C. Elucidating the effective rearing conditionalities of this important vector species will be helpful to study the transmission cycles of pathogens.

Host blood meal analysis of Culicoides oxystoma (Diptera: Ceratopogonidae) in Tunisia

Culicoides are small hematophagous biting midges belonging to the family Ceratopogonidae. The genus is distributed worldwide yet remains poorly studied. This study investigated the vector and host specificity of Culicoides oxystoma, a species of significant relevance to the surveillance of vector-borne diseases in Tunisia and globally. The research was conducted in two Tunisian governments: Tozeur and Kairouan. A total of 24,366 adult midges were collected using two types of suction traps: the Center for Disease Control trap and the Onderstepoort Veterinary Institute trap. Females of Culicoides oxystoma were isolated, carefully dissected, and slide mounted in a phenol alcohol balsam mixture. A portion of the abdomen was excised for total DNA extraction to identify the origin of the blood meal. A total of 108 engorged females were analyzed using polymerase chain reaction (PCR) to amplify specific fragments of the cytochrome b gene, followed by sequencing and sequence analysis. However, DNA sequences were successfully obtained for only 56 individuals. Sequence analysis revealed that the midges fed on a variety of mammalian hosts, including humans, with a prevalence of Mus musculus and Bos taurus. This represents the first study aiming to identify a wide range of hosts in Tunisia and North Africa, providing valuable insights into the hosts utilized by Culicoides oxystoma for blood feeding.

Investigating the influence of blood meal sources on the composition of culturable haemolytic gut bacteria of a wild-caught BTV vector Culicoides oxystoma Kieffer (Diptera: Ceratopogonidae)

Culicoides oxystoma Kieffer (Diptera: Ceratopogonidae) transmits many pathogens, including seven viruses, four protozoa and one nematode. This species has a wide distribution range across northern Afro-tropical, Palearctic, Australian, Indo-Malayan realms with a broad host spectrum, including cattle, buffaloes, sheep, pigs, dogs, horses and even humans. The heterogeneous nature of Culicoides' blood-feeding patterns is well documented, but the influence of various host blood meal sources on gut bacterial composition remains scant. Adult midges were collected during April (2023) by operating UV light traps in cattle, buffalo sheds and poultry farm in Purulia (India). Besides C. oxystoma, eleven Culicoides species were collected across the sheds and farm, seven of which are vectors. Culicoides liui Wirth and Hubert and C. thurmanae Wirth and Hubert are reported from India for the first time. In all the sheds, engorged females of C. oxystoma were ubiquitous. Identification of culturable gut bacteria and the host blood meal of C. oxystoma were done through the polymerase chain reaction (PCR)-based method. Blood meal analysis confirmed the following hosts: cattle, buffaloes and humans. Identification of blood meal of engorged C. oxystoma caught from poultry farm showed positive results for humans but not for birds. Among bacteria, Bacillus cereus was abundant in all of the engorged females. Bacillus paramycoides and Enterococcus faecium were identified from females feeding on cattle and buffaloes' blood, while Alcaligenes faecalis was found in the gut contents of females that fed on cattle and human blood. The gut bacteria Alcaligenes faecalis exhibited alpha haemolytic activity. In contrast, Bacillus sp., B. cereus, B. flexus, B. licheniformis, B. thuringiensis, B. paramycoides, E. faecium, Paenibacillus sp. and Pseudomonas sp. exhibited beta haemolysis. This is the first report on the composition of gut bacteria, with particular emphasis on the haemolytic bacteria of C. oxystoma with different host blood meals. The pathogenic bacteria B. cereus, B. licheniformis and A. faecalis within the females could potentially impact pathogen acquisition and increase the probability of their zoonotic transmissibility.

A preliminary account of Culicoides (Diptera: Ceratopogonidae) from the Andaman and Nicobar Islands with 13 new records and updated species inventory from India

BACKGROUND

The detection of multiple bluetongue virus serotypes, increasing trend in livestock density, rich biological diversity with high endemism, and the status of the Andaman and Nicobar Islands as a popular tourist destination underscore the need for a faunistic survey of medically and veterinary significant vector species, specifically Culicoides, in this region. Moreover, scattered information on Indian Culicoides species complicates the planning and implementation of preventive measures for pathogens transmitted by these vectors. This study aims to provide the first comprehensive account of the Culicoides fauna in the Andaman and Nicobar Islands, India, along with an updated checklist of Indian Culicoides species and their state-wise distribution.

METHODS

Surveys were conducted across various habitats in the Andaman and Nicobar Islands in September 2022 and 2023. Midges were collected using CDC light traps, light sheets, Malaise traps, and manual collection from exposed body parts of the author and volunteers (biting collection). Identification was carried out using relevant taxonomic keys and original descriptions. Additionally, an updated checklist of Indian Culicoides, based on published and grey literature from 1910 to the present, is provided, with an emphasis on their potential role in pathogen transmission.

RESULTS

A total of 3529 adult Culicoides were trapped during the survey, representing 5 subgenera and 3 unplaced species groups. The study recorded 23 Culicoides species, including 13 new species records for India: C. barnetti, C. gouldi, C. flaviscutellaris, C. flavipunctatus, C. hui, C. histrio, C. guttifer, C. perornatus, C. okinawensis, C. quatei, C. obscurus, C. coronalis, and C. kusaiensis.

CONCLUSIONS

The Indian Culicoides fauna now includes 93 valid species, with many of them recognized as confirmed or potential vectors of important pathogens of animal health. The enriched species composition highlights the importance of systematic surveys in this island ecosystem and the need to determine the role of midges, if any, in pathogen transmission.

Isolation and comparative analysis of culturable bacterial communities associated with life stages, breeding and rearing substrates of Culicoides oxystoma Kieffer (Diptera: Ceratopogonidae) vector of bluetongue virus

Culicoides oxystoma Kieffer (Diptera: Ceratopogonidae) has been vectoring several arboviruses, protozoa and nematodes, leading to mortality and morbidity of livestock and wild ruminants in the tropics and subtropics. Insight into the bacterial communities associated with the vector species must be worked out. This work tries to inventorize the bacterial communities associated with this important vector species. Acquisition of gut microbiota may be the parental origin, while some are obtained through feeding during larval stages. Culicoides oxystoma possesses semi-aquatic life cycle strategies for egg-laying and larval survival. The bacteria associated with C. oxystoma were compared throughout (i) life stages: egg, larval instars, pupa, adult: male and female obtained from laboratory colony; (ii) field-collected adult: male and age-graded females; and (iii) natural breeding substrate and artificial rearing substrate. The culture-dependent bacteria were identified by Sanger sequencing of 16S rRNA, and haemolytic bacteria were screened on blood agar. Results show that Firmicutes and Proteobacteria are the predominant Phyla, of which Bacillus spp. was the most abundant across the life stages. Across the life history, Bacillus cereus, Bacillus pumilus, Bacillus tropicus, Lysinibacillus sp. and Paenibacillus sp. were retrieved routinely. Bacillus cereus and Alcaligenes faecalis were detected in the lab-reared specimens and shared between the natural breeding site and rearing medium. From the adults trapped across two locations, B. cereus, Bacillus flexus, A. faecalis, Enterococcus faecium and Pseudomonas sp. were isolated. The bacterial species associated with this vector may influence various physiological traits, such as vectorial capacity, digestion and larval development, which need further investigation.

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.

Molecular identification of Culicoides oxystoma and Culicoides actoni vectors of bluetongue virus

Bluetongue is a non-contagious viral disease causing significant economic losses throughout the world. The bluetongue vectors Culicoides oxystoma and Culicoides actoni, which play a significant role in the transmission of various pathogens, are distributed across different geographical realms. Adults are minute in size with wide phenotypic variation, so morphology-based species identification is severely constrained by preparatory time and shortage of taxonomic expertise. To make the identification process rapid and effective, a specific primer was designed for the identification of C. actoni based on the multiple sequence alignment of ITS1 sequences of 11 Culicoides species. Along with this, a refined version of existing C. oxystoma specific primer was proposed. The primer sets distinguished C. oxystoma and C. actoni from a pooled sample consisting of other Culicoides species as well as closely related genera such as Forcipomyia and Alluaudomyia. Our findings suggest that the primers were species specific, sensitive and have potential to discriminate vector species C. oxystoma and C. actoni from pooled samples. To the best of our knowledge, these are the first ITS1 sequences generated and submitted in GenBank for Culicoides innoxius, Culicoides shortti, Culicoides palpifer and Culicoides anophelis and the first for Culicoides peregrinus, Culicoides fulvus and C. actoni from India.

Development of ELISA for the detection of antibodies against VP2 protein of bluetongue virus serotype-1

Serotype-specific diagnosis of bluetongue virus (BTV) is necessary for sero-surveillance and taking effective control measures. The VP2 is the major serotype determining protein and BTV-1 is the most predominant serotype in India. In the present study, an indirect ELISA (i-ELISA) was optimized for the detection of serotype-specific antibody against BTV-1 serotype. The VP2 protein of BTV-1 was expressed in a prokaryotic expression system and used to optimize i-ELISA to detect VP2 antibodies of BTV-1 in serum samples of both small and large ruminants. Serum samples (n = 363) classified as positive and negative for antibodies to BTV-1 by serum neutralization test (SNT) and also positive and negative for BTV antibodies by c-ELSIA kit (VMRD, USA) were used to determine the cut-off value, diagnostic sensitivity (DSn), and diagnostic specificity (D-Sp) using receiver operating characteristic (ROC) analysis. The percent positivity (PP) value >30.10% was accepted as the cut-off for i-ELISA at which DSn of 99.52% and D-Sp of 99.35% was observed with a 95% confidence interval. Further, there was no cross-reactivity with other available BTV serotypes in the country. The study indicated serotype-specific i-ELISA is sensitive, specific and suitable alternative to tedious SNT method for determining serotype. The assay will also help in the serotype-specific epidemiological studies and implementation of future control strategies including vaccination and selection of suitable serotype as a vaccine candidate.

Preliminary Study on Comparative Efficacy of Four Light Sources for Trapping Culicoides spp. (Diptera: Ceratopogonidae) in Prachuap Khiri Khan Province, Thailand

The light trap is an important tool to determine the presence and abundance of vectors in the field. However, no one has studied the efficiency of light traps for collecting Culicoides in Thailand. In the present study, the efficacy of four light sources was evaluated in Prachuap Khiri Khan province, Thailand. Incandescent (INCND) light, white fluorescent (WHT-FLR) light, ultraviolet fluorescent (UV-FLR) light, and UV light-emitting diode (UV-LED) light were tested using commercial traps. In total, 30,866 individuals of Culicoides species were collected from November 2020 to June 2021, of which 21,016 were trapped on site 1 and 6,731 were trapped on site 2. The two most abundant Culicoides species were C. imicola (54%) and C. oxystoma (31.2%). UV-FLR was highly effective, followed by UV-LED light, WHT-FLR light, and INCND light, respectively, for Culicoides collection. Significantly, more Culicoides species were collected in those traps baited with UV-FLR light, UV-LED light, or WHT-FLR light than for INCND light traps. Traps equipped with UV-FLR lights can be recommended to trap Culcoides biting midges for monitoring purposes.

Morphological and molecular differentiation between Culicoides oxystoma and Culicoides kingi (Diptera: Ceratopogonidae) in Tunisia

Background

Culicoides kingi and Culicoides oxystoma belong to the Schultzei group of biting midges. These two species are vectors of disease in livestock of economic importance. As described in the literature, morphological identification for discrimination between them is still unclear. However, species-specific identification is necessary to solve taxonomic challenges between species and to understand their roles in disease transmission and epidemiology. This study aims to develop accurate tools to discriminate C. oxystoma from C. kingi using traditional morphometry and polymerase chain reaction-restriction fragment length polymorphism (PCR RFLP) assays for use in developing countries.

Methods

Specimens were collected from the region of Kairouan in central Tunisia. A total of 446 C. oxystoma/C. kingi individuals were identified using traditional morphometric analyses combined with PCR–RFLP of the cytochrome c oxidase subunit I gene. Thirteen morphometric measurements were performed from the head, wings, and abdomen of slide-mounted specimens, and six ratios were calculated between these measurements. Multivariate analyses of the morphometric measurements were explored to identify which variables could lead to accurate species identification.

Results

Four variables, namely antennae, wings, spermathecae, and palpus length, were suitable morphometric characteristics to differentiate between the species. Digestion with the SspI restriction enzyme of the PCR product led to good discriminative ability. Molecular procedures and phylogenetic analysis confirmed the efficiency of this simple and rapid PCR–RFLP method.

Conclusions

This study highlights for the first time in Tunisia the presence of C. oxystoma and its discrimination from C. kingi using abdominal measurements and the PCR–RFLP method. This approach could be applied in future epidemiological studies at the national and international levels.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-05084-8.

Abundance, diversity and temporal activity of adult Culicoides spp. associated with cattle in West Bengal, India

Relative abundance, species composition and temporal activity of Culicoides midges were studied for a period of 2 years (2012-2014) using suction ultra violet light traps at two sites located in the agriculture heartland of West Bengal, India. Surveillance in close proximity to cattle recorded predominance of five species with C oxystoma and C. peregrinus as the most dominant species followed by C. fulvus, C. innoxius and C. anophelis. The temporal activity of midges was investigated for seven consecutive nights at one site in August-September, 2012 and the predominant species was Culicoides oxystoma followed by Culicoides peregrinus. All of the species exhibited crepuscular activity with their flight activity increasing from dusk to dawn. Engorged adults constituted dominant age group in collections. Studies on population ecology of the adults midges are of considerable importance predicting for the epidemicity of midge-borne diseases in cattle.

Ecological niche modelling to estimate the distribution of Culicoides, potential vectors of bluetongue virus in Senegal

BACKGROUND

Vector-borne diseases are among the leading causes of morbidity and mortality in humans and animals. In the Afrotropical region, some are transmitted by Culicoides, such as Akabane, bluetongue, epizootic haemorrhagic fever and African horse sickness viruses. Bluetongue virus infection has an enormous impact on ruminant production, due to its high morbidity and mortality rates.

METHODS

A nationwide Culicoides trapping campaign was organized at the end of the 2012 rainy season in Senegal. A Maximum Entropy approach (MaxEnt), Boosted Regression Tree (BRT) method and Ecological Niche Factor Analysis (ENFA) were used to develop a predictive spatial model for the distribution of Culicoides, using bio-climatic variables, livestock densities and altitude.

RESULTS

The altitude, maximum temperature of the warmest month, precipitation of the warmest quarter, mean temperature of the wettest quarter, temperature seasonality, precipitation of the wettest quarter and livestock density were among the most important factors to predict suitable habitats of Culicoides. Culicoides occurrences were, in most of the cases, positively correlated to precipitation variables and livestock densities; and negatively correlated to the altitude and temperature indices. The Niayes area and the Groundnut basin were the most suitable habitats predicted.

CONCLUSION

We present ecological niche models for different Culicoides species, namely C. imicola, C. oxystoma, C. enderleini and C. miombo, potential vectors of bluetongue virus, on a nationwide scale in Senegal. Through our modelling approach, we were able to determine the effect of bioclimatic variables on Culicoides habitats and were able to generate maps for the occurrence of Culicoides species. This information will be helpful in developing risk maps for disease outbreaks.

Isolation of haemolytic bacilli from field-collected Culicoides oxystoma and Culicoides peregrinus: potential vectors of bluetongue virus in West Bengal, India

Two haemolytic bacterial strains of Bacillus pumilus (CU1A, CU1B) and one blood-utilizing strain of Bacillus licheniformis (CU2B) were isolated from relatively low numbers of field-collected females of Culicoides oxystoma and Culicoides peregrinus (Diptera: Ceratopogonidae). A total of 36 females, including 18 of each of C. oxystoma and C. peregrinus (consisting of one and a pool of eight blood-engorged specimens, and one and a pool of eight non-engorged specimens for each species), were tested. In C. oxystoma, all three strains of bacteria were isolated from the one non-engorged, the pool of non-engorged and the pool of blood-engorged females tested, but CU1A and CU2B were not found in the one blood-engorged female tested. In C. peregrinus, all three strains were present in the pool of blood-engorged females. However, the strain CU2B was not found in the pool of non-engorged females. In the one blood-engorged and one non-engorged female tested, CU1A and CU2B were detected. The bacterial strains were identified based on Gram staining, enzyme activity (amylase and protease) and alignment of the 16S rRNA partial gene sequence to that available in the National Center for Biotechnology Information (NCBI) database GenBank. The functional role and significance of these haemolytic and blood-digesting bacteria within the genus Culicoides remain to be determined.

Circadian activity of Culicoides oxystoma (Diptera: Ceratopogonidae), potential vector of bluetongue and African horse sickness viruses in the Niayes area, Senegal

Culicoides biting midges (Diptera: Ceratopogonidae) are important vectors of arboviruses in Africa. Culicoides oxystoma has been recently recorded in the Niayes region of Senegal (West Africa) and its high abundance on horses suggests a potential implication in the transmission of the African horse sickness virus in this region. This species is also suspected to transmit bluetongue virus to imported breeds of sheep. Little information is available on the biology and ecology of Culicoides in Africa. Therefore, understanding the circadian host-seeking activity of this putative vector is of primary importance to assess the risk of the transmission of Culicoides-borne pathogens. To achieve this objective, midges were collected using a sheep-baited trap over two consecutive 24-h periods during four seasons in 2012. A total of 441 Culicoides, belonging to nine species including 418 (94.8%) specimens of C. oxystoma, were collected. C. oxystoma presented a bimodal circadian host-seeking activity at sunrise and sunset in July and was active 3 h after sunrise in April. Daily activity appeared mainly related to time periods. Morning activity increased with the increasing temperature up to about 27 °C and then decreased with the decreasing humidity, suggesting thermal limits for C. oxystoma activity. Evening activity increased with the increasing humidity and the decreasing temperature, comprised between 20 and 27 °C according to seasons. Interestingly, males were more abundant in our sampling sessions, with similar activity periods than females, suggesting potential animal host implication in the facilitation of reproduction. Finally, the low number of C. oxystoma collected render practical vector-control recommendations difficult to provide and highlight the lack of knowledge on the bio-ecology of this species of veterinary interest.

Culicoides (Diptera: Ceratopogonidae) midges, the vectors of African horse sickness virus--a host/vector contact study in the Niayes area of Senegal

BACKGROUND

African horse sickness (AHS) is an equine disease endemic to Senegal. The African horse sickness virus (AHSV) is transmitted to the mammalian hosts by midges of the Culicoides Latreille genus. During the last epizootic outbreak of AHS in Senegal in 2007, 1,169 horses died from this disease entailing an estimated cost of 1.4 million euros. In spite of the serious animal health and economic implications of AHS, very little is known about determinants involved in transmission such as contact between horses and the Culicoides species suspected of being its vectors.

METHODS

The monthly variation in host/vector contact was determined in the Niayes area, Senegal, an area which was severely affected by the 2007 outbreak of AHS. A horse-baited trap and two suction light traps (OVI type) were set up at each of five sites for three consecutive nights every month for one year.

RESULTS

Of 254,338 Culicoides midges collected 209,543 (82.4%) were female and 44,795 (17.6%) male. Nineteen of the 41 species collected were new distribution records for Senegal. This increased the number of described Culicoides species found in Senegal to 53. Only 19 species, of the 41 species found in light trap, were collected in the horse-baited trap (23,669 specimens) largely dominated by Culicoides oxystoma (22,300 specimens, i.e. 94.2%) followed by Culicoides imicola (482 specimens, i.e. 2.0%) and Culicoides kingi (446 specimens, i.e. 1.9%).

CONCLUSIONS

Culicoides oxystoma should be considered as a potential vector of AHSV in the Niayes area of Senegal due to its abundance on horses and its role in the transmission of other Culicoides-borne viruses.

Epidemiology of Bluetongue in India

Bluetongue (BT) is an insectborne endemic disease in India. Although infections are observed in domestic and wild ruminants, the clinical disease and mortality are observed only in sheep, especially in the southern states of the country. The difference in disease patterns in different parts of the country could be due to varied climatic conditions, sheep population density and susceptibility of the sheep breeds to BT. Over the five decades after the first report of BT in 1964, most of the known serotypes of bluetongue virus (BTV) have been reported from India either by virus isolation or by detection of serotype-specific antibodies. There have been no structured longitudinal studies to identify the circulating serotypes throughout the country. At least ten serotypes were isolated between 1967 and 2000 (BTV-1-4, 6, 9, 16-18, 23). Since 2001, the All-India Network Programme on Bluetongue and other laboratories have isolated eight different serotypes (BTV-1-3, 9, 10, 12, 16, 21). Genetic analysis of these viruses has revealed that some of them vary substantially from reference viruses, and some show high sequence identity with modified live virus vaccines used in different parts of the world. These observations have highlighted the need to develop diagnostic capabilities, especially as BT outbreaks are still declared based on clinical signs. Although virus isolation and serotyping are the gold standards, rapid methods based on the detection of viral nucleic acid may be more suitable for India. The epidemiological investigations also have implications for vaccine design. Although only a handful serotypes may be involved in causing outbreaks every year, the combination of serotypes may change from year to year. For effective control of BT in India, it may be pertinent to introduce sentinel and vector traps systems for identification of the circulating serotypes and to evaluate herd immunity against different serotypes, so that relevant strains can be included in vaccine formulations.

Advances in diagnosis of respiratory diseases of small ruminants

Irrespective of aetiology, infectious respiratory diseases of sheep and goats contribute to 5.6 percent of the total diseases of small ruminants. These infectious respiratory disorders are divided into two groups: the diseases of upper respiratory tract, namely, nasal myiasis and enzootic nasal tumors, and diseases of lower respiratory tract, namely, peste des petits ruminants (PPR), parainfluenza, Pasteurellosis, Ovine progressive pneumonia, mycoplasmosis, caprine arthritis encephalitis virus, caseous lymphadenitis, verminous pneumonia, and many others. Depending upon aetiology, many of them are acute and fatal in nature. Early, rapid, and specific diagnosis of such diseases holds great importance to reduce the losses. The advanced enzyme-linked immunosorbent assays (ELISAs) for the detection of antigen as well as antibodies directly from the samples and molecular diagnostic assays along with microsatellites comprehensively assist in diagnosis as well as treatment and epidemiological studies. The present review discusses the advancements made in the diagnosis of common infectious respiratory diseases of sheep and goats. It would update the knowledge and help in adapting and implementing appropriate, timely, and confirmatory diagnostic procedures. Moreover, it would assist in designing appropriate prevention protocols and devising suitable control strategies to overcome respiratory diseases and alleviate the economic losses.

Type-specific seroprevalence of bluetongue in Andhra Pradesh, India, during 2005-2009

Bluetongue (BT) is an infectious, arthropod-borne viral disease of domestic and wild ruminants caused by bluetongue virus (BTV), which is a double-stranded segmented RNA virus. Of the 26 confirmed BTV serotypes, 23 were reported in India based on the detection of antibodies or virus. In order to assess the prevalence of different serotypes in Andhra Pradesh, serum samples which were positive for BTV by group-specific antibody ELISA were subjected to type-specific neutralization of BTV serotypes 1, 2, 9, 10, 21 and 23. Of the 52 samples tested, 50.0, 44.23, 21.15, 26.92, 0, and 15.38 % neutralized BTV serotypes 1, 2, 9, 10, 21 and 23, respectively. However, 32.69 % of the ELISA positive sera could not neutralize any of these serotypes, indicating that there could be other serotype viruses (e.g., BTV-3 and -16) circulating in the State. This method can be used for surveillance of the circulating serotypes as well as for assessing the level of herd immunity, and assist in determining the vaccine strains to be used in multivalent vaccines.