Full genome sequence of bluetongue virus serotype 1 from India

An updated review on bluetongue virus: epidemiology, pathobiology, and advances in diagnosis and control with special reference to India

Bluetongue (BT) is an economically important, non-contagious viral disease of domestic and wild ruminants. BT is caused by BT virus (BTV) and it belongs to the genus Orbivirus and family Reoviridae. BTV is transmitted by Culicoides midges and causes clinical disease in sheep, white-tailed deer, pronghorn antelope, bighorn sheep, and subclinical manifestation in cattle, goats and camelids. BT is a World Organization for Animal Health (OIE) listed multispecies disease and causes great socio-economic losses. To date, 28 serotypes of BTV have been reported worldwide and 23 serotypes have been reported from India. Transplacental transmission (TPT) and fetal abnormalities in ruminants had been reported with cell culture adopted live-attenuated vaccine strains of BTV. However, emergence of BTV-8 in Europe during 2006, confirmed TPT of wild-type/field strains of BTV. Diagnosis of BT is more important for control of disease and to ensure BTV-free trade of animals and their products. Reverse transcription polymerase chain reaction, agar gel immunodiffusion assay and competitive enzyme-linked immunosorbent assay are found to be sensitive and OIE recommended tests for diagnosis of BTV for international trade. Control measures include mass vaccination (most effective method), serological and entomological surveillance, forming restriction zones and sentinel programs. Major hindrances with control of BT in India are the presence of multiple BTV serotypes, high density of ruminant and vector populations. A pentavalent inactivated, adjuvanted vaccine is administered currently in India to control BT. Recombinant vaccines with DIVA strategies are urgently needed to combat this disease. This review is the first to summarise the seroprevalence of BTV in India for 40 years, economic impact and pathobiology.

Molecular analysis of genome segment-3 of bluetongue virus serotype 12 isolates from Haryana

Aim

The present study was designed to characterize the genome segment 3 (Seg-3) of bluetongue virus (BTV) serotype 12 isolates from different outbreaks of Bluetongue disease in Haryana, India.

Materials and Methods

Blood and swab samples were collected from goat and sheep suspected to be suffering of BT from different outbreaks from Gurugram, Sirsa, Hisar, and Karnal districts of Haryana. The samples were grown in insect and mammalian cell lines. After preliminary identification, serotyping was done using BTV type-specific quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assays. Sequencing was performed using terminal and walking internal primers specific for Seg-3 on ABI Capillary Sequencer 3130 using a "BigDye cycle sequencing kit." The obtained sequence data were analyzed with various bioinformatic tools.

Results

Real-time PCR results confirmed the samples to be positive for BTV-12. The Seg-3 of Indian isolates was most closely related to that of a south Indian isolate of BTV-12 from Andhra Pradesh (KC662614) with 97% nucleotide identity.

Conclusions

The study confirmed the circulation of BTV-12 in Haryana, India. The variations shown in genome Seg-3 of BTV-12 isolates may have some significance and need to be further explored.

Blue tongue - A modelling examination of fundamentals - Seasonality and chaos

A deterministic mathematical model is developed for the dynamics of bluetongue disease within a single farm. The purpose is to examine widely the possible behaviours which may occur. This is important because of the increasing impact of blue tongue due to global warming. The model incorporates a recently suggested modification of logistic growth for the vectors which can greatly affect early disease dynamics and employs a variable number of up to 10 sequential pools for incubating vectors and for incubating and infectious hosts. Ten sequential pools represent the possible loss of immunity of recovered hosts over a 3-year period. After formally describing the model, the impact of the two logistic growth scenarios considered is examined in Section 3.1. The scenarios are applied with parameters that give identical long-term consequences but the early dynamics can be greatly affected. In the two scenarios, the effect of varying the assumed constant birth rate (scenario 1) or constant mortality rates (scenario 2) is considered. If the recovered (and immune) hosts, are assumed to lose their immunity, then, given particular values of the host-vector coupling constants, the system can exhibit autonomous oscillations (Section 3.2). Seasonality is represented by air temperature, and it is assumed that air temperatures below a threshold can increase vector mortality (Section 3.3). Adding seasonal effects on mortality to the autonomous oscillations resulting from recovered and resistant hosts losing immunity can give rise to chaos (Section 3.4). This could help explain the unusual persistence and re-occurrence of the disease. Finally (Section 3.5), the roles of host birth and mortality rates in examined, particularly in relation to placental transmission of the virus to offspring. It is concluded that the latter does not make an appreciable contribution to disease dynamics.

Full-Genome Sequencing as a Basis for Molecular Epidemiology Studies of Bluetongue Virus in India

Since 1998 there have been significant changes in the global distribution of bluetongue virus (BTV). Ten previously exotic BTV serotypes have been detected in Europe, causing severe disease outbreaks in naïve ruminant populations. Previously exotic BTV serotypes were also identified in the USA, Israel, Australia and India. BTV is transmitted by biting midges (Culicoides spp.) and changes in the distribution of vector species, climate change, increased international travel and trade are thought to have contributed to these events. Thirteen BTV serotypes have been isolated in India since first reports of the disease in the country during 1964. Efficient methods for preparation of viral dsRNA and cDNA synthesis, have facilitated full-genome sequencing of BTV strains from the region. These studies introduce a new approach for BTV characterization, based on full-genome sequencing and phylogenetic analyses, facilitating the identification of BTV serotype, topotype and reassortant strains. Phylogenetic analyses show that most of the equivalent genome-segments of Indian BTV strains are closely related, clustering within a major eastern BTV 'topotype'. However, genome-segment 5 (Seg-5) encoding NS1, from multiple post 1982 Indian isolates, originated from a western BTV topotype. All ten genome-segments of BTV-2 isolates (IND2003/01, IND2003/02 and IND2003/03) are closely related (>99% identity) to a South African BTV-2 vaccine-strain (western topotype). Similarly BTV-10 isolates (IND2003/06; IND2005/04) show >99% identity in all genome segments, to the prototype BTV-10 (CA-8) strain from the USA. These data suggest repeated introductions of western BTV field and/or vaccine-strains into India, potentially linked to animal or vector-insect movements, or unauthorised use of 'live' South African or American BTV-vaccines in the country. The data presented will help improve nucleic acid based diagnostics for Indian serotypes/topotypes, as part of control strategies.

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.

Complete genome sequence analysis of a reference strain of bluetongue virus serotype 16

The entire genome of the reference strain of bluetongue virus (BTV) serotype 16 (strain RSArrrr/16) was sequenced (a total of 23,518 base pairs). The virus was obtained from the Orbivirus Reference Collection (ORC) at IAH, Pirbright, United Kingdom. The virus strain, which was previously provided by the Onderstepoort Veterinary Research Institute in South Africa, was originally isolated from the Indian subcontinent (Hazara, West Pakistan) in 1960. Previous phylogenetic comparisons show that BTV RNA sequences cluster according to the geographic origins of the virus isolate/lineage, identifying distinct BTV topotypes. Sequence comparisons of segments Seg-1 to Seg-10 show that RSArrrr/16 belongs to the major eastern topotype of BTV (BTV-16e) and can be regarded as a reference strain of BTV-16e for phylogenetic and molecular epidemiology studies. All 10 genome segments of RSArrrr/16 group closely with the vaccine strain of BTV-16 (RSAvvvv/16) that was derived from it, as well as those recently published for a Chinese isolate of BTV-16 (>99% nucleotide identity), suggesting a very recent common ancestry for all three viruses.