BTV-16-specific antibodies were detected in the serum of infected animals 7 days and 15 days after infection and superinfection, respectively. prominent signs of infection in BTV-4 infection, mild or no clinical signs in BTV-16-infected and superinfected animals, and non-seroconversion of one of the BTV-16-superinfected animals. In addition, BTV was isolated from infected sheep in all the experimental conditions except BTV-16 superinfection. Furthermore, it was observed that immune response in the form of type-specific antibodies was slower with BTV-16 superinfection. Conclusion: Superinfection of a sheep with more than one serotype of BTV is a common phenomenon in BT endemic countries like India. Such situation was replicated in an experimental infection in the current study, and the findings to our knowledge are first of a kind and are likely to aid in unfolding the newer aspects of BTV pathogenesis and virulence. within the family [1]. Twenty nine serotypes of BTV have been recognized to date [2,3], and a total of 24 serotypes have been reported from India [4,5]. A very flexible reassortment involving any of the genomic segments contributes majorly to the observed phenotypic variations in the BTV strains [6]. Although VP2 protein encoded by the highly variable segment 2 is the determinant of serotype, the other viral protein VP5 is also known to codetermine serotype along with VP2 [7]. Diagnosis of BT traditionally required isolation of virus and standard serological methods; however, recent advances in molecular biology made antigen and nucleic acid detection assays much simpler [2,8]. Curtailing the initial introduction into regions which harbor susceptible host and vector species and vaccination of the susceptible animal species may aid in effective prevention and control of BT [9]. The severity of the disease varies, not only between different species but also between different breeds within the same species. This can possibly be attributed to the basic differences in the inherent susceptibility of the cells of different hosts to BTV infection [10], the nature of the inflammatory mediators, and active components of the vascular system which take part in eliciting the response to infection [11,12]. The clinical manifestation of BT appears to be an outcome of the interplay of several factors in a fashion yet to be understood. Several studies including experimental infection of highly susceptible hosts such as sheep have essentially been carried out by different investigators worldwide to understand the nature of such interplay [13]. Such studies are helpful not only in unraveling the fundamental events in the pathogenesis of the disease but also in understanding the active role played from the sponsor immune system and the design of effective control strategies. The history of experimental infections dates back to the late 18th century, but those of more systematic nature were only reported in the early 20th century. Scientists have tried different routes of inoculation of the disease [14,15]. Interestingly, blood from an infected ill sheep was found to be effective in establishing the infection in a vulnerable sponsor [16]. Studies on experimental infections possess significantly contributed to our understanding of the pathogenicity, viral replication, virulence, induced immune response, transmission of the disease as well as reproductive failures due to BTV illness [17]. From these studies, it is very much apparent that, besides the sponsor system, several aspects of the infecting disease including its serotype contribute to the great variability in the medical outcome of the disease. The various serotypes of BTV, those that have been isolated to day, show higher genetic heterogeneity which is also reflected in the degree and pattern of CC-930 (Tanzisertib) virulence [10]. This is an important aspect that needs to be analyzed to a greater CC-930 (Tanzisertib) extent. To our knowledge, until now, no studies were reported on illness kinetics of Indian isolates of BTV-4 and BTV-16 with very few becoming reported on BTV-4 in other countries [18,19]. With this perspective, the present study was targeted to understand the pathogenesis of and immune reactions to BTV serotypes 4 and 16 on their experimental illness and superinfection in Deccani breed of sheep. RGS17 Materials and Methods Animals and ethical authorization The institutional animal ethics committee authorization was obtained before beginning of the study. Sheep of Deccani breed was managed in insect-proof facility in the sheep farm of Instructional Livestock Farming Complex, College of Veterinary Technology, Hyderabad. The sheep used in the study were those which were confirmed to become BTV seronegative by c-ELISA. Eight such seronegative Deccani breed sheep between the ages of 6 months and 1 year were selected, of which three were inoculated with BTV-4 (09/NLR/15), three with BTV-16 (08ALG/15) isolated from field outbreaks of BT in Andhra Pradesh in 2014, and the remaining two CC-930 (Tanzisertib) animals were kept as control. CC-930 (Tanzisertib) This animal grouping was the same for both the models of illness and superinfection. Animals were provided with feed, fodder, and water throughout the study for 2 weeks. Virus.