Emerging and Re-Emerging Bluetongue Virus Serotypes in Indian Ruminants: A Systematic Review

Background:
Bluetongue (BT) is a major vector-borne disease of domestic and wild ruminants caused by bluetongue virus (BTV), a member of the genus Orbivirus (family: Sedoreoviridae). India is a global hotspot for BTV because of its diverse agro-climatic conditions, widespread distribution of Culicoides vectors, and the circulation of multiple viral serotypes. The emergence of genetically diverse strains and frequent genomic reassortment continue to challenge disease surveillance, diagnosis, and vaccine development.

Methods:
A systematic review of peer-reviewed literature published between 2009 and 2025 was conducted using PubMed, Scopus, Web of Science, ScienceDirect, and Google Scholar. Studies reporting BTV serotypes, molecular epidemiology, phylogenetic analysis, diagnostics, and disease surveillance in Indian livestock were screened according to predefined inclusion criteria and synthesized qualitatively.

Results:
The review identified the circulation of at least 23 BTV serotypes in India, with BTV-1, BTV-2, BTV-3, BTV-9, BTV-10, BTV-12, BTV-16, BTV-21, BTV-23, and BTV-24 being the most frequently reported. Studies published between 2009 and 2015 established the co-circulation of eastern and western topotypes and documented extensive genomic reassortment. From 2015 onward, whole-genome sequencing substantially improved understanding of viral evolution, transmission dynamics, and genetic diversity. Studies available through 2025 further highlighted the expansion of surveillance into eastern and north-eastern India, increasing recognition of climate-driven changes in Culicoides vector distribution, and continued detection of reassortant BTV strains. Collectively, these findings reinforce the role of cattle and buffaloes as important reservoir hosts for virus maintenance and transmission.

Conclusion:
The continued circulation of genetically diverse BTV serotypes poses a significant challenge to bluetongue control in India. Strengthening genomic surveillance, integrated vector monitoring, and region-specific multivalent vaccine development will be essential for early detection of emerging variants and effective disease management.