The Bluetongue Virus (BTV) belongs to the phylum Duplornaviricota, class Resentoviricetes, order Reovirales, family Sedoreoviridae, and genus Orbivirus. It is the causative agent of Bluetongue disease, an arboviral infection transmitted by blood-feeding midges of the genus Culicoides (biting midges), which primarily affects ruminants. The disease has significant impacts on animal health, the economy, and conservation, being a notifiable disease under the World Organisation for Animal Health (WOAH).
BTV naturally circulates in wild environments, where bovids and cervids act as reservoirs. Due to the nature of its vector (Culicoides), humid and warm regions favor viral dissemination during seasonal periods. Under normal conditions, wild ruminants tend to exhibit milder forms of the disease, contributing to the virus’s maintenance in the ecosystem. However, sporadic outbreaks can cause significant mortality, especially in vulnerable ruminant populations, whether due to environmental or genetic pressures.
Nevertheless, with the increasing exploitation of natural environments, the interaction between wildlife and livestock has intensified the phenomenon of spillover—that is, the transmission of pathogens from domestic to wild species. As cattle density rises and habitats become more fragmented, wild bovids and cervids are exposed to BTV strains often adapted to domestic ruminants, which can result in more pathogenic variants for these atypical hosts. Furthermore, this pathogen can also undergo spillback, meaning the retransmission of the virus from wild species back to domestic ones, creating a viral amplification cycle where different hosts contribute to the virus's genetic diversity (Lobato et al., 2015). This increased variability can lead to more aggressive strains and severe outbreaks, often affecting immunologically unprepared species with already reduced populations, causing significant declines and putting entire populations at risk.
A relatively recent and well-documented example is the case of the saiga (Saiga tatarica), an iconic species of the Central Asian steppes, already facing severe pressures due to poaching, habitat loss, and climate change. In Kazakhstan, in 2015, Bluetongue disease, along with Epizootic Hemorrhagic Disease Virus (EHDV), were predisposing factors for immunosuppression in wild populations of this species (Koch, 2018). Severe immunodepression caused by these viral agents led to high mortality in the saiga population due to secondary infections. Various bacterial agents caused entire groups of saigas to die from sepsis, with over 200,000 individuals reported dead within three weeks. As a result, the saiga was classified as a critically endangered species at that time (Koch, 2018). The outbreak's origin was linked to interactions with infected domestic ruminant herds in the region.
The primary lesions caused by Bluetongue virus are edema and hemorrhages, resulting from inflammatory processes and vascular damage. Endothelial destruction caused by these processes can lead to thrombosis and ischemia, resulting in cyanosis and necrosis of soft tissues, primarily the tongue (giving the disease its name), oral mucosa, and coronary band of the hooves (Pini, 1976). In domestic ruminants, BTV manifests with symptoms such as fever, oral lesions, respiratory distress, edema, and lameness. The economic impacts include direct losses due to mortality, decreased meat and wool productivity, and restrictions on international trade due to sanitary barriers (Konrad et al., 2003). In wild ruminants, the pathogenesis follows a course similar to that observed in domestic animals but can vary in severity depending on the species. For example, deer and antelopes tend to develop fatal hemorrhagic symptoms (Favero, 2013).
Thus, BTV exemplifies how emerging diseases connect animal health, conservation, and the economy. Addressing the challenges posed by this type of disease requires integrated strategies such as vector control, epidemiological monitoring, targeted vaccination, and reducing contact between domestic and wild fauna. Collaborative solutions are essential to protect biodiversity and economic sustainability, as the loss of key species—such as wild ruminants—destabilizes ecosystem health and balance, compromising essential environmental services.
Author: Gustavo Gomes da Luz Pereira – Director of Languages and Accessibility at GEAS Brasil
Review: Iago Junqueira – The Wild Place
References:
● KOCH, R. A. et al. Saigas on the brink: Multidisciplinary analysis of the factors influencing mass mortality events. Science Advances, v. 4, n. 1, p. eaao2314, 2018. DOI: 10.1126/sciadv.aao2314.
● RIVERA, N. A. et al. Bluetongue and Epizootic Hemorrhagic Disease in the United States of America at the Wildlife–Livestock Interface. Pathogens, v. 10, p. 915, 2021. DOI: 10.3390/pathogens10080915.
● DIDKOWSKA, A. et al. A serological survey of pathogens associated with the respiratory and digestive system in the Polish European bison (Bison bonasus) population in 2017–2022. BMC Veterinary Research, v. 19, p. 74, 2023. DOI: 10.1186/s12917-023-03627-y.
● FAVERO, C. M. et al. Epizootic Hemorrhagic Disease in Brocket Deer, Brazil. Emerging Infectious Diseases, v. 19, n. 2, p. 346-348, Feb. 2013. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3559040/. Accessed on: [date of access].
● PINI, A. Study on the pathogenesis of bluetongue: replication of the virus in the organs of infected sheep. Onderstepoort Journal of Veterinary Research, v. 43, p. 159-164, 1976.
● KONRAD, P. A.; RODRIGUES, R. O.; CHAGAS, A. C. P.; PAZ, G. F.; LEITE, R. C. Antibodies against the blue tongue virus in dairy cattle in the state of Minas Gerais, Brazil and associations with reproductive problems. Revta Fac. Zootec. Vet. Agron., Uruguaiana, 10:42-51, 2003.
● LOBATO, Z. I. P.; GUEDES, M. I. M. C.; MATOS, A. C. D. Bluetongue and other orbiviruses in South America: gaps and challenges. Veterinaria Italiana, v. 51, n. 4, p.s in South America: gaps and challenges. Veterinaria Italiana 51(4):253-262.
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