Scientists at The Pirbright Institute have measured the risk of different insect species transmitting lumpy skin disease virus (LSDV) for the first time. LSDV causes severe disease in cattle and is rapidly emerging into new regions. It has recently spread from Africa and the Middle East into cattle populations in Europe and Asia.
Pirbright’s research shows that insects are unlikely to acquire the virus if they bite infected cattle that are not displaying clinical signs, meaning these animals pose a limited risk of transmitting disease. This information fills a critical knowledge gap and could change the design of control programmes aimed at managing LSD outbreaks.
Animals infected with LSDV can show clinical signs of disease in the form of fever, weight loss and large nodules on the skin, but some animals are subclinically infected and display no symptoms of the disease. Until now it was not clear if insects feeding on these subclinical animals were able to acquire the virus and spread disease. Some control programmes had therefore adopted a cautious approach to outbreaks, culling all animals in an affected herd to prevent LSD spread.
Findings published in the Journal of Virology reveal that insects feeding on subclinical animals were 97 percent less likely to acquire LSDV than those feeding on clinically infected animals. Insects were also unable to acquire the virus from cattle in the seven days prior to clinical signs developing (preclinical animals).
Stable flies (Stomoxys calcitrans) were the most efficient transmitters of LSDV followed by mosquitoes (Aedes aegypti). Scientists also demonstrated that insects spread the virus through mechanical transmission, meaning LSDV does not replicate in the insects, despite the virus still being associated with the stable fly and the mosquito for eight days after feeding and possibly longer.
Together, this information establishes the risk of disease spread posed by different insects and cattle at different stages of the disease cycle. This knowledge can be used to shape evidence-based LSD control policies particularly in low- and middle-income countries where vaccination campaigns are difficult to establish and people’s livelihoods are highly reliant upon their herd animals.
Dr Beatriz Sanz‐Bernardo, lead author of the paper, said: “By combining the unique expertise and resources available at Pirbright, we were able to create models of transmission in unprecedented detail. The data we have obtained through studying transmission in live animal models and using mathematical modelling have answered crucial questions that can now deliver real world impact.”
Dr Pip Beard, Head of the Large DNA Viruses group at Pirbright, said: “The uncertainties surrounding the risk of LSDV transmission have hampered our ability to generate evidence-based control programmes that protect animal welfare and human livelihoods. The data we have compiled provides this vital knowledge which authorities can now use to inform control policies. In particular, the discovery that preclinical and subclinical animals both pose a very limited risk of spreading disease supports LSD control programmes which target clinically-affected cattle for rapid removal, rather than complete stamping‐out of all cattle in an affected herd.”
This study was funded by the Biotechnology and Biological Sciences Research Council (BBSRC), part of UK Research and Innovation (UKRI), and by MSD Animal Health.