Vector-borne transmission of lumpy skin disease virus II

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Lumpy skin disease is a severe poxviral disease of cattle caused by LSDV. Previously found only in Africa, it entered southeast Europe for the first time in 2015 as part of the 2012-2018 Eurasian LSD epidemic. The spread of the virus slowed in 2017 and effectively halted in 2018 as a result of strict movement restrictions on animals and animal products in affected areas, thousands of cattle culled, and national vaccination campaigns. Annual vaccination with a live attenuated LSDV strain is still practiced in affected countries in order to prevent recurrence of disease.Dr Beard (PI) and Dr Gubbins (co-I) were consulted as expert advisors on the response to the LSD epidemic in Europe and neighbouring countries, and experienced how lack of knowledge of LSDV transmission hampered control of the epidemic, especially when setting quarantine zones around an outbreak and prioritising areas for urgent vaccination. Lack of scientific evidence regarding the transmission of LSDV even led some countries to implement unwise choices of control measures such as poorly-targeted aerial insecticide use. These experiences were used to shape a two-stage research programme to investigate the vector-borne transmission of LSDV. The first stage of the programme (short name LIMT) has provided key information about the acquisition and retention of LSDV in the vector. This proposal describes the second stage of the research programme, and incorporates the findings of LIMT into the design of experiments to study insect to bovine transmission of LSDV. Previously published work (Chihota et al 2001, Chihota et al 2003) reported retention of LSDV in Aedes aegypti for 6 days post feeding (DPF) on a clinically affected donor animal and successful transmission of LSD from donor to recipient bovine via Ae. aegypti mosquitoes. However the work failed to demonstrate retention of LSDV in other vectors (including Stomoxys calcitrans and Culicoides nubeculosus) for longer than 1 DPF, and attempts to transmit the virus or disease from donor to recipient using these vector groups failed. The work by Chihota and colleagues used a narrow and inconsistent experimental design, and in particular did not calculate feeding efficiency which limits the value of the data for estimating transmission efficacy of LSDV by vector groups. In order to address this the LIMT study used a greater number of insects, more robust and thorough protocols, and more sensitive detection methods. LSDV was detected up to 8 DPF in S. calcitrans and Ae. aegypti, and 4 DPF in C. nubeculosus, indicating that the virus can be acquired and retained by a range of insect vector groups. These data from the LIMT studies were combined with life history parameters of the insects to estimate R0 (the basic reproduction number, which is the number of secondary infections produced by a typical case of an infection in a population that is totally susceptible). S. calcitrans, C. nubeculosus and Ae. aegypti all had a R0 of >1, indicating they are all potential vectors of the virus. In order to complete our studies of the LSDV transmission cycle objective 1 of this proposal will use the experimental model of LSDV developed in LIMT to carry out donor to recipient transmission studies to examine insect to bovine transmission of LSDV by S. calcitrans, C. nubeculosus and Ae. aegypti. In objective 2 the outputs of these experiments will be used to update assessments of the risk posed by LSDV and the impact of different control measures using three approaches: (i) computation of the basic reproduction number for LSDV (R0) to estimate the risk of transmission; (ii) a stochastic model for the within-herd transmission of LSDV to investigate the impact of control measures (in particular, vaccination and culling) at the herd level; and (iii) a stochastic model for the spread of LSDV between herds to scale up and explore the impact of control measures at a regional level.