Abstract:
The transmission of “lumpy skin disease virus” (LSDV) has prompted intensive research efforts due to
the rapid spread and high impact of the disease in recent years, especially in Eastern Europe and Balkan
countries. In this study, we experimentally evaluate the vaccine-derived virulent recombinant LSDV
strain (Saratov/2017) and provide solid evidence on the capacity of the virus for transmission in a vectorproof
environment. In the 60-day long experiment, we used inoculated bulls (IN group) and two groups
of in-contact animals (C1 and C2), with the former (C1) being in contact with the inoculated animals at
the onset of the trial and the latter (C2) being introduced at day 33 of the experiment. The infection in
both groups of contact animals was confirmed clinically, serologically and virologically, and viremia was
demonstrated in blood, nasal and ocular excretions, using molecular tools. Further studies into LSDV
biology are a priority to gain insights into whether the hypothesized indirect contact mode evidenced
in this study is a de novo-created feature, absent from both parental stains of the novel (recombinant)
LSDV isolate used, or whether it was dormant, but then unlocked by the process of genetic
recombination. Author summary: In global terms, LSD has been termed a “neglected disease” due to its
historic natural occurrence of being restricted to Africa and, occasionally, Israel. However, after its slow
spread throughout the Middle East, the disease is now experiencing a resurgence of research interest
following a recent and rapid spread into more northern latitudes. Given the dearth of solid findings on
potential transmission mechanisms, no efficient or reliable control program currently exists, which does
not involve the use of live attenuated vaccines or stamping out policies – both of which are controversial
for implementation in non-endemic regions or countries. The vector-borne mode is the only working
concept currently available, but with scarce evidence to support the aggressive spread northwards
– except for human-assisted spread, including legal or illegal animal transportation. The emergence
of outbreaks is not consistently linked to weather conditions, with the potential for new outbreaks
to occur and spread rapidly. Here, for the first time, we provide evidence for indirect contact-mode
transmission for a naturally-occurring recombinant LSDV isolated from the field. In an insect-proof
facility, we obtained solid evidence that the novel LSDV strain can pass to in-contact animals. Given the
recombinant nature of the virus utilised, its genetic background relating to the observed transmission
pattern within the study needs to be delineated.
