While the COVID-19 pandemic continues to dominate media reports, and African swine fever (ASF) occupies the farming trade publications, a third disease, unknown to many, is spreading at pace across the globe. Lumpy skin disease (LSD) is a devastating disease of cattle and water buffalo that has spread rapidly across the Middle East and Asia in recent years, resulting in the death of countless animals and threatening people’s livelihoods.
We interview Dr Pip Beard, Pirbright’s resident World Organisation for Animal Health (OIE) Disease Expert for LSD, about how the epidemic is evolving and the path we need to take to curtail its rampant spread.
What is LSD?
Lumpy skin disease is a disease of cattle caused by infection with lumpy skin disease virus (LSDV). LSDV causes characteristic nodules in the skin of an affected animal, which give the disease its name. The virus also causes fever, weight loss and a reduction in milk production. LSDV is transmitted by biting insects such as stable flies, mosquitoes and midges, which makes controlling the spread of the disease difficult.
LSD is a substantial economic burden on affected farmers and regions. The disease causes loss of animals, reduced meat and milk production, and the hides of surviving animals are scarred and reduced in value. Implementation of control measures to reduce its spread is costly, and regional and international trade in cattle and cattle products from affected countries can also be blocked. LSD severely impacts livestock farmers, whilst at a regional and country level it can be devastating to the cattle industry.
Where is LSD now?
Traditionally LSD was found in Africa but in the last decade it has rapidly expanded its geographic range. From 2012 it was identified in Middle Eastern and Mediterranean countries such Lebanon, Jordan, Saudi Arabia, Iran and Turkey and in 2015-16 it spread to countries in southeast Europe and Russia.
In 2019, China, India and Bangladesh recorded their first cases of LSD and it has now spread further into Asia with outbreaks reported in Hong Kong, Thailand, Vietnam, Malaysia and other countries. There are fears LSDV may spread further, for example to Indonesia or Australia.
Why has LSD spread so rapidly?
We still don’t fully understand why LSDV suddenly started to spread so quickly in 2012. However, its insect-borne transmission route has been key in enabling rapid virus spread through new cattle populations, particularly in wet and warm conditions. Even stringent animal movement restrictions and harsh culling regulations can be insufficient to halt the spread of the virus. For example, widespread vaccination programmes were also required in order to bring the LSD epidemic under control in southeast Europe in 2016-2018.
Another point to remember is that the LSD epidemic is not happening in isolation. The entire world is grappling with the COVID-19 pandemic, with resources being diverted to contain the disease and preserve human life and livelihoods. To compound matters further, many Asian countries are also dealing with the African swine fever epidemic, a lethal swine disease which is decimating pig populations. With limited resources, LSD control is compromised.
What do we know about LSD in Asia?
Not as much as we would like. The emergence of LSD in Asia represents an entirely new ecosystem for the virus. The climate, cattle breeds, husbandry practices and co-incident diseases are all different. The insect populations in Asia are also distinct from those in Europe, which could influence the transmission parameters of LSDV.
We have also identified that the LSDV strains circulating in Asia are different to those seen in Europe and the Middle East. We do not yet have a good understanding of whether these strains are more easily transmitted, or cause more severe disease.
Can LSD be controlled?
The reality is that LSD is an extremely difficult disease to eliminate once it is established in a region. Vaccination is absolutely key to controlling disease outbreaks, and there are very safe and effective LSD vaccines commercially available. High vaccination rates in cattle populations across large areas are required for disease control, for example, the regional vaccination programme undertaken by southeast Europe was effective in controlling LSD. A similar co-ordinated and comprehensive vaccination programme involving multiple countries may be required in Asia.
Learning about LSD in Asia is essential to controlling the disease in the region. We can only extrapolate from experience in Africa and Europe to a limited extent as the virus, host, and environment are all different in Asia. Data from outbreaks in the field in Asia is like gold dust at the moment. Information such as infection and mortality rates as well as how effective the vaccines are against the new strains will help us to tailor control programmes to suit the new environment and tackle LSD more effectively.
Education is also very important. The OIE is also training people in local animal health services on how to spot and report LSD cases, as well as running webinars from OIE experts like myself to improve awareness and knowledge levels. OIE experts are playing an essential role in advising on the design of control plans.
What is Pirbright doing?
Our unique facilities enable us to undertake research involving both insects (vector) and cattle (host) to develop a detailed understanding of how the disease is transmitted. We recently published a landmark study that shows 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. We also demonstrated that stable flies were the most efficient transmitters of LSDV followed by mosquitoes. These essential findings fill critical knowledge gaps and will help us improve the design of control programmes.
As an OIE reference laboratory for lumpy skin disease, we also form a vital part of LSDV surveillance. By analysing samples from around the world we can better understand how the disease is spreading and highlight potential new threats. This activity led to our discovery of the new LSDV strain that is circulating in Asia.
We are leading international research into LSDV through collaborations like the DEFEND consortium, which involves scientists from 30 different countries that are tackling LSD and ASF through 11 different work packages that investigate virus transmission and aim to develop diagnostics and vaccines.
LSD’s uncontained spread has made our work more pertinent than ever and we hope that our continued efforts will help to prevent the further spread of LSD and protect both animal and human health and ultimately save lives.
