By Kirsty OUP-UK
The UK news reports have recently been dominated by stories of two infectious diseases that have been attacking farm animals: Foot and Mouth Disease, and the bluetongue virus. OUP author Dorothy Crawford is Professor of Medical Microbiology and Assistant Principal for the Public Understanding of Medicine at the University of Edinburgh, and is the author of many publications on viruses. Her new book, Deadly Companions: How Microbes Shaped Our History, looks at how human history is inextricably linked with the history of microbes and the spread of infection and disease. Here she turns her attentions to our animal friends, and looks at how to deal with the spread of disease in British livestock.
As the wettest summer on record comes to a close Britain is in the throws of not just one but two infectious disease outbreaks. The good news is that neither disease poses a threat to humans, but there is also plenty of bad news. Both foot and mouth disease and the bluetongue virus can spread rapidly and cause devastating disease in farm animals. So, in an action replay of the 2001 UK foot and mouth disease outbreak, animals are once again being slaughtered in the fields, and with the movement of their animals restricted farmers can not get their valuable stock to market. So far both outbreaks are confined to the South East corner of England, but who can tell where these viruses will turn up next week, let alone next month.
Although both viruses infect livestock, they have emerged from quite distinct sources and for very different reasons. The story behind the bluetongue virus outbreak can be blamed on climate change; with the recent milder weather its arrival in the UK was almost inevitable. The virus started life in South Africa, but broke free in the 1950s to colonise other tropical and subtropical regions. Since then it has moved steadily north and in 2006 it invaded Germany, France, Holland and Belgium. Clearly, it was only a matter of time before it jumped across the English Channel. However, this virus does not spread directly from one victim to another; it hitches a ride with the midge, so its distribution depends on the whim of this tiny flying insect. Midges can only survive where winters are mild, and they undergo a population explosion in warm wet summers. Global warming, therefore, assisted the virus in its relentless spread northwards; it survived last winter in northern Europe, but we are yet to find out whether it can do so in the coming UK winter. If it can, then bluetongue virus will be difficult to eliminate by just culling infected animals.
In 2001 foot and mouth disease virus probably arrived in the UK in illegally imported meat products from South East Asia. The devastating country-wide epidemic, with its pyres of burning carcasses, horrified the nation. But since then, with tighter regulations on animal movements in place, the UK has thankfully been virus free, so the report of an infected cow on a farm in the Surrey countryside was a total shock. Where had the virus come from?
It turns out that the infected farm is suspiciously close to two laboratories working with foot and mouth disease virus; the government run Institute for Animal Health, and a vaccine production plant run by the company Merial. Scientific detectives quickly discovered that the genetic sequence of the outbreak virus was identical to the vaccine strain used in both these labs. Since workers at the Merial lab were growing up huge 6000 litre vats of virus at the time, the escapee most likely came from there. However it took a very circuitous route to the outside world. The two laboratories have shared a chemical decontamination plant for years, but on this occasion its 50 year old pipes leaked, contaminating the surrounding soil with live virus. Then, in a combination of heavy rain, overflowing drains, construction teams digging holes, and heavy trucks driving through the contaminated area, virus laden mud was transported to the unfortunate farm.
Although both foot and mouth disease and bluetongue viruses can cause severe disease in livestock they don’t necessarily kill previously healthy adult animals, but these days nursing them back to health is not a commercially viable option. In the UK infected animals are culled, often along with the surrounding herds, to prevent the outbreak spreading. But is this attempt at total virus eradication a realistic proposition?
Perched on the Western extremities of continental Europe and surrounded by water, the British Isles have been relatively protected from microbes intent on infecting domestic animals. But on several recent occasions, they have succeeded in hopping across the English Channel and taking the natives by storm. If we humans were threatened by similar epidemics we would be clamouring for vaccines, so why not vaccinate our four legged friends?
Vaccines that could protect against these viruses do exist, and although they are not necessarily ideal from the particular outbreak virus strains, more are now in production. They are not currently used in the UK because they would interfere with the total elimination policy by making vaccinated animals indistinguishable from infected ones. This policy may have sufficed in the 1950s but it is really sustainable in the 21st century?
The juxtaposition of these two outbreaks in the UK is not so much of a coincidence as may be thought. Ever since our ancestors gave up the hunter gatherer lifestyle and settled into farming communities some 10,000 years ago microbes have exploited the crowded conditions of man and his animals, jumping with ease from one victim to the next. And with the opening up of trade routes to more and more distant lands, microbes followed the travellers causing epidemics along the way. Now, with intensive farming methods, lightening quick travel and increased animal transportation, aided and abetted by our present unstable weather conditions, microbes are going global.
History tells us that microbes are unaware of international boundaries; they will always find a way to invade these tiny islands. So let’s make vaccination a priority!