Now that I'm a few weeks into my time here, I've been kitted out with a desk, lab book and Roslin coffee cup.There have been a lot of induction talks on science, safety and security. I've been allowed to get my hands dirty by helping out in lab. I've met loads of people and even remembered a few names. A group of students at the Institute run a social committee who arranged a tour of the vaults below Edinburgh followed by a meal at the Elephant House (where JK Rowling wrote several of the Harry Potter books - the toilets are well worth a visit to see the extensive graffiti of a dedicated Fandom) and a trip to the union bar (which ended with me staggering home from a club in the wee hours of the morning), needless to say they are a lovely bunch.
In my last post, I said I'd talk about Blue-Ear Pig Disease and maybe even start on my PhD project however there's quite a lot of info to cover so I'm going to break this up into several posts. In this post I'll cover the disease including its effects, its history and the many names it has received; in the second post I'm going to cover the virus itself, looking at how it's put together, the way it copies itself and some of its relatives.
The disease was first noticed in the late 80s, during the early 90s when papers were first documenting the disease and identifying the virus it was given many names including mystery swine disease (MSD), Porcine Epidemic Abortion and Respiratory Synrdome (PEARS), Lelystad Virus (for the European type, more on that later), Pig High Fever Disease, Blue-Ear Pig Disease, Porcine Reproductive & Respiratory Syndrome Virus (PRRSV) and even pig AIDS (because of its tendency to wreck the pigs immune system). Whilst Blue-Ear Pig Disease gives a pretty good blog title, I'm going to call it PRRSV from now on since that's standard name nowadays; this name has the bonus of being sounding like it was chosen by a happy cat ("purrs virus"), which is always a cute concept.
Moving swiftly away from cute concepts, I want to look at the effects of the virus on pigs, and the results for herds. The symptoms of a pig which is infected with PRRSV can be vary greatly depending on the strain of the virus and the immune system of the pig, some animals will remain seemingly healthy whilst passing the virus on to their neighbors whilst others will suffer from reproductive disorders (pregnant sows may abort fetuses, or give birth to weak piglets), stunted growth, pneumonia or a weakened immune system (that allows other diseases to do damage) which can result in death. With this range in severity, it is practically impossible to distinguish sick animals from others so outbreaks often require the destruction of entire herds. All in all, the result of the virus is a lot of suffering for animals and a loss of livelihoods for farmers.
The virus seemed to appear for the first time in Europe and North America simultaneously however it was quickly noticed that these outbreaks were actually caused by two different types of the same virus which were only about 60% genetically identical. The European strain is called Type 1, whilst the American strain is named Type 2.
Mistakes by their copying machinery cause viruses to mutate over time, these changes occur randomly however they can be guided by their environment. A change that leads to a slower copying virus will probably die out, whilst a change that helps the virus avoid the host immune system is likely to spread as would a change that lets the virus infect a new type of animal. Some changes don't make much difference either way so they will build up over the generations at a pretty steady rate.
Lucky for us, viral generations can be as short as hours allowing us to grow virus in a lab for many generations and figure out what this rate of mutation is. We can then use this rate to figure out how long ago two strains of a virus were the same, or when their last common ancestor was. By we I mean geneticists with a knack for computing, I don't personally know how to do it.
This analysis has been done for PRRSV and it seems likely that the two types branched off around 1880 (give or take 15 years), the current theory is that a disease of mice got into wild European boars around this time, when boars were shipped to America throughout the first half of the 20th century some took the virus with them and managed to spread it to escaped domestic pigs. Over the following years during which the different types were separate, they picked up mutations independently of each other resulting in the two types that appeared in the 90s.
Since that time, the virus has spread (or been noticed for the first time) across the whole of Europe, North America and China as well as parts of East Asia, Africa and South America. The disease costs around $600 million annually to the United States alone and despite several vaccines, it remains hard to control.
There are many questions still to be answered in PRRSV research, why both types popped up at the same time in different places, why vaccines seem so ineffective and - importantly - how we stop the virus from doing even more damage.
