If flu viruses have favoured hook-up spots, then pig pens would be high on the list. Their airways contain molecules that both bird flu viruses and mammalian flu viruses can latch onto. This means that a wide range of flu strains can infect pigs, and if two viruses infect the same cell, they can shuffle their genes to create fresh combinations.
This process is called reassortment. In 2009, it created a strain of flu that leapt from pigs to humans, triggering a global pandemic. If we needed proof that pigs are “mixing vessels” for new and dangerous viruses, the pandemic was it.
Now, scientists have found a new strain of flu in Korean pigs that remphasises the threat. It’s an H1N2, subtly different to the H1N1 virus behind the recent pandemic. But it’s got all the makings of a serious problem. It can kill ferrets – the animal of choice for representing human flu infections. And it spreads through the air between them. I’ve written about this new strain for Nature News, so head over there for more details.
Image by US Dept of Agriculture
As the world is now painfully aware, pigs can act as reservoirs for viruses that have the potential to jump into humans, triggering mass epidemics. Influenza is one such virus, but a group of Texan scientists have found another example in domestic Philippine pigs, and its one that’s simultaneously more and less worrying – ebola.
There are five species of ebolaviruses and among them, only one – the so-called Reston ebolavirus – doesn’t cause disease in humans. By fortuitous coincidence, this is also the species that Roger Barrette and colleagues have found among Philippine pigs and even among a few pig farmers.
The team were called in last July by the Philippine Department of Agriculture to identify a mystery illness that was sweeping across the country’s pigs, infecting their lungs and airways and causing miscarriages. Barrette’s group collected tissue samples from five groups of pigs throughout the island and through a battery of tests, they gradually ruled out their list of potential candidates – foot-and-mouth disease, African swine fever, and others.
The first positive hit was an infection known as blue ear disease, or to give it its formal name – porcine reproductive and respiratory syndrome virus (PRRSV). It was already the primary suspect for the pig illness, and the Philippine strain was genetically similar to one that was sweeping through China at the time. It seemed like the mystery was solved. But not so – when Barrette incubated an infected lymph node with monkey cells that are immune to PRRSV, the cells still started dying. There was another virus.
To identify it, Barrette used a powerful tool called a “panviral microarray” – a small slide that contains the genetic signatures of tens of thousands of viruses, neatly arranged in a grid. Similar tools have already proved their worth in viral detective work – the closely related Virochip was used to identify the SARS virus in 2002. This time, the technique brought up a strong hit for Reston ebola.
Methicillin-resistant Staphylococcus aureus (MRSA) is very difficult to kill. This notorious “superbug” can withstand a broad and growing range of antibiotics, and is the leading cause of hospital infections in many countries. But it’s not restricted to hospitals. According to studies coming in from all over the world, MRSA has found a new route into our bodies -piggyback.
Pig farms throughout the world have become breeding grounds for strains of MRSA that can jump from swine to humans. These strains have already been isolated in the Netherlands, Denmark and Canada, and now, the latest study adds the USA to that list. The research was led by Tara Smith from the University of Iowa, who I know as a Scibling and who many of you will recognize as the author of the excellent Aetiology blog.
Smith found widespread traces of MRSA in two different production systems in the states of Iowa and Illinois. Within the nostrils of 49% of pigs and 45% of pig farmers, her team detected traces of the “superbug” (although it’s worth noting that none of the farmers had experienced any actual infections). Piglets had the highest rates of infection and in fact, every single pig under the age of 12 weeks harboured MRSA colonies.
The high levels of the bacterium in both man and pig suggest that it can spread readily between the two species. To MRSA, both four leg and two legs are good…