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.