Yeah, I considered biotech when I noticed that the WHO was involved, because I'm very suspicious of those guys.
But when it was suggested that the disease is caused by a pair of viruses... I thought, "What a treat!" Spread two harmless-by-themselves viruses in different areas and wait for their populations to intermingle, after which the disease "magically" appears. What a coinkydink!
If a similar theme hadn't already been used by The Joker in the original Batman movie... heh heh heh...