A final challenge, the most tragic of the three, was a matter of public health. Immediately after the end of the Third Interstellar War, a series of plagues began to spread through Vilani populations, especially on worlds close to the Imperial border. Nusku appeared to be the epicenter of these plagues, and it was soon proven that the disease outbreaks always followed contact with Terrans.
Working on Nusku and elsewhere, Terran physicians discovered that simple Terran viral diseases – especially influenza, measles, and mumps – caused the plagues. To their horror, they found that much of the Vilani population was vulnerable to these diseases and had no evolved resistance to them. As it happened, the Vilani had often dealt with "alien" diseases in their thousands of years of starfaring history – but Terran viruses seemed particularly virulent and deadly when introduced to Vilani populations.
Terran physicians fought a fierce battle against the plagues on Nusku, and also traveled deep into Imperial territory to help deal with disease outbreaks there. Vaccines and anti-viral therapies were mass-produced and
shipped everywhere, saving millions if not billions of Vilani lives. This work was critical in winning the respect of Vilani populations – but the plagues had already presented the Vilani ruling class with yet another reason to deal decisively with the Terran challenge.