I have an interstellar war in which us humans fight an alien nomad fleet. The aliens begin to lose the war and need something to fall back on. Humanity over many millennia has built star gates(kinda like Star Gate) and has ten colonies. The aliens took one and are using the gate in that system to attack other human colonies. They designed a flu virus that, like the natural flu, spreads through the air, but causes the infected human's brain to lose the ability to absorb serotonin and hypes adrenalin levels, giving it the ability to cause a planet-wide riot on a selected human world.
Since humanity has all but won the war, human ships patrol the star gates for any incoming attacks. Since the gates are so well defended and the alien fleet is so depleted, they don't want to risk trying to break through the blockades. They send a spy with the virus through. At this point, the spy has to figure out how to release it.
The obvious options are infecting swine or earth birds, or directly infecting people. Which has the ability to reach and infect the most people assuming the population densities on this colony are equal to that on modern earth and the locations of the population, like earth, is generally near coasts, rivers, and strategic positions?
It should also be noted that this flu, other than its serotonin-destroying properties, can infect all vectors that H1N1 can infect, as well as being transmitted via contact with infected blood.
What is the best way to introduce this virus into one of the colonies?