The way I did this was to buy a couple of N-ray weapon mods. Now these are quite rare to pop up, so if you're lucky like me, you can get it done quickly.
I modded two weapons, I chose two fairly powerful Assault Rifles. And modded them both to deal N-ray damage. Then I gave one to Nyoka and one to Parvati.
In combat, watch which two they hit. You want to then make sure you use TTD to kill the ones those infect with N-rays, you want a fairly strong ranged weapon, such as a highpowered pistol or Rifle, and modded with a higher crit chance mod. Aim for the head if you can to make sure you can really make the use of your own mod.
Both Humanoid and animal kills count.