The virus was designed to attack the bacteria which allowed a plant to extract nutrients from the soil. This virus was usualy deadly to an ecosystem causing massive wild life destruction. The virus was distributed to a planet by means of missiles launched at the surface.
In 2372 a faction of the Kazon-Oglamar managed to acquire the virus and used it on the surface of Praja. Eventually the crew of the USS Voyager managed to counter its effects. (VOY comic: "Homeostasis, The Conclusion")