The Phantom Thorn

One disease. Originated from the thorns of a plant by the name Phantom Mist, just the slightest touch is enough to give any person the contagious disease. 8 countries now have to find the culprit, whom they have understood, is one among them. The thorns are being harvested and put into random food, to spread it all over the 8 countries.
The disease causes hallucinations. It makes the one infected believe that a loved one they had lost has come back to life. But in reality, they would be assuming one of their own family members to be them. If the person infected is allowed near the one they presume as their loved one, once the effect of the thorn's poison increases, they are likely to lose their ability to think straight. In other words, they turn into a maniac. Once the disease reaches its full potential, the infected person is likely to kill both, the person they presumed as their loved one and themselves. But if the infected person is isolated, the effects of the disease will accelerate quite quickly and only that person will die. If the 8 countries don't find the culprit soon, they must be prepared to sacrifice more blood in their names.