The sickness was introduced via the rival pack but on accident. They are from a much wetter climate than the pack. A bacteria specific to their home that helps keep there coats more water resistant than other wolves. Now this bacteria is not common so when they started to move with the bacteria in there coats, it spread via fur to ground contact. It can easily be absorbed by the trees through there roots which makes there bark brittle and unable to absorb water well. This ,in turn, allows the trees to become vulnerable to rot. The rot produces toxins that spread to the environment such as plants and animals thus making them carry deadly poison when consumed by werewolves and humans alike. It is undetectable by scent and taste because of its origins being a wet area where scent and taste are useless.
The minor symptoms would be very similar to the common cold with a fever, cough, sore throat, nausea, fatigue and congestion. It would pretty much seem like the cold so you would naturally try and rest it off. However, the disease becomes worse the less you move. It attacks the digestion system first by eating away the good bacteria in your stomach making it impossible to properly obtain the nutrients from food and drink. This will induce further fatigue and nausea. It then moves through the circulatory system causing poor circulation of oxygen and makes it difficult for the affected to walk or breathe. At this point, it would deal the finishing blow to the nervous system inducing the major symptoms of throwing up blood, jaundice, dehydration, muscle loss, paralysis and fainting spells. Eventually, the lungs will fill up with fluid which subsequently "drowns" the victim and killing them slowly. It is divided into three stages and once you reach stage three, nothing else can be done.
✦ credit to .mama shin for these details✧
The pack tries to go to the humans for help, trying to show that they are not a threat. However, this means that they must subject themselves to testing in order for scientists to be able to come up with a cure that will benefit both their human and wolf forms, and not harm them any further. In hearing word of this, the rival pack begins to cause a little bit of mischief and trouble as they are still aiming to get what they want. Hostility arises between the two packs until, hopefully, a deal can be worked out to benefit both packs.
(c)trexgirl