This could be a big stretch...

It looked like Shannon playfully bit Sayid on the chest while laying in the tent. Then she started to get up and said she was going to get some water. She also saw Walt or perhaps imagined him. As we all know, she has thought she's seen Walt before and became hysterical every time.

I believe that biting, thirst, hallucinations and perhaps, hysteria, are all symptoms of rabies...

Not sure how she would have been infected since I think you have to be bitten by someone infected.

Just thought it was worthy of consideration since the Dharma Initiative studied zoology, there's no certain cure for rabies, and Danielle said she had to kill the other members of her team that had the sickness. Maybe the above are hints to what the sickness is, even if Shannon is/was not infected with it?

I doubt it.... Although it could be. But I think the sickness would be less common and freakier. Could be though. But nobody bit anyone.

But the Dharma project or The Island may have introduced another way to contract it. Those could just be subtle hints. Time will tell!

Maybe Danielle's team all got bit by polar bears :lol2:

Yes, we will see :-D

Rabies develops slowly (the incubation period is 15 days to several months), is transmitted via saliva (that means, the saliva needs to get in contact with blood or lymph fluid), affects the central nervous system causing rage, apathy, paralysis and difficulties to eat and drink.
Unfortunately I don´t think the symptoms and characteristics of rabies fits into the vague descriptions we have of "the sickness".