According to reports, Arafat has the exact opposite of AIDS. An overactive immune system, not a depressed one. His immune system is attacking his own body, as with Lupus or a long list of autoimmune disorders.
Lies, all lies. He's got aids and he's trying to hide it. That's why his wife has been living in Paris all this time. He didn't want her around while the barebackers from San Fran were in town.
Then it must not have been treated at all. Quite a few of the autoimmune reponse diseases are treatable with low doses of chemotherapy drugs (like methotrexate) or with the new TNF suppresor drugs like Enbrel or Remicade. Both are pretty successful with lupus.
If he has ALS, all of what I said above doesn't apply.