You guys are a bit paranoid. The chances of one transmitting HIV during Aikido training is damned near impossible, EVEN IF THE HIV+ PERSON HAS A BLEEDING CUT ON THEIR WRIST DURING TRAINING. It would have to be very deliberate and quite difficult as well as time consuming. HIV does not "soak through skin", nor does it transmit through sweat or saliva. Transmission of the HIV virus is more difficult than cops and nurses would lead one to believe. Ask Colleen :O
I would imagine a LOT of blood would have to be spilled by one apparently unfortunate HIV positive aikidoka, onto the gaping wound of another unfortunate aikidoka. Then I would imagine that both would have to just ignore the blood and continue training (to the horror of the rest of the class), or actually sit there and perform some sort of "blood brother" style transfusion by connecting both of their open wounds together, all on the mat without any concern for, or from, their peers. Fortunately, I've never seen anything this macabre in any dojo, but then I haven't been to very many.
If this type of training happens regularly in one's dojo, I would suggest that person leave it immediately, and not before they called the proper health and sanitation authorities. If it's a normal dojo where injuries are rare and MINOR cuts are rarer, and those "victims" are excused to go politely grab a bandaid when the occasional and inevitable "toenail/fingernail cut" happens, then I can't see HIV being transmitted from person to person in the aikido training environment.
But, I guess if people would rather "be safe than sorry", there's certainly nothing "wrong" with that. I guess one could always snap on their latex gloves before training...
I would be more concerned about borrowing someone's else's cellphone than grabbing someone's wrist if I were THAT worried about diseases....