This mob will spawn at neg1515, neg75 and then wander to the NW corner of the zone, on the ledge.
Spawn time has been reported recently as 4 minutes, 45 (or 48) seconds. It was noted as being about a minute longer than that in the past.
Best strategy is to initially get a ranger to kill PHs (tottering apes and possibly tottering gorillas) up on ledge while you wait at the spawn point. The PH has less than 4K hp.
Map File Location:
P 97.0854, 1519.7745, -333.3568, 0, 0, 0, 2, Disease-Ridden_Gorilla