Lions killed by perfect storm of changing climate, virus and parasites

In 1994, a third of the lions in the Serengeti were killed off by a massive epidemic of canine distemper virus (CDV), an often fatal infection that affects a wide range of carnivorous mammals. Seven years later, a similar epidemic slashed the lion population in the nearby Ngorongoro Crater. While CDV was undoubtedly involved, the scale of the deaths was unprecedented. What was it about the 1994 and 2001 epidemics that claimed so many lives?