What's ailing hybrid lions?

I ran across this story about unusual disease affecting hybrids of Asiatic and African lions in Indian zoos:

NEW DELHI - Nearly two dozen crossbred lions are slowly dying in northern India from a mysterious disease afflicting the hybrid offspring of Asiatic and African cats paired in a discontinued experimental program.
Zookeepers are mournfully watching the results of the program, which began in the late 1980s at the Chhatbir Zoo and was ended in 2002 after many of the nearly 80 crossbred lions were struck by a mysterious disease linked to inbreeding and a weakened gene pool, said Kuldip Kumar, Punjab state's conservator of forests and wildlife.

This is very curious. I did a little search to see if anything more detailed had been written. The best I could find was an article from 1990 that mentioned possible problems related to inbreeding Asiatic lions in American zoos, which turned out to be genetic hybrids:

Meanwhile, Paul Joslin was not quite sure whether the "Asiatic lions" in US zoos were really Asiatic lions. Joslin, then assistant director of Chicago's Brookfield Zoo and now an independent zoo consultant, had noticed that many of the lion males lacked a telltale belly fold, a flap of loose skin on their undersides that distinguishes Asiatic from African lions. He was also worried that increased infant mortality among "Asiatic lions" in US zoos signaled inbreeding problems.
...
O'Brien and Martenson eventually found that almost all Asiatic lions in US zoos and some in Asian ones as well were hybrids. As a result, US zoos agreed to suspend mating Asiatic lions and allow the hybrid animals to die off naturally (Cohn 1990:168).

So I wonder if this is some infectious disease that has been affecting their chronic health, or if -- as the reports seem to suggest -- there is some postzygotic incompatibility between the lion subspecies.

References:

Cohn JP. 1990. Genetics for wildlife conservation. BioScience 40:167-171.