From the New Scientist:

Bird flu hasn't gone away. The discovery, announced last week, that the H5N1 bird flu virus is widespread in cats in locations across Indonesia has refocused attention on the danger that the deadly virus could be mutating into a form that can infect humans far more easily.

In the first survey of its kind, 1 in 5 cats have been found to be infected with the virus and survived. This suggests that as outbreaks continue to flare across Asia and Africa, H5N1 will have vastly more opportunities to adapt to mammals than had been supposed.

The infection has also been found in dogs and cats on the Indonesian island of Bali, which has also had outbreaks of H5N1. The new findings follow reports that unusually large numbers of dead cats have been found near many outbreaks of H5N1.

Infected cats may not directly increase the danger of people catching the virus, as humans seem to catch the current strain only with difficulty even from birds, which they kill, pluck and eat. The main worry is that as the virus replicates in cats it will further adapt to mammals and acquire the ability to spread more efficiently to people and from person to person, unleashing a human pandemic.

The 1918 pandemic was a bird flu virus that adapted to mammals in some intermediate mammalian host, possibly pigs. Maybe for H5N1 the intermediate host is cats. Killing cats won't solve the problem. Like shooting wild birds, it is unlikely to have much impact and could send infected animals elsewhere. It would also lead to a population explosion of disease-carrying rodents, which the cats normally keep in check.

If you remember your lessons from history, the rodents carried fleas, which were the vector for the plague--bubonic, pneumonic and septicemic.