Any pathogen that would take over it's host to such a degree would likely have some defenses to microscopic organisms and possibly other carrion feeders.
Falcon has a point. While the government would probably give citizens some idea at first, they wouldn't want to disclose all the facts immediately. Any outbreak in the states would have to be dealt with smoothly and quietly. Keeping the population 100% ignorant would be a bad idea, but alerting them to the full extent of the outbreak would be a bad idea, at least at certain stages
Even a rouge zombie inside a city would be tough to track. All it takes is for a couple of homeless guys, or some drunk people staggering home from a party to bitten, and it starts all over.
So a pathogen is immune to the carrier being killed by an animal now? To falling off a cliff? Getting swept up in a river?
No, he doesn't. If someone want to claim a world government (in his case, the US government) has suffered some sort of epidemic or disaster (as what we are assuming a zombie outbreak would be) and never told anyone or kept the population in the dark on some issues, he can show some past historical examples. I mean really, what do you guys think a government would not tell people, or why it would be in their best interested to tell the people?
Let's see: outbreak of zombie plague. Important, so tell people.
Outbreak spreads through contact with infected. Important, so tell people.
The military and health organizations are quarantining areas. Important, so tell people.
What, exactly, is important information during this outbreak that is not important enough to share with the local population that is at risk?
Also, no, it wouldn't. You seem to want a zombie to be able to sneakily stealth around a city until it can infect someone (and, presumably, for that someone to not be smart enough to say "Oh hey,t here was a zombie outbreak in this city before. Last night some wierd dude bit me... NOT RELATED! HA!" A zombie is mindless, their only drive seems to be to attack people. There's no way a zombie is goign to be hanging out in a city without attacting attention to itself.
There's also no way a city would go "Mmmh, ok, we THINK we got all the zombies during the last sweep. There's a chance some of them were missed. We can either pack up and go back home and risk another outbreak, or just pay our cops/soldiers overtime to do another sweep, and then another and THEN still tell the people to be on the lookout for anything odd."