Food safety after rodent issue
It is not just the food that the rat has eaten that is of concern, any cross-contamination on food due to rat urine or faeces is also a major health risk factor.

Leptospirosis and Listeriosis, while not generally fatal, do carry a wide range of risks from flu-like symptoms to meningitis and organ failure.

If you were a restaurant or cafe, most health inspectors in the UK or Europe would seriously consider closing down your operation until the rodent problem was properly dealt with. As an individual though, obviously you have more latitude and choice in the matter. Provided the outer layers are not damaged or stained I would inspect the remaining corn with an ultra-violet torch (to check for any  protein staining from the rat urine) and then dispose of those cobs. I would also spray the remaining "clean" cobs (once the outer leaves are removed) in a undiluted vinegar solution followed by a 3% Hydrogen Peroxide solution, let sit for 10 minutes, then gently scrub under running water to remove the solution. 

To be honest though, unless you have a large quantity of corn, I'd err on the side of caution and skip on the corn this once. I personally would not feel comfortable serving it to family or friends unless I was sure there was absolutely no risk of infection. 

References: 

http://www.grubstreet.com/2014/04/possible-effects-of-eating-rat-and-mouse-tainted-food.html

https://clearandwell.com/diy-fruit-vegetable-wash-remove-dirt-bacteria-pesticides/