My 13 month old has had diarrhea for 2 weeks. does this sound like a virus?

Common pattern: Most of these start with a gut virus but may persist because of transient changes in the digestive tract. Many will transiently loose their ability to digest the sugar in cow milk products, leaving it to act as a mild laxative. Omitting lactose containing products for a week or so and feeding the kid applesauce/fresh bananas will often plug them. If not they need to be evaluated.