1. When you sent in the manuscript, didn't you use Delivery Confirmation from the USPS or similar service from FedEx or UPS? That way, you would have known it got there and when. You should always use something traceable when sending in anything other than a simple query, I feel.
2. If you know the agent got it, why are you following up? Do you believe this agent is capable of outright losing material? If so, why would you want this agent?
3. Did the agent ask for an SASE and did you send one? Did it have your current address on it and do you still live there? If so, is there a reason to expect it would not have reached you?
4. Don't you think that if the agent wanted to represent you, he or she would have called or called to follow-up if he or she sent a written offer of representation and not heard back?
Seems to me that all indicators are that the agent has not yet read the manuscript and following up in the absence of any reason to follow-up is unneeded.
Best,
Andy