I thought fleas were species specific? So dog fleas won't live on rabbits, cats etc and vice versa? Though fleas may hop off one creature, sit on there for a while before moving on, so if you've just seen the one it might've been a stray catcihng a lift.
Ivermectin is what you use for little unwanted visitors in other small furries, like rats, mice and guinea pigs etc. and Beaphar do one you can buy in petshops for buns, not the Bob Martins one as that uses permethrins which bugs have got quite resistant to now.
Ivermectin supposedly stays in the body for 30 days (in rats anyway) so other than treating your carpet to stop any stray fleas jumping on and irritating him (or you!) you shouldn't really need to keep up a strict regime as any fleas that hop back on him should get a dose of the Ivermectin still, it'll last longer than their lifecycle.
What you can do is try rubbing a white bit of tissue on him, if dark red/browny bits come off there's a good chance he has fleas (cause you'll have rubbed off flea poo :lol