My son took a sip from guinea pigs bottle?

Don't worry, he'll be fine.

Your toddler will give you cause to freak out about stuff like this many many times in the coming few years, but really, unless he has an immune deficiency disorder (and even then only if the guinea pigs are sick with something that is catching to humans, not very likely) the gross stuff will rarely affect him at all, and at most cause a mild stomach upset when it does affect him.

The water bottle should be secured INSIDE the guinea pig cage. The only way for your 18mt to get a drink from it would be if he went inside the cage which shouldn't be big enough for a toddler's head. How did your child get to the bottle & get around the guinea pigs in the cage?

Call your doctor.

I am in no way a guinea pig expert (honestly, I probably couldn't even recognise one if you showed me a few pictures of small rodent-type animals) so take my thoughts with a grain of salt... but I'm thinking that if it was just water in the bottle, the only way that would be bad is if the guinea pig had some sort of contagious disease, in which case, you'd probably know, right? I mean dogs lick people all the time and nobody dies from that, so what difference would it make if it was a guinea pig whose saliva your toddler ingests?

Relax. It's nothing to worry about. Over the years your child might eat dirt, worms, dog food, cat food, all kinds of gross stuff. They might even eat something that gives them a tummy ache. It's OK, your stress becomes their stress so take a deep breath and move on.

Do not worry, I do not think you have anything to worry about. Toddlers get their mouthes on all kinds of things and are usually fine. Tell him not to do it, as he is old enough to learn at 18 months and pull him away if you catch him trying again, but I do not think this will hurt him.