Are there any specific signs my cat will show if he has worms?
I know that horses can get diarrhea, loose weight or don't gain weight and that you can detect some of the worms in their fecal.
But as my cat always goes out to poop, it's difficult to test his fecal for worms or see if he has diarrhea or something like that.
Is there any other way to find out if I have to deworm him?
Yes, there are general signs related to their stool as you noted, including diarrhea, blood, or constipation. For other signs, you should be looking for:
In general, though, being able to see them poop (or the outcome of it) is the most effective way to detect the presence of certain worms as not all symptoms may apply to varieties of worms. For example, the stool is important for detecting roundworms and hookworms. The weight loss and vomiting would more likely signal a tapeworm and coughing/breathing issues for lungworm.
If you're really concerned, take him into the vet for an examination. The risk is higher for outdoor cats who are more likely to be exposed to fleas and other parasites.
I don't know whether this is the case for all species of worm infection and I rather doubt that it is, but at least some worms can be seen by examining the cat's anus. Don't worry, nothing invasive, just lift the tail out of the way and have a look. You can sometimes see small white worms there.
I have seen this in a few of my cats over the years and promptly took them to the vet, fed them a pill for a few days and everything was fine.
