Roundworms...do i need to deworm all my cats?

So we took in a stray cat & he has roundworms (which I expected).
Do I need to de-worm my other cats (they are indoor only) aswell since they've had contact with eachother & have used the same litter box etc.?

Thanks

Yes, I would personally.  Roundworms can be transmitted through the litterbox, so if they've all shared one, I would just go ahead and deworm all of them.  Has the stray been checked out by a vet for any other health problems?  You should isolate him and get him checked for FIV/FeLV before letting him mingle with your indoor only cats.  

what are the signs of round worm? i think my cat has some sort of infection. she has little crumbles of looks like cat litter around her butt hole

karmahcat2013 said:

 
what are the signs of round worm? i think my cat has some sort of infection. she has little crumbles of looks like cat litter around her butt hole

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The cat's stomach might be really round. He'll eat a lot because the worms are leeching the nutrition, and he might throw up/ poop worms.  

http://www.petsandparasites.org/cat-owners/roundworms/

I'm not sure what condition your cat has but you should get it checked out by a vet.  

Does it kind of look like rice? If so that is tapeworm.