Kristen Bell's daughter has anal worms again.

The 37-year-old actress revealed at the end of February that she couldn't stop scratching her butt after she contracted the infection - also known as threadworm - from her three-year-old daughter Delta.

And, despite thinking she'd got rid of them with the help of strong medication, she was horrified to find the little white worm wriggling around in her little girl's poop.

In a video on her Instagram Story, the 'Frozen' star said: ''I just want to explain to you what I'm looking at right now... It's a piece of s**t, literally. And at the top of it, is a little white pinworm. Now, I thought we had rid ourselves of these. And the irony here is so deep, because I did 'The Joel McHale Show', two weeks ago.

''We had pinworms three weeks ago. The day after I post [about it], I find another worm... Like, are they following me? I mean, are they litening through my phone just waiting to appear when I least expect it?

''Or you have to dose twice for pinworms? The answer is B you have to dose twice for pinworms, because I looked it up and apparently they can stick around and the point is we're all dosing a second time because the little one has been reinfected. (sic)''

However, the actress confirmed that she doesn't think she has got the anal worms but told her 5.7m followers that she will be keeping them updated on her symptoms.

She said: ''Now I don't currently have pinworms, I don't think. But I dose and you bet your bottom dollar, I will keep you updated on my symptoms. (sic)''

Although it's a highly contagious infection, Kristen's husband Dax Shepard and their daughter Lincoln, four, have managed to avoid catching the parasite.