Invasive grey squirrels carry a parasite that makes their native red cousins sluggish

Daily Mail - Science & tech 

Invasive grey squirrels carry a parasite that makes their native red cousins sluggish and threatens to further reduce their numbers, a study has found. Scientists say that the parasite -- carried only by the greys -- causes red squirrels to forage for food less efficiently and makes competition from the greys harder to face. The problem is so severe that it could wipe out red squirrels entirely where they share woodlands with the intruders. Red squirrels normally carry only one type of parasitic worm, or'helminth', in their stomach and intestines -- those of the species Trypanoxyuris sciuri. This means that they are therefore sensitive to foreign parasites transmitted by other animals -- including those of the alien grey squirrel.