A pinworm is white, very thin, and about one - quarter inch long and usually occur when an animal has lived in unhygienic conditions. (boingonline.com)
Because their immune systems are still developing, they are especially at risk of malnutrition and even death from food which is improperly prepared in unhygienic conditions. (unicef.org)
In a bad scenario many kittens of different ages from different litters (and thus probably exposure to different viruses and organisms which will be shared with the other vulnerable kittens) are kept in crowded and unhygienic environments, without being vaccinated, and perhaps not getting the appropriate nutrition for kittens. (icatcare.org)