Pin-prick holes are quite common in all latex gloves. Simply blowing a glove up will not necessarily show that the glove is damaged enough to let in a virus. This is why gloves alone are not sufficient protection. Oil-based substances and hydrocarbon solvents weaken latex very quickly. This damage cannot be seen, and so unsuitable gloves will give a false sense of security.
Many chemicals can actually work their way through a glove by permeation.
This means the coating is uneven and, on occasion, the fibres may show up on the surface of the glove making it useless as a barrier to chemicals. Separate cotton linings worn underneath the glove are a much better idea, so long as they are changed regularly. It gives six classes of protection. Make sure that the gloves used are suitable for the purpose they are being used for. Note that some other substances found in gloves, such as thiurams and dithiocarbamates can also act as sensitisers.