Contamination of animal products: the minimum pathogen dose required to initiate infection.

When an animal product contains a low level of contamination (perhaps less than the minimum infective dose of a pathogen as determined experimentally), the theoretical probability remains that if a large number of animals are exposed to that product, at least one animal in the group will become infected. Such an infected animal could start an outbreak of the disease. These aspects, therefore, should be considered when risk assessments are performed. Foot and mouth disease virus in milk is used as an example.