Data on the amount
necessary to cause human disease by ingestion is not available.
O'Reilly and Daborn (1995) summarised research findings based on
animal models, which suggested that 3 to 300 cells of M. bovis were
able to cause pulmonary infection by inhalation,whereas one thousand
to 18million times larger doseswould be required to cause TB by ingestion.
These required doses are expected to be much lower in immune
deficient populations that characterise most of sub-Saharan African
countries.