Natural resistance to tuberculosis infection in cattle

Bovine tuberculosis (bTB) is a chronic disease of cattle and other animal species caused by Mycobacterium bovis. The importance of bTB is that it represents a risk to public health, and causes economic losses to the livestock industry. Because of this, many countries have established control and eradication programs with partial success. Therefore, the search for new strategies to control this disease is relevant. In Mexico, the prevalence of bTB is estimated in 16 % in dairy cattle and in less than 1 % in beef cattle; however, field studies have proved that in spite of the high prevalence in some herds (25-35 %), and long periods of exposure (3 to 5 yr average), the prevalence never reaches 100 %; this suggests that some animals are naturally resistant to tuberculosis. Considering that clinical manifestation of bTB depends on the interaction of various factors, it is reasonable to think that genetic variations in the host can be associated to resistance to this disease. This review, presents the state of the art in this matter; it describes the results of studies performed in different animal species and humans with the purpose of detecting genetic variation associated with disease resistance. The main genes associated with resistance are described and discussed individually. The conclusion is that genetic variation in cattle is associated with resistance to tuberculosis, and that this variation can be identified, measured, and incorporated into the current process of animal selection in the livestock industry to obtain animals more resistant to infection.