The safety of BCG vaccination in cattle: results from good laboratory practice safety studies in calves and lactating cows

Bovine tuberculosis (bTB) is a global disease of livestock that has damaging economic, animal health and public health consequences. Conventional bTB disease control strategies, based around the testing and slaughter of cattle infected with bTB, are typically used to help limit or reduce the transmission of this disease but in many low- and middle-income countries such strategies may often be economically unviable, culturally unacceptable or logistically impracticable. The use of vaccination to protect cattle against bTB could provide a potentially more affordable, ethically acceptable and practical additional disease control measure. The protective efficacy of the commercially produced and readily available human vaccine against tuberculosis (Mycobacterium bovis Bacille Calmette-Guérin; BCG) in cattle has been demonstrated in many experimental laboratory and field studies. However, Good Laboratory Practice (GLP) studies assessing the safety of BCG vaccination in cattle have not previously been reported. We describe here the results of two GLP safety studies in which calves and lactating cows were vaccinated with BCG (Danish 1331 strain). From an animal health and welfare perspective, the results of these studies indicate that BCG vaccine is well tolerated in these categories of cattle with only transient and minor local or systemic reactions. Furthermore, there was no evidence that BCG was shed in raw milk, saliva or faeces collected from vaccinates and vaccination did not have a detrimental effect on milk yields in lactating cattle. These data, underpinned by GLP principles, further support the existing data on the safety of BCG vaccine in cattle and complement the abundant available cattle efficacy data for this potential cattle bTB vaccine.