Animals infected with bTB shed bacteriathrough bodily fluids including saliva, feces and milk. In humans and animals, M.tuberculosis and M. bovis arecommonly spread through aerosol exposure (Waters and Palmer 2015). This leads to thecommon assumption that any lesion restricted to the respiratory tract wascontracted through aerosols or lesions restricted to intestines were contractedthrough ingestion of M.

tuberculosisor M. bovis. However,studies have fed calves with milk infected with M. bovis and calves developed lesions in the lungs with no evidenceof infection in the intestines or lymph nodes (Edwards 1937; Jones et al.

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2016). Castillo-Velázquez et al. (2013) found in their study that a single bacterium can cause infection through therespiratory tract but a higher infectious dose is required to infect throughthe digestive tract.

This shedding allows for easy spread of disease to othercattle, their calves and humans. For humans theprimary exposure to M. bovis is fromunpasteurized milk and other unpasteurized dairy products but it can also comefrom contaminated meat (Edwards 1937;Grange 2001; Waters and Palmer 2015). The spread of bTB is mostly through directcontact with infected animals (Khatri et al.

2012). Housing of animals in close quarters or crowding can increasethe spread of bTB to young animals (Waters and Palmer 2015). The European Food Safety Agency (EFSA) reported slaughterhouse meat inspection is a main method ofbTB surveillance in Europe. Inspection involves examination of the slaughteredcattle for characteristic lesions and collecting microbial samples from thelungs and lymph nodes (EFSA 2013).

In Canada, the CanadianFood Inspection Agency (CFIA) controls the spread of positive bTB animalsthrough strict quarantine and animal movement controls, humane destruction ofinfected and exposed animals, testing of at-risk herds or herds on previouslyinfected properties. If animals are infected, they are ordered to be destroyedowners will be compensated based on market value (CFIA 2017). After infected animals are disposed of,CFIA requires all areas where infected animals may have come into contact withmust be cleaned and disinfected, in accordance with international standards (CFIA 2017). In one Argentina study where cattle wereroutinely inspected in their National Program of bTB control program theyisolated M.bovis in 5 of 178 cattlerandomly sampled that had no signs of visible lesions (Kantor et al. 1987). The EFSA (2013) concludedthat there is no significant evidence of transmission of M.

bovis during handling or consumption of the meat since it is notmeat-borne by nature. Due to difficulties in designing experiments it is challengingto determine if meat-borne illness can infect humans. Accidental incision of thelymph nodes during slaughter can result in cross-contamination with other high-prioritydiseases such as Salmonella spp. (EFSA 2013) and it is believed thatbovine meat safety may be compromised in a similar manner (EFSA 2013). Minimizing interactionwith lymph nodes by excluding contact and incision of the lymph nodes candecrease the risk of cross-contamination of the meat (EFSA 2013) and increase public health safety. Humans thatwork in close contact with infected cattle can inhale aerosols containing thebacteria or through direct contact with infected animals (occupational hazard).A less common pathway of infection is through the skin. For example, butchers handling contaminated beef may developlocal lesions called “Butcher’s Wart” (Grange 2001).

However, thereare no documents of skin lesions developing on cattle. For most people living in high-income countries such as Canada, USA,and in the EU the risk to humans is very low because of pasteurized milk andgovernment run programs to control bTB.The greatestchallenge when trying to manage bTB in cattle is that there is a broad range ofwildlife reservoirs, which act as a vector for transmission to cattle (Brook et al. 2013). Spread of TB is not limited topolitical borders as infected wildlife can wander across borders and liveanimals, including cattle, are imported from endemic-countries (Tsao et al.

2014). M. bovis is at an increased risk of spreading due to loss ofwildlife habitats, and imports and exports of animals and animal products(Pollock and Neill 2002; Smith 2012), which isinspected by and cases are reported to CFIA in Canada.