Diagnosis of mycobacteria in bovine milk: an overview

Abstract

Tuberculosis remains as the world’s biggest threat. In 2014, human tuberculosis ranked as a major infectious disease by the first time, overcoming HIV death rates. Bovine tuberculosis is a chronic disease of global distribution that affects animals and can be transmitted to humans by the consumption of raw milk, representing a serious public health concern. Despite the efforts of different countries to control and eradicate bovine tuberculosis, the high negative economic impact on meat and milk production chains remains, given the decreased production efficiency (approximately 25%), the high number of condemned carcasses, and increased animal culling rates. This scenario has motivated the establishment of official programs based on regulations and diagnostic procedures. Although Mycobacterium tuberculosis and Mycobacterium bovis are the major pathogenic species to humans and bovines, respectively, nontuberculous mycobacteria within the Mycobacterium genus have become increasingly important in recent decades due to human infections, including the ones that occur in immunocompetent people. Diagnosis of mycobacteria can be performed by microbiological culture from tissue samples (lymph nodes, lungs) and secretions (sputum, milk). In general, these pathogens demand special nutrient requirements for isolation/growth, and the use of selective and rich culture media. Indeed, within these genera, mycobacteria are classified as either fast- or slow-growth microorganisms. Regarding the latter ones, incubation times can vary from 45 to 90 days. Although microbiological culture is still considered the gold standard method for diagnosis, molecular approaches have been increasingly used. We describe here an overview of the diagnosis of Mycobacterium species in bovine milk.

Screening milk for bovine tuberculosis in dairy farms in Central Province, Sri Lanka

“…Similarly, saprophytic mycobacteria were recovered from 13% out of 285 milk samples in a study conducted in Michigan (Sanchez and Rosell, 1983). Although M. tuberculosis and M. bovis act as the major pathogenic species, NTM have become increasingly important in causing human infections in recent years (Bolaños et al, 2017). According to World Health Organization estimates, cow milk may be the source of approximately 15 foodborne bacterial infections including M. bovis (Abrahão et al, 2005).The sensitivity of the PCR assay was confirmed by using DNA extracted from whole milk added with M. bovis BCG vaccine 1 5 2 3 4 M 6 7 8 9 10 strain at concentrations of 10 1 to 10 6 CFU/mL ( Figure 2).…”

“…Bovine tuberculosis can be transmitted to human through inhalation of aerosols, consumption of contaminated food such as milk and meat products or direct contact with infected animals (Une and Mori, 2007). Consumption of unpasteurized milk and dairy products, especially soft and hard cheeses has been identified as the primary risk factor of M. bovis infection in humans (Bolaños et al, 2017).…”

“…Mycobacterium bovis and atypical mycobacteria have been isolated from raw cow milk in many studies conducted in several countries such as Tanzania, Turkey, Zambia, Tunisia and Brazil (Bolaños et al, 2017). Bovine tuberculosis has been reported and confirmed in cattle in Sri Lanka since 2012 as reported by Department of Animal Production and Health (Anonymous, 2014;Kumara et al, 2014;Kumara et al, 2015).…”

Difficulties in diagnosis of bovine tuberculosis in suggestive lesions on post-mortem inspection in carcasses

“…Differently, the lepromatous TH2-type granulomatous lesions, caused by MOTT (Mycobacteria Other Than Tuberculosis) or atypical mycobacteria, which characteristic is the disorganization of the cellular layers, the absence of fibrous capsule and necrotic center, bring, when identified, another epidemiological meaning; by these characteristics the presence of high mycobacterial load is frequent (Arckermann, 2013). Despite that, Bolaños et al (2017) emphasizes that these atypical mycobacteria present no risk to the immunocompetent population. However, it should be noted that the number of people with debilitating diseases with neoplastic, metabolic, autoimmune and infectious origins has increased.…”

Risk Factors for the Transmission of Mycobacterium Bovis to Slaughterhouses Workers in Brazzaville, Republic of the Congo

“…Transmission of bovine TB from infected cattle to humans occurs primarily through consumption of raw (unpasteurized) milk or raw milk products containing the bacteria (16). Transmission can also occur through prolonged exposure to bacteria in the air in the immediate vicinity of live infected cattle or their carcasses (17).…”