Bacteriological and molecular detection of Mycobacterium bovis in cattle with inconclusive results to intradermal tuberculin tests

Abstract

A dairy herd (77 cows) from Rio de Janeiro, Brazil, with a history of tuberculosis infection was tested by a comparative cervical test (CCT). Seventeen cows were reactive and seven were inconclusive (swelling ≥ 2.0 mm and ≤ 3.9 mm, respectively). All of these 24 cows were slaughtered and necropsied ; samples from lungs and lymph nodes were collected for multiplex polymerase chain reaction (PCR) and culturing. Infection was confirmed in 23/24 (95.8%) of the slaughtered animals (five by culturing, four by PCR, and 14 by both tests). All cows with inconclusive results at CCT were confirmed as infected. Although slaughter of inconclusive reactor cows is not mandatory in many countries, our study provided evidence to support the slaughter of these cows, at least during an outbreak.

Bovine Tuberculosis in East Africa

“…Similar findings were reported in Brazil when six out of seven inconclusive cases by the skin test, were positive by PCR and culture (Zarden et al, 2013). Medeiros et al (2010) reported that anergic animals may be harbouring TB, yet were not reactive to the skin test; while delayed hypersensitivity may take 3 to 6 weeks, following infection (OIE, 2009).These are probable reasons for obtaining inconclusive results in this study.…”

Risk factors associated with the presence of Mycobacterium bovis in macroscopic lesions suspected as being caused by bovine tuberculosis detected in slaughterhouses

“…Fráguas et al (2008) indicated that, from a total of 97 bovine animals reactive to the intradermal test, only 11.34% (11/97) were confirmed as M. bovis in bacterial cultures and postulated that this low bacterial recovery rate may be related to the difficulty of carrying out M. bovis cultures, which requires a minimum amount of viable bacilli, in addition to a decontamination technique applied during the process that can render this microorganism unfeasible. Zarden et al (2013) followed the slaughter of 24 cattle reactive to the tuberculin skin test, with 29.16% (n = 7) presenting suspicious lesions for bTB. When submitting samples without lesions for laboratory analysis, it was found that 73.16% (n = 19) of the animals tested positive when using bacterial culture, while 75.16% (n = 18) tested positive by the molecular method.…”

“…Humans acquire the infection through contact with aerosols expelled by infected animals or mainly, through the consumption of milk and dairy products not pasteurized or not heat treated from contaminated animals. It is, therefore, a serious public health problem, considered a cosmopolitan and re-emerging zoonosis (Medeiros, Marassi, Figueiredo, & Lilenbaum, 2010;Zarden, Marassi, Carvalho, Figueiredo, & Lilenbaum, 2013;Carvalho et al, 2016).…”

Risk Factors Associated With the Presence of Mycobacterium Bovis in Macroscopic Lesions Suspected as Being Caused by Bovine Tuberculosis Detected in Slaughterhouses

“…Humans acquire the infection through contact with aerosols expelled by infected animals or mainly, through the consumption of milk and other foods from contaminated animals. It is, therefore, a serious public health problem, as it is a zoonosis (Medeiros et al 2010; Zarden et al 2013;Carvalho et al 2016).…”