Identificação de Mycobacterium bovis em bovinos e sua importância na ocorrência de tuberculose zoonótica

Abstract

Bovine tuberculosis is a zoonotic disease, infection which is naturally transmissible between the vertebrate animals and man, caused by Mycobacterium bovis, whose primary host is the cattle, but several species of domestic mammals, wild animals and man are also liable to the same bacillus. To identify cases of bovine tuberculosis in Mato Grosso do Sul state and correlate this finding with zoonotic tuberculosis, the clinical, bacteriological and molecular diagnosis of infection was carried out and proved the presence of M. bovis in bovine products commonly used as food. Two studies were conducted. At first, the objective was to evaluate the contribution of health surveillance for the retrospective epidemiological studies of outbreaks of tuberculosis in herds of Mato Grosso do Sul state. From macroscopic lesions detected at slaughter of the cattle during routine health inspection, 200 cattle were examined through single intradermal comparative tuberculin test (SICTT). Animals with positive or inconclusive SICTT result were slaughtered. During the macroscopic examination, samples of organs with lesions suggestive of tuberculosis were collected and sent for culture on Stonebrink medium, search for acid-resistant bacilli (AFB) by Ziehl-Neelsen stain (ZN) and molecular identification isolates by polymerase chain reaction (PCR) with primers JB21/JB22. Tuberculosis was diagnosed by SICCT in 24/200 (12%) of the cattle. Of these, 23 were positive and one was inconclusive. All 24 cattle had gross lesions of tuberculosis. The microbiological examination (culture and ZN) of these lesions allowed the isolation of AFB, and PCR identified the presence of M. bovis in all isolates. We conclude that, by detecting lesions suggestive of tuberculosis in one cattle, the slaughter sanitary inspection contribut to the retrospective epidemiological investigation of an outbreak of tuberculosis in cattle. In the second study, the aim was to isolate and identify M. bovis in the milk of lactating cows originated from the same herd diagnosed with tuberculosis through the SICCT. Samples of fresh milk from 27 cows were cultured in a Stonebrink medium and incubated for 90 days. The isolated colonies were stained by ZN technique and identified by PCR using two pairs of primers: TB11/TB12 for identification of Mycobacterium spp JB21/JB22 and to identify the species M. bovis. Of the 27 samples of fresh milk subjected to cultivation, 12 were AFB and all confirmed as Mycobacterium spp by TB11/TB12 primers. Of these, four were of M. bovis detected by the presence of amplification product generated by the use of primers JB21/JB22. We conclude that the presence of M. bovis and other mycobacteria in raw milk of cows from herds with a diagnosis of tuberculosis poses a risk for human consumption, not only by the possibility of contracting zoonotic tuberculosis, but also other mycobacteria. The results of this study indicate that M. bovis is present in cattle from Mato Grosso do Sul and can be found both in tissues and in the fresh milk of cows coming from herds diagnosed with tuberculosis. Besides the risk predominantly occupational of human infection by M. bovis through respiratory (inhalation of infected droplets) and cutaneous (through interruption of the skin) routes, measures such as boiling / pasteurizing milk and dairy products and total cooking the meat for consumption are essential to prevent transmission of M. bovis to humans through the digestive system and strengthen the prevention and control of zoonotic tuberculosis.