Feliciano Milián Suazo

A review of M. bovis BCG protection against TB in cattle and other animals species

Bovine tuberculosis (TB) causes severe economic losses in livestock due to low production, animal deaths and condemnation of carcasses. It is also an important constraint in international trade of animals and animal products. A scientific committee in Great Britain in 1997 concluded that the development of a cattle vaccine would be the best option for long-term control of TB. However, vaccination of cattle currently is not accepted because the vaccine interferes with the skin reaction to the tuberculin test in the field. Efficacy of M. bovis BCG in protecting bovine and other animal species against tuberculous infection has received much study. Vaccination of cattle prevents the spread of the disease in populations by reducing the number and size of the lesions, and the load of bacteria (rather than by preventing infection). We review the literature about the efficacy of BCG in protecting cattle and other animal species against infection with field strains of M. bovis and discusses its potential use in programs of TB control in high-prevalence populations.

Population structure of Mycobacterium bovis isolates from cattle in Mexico

The molecular fingerprints of 878 isolates of Mycobacterium bovis collected from cattle between 2009 and 2010 in different regions of Mexico were used in this study. One hundred and ninety-four spoligotypes were observed in total with a high degree of heterogeneity. Sixty-four percent of the isolates grouped into just nine spoligotypes, and 27% fell into only two spoligotypes: SB0673 and SB0669; 149 were orphan spoligotypes. The two predominant spoligotypes were found in almost all states in Mexico, especially in central Mexico, where there is a high concentration of dairy cattle; however, some spoligotypes were closely associated with restricted geographical areas. The hypothetical evolutionary relationship among spoligotypes was estimated using the spoligoforest program in the spolTools webpage. Four trees with connected components and nine unconnected nodes were found. The biggest tree had SB0140 strain as a root, suggesting this as the oldest strain in the tree. However, the relationship of this spoligotype with SB0673 and SB0669 was weak. The discriminatory power of spoligotyping for this M. bovis sample of isolates was 0.94, and the recent transmission index (RTI) 0.83, suggesting a high rate of recent transmission of some strains of M. bovis in the population. This parameter indicates that new measures are required to stop the dissemination of tuberculosis in cattle.

Efficacy of a Vaccine Formula against Tuberculosis in Cattle

“Test-and-slaughter” has been successful in industrialized countries to control and eradicate tuberculosis from cattle; however, this strategy is too expensive for developing nations, where the prevalence is especially high. Vaccination with the Calmette-Guérin (BCG) strain has been shown to protect against the development of lesions in vaccinated animals: mouse, cattle and wildlife species. In this study, the immune response and the pathology of vaccinated (BCG-prime and BCG prime-CFP-boosted) and unvaccinated (controls) calves were evaluated under experimental settings. A 106 CFU dose of the BCG strain was inoculated subcutaneously on the neck to two groups of ten animas each. Thirty days after vaccination, one of the vaccinated groups was boosted with an M. bovis culture filtrate protein (CFP). Three months after vaccination, the three groups of animals were challenged with 5×105 CFU via intranasal by aerosol with a field strain of M. bovis. The immune response was monitored throughout the study. Protection was assessed based on immune response (IFN-g release) prechallenge, presence of visible lesions in lymph nodes and lungs at slaughter, and presence of bacilli in lymph nodes and lung samples in histological analysis. Vaccinated cattle, either with the BCG alone or with BCG and boosted with CFP showed higher IFN-g response, fewer lesions, and fewer bacilli per lesion than unvaccinated controls after challenge. Animals with low levels of IFN-g postvaccine-prechallenge showed more lesions than animals with high levels. Results from this study support the argument that vaccination could be incorporated into control programs to reduce the incidence of TB in cattle in countries with high prevalence.

Genetic diversity based on MIRU-VNTR profile of isolates of Mycobacterium bovis from Mexican cattle.

Bovine tuberculosis (bTB) is a disease caused by Mycobacterium bovis (M. bovis), which affects cattle, animal species and humans. To determinate the genetic structure of strains of M. bovis in mexican cattle, 467 isolates obtained from 2009 to 2010 from different regions of Mexico with known spoligotype were included in the study. The isolates were genotyped by interspersed repeated mycobacterial units-variable number tandem repeats (MIRU-VNTR) obtaining 13 MIRU-VNTR groups. When combining MIRU-VNTR patterns with its spolygotypes, the Hunter genetic discrimination index (HGDI), we obtained 421 genetic patterns distributed in 17 groups. The HGDI for the total loci was 0.99. The locus that presented the higher HGDI was 2461 (0.857), while the locus with the lowest HGDI was 2686 (0.239). When we analyzed our results, using just 6 or 8 MIRU-VNTR we obtained an discriminatory power of 0.8499 and 0.8875 respectively indicating lower HGDI than 12 MIRU-VNTR locus.

Molecular epidemiology of cattle tuberculosis in Mexico through whole-genome sequencing and spoligotyping

Mycobacterium bovis infection in cattle persists in Mexico, posing a threat to human health. Control of bovine tuberculosis, through the National Program Against Bovine Tuberculosis, has led to the decrease of disease prevalence in most of the country, except for high dairy production regions. Genotyping of M. bovis has been performed mainly by spoligotyping and variable number tandem repeats (VNTR), but higher resolution power can be useful for a finer definition of the spread of the disease. Whole genome sequencing and spoligotyping was performed for a set of 322 M. bovis isolates from different sources in Mexico: Baja California, Coahuila, Estado de Mexico, Guanajuato, Hidalgo, Jalisco, Queretaro and Veracruz, from dairy and beef cattle, as well as humans. Twelve main genetic clades were obtained through WGS and genetic diversity analysis. A clear differentiation of the Baja California isolates was seen as they clustered together exclusively. However, isolates from the central states showed no specific clustering whatsoever. Although WGS proves to have higher resolving power than spoligotyping, and since there was concordance between WGS and spoligotyping results, we consider that the latter is still an efficient and practical method for monitoring bovine tuberculosis in developing countries, where resources for higher technology are scarce.

Whole Genome Sequencing for Detection of Zoonotic Tuberculosis in Queretaro, Mexico

A total of 2,736 samples, sputum, urine, and other fluids, collected from 1,154 tuberculosis suspicious patients in Queretaro, Mexico were included in the study. Acid-fast staining and culture in selective mediums, Stonebrink and Lowenstein-Jensen, were performed in all samples. Genotyping of isolates was performed by spoligotyping and single nucleotide polimorfism (SNP) whole genome sequencing. Mycobacterium bovis spoligotypes and SNP-types obtained were compared to those of cattle found in a database. Twenty-one (1.8%) isolates of Mycobacterium were obtained by culture, all from sputum; two (13%) were identified as M. bovis by spoligotyping, SB0673 and SB0971, which are frequently found in cattle in Mexico. From the isolates´ total, 15 were whole genome sequenced, confirming two as M. bovis. The SNP patterns of the two M. bovis isolates from human were similar to those found in cattle in different parts of Mexico.

Determinación de la estabilidad genética de una cepa de Mycobacterium bovis por infecciones seriadas en cobayos

This research was performed in order to determine the origin of the «direct repeat» (DR) region variability in one M. bovis strain when passed serially in ginea pigs. Three 6-guinea-pig groups were inoculated intraperitoneally with 103 M. bovis organisms/animal, using a strain isolated from a cattle lesion. Five weeks after inoculation the animals were killed. Tissue samples were obtained for M. bovis isolation. Fifteen of the 18 guinea pigs survived until sacrifice. All animals showed some type of lesion, and M. bovis was isolated from 14 of them. The molecular analysis was performed using the spoligotyping technique. The DNA from 13 isolates was harvested, out of which two clusters were obtained. The first cluster included six isolates: two from group 1, two from group 2, and two from group 3. The second cluster also included six isolates: three from group 1, two from group 2, and 1 from group 3. Each of the three reference strains (MTB, AN5, and h37rv), formed a different spoligotype. Two clusters were obtained specifically from the first group of guinea pigs: the first cluster includes three isolates, and the second cluster included three isolates. Once again, reference strains formed a different spoligotype. Results show that diversity in the DR region of M. bovis can occur in guinea pigs even if no external infections sources are present. This is likely to occur due to the generation of non-lethal mutations during bacterial reproduction, and this might be happening also in cattle.

Análisis descriptivo de un estudio epidemiológico de la razones de desecho en ganado lechero

Se realizo un estudio epidemiologico en 7,767 lactancias de vacas Holstein en 34 hatos lecheros del estado de Nueva York