Molecular characterization of Bacillus anthracis directly from patients' eschar and beef in an anthrax outbreak in Jiangsu Province, China, 2012

Molecular characterization of B. anthracis isolates from the anthrax outbreak among cattle in Karnataka, India

Background

Anthrax, a zoonotic disease is caused by the Gram positive bacterium Bacillus anthracis. During January 2013, an anthrax outbreak among cattle was reported in Gundlupet Taluk, neighboring Bandipur National Park and tiger reserve, India. The present study aims at the molecular identification and characterization of 12 B. anthracis isolates from this outbreak by 16S rRNA gene sequencing, screening B. anthracis specific prophages and chromosomal markers, protective antigen (pag) gene and canonical single nucleotide polymorphism (canSNP) analysis to subtype the isolates into one of the twelve globally identified clonal sub-lineages of B. anthracis.

Results

These isolates had identical 16S rDNA nucleotide sequences with B. anthracis specific dual peaks showing mixed base pair R (G/A) at position 1139 with visual inspection while the automated basecaller software indicated a G. Alternatively the nucleotide A at 1146 position was indicative of the 16S rDNA type 7. Multiple sequence alignment with additional 170 (16S rDNA) sequences of B. cereus sensu lato group from GenBank database revealed 28 new 16S types in addition to eleven 16S types reported earlier. The twelve B. anthracis isolates were found to harbor the four B. anthracis specific prophages (lambdaBa01, lambdaBa02, lambdaBa03, and lambdaBa04) along with its four specific loci markers (dhp 61.183, dhp 77.002, dhp 73.019, and dhp 73.017). The pag gene sequencing identified the isolates as protective antigen (PA) genotype I with phenylalanine-proline-alanine phenotype (FPA phenotype). However, sequence clustering with additional 34 pag sequences from GenBank revealed two additional missense mutations at nucleotide positions 196 bp and 869 bp of the 2294 bp pag sequence among the 5 B. cereus strains with pXO1 like plasmids. The canSNP analysis showed that the isolates belong to A.Br.Aust94 sub-lineage that is distributed geographically in countries of Asia, Africa, Europe and Australia.

Conclusions

The analysis of 16S rDNA sequences reiterated the earlier findings that visual inspection of electropherogram for position 1139 having nucleotide R could be used for B. anthracis identification and not the consensus sequence from base caller. The canSNP results indicated that the anthrax outbreak among cattle was caused by B. anthracis of A.Br.Aust94 sub-lineage.

Genotyping and population diversity of Bacillus anthracis in China based on MLVA and canSNP analysis

In pastoral parts of China, anthrax still presents a major risk to livestock and threatens the health of local human populations. Currently, whole-genome-based molecular markers, such as single-nucleotide polymorphisms (SNPs) and variable number tandem repeats (VNTRs), are the most effective tools for genotyping Bacillus anthracis. In this study, 191 isolates were selected to assess the diversity of B. anthracis in China. Five isolates were confirmed not to be B. anthracis by clustered regularly interspaced short palindromic repeat analysis, while the remaining 186 isolates were typed using canonical SNP (canSNP) and VNTR analyses. Five sublineages/subgroups, A.Br.001/002, A.Br.Vollum, A.Br.Aust.94, A.Br.Ames, and A.Br.008/009, were detected based on 13 canSNP sites. The 186 isolates were further assigned 114 sequence types based on 27 VNTR loci, with major branches correlating with the canSNP analysis. We then used a simplified multiple-locus variable number tandem repeat analysis (MLVA) protocol (MLVAmin) based on eight high-resolution VNTR sites to analyze the Chinese isolates, with the resulting phylogeny again agreeing with the canSNP analysis. We also developed two schemes, MLVAc and MLVAp, using various numbers of VNTRs to analyze different canSNP sublineages to increase the typing resolution of the canSNP protocol. The results showed a highly imbalanced geographical distribution of the B. anthracis population, with four different sublineages observed in Xinjiang Province, while only one sublineage, A.Br.001/002, was found in the other six provinces, except for three A.Br.Ames strains isolated from Inner Mongolia. Based on the MLVA and canSNP analysis, the spread of B. anthracis appears to have occurred from west to east via three independent routes.

Genetic characteristics of Bacillus anthracis isolated from northwestern China from 1990 to 2016

Anthrax is a global re-emerging zoonotic disease and is an endemic disease in China, especially in rural regions. In this study, the general characteristics of human anthrax outbreaks that occurred in areas of northwestern China over the past decade have been described. Meanwhile, the genetic characteristics of Bacillus anthracis isolated from these areas from 1990 to 2016 were analyzed by means of canonical single-nucleotide polymorphism (canSNP) analysis and multilocus variable-number tandem repeat analysis (MLVA) with 15 markers. Five sublineages/subgroups, namely, A.Br.001/002, A.Br.Vollum, A.Br.Aust94, A.Br.Ames and A.Br.008/009, were detected by using 13 canSNP sites. All of the sublineages were found in Xinjiang province, while one sublineage was found in Shaanxi, two in Gansu, three in Qinghai and four in Inner Mongolia. However, the geographical distribution of the B. anthracis populations exhibited different canSNP characteristics from those of the strains isolated before 1990 in China. In contrast to previous data, the A.Br.Ames subgroup was also observed to be scattered from Inner Mongolia to other provinces. All 106 strains were assigned to 36 MLVA15 genotypes, and 21 of these types were first observed in this study. The strains collected from anthrax outbreaks in recent decade were classified as subgroups A.Br.001/002 and A.Br.Ames and identified as genotypes MLVA15-28, MLVA15-30, MLVA15-31, MLVA15-38, MLVA15-CHN3, and MLVA15-CHN18. By canSNP analysis and MLVA, we found that the diversification of MLVA genotypes and the geographical distribution of B. anthracis populations is gradually becoming balanced across northwestern China. This study also provides preliminary survey results regarding the population diversity of B. anthracis in China, which will help promote the prevention and control of this important disease.

In this study, the general characteristics of human anthrax outbreaks that occurred in northwestern China over the past decade were described. Meanwhile, the genetic characteristics of Bacillus anthracis isolated from these areas from 1990 to 2016 were analyzed with the canSNP and MLVA15 methods. Our results showed a diversity of MLVA genotypes. We also observed gradual balancing of the geographical distribution of B. anthracis population in northwestern China according to the canSNP analysis. In particular, the A.Br.Ames subgroup now seems to be scattered from Inner Mongolia to other provinces, in contrast to the data before 1990. This study also provides preliminary survey results on the population diversity of B. anthracis in China, which will help to promote the prevention and control of this important disease.

Investigation and source-tracing of an anthrax outbreak in Gansu Province, China

Anthrax is an endemic disease in China. Cases are reported every year, especially in the northwestern areas. In August 2016, an outbreak of 21 cutaneous anthrax cases was reported in Min County, Gansu Province, China. In this study, the general characteristics of the anthrax outbreak are described. Two molecular typing methods, canonical single-nucleotide polymorphism (canSNP) and multiple-locus variable-number tandem repeat analysis with 15 markers (MLVA15), were used to investigate the possible source of transmission and to identify the genetic relationship among the strains/samples isolated in this outbreak as well as previous isolates. In this outbreak, all patients were infected through contact with diseased livestock or contaminated animal products. Livestock had been introduced into the local area shortly before the outbreak from Gannan Prefecture (in Gansu Province), Sichuan and Qinghai Provinces. In the molecular typing analysis, there were two canSNP subgroups found in Gansu, A.Br.001/002 and A.Br.Ames, and five MLVA15 genotypes were observed. The strains collected from the anthrax outbreak in Min County in 2016 belonged to the A.Br.001/002 canSNP subgroup and the MLVA15-28 and MLVA15-30 genotype. Strains previously isolated from Sichuan, Inner Mongolia and Maqu County (in Gannan Prefecture, Gansu Province) were clustered with these outbreak-related strains/samples according to the MLVA15-30 genotype. The MLVA15-28 genotype was found in strains isolated from Gansu and Xinjiang in previous studies. Combining the epidemiological investigation and molecular typing results, we conclude that the patients in this outbreak were infected by a local pathogen present in the adjoining area of Gansu, Sichuan and Qinghai Provinces.

Source and risk factors of a cutaneous anthrax outbreak, Jiangsu, Eastern China, 2012

Anthrax is still a severe public health problem and threat to human health. A cutaneous anthrax outbreak occurred in Jiangsu Province, a non-endemic anthrax region of eastern China, from July to August 2012. Epidemiological and laboratory investigation were initiated to trace the source of infection and identify the risk factors of the outbreak. On 25 July 2012, 17 persons were exposed to a sick cow, which had been imported from northeast China a few days previously. Of the 17 exposed, eight developed symptoms between 1 and 8 days and were diagnosed as cutaneous anthrax cases. Three main genes of Bacillus anthracis were detected from both human and cow meat samples, indicating that the outbreak was associated with this infected cow. A retrospective cohort study showed that contact with blood and presence of skin damage contributed to the case infection with B. anthracis. The outbreak highlights the need to enhance quarantine for imported livestock, which should have been vaccinated prior to importation, the significance of education for high-risk individuals, and training for primary healthcare workers even in anthrax-free areas.

Mapping the Distribution of Anthrax in Mainland China, 2005-2013

Background

Anthrax, a global re-emerging zoonotic disease in recent years is enzootic in mainland China. Despite its significance to the public health, spatiotemporal distributions of the disease in human and livestock and its potential driving factors remain poorly understood.

Methodology/Principal Findings

Using the national surveillance data of human and livestock anthrax from 2005 to 2013, we conducted a retrospective epidemiological study and risk assessment of anthrax in mainland China. The potential determinants for the temporal and spatial distributions of human anthrax were also explored. We found that the majority of human anthrax cases were located in six provinces in western and northeastern China, and five clustering areas with higher incidences were identified. The disease mostly peaked in July or August, and males aged 30–49 years had higher incidence than other subgroups. Monthly incidence of human anthrax was positively correlated with monthly average temperature, relative humidity and monthly accumulative rainfall with lags of 0–2 months. A boosted regression trees (BRT) model at the county level reveals that densities of cattle, sheep and human, coverage of meadow, coverage of typical grassland, elevation, coverage of topsoil with pH > 6.1, concentration of organic carbon in topsoil, and the meteorological factors have contributed substantially to the spatial distribution of the disease. The model-predicted probability of occurrence of human cases in mainland China was mapped at the county level.

Conclusions/Significance

Anthrax in China was characterized by significant seasonality and spatial clustering. The spatial distribution of human anthrax was largely driven by livestock husbandry, human density, land cover, elevation, topsoil features and climate. Enhanced surveillance and intervention for livestock and human anthrax in the high-risk regions, particularly on the Qinghai-Tibetan Plateau, is the key to the prevention of human infections.

Anthrax is a worldwide zoonosis affecting mostly grazing herbivores, with occasional spillover to humans who have contact with infected animals or contaminated animal products. We characterized the distributional patterns of both human and livestock anthrax in China from 2005 to 2013, and identified agro-ecological, environmental and meteorological factors contributing to the temporal and spatial distributions of the disease. We found that the spatial distribution of human anthrax in China was mainly driven by densities of cattle, sheep and humans, coverage of meadow, coverage of typical grassland, elevation, pH level of topsoil, concentration of organic carbon in topsoil, and meteorological factors. We also identified the regions with higher probabilities for the occurrence of human cases. Our findings provided a clear qualitative and quantitative understanding of the epidemiological characteristics and risk recognition of anthrax in China, and can be helpful for prioritizing surveillance and control programs in the future.

Investigation of Anthrax Cases in North-East China, 2010-2014

We determined the genotypes of seven Bacillus anthracis strains that were recovered from nine anthrax outbreaks in North-East China from 2010 to 2014, and two approved vaccine strains that are currently in use in China. The causes of these cases were partly due to local farmers being unaware of the presence of anthrax, and butchers with open wounds having direct contact with anthrax-contaminated meat products. The genotype of five of the seven recovered strains was A.Br.001/002 sub-lineage, which was concordant with previously published research. The remaining two cases belongs to the A.Br.Ames sub-lineage. Both of these strains displayed an identical SNR pattern, which was the first time that this genotype was identified in North-East China. Strengthening education in remote villages of rural China is an important activity aimed at fostering attempts to prevent and control anthrax. The genotype of the vaccine strain Anthrax Spore Vaccine No.II was A.Br.008/009 and A.Br.001/002 for the vaccine strain Anthrax Spore Vaccine Non-capsulated. Further studies of their characteristics are clearly warranted.