| Anthrax is a human-animal infectious disease caused by the bacterium Bacillus anthracis.Humans usually get the disease by slaughtering,eating,and coming in contact with infected animals.There are three main types of anthrax depending on the route of infection:pulmonary anthrax,gastrointestinal anthrax,and cutaneous anthrax,of which more than 95%is cutaneous anthrax.Bacillus anthracis is extremely viable and has been used as a biological warfare agent and biological weapon by some countries and terrorism.In China,the number of reported anthrax cases over the past decade is below 500,with outbreaks concentrated in the northwestern region with a well-developed livestock industry.2021 saw a dramatic increase in anthrax cases in China,with successive cases of anthrax in areas with no previous outbreaks.2021 In August,13 cases of cutaneous anthrax were reported in Cao County,Heze City,Shandong Province.In order to identify the source of infection and investigate possible transmission routes,an outbreak investigation and pathogenic analysis of this outbreak was conducted to provide a scientific basis and scientific research base for anthrax prevention and control in Shandong Province.Objective1.To analyze the causes and epidemiological characteristics of a skin anthrax outbreak in Cao County,Heze City,Shandong Province,to provide experience for anthrax prevention and control and outbreak management in Shandong Province.2.To analyze the molecular typing and gene tracing of Bacillus anthracis from this outbreak,and to grasp the basic characteristics of its genome,so as to provide scientific basis and important basic data for anthrax prevention and control.Methods1.A total of 13 cases of cutaneous anthrax were reported in this outbreak,including 12 clinically diagnosed cases and 1 confirmed case,mainly engaged in occupations related to the slaughter of cattle and the collection and sale of cattle products.After epidemiological investigation with qPCR and pathogen isolation culture,the infectious source of this outbreak was identified as sick cattle,and the transmission route was through slaughter of sick cattle,contact with contaminated utensils and related cattle products.Examine the close contact 83 people,of which 7 people involved in handling and selling sick cattle and cattle products were key observation subjects;76 people purchased,processed and consumed cattle products into general observation subjects.2.The drug sensitivity results showed that all isolates were consistent in terms of drug resistance.A total of 8 strains were obtained from bacterial isolation and culture,including 1 strain from the scorched skin of the case,2 strains from the surface smear of the cattle truck,1 strain from the smear on the inside of the cold storage door where beef was stored,2 strains from the smear of the slaughter knife,1 strain from the smear on the floor of the slaughter cattle,and 1 strain from the beef.The drug sensitivity results showed that the eight strains had the same drug sensitivity profile(Figure 1):moderately sensitive to erythromycin,resistant to rifampicin,and sensitive to all other antimicrobials.Genome-wide analysis showed that the eight strains had the same resistance and virulence gene profiles.canSNP results showed that all eight B.anthracis strains belonged to the A.Br.001/002 tyle,and the mutation site SNP was T-A-G-C-A-T-T-A-T-G-G-G-T-A.MLVA15 typing showed that all eight strains had 15 tandem repeat sites with the same amplicon length.Among the 15 tandem repeats,the length of the VrrB1 locus was 193 bp,which was different from that of the domestic strains.SNPs analysis showed that the eight outbreak strains clustered together and were closely related to strain G1392 827.Results1.A total of 13 cases of cutaneous anthrax were reported in this outbreak,including 12 clinically diagnosed cases and 1 confirmed case,mainly engaged in occupations related to the slaughter of cattle and the collection and sale of cattle products.After epidemiological investigation with qPCR and pathogen isolation culture,the infectious source of this outbreak was identified as sick cattle,and the transmission route was through slaughter of sick cattle,contact with contaminated utensils and related cattle products.Examine the close contact 83 people,of which 7 people involved in handling and selling sick cattle and cattle products were key observation subjects;76 people purchased,processed and consumed cattle products into general observation subjects.2.The drug sensitivity results showed that all isolates were consistent in terms of drug resistance.A total of 8 bacillus anthracis strains were obtained from bacterial isolation and culture,including 1 strain from the scorched skin of the case,2 strains from the surface smear of the cattle truck,1 strain from the smear on the inside of the cold storage door where beef was stored,2 strains from the smear of the slaughter knife,1 strain from the smear on the floor of the slaughter cattle,and 1 strain from the beef.The drug sensitivity results showed that the eight strains had the same drug sensitivity profile(Figure 1):moderately sensitive to erythromycin,resistant to rifampicin,and sensitive to all other antimicrobials.3.Genome-wide analysis showed that the eight strains had the same resistance and virulence gene profiles.canSNP results showed that all eight B.anthracis strains belonged to the A.Br.001/002 type,and the mutation site SNP was T-A-G-C-A-T-T-A-T-G-G-G-T-A.MLVA15 typing showed that all eight strains had 15 tandem repeat sites with the same amplicon length.Among the 15 tandem repeats,the length of the VrrB1 locus was 193 bp,which was different from that of the domestic strains.SNPs analysis showed that the eight outbreak strains clustered together and were closely related to strain G1392 827.Conclusion1.This anthrax outbreak was caused by a slaughterer who purchased and slaughtered infected cattle from illegal sources.It is recommended that governmental departments should strengthen market supervision and disseminate knowledge about the prevention and control of anthrax and other human-animal diseases to breeders.2.In this study,eight B.anthracis isolates were found to be of the same canSNP genotype with consistent MLVA15 typing and clustered in the same branch as a new MLVA15 genotype named MLVA15-CHN77.Analysis of SNPs showed that the eight outbreak strains clustered together.Combined with the epidemiological findings of the 2021 anthrax outbreak,it was inferred that the strains of this outbreak were of the same origin.3.The eight Bacillus anthracis strains differed somewhat in their genomic structural characteristics and warranted further study. |
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