Anthrax is an acute zoonotic infectious disease caused by
Bacillus anthracis.
B. anthracis forms dormant spores that are resistant to extreme environmental conditions and persist in soil for long periods. Herbivorous animals, such as cattle, sheep, and goats, ingest spores in the soil and become infected. There are three primary forms of the disease in humans, including inhalational, gastrointestinal, and cutaneous anthrax. Inhalational anthrax is caused by inhaling aerosolized
B. anthracis spores
. B. anthracis has long been considered a potential biological weapon. In the fall of 2001,
B. anthracis spores were spread through letters mailed in the United States, resulting in 22 cases of anthrax and 5 deaths [
1]. These anthrax bioterrorism attacks affirmed the potential of
B. anthracis as a biological weapon, and the strains were found to belong to the
B. anthracis A.Br.Ames lineage [
2].
Investigations of bioterrorism-associated anthrax led to the establishment and improvement of a molecular typing method.
B. anthracis is a relatively homogeneous bacterial species [
3] due to its long lifecycle, which includes dormant endospores. The global phylogenetic structure of
B. anthracis was previously defined using a canonical single-nucleotide polymorphisms (canSNPs) method [
4] in which 13 representative SNPs were used to establish a SNP-derived phylogenetic tree. The global genetic population polymorphisms were previously defined using multiple-locus variable-number tandem repeat analysis (MLVA) with 8, 15, 25, and 31 markers [
5‐
8]. These strategies were used to trace the sources of naturally occurring anthrax outbreaks. In the worldwide population of
B. anthracis, three major lineages (A, B and C) and 12 minor lineages/groups were identified; five canSNP lineages/groups were found in China, including A.Br.001/002, A.Br.Ames, A.Br.Vollum, A.Br.Aust94, and A.Br.008/009. The A.Br.Ames lineage descended from the A.Br.001/002 lineage, which has a major presence in China [
9]. The phylogenetic analysis also indicated that the original Ames strain and a subset of 10 Texas Ames-like isolates as well as Ames-like isolates from China shared common ancestors that originated in Inner Mongolia, China [
9]. In the USA, the Ames strains were thought to be rare in nature even though other Ames isolates were shown to be closely related to the Ames strain isolated in Texas [
10]. A number of
B.anthracis strains were collected in Chinese CDC, these strains had been checked using 13 canSNP markers according to Van Ert [
4] and assigned to different canSNP lineages. Strains belonging to the Ames lineage were isolated in China as early as 1954 [
11]. During 2007–2018, a total of 99 strains (Liaoning, Sichuan, Yunnan, Guizhou, Shaanxi, Gansu, Beijing, Xinjiang and Inner Mongolia) were collected in Chinese CDC, 71 were assigned to lineage A.Br.001/002, 27 to A.Br.Ames and 1 to A.Br.008/009 (National surveillance data). The Ames lineage has been the second predominant group in recent years. In fact, human anthrax outbreaks caused by the Ames lineage strains are frequently reported in the northern regions of China [
11,
12]. In this study, we reported 21 outbreaks associated with Ames lineage strains from 2007 to 2018 in China. To reveal genetic diversity of these isolates and to investigate the potential relationships of strains responsible for persistent human anthrax outbreaks, a total of 30 Ames lineage strains were further identified by MLVA.