The Role of China in the Global Spread of the Current Cholera Pandemic

Abstract

Epidemics and pandemics of cholera, a severe diarrheal disease, have occurred since the early 19th century and waves of epidemic disease continue today. Cholera epidemics are caused by individual, genetically monomorphic lineages of Vibrio cholerae: the ongoing seventh pandemic, which has spread globally since 1961, is associated with lineage L2 of biotype El Tor. Previous genomic studies of the epidemiology of the seventh pandemic identified three successive sub-lineages within L2, designated waves 1 to 3, which spread globally from the Bay of Bengal on multiple occasions. However, these studies did not include samples from China, which also experienced multiple epidemics of cholera in recent decades. We sequenced the genomes of 71 strains isolated in China between 1961 and 2010, as well as eight from other sources, and compared them with 181 published genomes. The results indicated that outbreaks in China between 1960 and 1990 were associated with wave 1 whereas later outbreaks were associated with wave 2. However, the previously defined waves overlapped temporally, and are an inadequate representation of the shape of the global genealogy. We therefore suggest replacing them by a series of tightly delineated clades. Between 1960 and 1990 multiple such clades were imported into China, underwent further microevolution there and then spread to other countries. China was thus both a sink and source during the pandemic spread of V. cholerae, and needs to be included in reconstructions of the global patterns of spread of cholera.

Origins of the current seventh cholera pandemic

“…1 and 2 and Fig. S1) is in agreement with results of previous studies (9,22,24), and the very short length of branch 2 makes it virtually certain that the strains along this branch were in the Middle East, in agreement with the location for the first observations of the El Tor strain. A large number of pilgrims travel to the Middle East during the annual Haj in Mecca, and there is a significant possibility that cholera carried by these pilgrims to Mecca could spread into neighboring countries (SI Text).…”

“…In the case of the US Gulf and Australian prepandemic-related strains, an alternative explanation is that the inability to spread rapidly was related to the quality of the water supply and the sewage infrastructure in those countries. However, this explanation does not apply to strain G320, because pandemic cholera persisted in China until ∼2000 (24), but prepandemic-related organisms were not involved in the pandemic (24). This finding suggests that the absence of these virulence-associated elements was an obstacle for those prepandemic-related strains in evolving pandemic capability.…”

“…However, for the six other available prepandemic strains, only three draft genome sequences (for A6, MAK757, and NCTC8457) have been reported. In addition, studies on the seventh pandemic itself have focused on strains isolated after 1970 (22,24), and there were no full genome sequences of seventhpandemic strains isolated in the first 10 y of the pandemic. Thus, the roles played by the Middle East and Makassar strains in the evolution of the seventh-pandemic strain remain unknown, as well as the many evolutionary events that occurred over the 60-y period from the first observations of El Tor strains in the Middle East through the prepandemic outbreaks in Makassar to the start of the seventh pandemic.…”

A globally distributed mobile genetic element inhibits natural transformation of Vibrio cholerae

“…The most common ICE in V. cholerae is VchInd5, which is present in ∼77% of currently sequenced clinical isolates (10,11). It is hypothesized that the current (seventh) pandemic of cholera originated in the Bay of Bengal, and strains have spread globally from this region in three overlapping waves of transmission (13,14). Strains containing VchInd5 are globally distributed, indicating that the original transfer of VchInd5 into V. cholerae may have occurred in this region.…”

Genomic and evolutionary features of two AHPND positive Vibrio parahaemolyticus strains isolated from shrimp (Penaeus monodon) of south-west Bangladesh

“…Nowadays, whole genome sequencing (WGS) has become a popular tool for the identification and detection the bacterial outbreaks in aquaculture (15). In whole genome sequencing, all of single nucleotide polymorphisms (SNPs) used to confirm the epidemiological links of outbreak strains with higher typing resolution (16). In this study, we have sequenced two AHPND positive V. parahaemolyticus strains (MSR16 and MSR17) which were isolated from shrimp farms of south-west region of Bangladesh and this is the very first genome sequencing report of AHPND positive V. parahaemolyticus strains isolated from shrimps of Bangladesh.…”