Limits...
The role of China in the global spread of the current cholera pandemic.

Didelot X, Pang B, Zhou Z, McCann A, Ni P, Li D, Achtman M, Kan B - PLoS Genet. (2015)

Bottom Line: 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.We therefore suggest replacing them by a series of tightly delineated clades.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectious Disease Epidemiology, Imperial College London, London, United Kingdom.

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.

Show MeSH

Related in: MedlinePlus

Cholera in China since 1950.(A) Numbers of cases of cholera per year in the Xinjiang region (red, scale at right) and the rest of China (black, scale at left). (B-D) Density of cases of cholera in China during three epidemiological waves of disease: 1961–1967, 1973–1990 and 1991–2005. Each province is colored by numbers of cases per million inhabitants per year.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4358972&req=5

pgen.1005072.g001: Cholera in China since 1950.(A) Numbers of cases of cholera per year in the Xinjiang region (red, scale at right) and the rest of China (black, scale at left). (B-D) Density of cases of cholera in China during three epidemiological waves of disease: 1961–1967, 1973–1990 and 1991–2005. Each province is colored by numbers of cases per million inhabitants per year.

Mentions: It is clear from the epidemiological literature that cholera flared in China repeatedly between 1817 and 1923, following earlier outbreaks in South and Southeast Asia, and possibly spread from China to Japan, Korea, eastern Siberia and western Asia [2]. Outbreaks in China also broke out on multiple occasions between 1923 and 1959 [1]. A detailed reconstruction of the causes of these outbreaks, and their chains of transmission, is likely to be difficult because only very few bacterial isolates from those periods are known to exist. On the other hand, the period after 1961 is more readily amenable to analysis, and for integration into reconstructions of the spread of cholera in other parts of the world. Since 1961, three successive waves of cholera were recorded in Southeast and Central China [10], each involving many thousands of cases of disease caused by El Tor V. cholerae (Fig. 1). Multiple, partially overlapping outbreaks with fewer cases of cholera also occurred in in the Autonomous Region of Xinjiang in Northwest China. These observations might reflect successive flares of cholera from endemic sources of V. cholerae within China. Alternatively, China may have been a ‘sink’ for bacteria from external sources, and each wave in China might have resulted from an independent import of these bacteria from elsewhere. Under both hypotheses, the Chinese waves might additionally have acted as a ‘source’ for spread to neighboring countries and possibly even acted as an ‘amplifier’ of epidemic spread. In order to address these questions, we compared 260 genomes of V. cholerae, including 181 that had been previously analyzed [6,9,11], 71 newly sequenced genomes from strains isolated in China between 1961 and 2010, and eight from other sources (S1A Table).


The role of China in the global spread of the current cholera pandemic.

Didelot X, Pang B, Zhou Z, McCann A, Ni P, Li D, Achtman M, Kan B - PLoS Genet. (2015)

Cholera in China since 1950.(A) Numbers of cases of cholera per year in the Xinjiang region (red, scale at right) and the rest of China (black, scale at left). (B-D) Density of cases of cholera in China during three epidemiological waves of disease: 1961–1967, 1973–1990 and 1991–2005. Each province is colored by numbers of cases per million inhabitants per year.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4358972&req=5

pgen.1005072.g001: Cholera in China since 1950.(A) Numbers of cases of cholera per year in the Xinjiang region (red, scale at right) and the rest of China (black, scale at left). (B-D) Density of cases of cholera in China during three epidemiological waves of disease: 1961–1967, 1973–1990 and 1991–2005. Each province is colored by numbers of cases per million inhabitants per year.
Mentions: It is clear from the epidemiological literature that cholera flared in China repeatedly between 1817 and 1923, following earlier outbreaks in South and Southeast Asia, and possibly spread from China to Japan, Korea, eastern Siberia and western Asia [2]. Outbreaks in China also broke out on multiple occasions between 1923 and 1959 [1]. A detailed reconstruction of the causes of these outbreaks, and their chains of transmission, is likely to be difficult because only very few bacterial isolates from those periods are known to exist. On the other hand, the period after 1961 is more readily amenable to analysis, and for integration into reconstructions of the spread of cholera in other parts of the world. Since 1961, three successive waves of cholera were recorded in Southeast and Central China [10], each involving many thousands of cases of disease caused by El Tor V. cholerae (Fig. 1). Multiple, partially overlapping outbreaks with fewer cases of cholera also occurred in in the Autonomous Region of Xinjiang in Northwest China. These observations might reflect successive flares of cholera from endemic sources of V. cholerae within China. Alternatively, China may have been a ‘sink’ for bacteria from external sources, and each wave in China might have resulted from an independent import of these bacteria from elsewhere. Under both hypotheses, the Chinese waves might additionally have acted as a ‘source’ for spread to neighboring countries and possibly even acted as an ‘amplifier’ of epidemic spread. In order to address these questions, we compared 260 genomes of V. cholerae, including 181 that had been previously analyzed [6,9,11], 71 newly sequenced genomes from strains isolated in China between 1961 and 2010, and eight from other sources (S1A Table).

Bottom Line: 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.We therefore suggest replacing them by a series of tightly delineated clades.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectious Disease Epidemiology, Imperial College London, London, United Kingdom.

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.

Show MeSH
Related in: MedlinePlus