Abstract
BackgroundLeptospirosis is one of the most important neglected tropical infectious diseases worldwide. Icterohaemorrhagiae has been throughout recent history, and still is, the predominant serogroup of this pathogen in China. However, very little in detail is known about the serovars or genotypes of this serogroup.Methodology/Principal FindingsIn this study, 120 epidemic strains from five geographically diverse regions in China collected over a 50 year period (1958~2008), and 8 international reference strains characterized by 16S rRNA sequencing and MLST analysis. 115, 11 and 2 strains were identified as L. interrogans, L. borgpetersenii, and L. kirschneri, respectively. 17 different STs were identified including 69 ST1 strains, 18 ST17, 18 ST128, 9 ST143 and 2 ST209. The remaining 12 strains belonged to 12 different STs. eBURST analysis demonstrated that, among the clonal complexes isolated (CCs), CC1 accounted for 73.3% (88/120) strains representing three STs: ST1, ST128 and ST98. ST1 was the most likely ancestral strain of this CC, followed by singleton CC17 (17/120) and CC143 (11/120). Further analysis of adding 116 serogroup Icterohaemorrhagiae strains in the MLST database and studies previously described using global eBURST analysis and MST dendrogram revealed relatively similar ST clustering patterns with five main CCs and 8 singletons among these 244 strains. CC17 was found to be the most prevalent clone of pathogenic Leptospira circulating worldwide. This is the first time, to our knowledge, that ST1 and ST17 strains were distributed among 4 distinct serovars, indicating a highly complicated relationship between serovars and STs.Conclusions/SignificanceOur studies demonstrated a high level of genetic diversity in the serogroup Icterohaemorrhagiae strains. Distinct from ST17 or ST37 circulating elsewhere, ST1 included in CC1, has over the past 50 years or so, proven to be the most prevalent ST of pathogenic leptospires isolated in China. Moreover, the complicated relationship between STs and serovars indicates an urgent need to develop an improved scheme for Leptospira serotyping.
Highlights
Leptospirosis, caused by pathogenic Leptospira species, is emerging as one of the most widespread zoonosis with an estimated global burden of more than 500,000 cases of severe human leptospirosis and 100,000 deaths as well as great economic burden in farm and pet animals per year [1]
Our focusing on serogroup Icterohaemorrhagiae strains of Leptospira using multilocus sequence typing (MLST) as a tool for phylogenetic analysis that has led to a better understanding of evolution of Leptospira
Among the 128 strains, 115 strains were identified as L. interrogans, 11 strains as L. borgpetersenii, and two reference strains isolated from Congo and Zaire as L. kirschneri (Fig 1 and S1 Table)
Summary
Leptospirosis, caused by pathogenic Leptospira species, is emerging as one of the most widespread zoonosis with an estimated global burden of more than 500,000 cases of severe human leptospirosis and 100,000 deaths as well as great economic burden in farm and pet animals per year [1]. The symptom of leptospirosis ranges from an asymptomatic or mild infection to severe manifestation causing multi-organ dysfunction and even deaths in humans [2, 3]. The classical taxonomy typing method of Leptospira spp. is mainly based on serological techniques including microscopic agglutination test (MAT) and cross-agglutinin absorption test (CAAT). It is the practical taxon at the subspecies level and remains extremely valuable for epidemiology analysis of Leptospira. Very little in detail is known about the serovars or genotypes of this serogroup
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