[Source: PLoS Neglected Tropical Diseases, full page: (LINK). Abstract, edited.]
OPEN ACCESS / PEER-REVIEWED / RESEARCH ARTICLE
One hypervirulent clone, sequence type 283, accounts for a large proportion of invasive Streptococcus agalactiae isolated from humans and diseased tilapia in Southeast Asia
Timothy Barkham , Ruth N. Zadoks, Mohammad Noor Amal Azmai, Stephen Baker, Vu Thi Ngoc Bich, Victoria Chalker, Man Ling Chau, David Dance, Rama Narayana Deepak, H. Rogier van Doorn, Ramona A. Gutierrez, Mark A. Holmes, Lan Nguyen Phu Huong, [ … ], Swaine L. Chen
Published: June 27, 2019 / DOI: https://doi.org/10.1371/journal.pntd.0007421
In 2015, Singapore had the first and only reported foodborne outbreak of invasive disease caused by the group B Streptococcus (GBS; Streptococcus agalactiae). Disease, predominantly septic arthritis and meningitis, was associated with sequence type (ST)283, acquired from eating raw farmed freshwater fish. Although GBS sepsis is well-described in neonates and older adults with co-morbidities, this outbreak affected non-pregnant and younger adults with fewer co-morbidities, suggesting greater virulence. Before 2015 ST283 had only been reported from twenty humans in Hong Kong and two in France, and from one fish in Thailand. We hypothesised that ST283 was causing region-wide infection in Southeast Asia.
We performed a literature review, whole genome sequencing on 145 GBS isolates collected from six Southeast Asian countries, and phylogenetic analysis on 7,468 GBS sequences including 227 variants of ST283 from humans and animals. Although almost absent outside Asia, ST283 was found in all invasive Asian collections analysed, from 1995 to 2017. It accounted for 29/38 (76%) human isolates in Lao PDR, 102/139 (73%) in Thailand, 4/13 (31%) in Vietnam, and 167/739 (23%) in Singapore. ST283 and its variants were found in 62/62 (100%) tilapia from 14 outbreak sites in Malaysia and Vietnam, in seven fish species in Singapore markets, and a diseased frog in China.
GBS ST283 is widespread in Southeast Asia, where it accounts for a large proportion of bacteraemic GBS, and causes disease and economic loss in aquaculture. If human ST283 is fishborne, as in the Singapore outbreak, then GBS sepsis in Thailand and Lao PDR is predominantly a foodborne disease. However, whether transmission is from aquaculture to humans, or vice versa, or involves an unidentified reservoir remains unknown. Creation of cross-border collaborations in human and animal health are needed to complete the epidemiological picture.
An outbreak due to a bacterium called Streptococccus agalactiae in Singapore in 2015 was caused by a clone called ST283, and was associated with consumption of raw freshwater-fish. It was considered unique as it was the only reported foodborne outbreak of this bacterium. Our new data show that invasive ST283 disease is far from unique. ST283 has been causing disease in humans and farmed fish in SE Asian countries for decades. Reports of ST283 are almost absent outside Asia. We suspect that human ST283 is fishborne in other Asian countries, as it was in Singapore, but we haven’t looked at this yet. We don’t know where ST283 originally came from; it may have been transmitted from humans to fish, or come from another animal. More studies are needed to determine ST283’s geographical extent and burden of disease, as well as its origin, how it is transmitted, and what enables it to be so aggressive. We may then be able to interrupt transmission, to the benefit of fish, farmers, and the general public.
Citation: Barkham T, Zadoks RN, Azmai MNA, Baker S, Bich VTN, Chalker V, et al. (2019) One hypervirulent clone, sequence type 283, accounts for a large proportion of invasive Streptococcus agalactiae isolated from humans and diseased tilapia in Southeast Asia. PLoS Negl Trop Dis 13(6): e0007421. https://doi.org/10.1371/journal.pntd.0007421
Editor: Alfredo G. Torres, University of Texas Medical Branch, UNITED STATES
Received: January 9, 2019; Accepted: April 29, 2019; Published: June 27, 2019
This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.
Data Availability: All relevant data are within the manuscript and its Supporting Information files.
Funding: Support for this project was provided by the Molecular Biology Laboratory and the Department of Laboratory Medicine, Tan Tock Seng Hospital; by the Environmental Health Institute, National Environment Agency, Singapore; by the Ministry of Health, Singapore, through the Singapore Infectious Diseases Initiative grant number SIDI/2016/002 (TB) https://www.moh.gov.sg, and the National Medical Research Council, Ministry of Health, Singapore grant number NMRC/CIRG/1467/2017 (SLC) http://www.nmrc.gov.sg, by the UK Global Challenges Research Fund via the Scottish Funding Council, SFC/AN/10/2018 (RNZ) http://www.sfc.ac.uk, and by the Global Disease Detection program of the U.S. Centers for Disease Control and Prevention. The BSAC resistance surveillance project is acknowledged for the provision of the UK data. The Lao PDR GBS were obtained during the work of LOMWRU, funded by the Wellcome Trust. The funders had no role in study design, data collection and analysis, or preparation of the manuscript: the US CDC approved the decision to publish.
Competing interests: I have read the journal’s policy and the authors of this manuscript have the following competing interests: SLC and TB are named applicants on a patent for the ST83-specific PCR test used in this study.
Keywords: Streptococcus agalactiae; Food safety; Human; Asia Region.