Tracking Marine sources of a Cholera outbreak using high throughput molecular methods on archival samples

Vibrio cholerae is a marine bacteria living and feeding on the surfaces of tiny microscopic animals called zooplankton in the upper oceans. Zooplankton are dispersed by ocean currents and so Vibrio cholerae bacteria can spread to different regions via this route potentially spreading infections. Vibrio bacteria increase in numbers when sea surface temperatures have increased and tiny microscopic animals called zooplankton are at high abundance.

In humans, V. cholerae causes Cholera, a diarrhoeal disease along with skin infections, meningitis and septicaemia if contaminated seafood is consumed or by bathing in contaminated waters. V. cholerae can also live in fresh or brackish water and so can infect people drinking contaminated freshwater too. There are many different variant forms of V. cholerae. In warmer climates, epidemic O1 and 0139 variants exist and are endemic. These cause severe gastrointestinal disease leading to fatalities. However, a multitude of non-severe variants exist in temperate Northern oceanic regions, such as UK and Canada, and these have a more favourable outcome. However non-severe types can evolve to become pathogenic thus it is important to monitor strain types to better predict and provide early warning for potential infectious events. Genetic methods are the best way to measure and track the multitude of ever changing Vibrio cholerae strains and several databases exist mapping the global distribution of different strains, including the European Union Reference Laboratory (EURL) hosted by CEFAS, the UK government lab that tests for food and water safety in UK waters. A recent outbreak of V. cholera occured in April 2018 in Vancouver Island, British Columbia on the Northwest coast of Canada causing four people to suffer cholera infection after consuming fish eggs. This is a rare occurence in temperate oceanic waters. This event happened soon after a recent unusal marine heatwave in this region between 2014-2016 and we are interested in determining whether the higher sea surface temperatures had altered zooplankton communities to enable pathogenic V. cholerae to thrive. Such events may happen in UK water as the English Channel and North sea are the fastest warming waters surrounding the UK. The waters surrounding BC Canada are regularly sampled by the Continuous Plankton Recorder (CPR) survey that also records zooplankton species and additionally by the Department of Fisheries and Oceans (DFO) in Canada that have captured water very near the site of infection. Although CPR samples are preserved in formalin which makes genetic detection difficult, we have nevertheless been able to quantify and detect variants of Vibrio from CPR samples. We propse a pilot study to concentrate up Vibrio cholerae using Whole Genome Enrichment in these samples to allow all of the variants of this bacteria to be detected using high-throughput sequencing. This will allow us to detect the infectious types and, by comparing them with strains from EURL, find out where they came from, whether the strain started out as infectious and if they are found elsewhere (such as UK waters) and the route they travelled to end up in Vancouver Island. We will also find out if the extent that increased sea surface temperatures allow human infectious Vibrio cholerae to increase and persist in local waters and in wider oceanic regions. As zooplankton act as hosts to Vibrio cholerae, we will determine if there are certain zooplankton species or groups of zooplankton that harbour this pathogen and facilitate its dispersal and persistence in oceanic waters. This will allow us to work out if this is these human infectious Vibrio cholerae strains are a transient or persistent threat and the environmental conditions in which they thrive. We will trasnmit this information to local governmental monitoring agencies to allow them to set up an early warning system if they find this bacteria again.

Grant reference
Natural Environment Research Council
Total awarded
£42,396 GBP
Start date
1 Feb 2019
0 years 11 months 30 days
End date
31 Jan 2020