Researchers find spread of bacteria in seafood likely impacted by trade

A Centers for Disease Control and Prevention study has found that international trade of shellfish might be involved in the dispersal of Vibrio parahaemolyticus populations into the United States and Spain. The study found that severe weather, such as El Niño conditions in Peru, provide ideal conditions for the proliferation of Vibrio parahaemolyticus, Vibrio alginolyticus and Vibrio vulnificus.

The CDC reports that compared to other major foodborne illnesses, Vibrio parahaemolyticus infections have been steadily increasing. Vibrio parahaemolyticus is the leading cause of seafood-related bacterial infections globally. The CDC estimates that the average annual incidence of all Vibrio infections increased 54 percent during 2006–2017. Vibrio parahaemolyticus is believed to be responsible for about 35,000 human infections each year in the United States and has been the leading cause of foodborne infections in China since the 1990s.

The transition of V. parahaemolyticus disease from a regional to a global pathogen is connected to the emergence of isolates with epidemic potential.

Study Process and Findings:

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  The CDC performed a genome-wide phylogenetic analysis of a global collection of 111 sequence type 36 isolates obtained during the past 30 years from the United States (west and east coasts), Canada, Spain, and Peru.

• Results indicated that the isolates from Peru were of 2 different genetic variants: 5 clustered with the modern (i.e., currently circulating) Pacific Northwest lineage, and 2 clustered in a distinctive group comprising isolates from the 2012 outbreak in Spain.
• The identification of sequence type 36 in Peru provides additional evidence of the extraordinary dynamics of Vibrio infections in this region.
• Since the emergence of cholera in 1991 and the subsequent implementation of an active surveillance system for Vibrio diseases in Peru, several instances of emergence of major epidemic clones of V. parahaemolyticus have been reported in the country.
• Although the sources and routes of introduction of these foreign clones remain yet undetermined, a growing body of evidence has linked the epidemic dynamics and spreading of disease in this particular region of South America to El Niño
• During the past 30 years, the emergence of cases in Peru associated with new clones of Vibrio has been sharply influenced by the onset of El Niño conditions, which has also shaped the extent and severity of epidemics.
• The arrival of extraordinary weather conditions brought on by El Niño (i.e., a combination of heavy rains and heat waves) provides the ideal conditions for the proliferation of Vibrio spp. in the environment.
• These circumstances, along with the disruption of sanitary infrastructure caused by floods and landslides, can help generate the perfect conditions for the explosive emergence of Vibrio diseases.
• Despite the evidence connecting the epidemiology of Vibrio in Peru to El Niño, little is known about the mechanisms of global dispersal and the introduction of foreign epidemic clones into the region. Ballast water from cargo ships and marine heatwaves have been associated with some instances of disease emergence elsewhere.
• Another mechanism that might be involved in the dispersal of V. parahaemolyticus populations is the international trade of shellfish, which was suggested to facilitate the introduction of sequence type 36 into the United States and Spain.

Study Conclusions:

• The study reported the transcontinental expansion of sequence type 36 V. parahaemolyticus into South America.
• The presence of sequence type 36 in clinical and environmental settings in Peru emphasizes the exceptional epidemic potential of the Pacific Northwest complex and V. parahaemolyticus as a human pathogen.
• The long-term persistence and presence of environmental isolates suggest the successful establishment of sequence type 36 in environmental reservoirs.
• Sequence type 36’s ability for intercontinental dispersal, along with its highly pathogenic nature, makes this Vibrio population a major public health concern.
• Peru has shown that implementation of systematic surveillance for Vibrio species can facilitate the detection of emerging transnational epidemic strains.
• This strategy will play a crucial role under exceptional climatic conditions where the enhanced risk for outbreaks is likely.

The full study can be found here.

This study was funded through the Natural Environment Research Council.

More about Vibriosis, its causes, prevention and symptoms can be found here.

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