Invited Perspective: Vibriosis—The Price Tag of a Warmer World

Ocean warming has continued unabated, owing to climate change.¹ Water has a much larger capacity to absorb heat than the atmosphere; thus, the heat content of the oceans has increased disproportionally. In fact, $>90\%$ of accumulated heat from global climate change is absorbed by the oceans, masking and slowing land surface warming.¹ The ocean warming process has accelerated over recent years and resulted in a range expansion of tropical marine species to higher latitudes and altered marine ecosystems.¹ Vibrio pathogens are part of these marine ecosystems, and their spread is being accompanied by human exposure and related illnesses and mortality, as well as their associated costs.²

Vibrio species are physically attached to tiny planktonic crustaceans known as copepods, which serve as the host organism in this commensal relationship.³ These bacteria can cause large-scale cholera epidemics or sporadic infections, mainly as a result of consumption of uncooked seafood or exposure to recreational seawater. Twelve Vibrio species are associated with infections in humans. These include V. cholerae (serogroups O1 and O139), the causative agent of cholera epidemics. Another three species—V. parahaemolyticus, V. alginolyticus, and V. vulnificus—can cause sporadic but potentially severe gastrointestinal illnesses and wound infections, which can advance to outcomes such as necrotizing fasciitis, amputation, septicemia, and death.⁴ The disease burden from these noncholera Vibrio infections is not extensive, but the incidence is increasing.⁴

Vibrio bacteria thrive in warm, brackish water and have expanded their habitat owing to the warming of the oceans.^5–7 In the summer of 2004, an outbreak occurred in Alaska as a result of the consumption of raw oysters contaminated with V. parahaemolyticus, $>\mathrm{1,000}\mathrm{km}$ north of any previously recorded infection with this pathogen.⁸ Similarly, V. parahaemolyticus has appeared in northern Spain,^9,10 where ocean warming has also contributed to the spread of pathogenic Vibrio bacteria.¹¹ There has been a documented cross-oceanic migration and northbound expansion of plankton in response to the warming of oceans,¹² and it is possible that Vibrio species are hitchhiking along with their hosts.¹³

A new study by Sheahan et al.¹⁴ in this issue of Environmental Health Perspectives examines the influence of climate change on vibriosis in the United States and projects future health and economic impacts. The authors took advantage of an invaluable resource that is available only in the United States. The Centers for Disease Control and Prevention (CDC) started collecting Vibrio cholera case data in 1997 and expanded their national surveillance efforts to all vibriosis cases in 2007.¹⁵ In contrast, there is no continent-wide surveillance data available for other Vibrio pathogens in Europe. For example, Vibrio cholera of serogroups O1 or O139 is a reportable disease in the European Union, but other Vibrio species are not.¹⁶ The authors analyzed the CDC’s rich Cholera and Other Vibrio Illness Surveillance (COVIS) database to address the study objectives. Although there are limitations to COVIS, such as underreporting and potential exposure misclassification, it is nevertheless unique and the largest database of its kind.

The authors applied an exposure–response function between sea surface temperature and vibriosis cases that has been validated in different settings¹⁷ and projected the annual disease incidence to the end of the century under the 4.5 and 8.5 Representative Concentration Pathway (RCP) scenarios. Their model projects an incidence increase of $>50\%$ and 100%, respectively, under these two RCPs. They further projected that the cost of illness will exceed $5.2 billion USD and $7.3 billion USD annually under RCP 4.5 and 8.5, respectively, up from $2.2 billion USD in 2018. These staggering economic impacts are due in part to the potential severity of health outcomes and losses in productivity but, most significantly, to the high mortality costs from V. vulnificus, which is the deadliest seafood-borne pathogen in the United States.^18,19

The potential human and financial costs of vibriosis attributable to climate change^15,20 quantified in this economic assessment by Sheahan et al.¹⁴ are compelling reasons to consider adaptation measures to attenuate climate change impacts.^21,22 The direct relationship between Vibrio infections and sea surface temperature lends itself to a climate-driven forecasting and early warning system.¹⁷ In the absence of continent-wide surveillance of Vibrio pathogens in Europe, the European Center for Disease Prevention and Control (ECDC) has operationalized an early warning system in Stockholm called the ECDC Vibrio Map Viewer.¹⁷ Through remote sensing, it monitors global environmental conditions and sea surface temperature and salinity to predict conditions that are suitable for Vibrio infections (Figure 1).^17,23

Figure 1.

ECDC Vibrio Map Viewer with a screen shot of the U.S. East Coast on 21 July 2021. Areas depicted in dark gray indicate high to very high environmental suitability for vibriosis, and areas in light gray indicate low to very low environmental suitability. Source: ECDC; https://geoportal.ecdc.europa.eu/vibriomapviewer/. Note: ECDC, European Center for Disease Prevention and Control.

ECDC staff monitor the Vibrio Map Viewer on a daily basis during the summer months to identify coastal areas suitable for Vibrio infections. Reports are published biweekly in the ECDC’s Communicable Disease Threats Report (CDTR), which is distributed to all government epidemiologists in Europe.²⁴ The CDTR can issue an alert when the 5-d forecast of the ECDC Vibrio Map Viewer predicts the environmental suitability for Vibrio infections to increase at a certain coastline, such as along the Baltic Sea. The CDTR provides options for prevention and control, such as beach closures, notifying health care providers, and encouraging at-risk individuals (e.g., children, the elderly, cancer patients, immunocompromised individuals) to avoid exposure to Vibrio bacteria from recreational water use or consumption of raw seafood.¹⁷

The ECDC Vibrio Map Viewer is a climate change adaptation tool that can be used for marine environments anywhere in the world, including the Chesapeake Bay, the largest estuary in the Mid-Atlantic Region of the United States. Needless to say, in light of global warming, these types of predictive models based on remote sensing data are needed not only for Vibrio bacteria^25,26 but also for other climate-sensitive pathogens.²¹ The analysis by Sheahan et al. presented in this issue of the EHP¹⁴ will serve as the backbone of cost-effectiveness analyses for these types of adaptation measures and can help reduce morbidity and mortality from climate change and their associated costs, increase the effectiveness of interventions, and make efficient use of scarce public health resources in the age of global environmental change.

Refers to https://doi.org/10.1289/EHP9999a