Empirical evidence to support pole-ward bound pathogenic Vibrios?

An increase in Vibrio related infections pushing pole-wards has been linked to increasing temperatures, however Baker-Austin et al. (2012) have now provided some empirical evidence linking long-term temperature increases around the Baltic sea with increased incidences of Vibrio related infections, particularly V. vulnificus.  The study looked at multi-decadal sea surface temperature (SST) data sets of the Baltic sea, which suggested that this area is warming at unprecedented rates, more so than virtually any other body of water on Earth.  Authors suggest that this study provides evidence that anthropogenic change is driving the increased incidents of Vibrio disease in temperate regions and in turn, affecting the distribution of human pathogenic bacteria globally.

V. vulnificus abundance peaks at temperatures > 19 °C and recent studies suggest that the pathogenic properties of some Vibrios is mediated by temperature and certainly emergence of increased Vibrio outbreaks in temperate regions such as Chile, Peru and NW Spain have been linked with warming patterns.  Many human pathogens, such as Vibrios, grow and replicate in warm (>15 °C), low salinity (< 25 ppt) marine environments, with the Baltic being semi-enclosed and predicted rising and warming seas, the authors predict increased Vibrio related incidents.  The study analysed the potential risk and presence of V. vulnificus in the Baltic area using a model based on low salinity (<25 ppt as is common in the region) and observed SST of >19 °C.  This was compared to models with temperature projections for 2050 and results suggest that temperature can be used as a predictor of Vibrio outbreaks.  Moreover, results predict significant expansion of waters capable of hosting large populations of pathogenic Vibrios. 

Whilst I am in agreement that changing temperatures are undoubtedly linked to increases in Vibrio clinical cases (Fig. 1), I am not convinced that this study provides the conclusive evidence that it proclaims to, in relation to humans driving the change.  Don’t get me wrong, I think humans are driving the temperature increases at unprecedented rates, but this paper doesn’t offer any evidence in this regard.  Other limitations of this study included the sourcing of epidemiological data, which was collated from several different sources, including ‘grey’ literature, and it was not clear whether all cases included in the study were actually from the Baltic region (eg, may have been infected abroad), potentially confounding results.   Furthermore, the models used offer some possible projections of pathogenic Vibrio distribution around the Baltic region however they are only applicable if SSTs continue along the same trend.   What may be beneficial however, as suggested by the authors, is the use of near-real-time remote sensing data reporting SSTs, which may serve as an indicator of the risk of pathogen outbreaks, allowing local authorities to inform bathers accordingly.  

 

Figure 1. Vibrio cases and SST. a, The relationship between Vibrio infections reported around the Baltic Sea area and maximum annual SST. Stars show observed data, dashed line shows GLM model predictions (based on the influence of SST alone). b, Time series of Baltic Sea Vibrio cases. Solid line shows observed cases and dotted line shows GLM model predictions based on the influence of maximum SST and time.

 

Baker-Austin, C., Trinanes, J. A., Taylor, N. G., Hartnell, R., Siitonen, A., & Martinez-Urtaza, J. (2012). Emerging Vibrio risk at high latitudes in response to ocean warming. Nature Climate Change, 3(1), 73-77.