It is estimated that mean air
temperature increase of as little as 1 °C in the UK could result in
4.5% increase in foodborne disease in the UK (DOH/HPA, 2008). By
2050 an additional 179,000 annual cases of food poisoning in
England and Wales as a result of climate change have been predicted
(Bentham and Langford, 1995). Most reports on the impact of climate
change on foodborne illness have focused on the potential increase
in cases caused by established pathogens like Salmonella
and Campylobacter from consumption of undercooked meat and
eggs. However, the burden of foodborne disease may also be
impacted by changes in relative contributions of different or
emerging pathogens. One such group of potentially emerging
pathogens, in Europe at least, are the marine vibrios,
predominantly Vibrio vulnificus and V.
parahaemolyticus which can cause seafood associated
gastro-enteric or septicaemia illnesses that may occasionally be
fatal.
Vibrio vulnificus and
Vibrio parahaemolyticus are Gram negative halophilic
bacteria. They are members of the same genus as the causal agent of
cholera (V. cholerae O1/O139) however unlike epidemic
V. cholerae they are not related to poor sanitation but
are found naturally in warm marine and estuarine waters
(>15 C). In sub-tropical world regions they are the leading
cause of seafood-associated bacterial illness. Illnesses, which can
be severe and even fatal, are usually reported after consumption of
raw oysters or contact with seawater containing pathogenic strains
of the bacteria. Increasing seawater temperature and flooding of
low-lying coastal areas due to rising sea levels as a result of
global climate change are important factors in the proliferation of
many bacterially mediated infectious diseases. In Europe and
elsewhere V. vulnificus and V. parahaemolyticus
infections have been increasing over recent years, with outbreaks
tending to follow regional climatic trends, typically after
episodes of unusually warm weather.
There are several well characterised
risk factors that may play a significant role in affecting the
regional impact of vibrio infections in the UK. Although absolute
information regarding many of these variables is incomplete, and
are based on predictions, many point towards an increase in these
types of infections nationally. Firstly, climate models suggest
increases of surface seawater temperature of several degrees
Celsius in the coming decades (see Figure 1). Previous studies of
disease associated with V. parahaemolytcius and V.
vulnificus indicate that sustained warming events
(>15 C) are the most significant risk factor associated
with these disease outbreaks. In addition, lower salinity water is
another significant risk factor associated with vibrio disease,
particularly with V. vulnificus which is rarely isolated
from seawater with salinities in excess of 30 ppt. Effects are
regional, with areas bordering the northeast Atlantic and the North
Sea showing a greater reduction in salinity than the Celtic and
Irish Sea, based on recent predictive modelling (UK Climate
Projections science report: Marine & coastal projections; Lowe
et al., 2009). Currently, these models do not indicate a reduction
in average salinity to levels below 30 ppt in the UK, thus the risk
from V. vulnificus remains low (Figure 2). Interestingly,
in continental Europe V. vulnificus infections have been
largely limited to Scandinavian countries where lower average
salinities are observed. Localised higher levels of rainfall with
consequent flooding causing sporadic periods of low salinity
coincident with higher seawater temperatures cannot be excluded and
may contribute to an increase in V. vulnificus exposure in
the UK. V. parahaemolyticus can be isolated from a wider
range of salinities within the existing UK range. Relatively small
increases in temperatures may also greatly extend the geographical
distribution of zooplankton, which act as important global vector
organisms for marine vibrios. Given the predicted warming of
surface waters in the coming decades a better understanding of the
factors driving the virulence, temporal and spatial distribution of
these thermodependent bacterial pathogens is critical.
Figure 1 Seasonal-mean SST
(top row) and change (bottom row), relative to model 1961-1990
conditions, in sea surface temperature (deg. C) for 2070-2098 are
shown above. As the ocean model was run only once (medium emission
scenario), there are no estimates of upper or lower bounds of
change. Black lines depict 'Charting Progress' regional borders.
(Lowe et al., 2009)
Figure 2 Seasonal mean sea
surface salinity (SSC) for 1961-1990 and predictions for 2070-2098.
(Lowe et al 2009)
