We've been warmed: climate change could fuel listeriosis
Hot weather extremes augment the replication cycles of the nasty microbe, scientists report
South Africa’s changing climate could fuel listeriosis outbreaks.
Several features of the microbe that causes the life-threatening disease make it especially climate-sensitive, scientists warn in the June edition of the South African Medical Journal.
“Spikes in ambient temperature and high summer temperature peaks, for example, have been linked to the occurrence of listeriosis, as with most diarrhoeal pathogens,” they say.
“Hot weather extremes that become more common with climate change augment the replication cycles of Listeria monocytogenes and could cause breakdowns in food cooling chains, with rapid rises in numbers of the bacteria on food products.”Altered rainfall patterns and longer dry seasons – such as those experienced in western regions of South Africa – may influence listeria transmission, says Matthew Chersich, from Wits University in Johannesburg, and fellow authors Fiona Scorgie, Helen Rees and Caradee Wright.
The world’s worst listeriosis outbreak – with more than 1,000 confirmed infections and 200 deaths – began early in 2017, and the source of the outbreak was traced to Tiger Brands’ Enterprise brand and Polokwane plant.
The plant was closed but Chersich says it is important that longer-term, structural factors are also dealt with.“Ultimately, infectious disease outbreaks, which may become more frequent with rising ambient temperatures and water scarcity, are the proverbial canary in a coal mine,” he says.Water scarcity may hamper efforts to clean machines used for slicing and chopping. “Intensive, deep cleaning is required to prevent persistence of Listeria monocytogenes on such machines, given that the bacterium can tolerate high salt and nitrate concentrations, desiccation, moderate heat, and both acidic and alkaline conditions.“The organisms can adhere to all food contact surfaces, forming biofilms, which are hard to eliminate. In a study in Gauteng, for example, the microbe was isolated from stainless steel surfaces in food plants after they had been cleaned and disinfected using a range of cleaning methods.
“The bacterium has even been found in delicatessens in Johannesburg, in 10% of cleaning cloths.”
Changes in the sources of water can also influence the spread of listeria, Chersich says. “In both rural and urban areas, roof-harvested rainwater is increasingly being used for irrigation and domestic purposes. A study of rainwater tanks in villages in three provinces found that 22% of samples were contaminated with Listeria monocytogenes, possibly from bird faeces and debris on rooftops.“The organism also proliferates in water within drainage ditches, which may then contaminate fruits and vegetables when used for irrigation.”
Finally, changes in rainfall patterns caused by climate disruption can also affect listeria dispersal.
“Rainfall occurring in short bursts of five to 10 minutes favours the dispersal of listeria and other pathogens from the soil onto plants, while lengthier downpours exert a washout effect,” says Chersich.
“As with fresh produce, run-off water may contaminate the water in fish farms, an effect especially noticeable during summer months. As this water filters through the fishes’ gills, they become contaminated with Listeria monocytogenes, and the organism is then introduced into food-processing plants.”
Chersich and his fellow authors call for closer monitoring of food industry standards, changes in dietary habits and heightened responses to listeriosis outbreaks, as well as greater efforts to ensure everyone has access to clean municipal water.
“Without concerted action to prepare for the health effects of climate change, and in the absence of efforts to reduce further environmental degradation, South Africans may face many more large outbreaks of infectious diseases in years to come,” they say.