Urban farmers growing vegetables in Africa could accidentally be helping to spread disease by irrigating crops with wastewater, according to researchers.
In a report published in the Environmental Research journal, the scientists found evidence in Burkina Faso canal water samples of virulent pathogens commonly responsible for waterborne diseases which could lead to people that are directly or indirectly exposed suffering from acute diarrhea, chronic gastritis and gastroenteritis.
If the water is used in food preparation, especially to wash vegetables that will be eaten raw, it can transfer pathogens and cause foodborne illnesses. Even if food is throughly cooked, some pathogens can remain infectious. Contaminated water can also cross contaminate utensils, thus transferring pathogens to food.
After identifying a range of antibiotic-resistant genes in the water, the research team concluded that using wastewater for urban agriculture in the city posed a high risk of spreading bacteria and antimicrobial resistance among humans and animals.
Metagenomics were used to investigate the microbial population, antibiotic-resistant genes and plasmids of medical interest in the wastewater.
Earlier this year, an outbreak of E. coli O157:H7 in the United States, which sickened 210 people and killed five, was traced to romaine lettuce from Yuma, AZ. The outbreak strain was found in water from open canals that run near romaine growing fields and concentrated animal feeding operations (CAFOs or feedlots).
For the wastewater study, University of Birmingham researchers in the United Kingdom led a team from the University Ouaga in Burkina Faso; University of Yaounde in Cameroon; and University of Trier in Germany.
They looked at wastewater samples from three open air canals near agricultural fields in three neighborhoods in the Burkina Faso capital of Ouagadougou. Samples were collected in October 2015 at the end of the rainy season.
Professor Laura Piddock, from the University of Birmingham’s Institute of Microbiology and Infection, said wastewater appears to be a “hot spot” for antibiotic resistant bacteria in Burkina Faso.
“Using wastewater for agricultural irrigation represents a very serious health risk, not least as it increases exposure to fecal pathogens. We urgently need further investigations to determine the extent that exposed populations are affected by this health issue,” Piddock said.
Dr. Blaise Bougnon, from the University of Yaounde, said urban agriculture relies on wastewater for irrigation because of its low cost, availability and so-called nutrient content.
“Some 200 million urban dwellers are reported to be engaged in urban agriculture worldwide and, in some cases, produce up to 90 percent of cities’ demand for perishable vegetables,” according to UN research. “Over 80 percent of domestic and industrial wastewater generated in low and middle-income countries is discharged untreated into the environment.”
Eleven pathogen-specific and 56 virulence factor genes were detected in wastewater samples. These virulence factors are usually found in human pathogens that cause gastroenteritis and/or diarrhea.
The identified virulence factor genes are commonly carried by E. coli, Shigella spp, Clostridium perfringens and Mycobacterium tuberculosis. The pathogen-specific virulence factors belonged to Streptococcus agalactiae, C. perfringens, M. tuberculosis, Legionnela pneumophila, Shigella spp, S. flexneri, Yersinia enterocolitica, and Bartonnella henselae.
“The presence of pathogen-specific and common virulence factor genes in urban waterways and which will be used for urban agriculture indicates that such waters represents a risk to human health. Most of the detected virulence factors belong to pathogens that are transmitted by direct water exposure or ingestion of water/food contaminated with human or animal feces and are commonly responsible for waterborne diseases,” according to researchers.
In low and middle-income countries 842,000 people die annually from diarrhea, according to the World Health Organization in 2017, because of inadequate water, sanitation and hygiene.
The project received funding from the European Union’s Horizon 2020 Research and Innovation Program.
(To sign up for a free subscription to Food Safety News, click here.)