Shiga toxigenic strains of E coli (STEC) are widely recognized as major pathogens for public health problems in developing countries and represent the leading etiological agent of diarrhea1,2. Serotype O157 has been the most reported STEC in humans and has been found to be responsible for most infections, sporadic cases and outbreaks of bacterial enteritis in humans, globally. On the other hand, there is increasing evidence that non-O157 STEC are acquiring greater importance as they are frequently associated with sporadic outbreak of both mild and severe STEC disease in humans globally3,4.
Many of the STEC strains are found in the gastrointestinal tracts of domesticated farm animals, hence these form the principal source of human infections. The most noxious E coli strains are those that are able to produce putative accessory virulence factors such as intimin (encoded by eaeA) and the plasmid-encoded enterohemolysin, encoded by enterohemorrhagic E. coli (EHEC) hlyA. Moreover, E coli strains producing Shiga toxin type 2 (Stx2, encoded by stx2) appear to be more commonly responsible for serious complications such as HUS than those producing only Shiga toxin type 15. On the other hand, Stx production is not restricted to serotype O157 strains, as over 100 STEC serotypes have been isolated from humans with diarrheal illness4.
Contaminated raw meat is one of the main sources of food-borne illnesses. The risk of the transmission of zoonotic infections is also associated with contaminated meat6. While meat is usually consumed well-done in Nigeria, thereby limiting infections from meat consumption, contamination of water bodies from abattoir waste constitutes significant environmental and public health hazards6, 7, 8. Bacteria from abattoir waste discharged into water columns can subsequently be absorbed to sediments, and when the bottom stream is disturbed, the sediment releases the bacteria back into the water columns presenting long-term health hazards9. In Nigeria, numerous abattoirs dispose of their effluents directly into the streams and waterways without any type of treatment and the butchered meat is washed by the same water10.
The incidence of Shiga toxigenic E coli varies by country, where such data is available. Shiga toxigenic E coli infections have been reported for most parts of the world, including a number of African countries4, however, specific incidence data are not always collected or readily available in most sub-saharan African countries, especially in Nigeria.
There are two main types of abattoirs available within the study area, namely, the slaughter slab and the batch systems. Slaughter slabs are the most commonly found in Nigeria. They are usually established and operated by municipal and local authorities. These operate in well-built areas and conform to a good extent with the WHO guidelines for abattoirs. On the other hand, the batch type of slaughter system are those where animals are killed and processed sometimes on bare floor or on corrugated roofing sheets placed on the floor. These are usually located in abandoned buildings or under the shade of trees and open exposed grounds that a butcher might find suitable for the business11.
The present surveillance work is aimed at screening for the incidence/ occurrence of Shiga Toxigenic Escherichia coli in selected abattoirs and retail meat sources in Osogbo metropolis in Osun State of Nigeria, using molecular and serotyping methods.
The work is expected to positively inform on best practices in the local abattoirs, and enhance effective planning, implementation and evaluation of public health practice within the study area.