Salmonella identified in pigs in Kenya and Malawi reveals the potential for zoonotic transmission in emerging pork markets. uri icon

abstract

  • Author summary
  • Healthy humans infected with non-typhoidal Salmonella (NTS) typically suffer from diarrhoeal disease which resolves without treatment. However, NTS infection of patients with an impaired immune system can lead to either bloodstream infection or infection in another part of the body; so-called 'invasive' NTS infection. Over the last twenty years, NTS have been the most prevalent bacteria to be isolated from human blood in sub-Saharan Africa.
  • In this study, we report that pigs in sub-Saharan Africa are able to carry a wide variety of non-typhoidal Salmonella serovars, such as S. Typhimurium, that have the potential to cause diarrhoeal disease in humans. No clades of NTS which have previously been associated with invasive NTS disease in sub-Saharan Africa were detected.
  • It is well known that pigs are able to carry a wide range of different NTS serovars without showing signs of disease themselves. Carrier pigs may be able to intermittently shed NTS in their faeces which may have the potential to cause disease in humans. If good hygiene protocols are not followed during the porcine slaughter process, pork intended for human consumption may become contaminated with NTS. In the next few years, pork consumption is projected to increase dramatically in sub-Saharan Africa. The degree of asymptomatic carriage of NTS by pigs in this region has never been investigated in detail.
  • Salmonella is a major cause of foodborne disease globally. Pigs can carry and shed non-typhoidal Salmonella (NTS) asymptomatically, representing a significant reservoir for these pathogens. To investigate Salmonella carriage by African domestic pigs, faecal and mesenteric lymph node samples were taken at slaughter in Nairobi, Busia (Kenya) and Chikwawa (Malawi) between October 2016 and May 2017. Selective culture, antisera testing and whole genome sequencing were performed on samples from 647 pigs; the prevalence of NTS carriage was 12.7% in Busia, 9.1% in Nairobi and 24.6% in Chikwawa. Two isolates of S. Typhimurium ST313 were isolated, but were more closely related to ST313 isolates associated with gastroenteritis in the UK than bloodstream infection in Africa. The discovery of porcine NTS carriage in Kenya and Malawi reveals potential for zoonotic transmission of diarrhoeal strains to humans in these countries, but not for transmission of clades specifically associated with invasive NTS disease in Africa.

publication date

  • 2020
  • 2020