Salmonella: Is the pig reservoir in sub-Saharan Africa a cause for concern?

Bacteria of the genus Salmonella, which are the primary cause of outbreaks of foodborne illness in France, can persist asymptomatically in pig populations. As disease reservoirs, pigs therefore pose a public health risk. While meat consumption in African regions is expected to increase significantly in the coming years, knowledge about Salmonella in this region remains largely fragmentary. A research team is addressing these gaps.    In Europe, bacteria of the genus Salmonella are the most common cause of foodborne outbreaks. In France as well, Salmonella is the leading confirmed pathogen in foodborne outbreaks. It is estimated that tens of millions of cases are reported in humans worldwide each year, resulting in approximately 100,000 deaths annually. In healthy individuals, infection with non-typhoid Salmonella usually results in a bout of diarrhea that resolves without treatment. However, in patients with weakened immune systems, the consequences are far more serious. An infection of the blood or other organs, known as invasive salmonellosis, can develop. Over the past twenty years, nontyphoid Salmonella have been the most commonly isolated bacteria from human blood in sub-Saharan Africa, and they continue to circulate in the agri-food sector. Pig farms contribute, in part, to this spread. Pigs can carry and transmit a wide variety of non-typhoid Salmonella asymptomatically and are therefore a major reservoir for these pathogens. Over the next few years, pork consumption is expected to increase significantly in sub-Saharan Africa. In Kenya, for example, it is projected to rise by 268% between 2010 and 2050. Although it represents a major public health concern, the circulation of non-typhoid Salmonella in pig populations in this region has never been studied in detail. Researchers naturally wanted to learn more about these African reservoirs, so they collected samples during the slaughter of domestic pigs in Nairobi, Busia (Kenya), and Chikwawa (Malawi) between October 2016 and May 2017. As a result, selective cultures, antisera tests, and whole-genome sequencing were performed on 647 samples. In 12.7%, 9.1%, and 24.6% of the samples collected in Busia, Nairobi, and Chikwawa, respectively, a wide variety of non-typhoid Salmonella strains were isolated. Pigs in these regions shed a wide range of Salmonella serotypes, such as Typhimurium, 66% of which (21 out of 32) have the potential to cause diarrheal diseases in humans. However, there is no evidence to suggest that pigs serve as a reservoir for new strains of S. Typhimurium and S. Enteritidis, or others, associated with invasive forms of non-typhoid salmonellosis in sub-Saharan Africa. The majority of Salmonella isolates from the pigs collected were susceptible to all antibiotics tested, and none were classified as multidrug-resistant (resistant to at least three classes of antibiotics). Consequently, only a limited number of isolates appear to be of critical importance to humans as potential zoonotic agents. However, African pig populations must remain under surveillance as the animal production sector continues to develop in this region of the world. Pigs do indeed pose a significant risk to public health, and it is important to better understand the transmission dynamics of zoonotic strains. This information will facilitate the development of intervention strategies aimed at limiting cases of human salmonellosis.