by May Murra

Over the past three decades several novel zoonotic infectious diseases have emerged due to human activities such as changes in ecosystems, land-use, intensification of agriculture, urbanization and international travel and trade. A collaboration involving animal, human and environmental health including wildlife health was needed. This collaboration started in the early 00’s as “One Health” with the goal to assess risk and develop plans for response and control of potential emerging zoonotic diseases by disease prevention, surveillance, control, and mitigation. A definition suggested by the One Health Global Network is: ‘One Health recognizes that the health of humans, animals and ecosystems are interconnected. It involves applying a coordinated, collaborative, multidisciplinary and cross-sectoral approach to address potential or existing risks that originate at the animal-human-ecosystems interface’.

Although Group B Streptococcus (GBS) is a human pathogen, diseases caused by this bacterium are not limited to humans. GBS also affects animals, including cattle, fish, camels, dog, cats, crocodiles. GBS is also known as Streptococcus agalactiae, with “agalactiae” meaning “no milk”. GBS was initially detected (and named S. agalactiae) as a pathogen in cases of bovine mastitis in cattle in the late 1880’s. It was first described in 1938 as a human pathogen in three cases of puerperal infections and in the 60’s, GBS emerged and was recognized as a major cause neonatal infections. In the 90’s GBS was recognized as a common cause of sepsis among adults with comorbidities. 

Some evidences across the world suggest that human GBS may originated from a bovine ancestor and that there is a temporal relationship between the emergence of neonatal GBS disease and the change in cowmilk collection (change from churns to bulk tanks) in the UK. Mastitis control programs were implemented in the 50’s and 60’s to reduce the GBS’ impact on milk production. Identification and antimicrobial treatment of infected cattle and prevention of GBS transmission during milking nearly eliminated bovine GBS in Northern Europe, the UK and Canada. Genetic studies support that the recent re-emergence of GBS in dairy herds is a result of host-species jumping as a potential reverse zoonotic origin of newly emerged GBS linages in cattle. Human GBS (both colonizing and disease-causing strains) has recently been detected in cases of bovine mastitis in northern Europe and a re-introduction of GBS must have occurred with lineage-replacement due to pathogen evolution. A study showed that cattle exposure could be associated with human colonization with humans sharing the same GBS strain as their bovine in farm environment, suggesting intraspecies transmission. Other recent genetic studies have shown that bovine GBS (serotype III) lineages distinct from human disease-causing GBS (serotype III), further comparative genomics studies are required to investigate the relationship between human and bovine GBS lineages.

Several outbreaks of GBS disease have been described in wild fish but also in farmed fish (specially tilapia) and consumption of fish have led to colonization of GBS in humans. The most know and only reported foodborne outbreak of GBS was in Singapore during 2015 and was linked to consumption of raw freshwater fish, which is widely practiced in Southeast Asia. At least 146 people were affected in this outbreak and over 20% of cases were healthy individuals. Subsequent investigations revealed that ST283 GBS had caused invasive disease in both human and tilapia across Southeast Asia for at least 20 years before that. In high intensity tilapia aquaculture, outbreaks can result in severe infections with up to 80% mortality. ST283 GBS have only been reported in a very few cases outside the region of Southeast Asia. In 2021 the Food and Agriculture Organization of the United Nation published a risk profile “GBS sequence type 283 in freshwater fish”to fill in some data gaps concerning consumption of freshwater fish and potential risk management options with application of good aquaculture practices and good safety measures throughout the supply chain. Risk mitigation options should be based on aquaculture, hygienic and manufacturing practices and hazard analysis and critical control point system during processing, transport, and retail. Risk management options at farm level would include vaccination, dietary supplements, glycoinhibitors and GBS surveillance. 

GBS is a versatile multi-host pathogen with host-specialist and host-generalist strains. And although further epidemiological studies and comparative genomic analysis on GBS are needed to provide insight interspecies transmission, current knowledge emphasizes that GBS inevitably should be perceived in a “One Health” -perspective on how “the health of humans, animals and ecosystems are interconnected”, when developing prevention and control strategies to prevent GBS transmission and invasive infections in different hosts should be considered. 

1 Comment

Ruth Zadoks · 15 September 2023 at 12:14 am

The suggestion that human GBS has arisin from a bovine ancestor has been dismissed by several subsequent studies (Sørensen UB, et al. doi: 10.1128/mBio.00178-10; Richards VP, et al. doi: 10.1093/molbev/msz169. PMID: 31350563). It is far more likely that the sexual revolution of the 1960s contributed to the widespread dissemination of GBS, which is sexually transmitted organism. This coincided temporally with technical revolutions such as the development of milking machines but there is no evidence that bovine GBS is the source of emergence of human GBS in the 1960. Indeed, human GBS started to expand in the 1910s, with subsequent expansion of additional clades in the 1920s and 1940s, well ahead of the mechanisation of milking (Da Cunha V, et al., doi: 10.1038/ncomms5544. )

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