What could you say unites all human beings? Love, death, humanity itself? I am going to go out on a limb and provide another suggestion… There is one encounter that every adult human has probably experienced that has the brute force to link us all together – that, my friends, is the complete and utter misery of contracting a stomach virus. It is a visceral experience that can push even the strongest individuals to their knees telling God that it might be time to take them home.

A couple of weeks ago I gave a brief warning about the possible transmission of salmonella from amphibians and reptiles to humans and this week, I would like to expand on this subject considering salmonella is among the infectious pathogens can cause the aforementioned despair. Enteric illnesses are quite important in terms of public health, being the second largest source of communicable diseases worldwide. Salmonella, although lesser known for this type of transmission, is especially interesting in that in can act as a zoonotic pathogen (pathogens that can be transmitted from vertebrate animals to humans). With this being said, salmonella is currently a possible spillover concern for humans and certainly for other animals. Recent findings of wild birds as a suspected source for human salmonella infections have caused a big stir. Not only has this discovery caused a certain public health scare, but it has also brought up concern for the ecological aspect of the afflicted birds. Prevention efforts to reduce further spillover of the pathogen have included various deterrents and demolition of the birds’ (and countless other animals’) habitats. Due to Salmonella spp. causing significant avian mortality, the downstream effects are coming into concern as well as conservation discussions regarding the infected wildlife species.

In a recent paper published by Smith et al., 33% of North American breeding bird species were tested for Salmonella spp. and found that a prevalence of 6.4% of those birds were positive. However, the study of salmonella spilling over from birds to humans is vast, complex, and data intensive feat that must be researched further to have a more complete viewpoint. Furthermore, transmission might not be that easy seeing as though the bacteria must survive in the feces of the bird long enough for human ingestion.

However, salmonella is well documented to spread among wildlife hosts and can depend on multiple exposure and infection routes, although it is typically spread through the fecal oral route. Cross-species spillover of salmonella has also been documented/confirmed in domesticated cats in Switzerland with a history of presumed consumption of passerine birds. The die off of the passerine birds was documented in 2010, was confirmed to be caused by Salmonella enterica, then causing the spillover to cats due to predation.   

Due to the fairly novel study of salmonella spillover and spread from birds, I find that the scientific community much attain a great amount more data to be able to draw any conclusions about the disease ecology associated with wildlife carriers and risks of Salmonella spp. It appears that the cases provided in current literature of salmonella outbreaks in birds and spillover to other animals and/or humans has always resolved on its own without the need for intense intervention. We must now conduct studies looking into the epidemiological factors influencing the pathogen within the avian hosts. Things to consider are migration patterns based on weather, food, and the repercussions of different environments/latitudes on the infection in bird populations, as well the role humans might play to perpetrate the disease, such as providing feeding stations where birds might crowd, enhancing the disease transmission.

I hope this has provided a bit of insight into the salmonella bacterium and how even poor little animals can suffer from it just like us. If nothing else, know that you can possibly transmit it from ingesting bird droppings in addition to the classic warnings of “don’t drink raw eggs” or “cook your chicken thoroughly”! I also will add my personal salmonella warning for a second time to not kiss frogs, please.

Sources

Becker, Daniel & Teitelbaum, Claire & Murray, Maureen & Curry, Shannon & Welch, Catherine & Ellison, Taylor & Adams, Henry & Rozier, R. & Lipp, Erin & Hernandez, Sonia & Altizer, Sonia & Hall, Richard. (2018). Assessing the contributions of intraspecific and environmental sources of infection in urban wildlife: Salmonella enterica and white ibis as a case study. Journal of The Royal Society Interface. 15. 20180654. 10.1098/rsif.2018.0654.

Giovannini, S & Pewsner, Mirjam & Hüssy, D & Hächler, Herbert & Ryser-Degiorgis, Marie-Pierre & Hirschheydt, J & Origgi, Francesco. (2012). Epidemic of Salmonellosis in Passerine Birds in Switzerland With Spillover to Domestic Cats. Veterinary pathology. 50. 10.1177/0300985812465328.

Plowright, Raina & Parrish, Colin & Mccallum, Hamish & Hudson, Peter & Ko, Albert & Graham, Andrea & Lloyd-Smith, James. (2017). Pathways to zoonotic spillover. Nature reviews. Microbiology. 15. 10.1038/nrmicro.2017.45.

Smith, Olivia & Snyder, William & Owen, Jeb. (2020). Are we overestimating risk of enteric pathogen spillover from wild birds to humans?. Biological Reviews. 10.1111/brv.12581.