Review - The Risk of Pathogen Spillover from Wild Birds

Wild birds can carry pathogens, such as Campylobacter and Salmonella, that can become contaminants for food. Most of our concern is in the fields with crops that will receive minimal processing, but also in instances where birds gain access into our processing facilities. A recent review of the research shows that we probably overemphasize the risk, but more research is needed in understanding transmission from birds to our food systems.

"We conclude that current data do not provide sufficient information to determine the likelihood of enteric pathogen spillover from wild birds to humans and thus preclude management solutions. The primary focus in the literature on pathogen prevalence likely overestimates the probability of enteric pathogen spillover from wild birds to humans because a pathogen must survive long enough at an infectious dose and be a strain that is able to colonize humans to cause infection."

From their paper:

"Campylobacter spp. 14.8%(64/431)of North American breeding birds had Campylobacter spp. prevalence data (1+ observations) meeting our inclusion criteria 1–9 (Data S2). The species with the most observations meeting our inclusion criteria 1–9 were rock pigeon [N= 3659from 15 studies, range 6–1800 individuals tested, 0.1–70% reported prevalence, estimated prevalence 16± 5.3%(SE)],European starling[N= 2094 from 12 studies, range 1–957 individuals tested, 0–75% reported prevalence, estimated prevalence 28 ± 6.0% (SE)],...."

"Salmonella spp. were the most studied bacteria with 33% (141/431) of North American breeding birds having prevalence data (1+ observations) meeting our inclusion criteria 1–9. The species with the most observations of data meeting inclusion criteria 1–9 were herring gull [N = 12470 from 10 studies, range 1–5324 individuals tested, 0–22% prevalence,estimated prevalence 8.2± 2.2%(SE)],house sparrow [N = 5581 from 19 studies, range 2–1124 individuals tested, 0–21% prevalence, estimated prevalence 2.5 ± 0.7% (SE)], rock pigeon [N = 5458 from 30 studies, range 4–1800 individuals tested, 0–100% prevalence, estimated prevalence 4.0 ± 0.9% (SE)..."

So birds can carry pathogens, and we need to keep them out of food processing facilities, but with field crops, further work is needed before we go to the levels of habitat destruction.

Biological Reviews
https://onlinelibrary.wiley.com/doi/full/10.1111/brv.12581
Are we overestimating risk of enteric pathogen spillover from wild birds to humans?
Olivia M. Smith  William E. Snyder  Jeb P. Owen
First published: 31 January 2020 https://doi.org/10.1111/brv.12581

CDC Report - 2016 Salmonella Outbreak in Children Associated with Playground Sand

A 2016 Salmonella outbreak in Madrid, Spain caused illness in 24 preschool students, aged 3 to 5 years old.  It was concluded that the source of the Salmonella was the sand in the playground.  The Salmonella likely got there through bird droppings.   

While these types of issues may be difficult to prevent, there are some preventive measures that can be taken.  Keeping children from putting their hands in their mouth when playing in the dirt. (Good luck with that).  Having kids wash their hands after playing.  Recognizing that bird droppings are a potential source of Salmonella, so placing sandboxes in areas away from trees and other overhead structures where birds may land (and poop).  Sure, trees provide shade, and in Spain, it is probably better to be in the shade.  However, structures such as large umbrellas may be used.  Umbrellas or other movable structures can be beneficial in allowing the sand to dry.

CDC - MMWR
https://www.cdc.gov/mmwr/volumes/66/wr/mm6609a3.htm?s_cid=mm6609a3_e
Notes from the Field: An Outbreak of Salmonella Typhimurium Associated with Playground Sand in a Preschool Setting — Madrid, Spain, September–October 2016
Weekly / March 10, 2017 / 66(9);256–257