Having investigated about livestock-induced particulate matter emissions and endotoxins and their potential health impacts on farm workers as well as neighbouring residents, let us look at one more aspect in this post today!

Micro-organisms and zoonoses

Another important component of livestock emissions is the existence of micro-organisms (or bacteria) as a result of livestock production. Micro-organisms are highly abundant in livestock farms due to the farm animals and especially their manure (de Rooij et al., 2019). Moreover, levels of micro-organisms are even more concentrated in confinement livestock farms, whereby farm animals are densely confined (Fig.1), resulting in the toxicity of microbial concentrations rising to harmful and even lethal levels once exposed to (National Agriculture Safety Database, n.d.).

Fig. 1 Cow confinement facility. Obtained from https://www.agupdate.com/iowafarmertoday/news/livestock/management-considerations-for-cattle-confinement-facilities/article_6f2ac70a-6fdb-11e8-84a0-6fe77ecf6b2c.html

Studies have shown that at a close distance of less than 200m from farms, increased levels of bacteria such as E-coli were measured (de Rooij et al., 2019). Not only that, air samples collected also consisted of zoonotic pathogens, which is capable in causing the spread of infectious diseases between human and animals. Some of the zoonotic pathogens carrying infectious diseases include salmonella, which is the most common zoonoses, as well as pathogens carrying antimicrobial resistance (AMR). This further heightens public health concerns as people began to associate livestock farms with higher potential of outbreak of zoonotic diseases.

Livestock farm workers experience occupational risk whereby they either end up being a carrier of micro-organisms or they suffer from an infection. This process can take place ranging from direct contact with animals to even dispersal through the air, especially from livestock manure (Health Council of the Netherlands, 2012). However, very little is known about the exposure-effect relationships between micro-organisms and impacts on farm workers or neighbouring residents. This is mainly because there is no standard measurement unit for micro-organisms and thus it is difficult to collect quantitative data and draw causal relationships. As such, endotoxins, which are relatively easier to measure, is often used as an indicator of microbial activity.

In de Rooij et al’s study on livestock-related microbial concentrations in air at residential areas, bacteria and AMR genes can be detected in air at distances of more than several hundred metres, extending to residential areas. This indicates that livestock-induced microbial exposure is indeed present in neighbouring residential areas, though the concentrations levels fluctuated with temporal and spatial variations. Their observations also indicated that the level of density of livestock farms, on top of the distance, also plays a significant role on increasing the microbial concentrations in the area. As such, even with the limitations in measuring microbial concentrations, close proximity is still a possible risk factor.

Concerns over outbreak of zoonotic diseases

Since micro-organisms can also carry zoonotic pathogens, public health concerns were also raised on the outbreak of zoonotic infections. However, it is very difficult to determine the risk of a zoonotic outbreak with any accuracy. Extrapolation method is often used to determine associations and hence the causal relationships between exposure and effect could not be determined explicitly (de Rooij et. Al, 2019; Smit and Heederik, 2017). As such, no direct conclusions can be drawn with all the uncertainties. Though, in the case of Netherlands, the only outbreak of zoonotic infections with substantial scientific evidence is the case of Q-fever from 2007 to 2010 (Health Council of the Netherlands, 2012).

That’s all for today. See you in the next post!

Detective Out,

Linying

References

de Rooij et al. (2019). Insights into Livestock-Related Microbial Concentrations in Air at Residential Level in a Livestock Dense Area. Environmental science & technology, 53(13), 7746–7758. Retrieved from: https://doi.org/10.1021/acs.est.8b07029

Health Council of the Netherlands (2012). Health risks associated with livestock farms. The Netherlands: Health Council of the Netherlands. Retrieved from: https://www.healthcouncil.nl/binaries/healthcouncil/documents/advisory-reports/2012/11/30/health-risks-associated-with-livestock-farms/advisory-report-health-risks-associated-with-livestock-farms.pdf

National Agriculture Safety Database (n.d.). Livestock confinement dust and gases. National Agriculture Safety Database. Retrieved from: https://nasdonline.org/1620/d001501/livestock-confinement-dust-and-gases.html

Smit, L. A. M. & Heederik, D. (2017, Sep 27). Impacts of intensive livestock production on human health in densely populated regions. Geohealth, 1(7), 272-277. Retrieved from: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GH000103