Welcome back dear Foodies!
For the past few posts, we have investigated how potential health risks associated with livestock emissions and gained a deeper insight into the difficulties in establishing causal exposure-effect relationships. To wrap up, here is a short review post!
Outbreak of Q-fever in the Netherlands
If you recall, we briefly mentioned about Q-fever in the last post. In the case of Netherlands, the only case study with robust scientific evidence is the outbreak of Q-fever from 2007 to 2010. Q-fever is a zoonotic disease caused by the Gram-negative bacteria Coxiella burnetii (C-burnetii) and is rather prevalent throughout across the globe (de Koeijer, Hagenaars, van Leuken, Swart and Boender, 2020). Evidence and spatial data have shown that there is increased incidence of Q-fever infections in the vicinity of goat pens up to around 5km within the vicinity of the livestock farms (Fig.1).
Often, infection occurs through direct contact with infected animals and as such occupational exposure is a common source of transmission. For most of the people, they may experience flu-like symptoms in the initial few weeks of exposure. Subsequently, they may develop symptoms such as fever, headache, nausea, diarrhea and even pneumonia for those with potential complications. Thus, it is also important to take into consideration certain groups of people who may be extremely vulnerable to potential complications, for instance, those with impaired immunity systems and even pregnant women.
Fig.1 Human population density data VS density of farms with at least 50 goats at municipality level in the Netherlands. Obtained from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0227491
In addition, C-burnetii can be attached to airborne and dust particles, highlighting that the possibility of the pathogen being transmitted through the air, increasing the potential risks on neighbouring residents (Clark and Soares Magalhaes, 2018).
A Short Review
To date, there is substantial evidence to show the exposure-effect relationship of livestock emissions and health impacts such as diminishing lung function, exacerbation of respiratory tract issues and even PM-related air pollution mortality (Smit and Heederik, 2017).
Whereas in the case of zoonotic infections, data set is often too limited in establishing a quantitative exposure-effect causal relationship. Hence, indirect information or extrapolation is used to help predict certain associations. Even though these may not necessarily be the most accurate results, it will, nevertheless, offer a point of reference for further research to be conducted and as a gauge for public health assessment.
On top of limited data on the causal relationships, it is also important to note that there are other factors hindering the measurements. Some of the common factors include the variations of farms’ emissions levels, types of farm animals, farm management practices, meteorological conditions and seasonal variations (Health Council of the Netherlands, 2012). As such, measurements of livestock pollutants are met with difficulties since the data recorded are highly dependent on weather conditions and local circumstances. Therefore, it is difficult to draw conclusions on long-term average measurements.
I hope these had provided us with greater insights as to why determining causal relationships are often met with so many challenges. That’s all and cheers!
Detective Out,
Linying
References
Clark, N. J. and Soares Magalhaes, R. J. (2018). Airborne geographical dispersal of Q fever from livestock holdings to human communities: a systematic review and critical appraisal of evidence. BMC Infectious Diseases, 18(218). Retrieved from: https://bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-018-3135-4#citeas
de Koeijer, A. A., Hagenaars, T. J., van Leuken J. P. G., Swart, A. N., Boender, G. J. (2020). Spatial transmissions risk during the 2007-2010 Q fever epidemic in The Netherlands: Analysis of the farm-to-farm and farm-to-resident transmission. PLOS ONE, 15(2). Retrieved from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0227491
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
Smit, L. A. M. & Heederik, D. (2017). 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
