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Research related to dairy and adjacent communities has recently attracted significant media attention.
Studies of children living in the vicinity of dairies and other livestock operations have shown that low level exposure to bioaerosols containing endotoxins from Gram negative bacteria and other microbial components at a very young age may be protective against the development of asthma later in life, possibly through priming of the immune system. The recent study of Swedish children with the suggestion that “pregnant women may benefit from spending time on dairy farms has attracted particular attention.”
Good or bad idea? (just one example drawback – listeria, not common but certainly possible?)
Other studies of large modern dairies have found that exposure to high levels of organic dusts generated during milking, moving cows, feeding and other tasks has been associated with increased inflammation and decreased lung function resulting in chronic obstructive pulmonary disease (COPD) and asthma-like diseases.
So what’s going on? How do dairy producers make sense of the science and respond appropriately? Or better yet how do they help science advance?
This presentation will take closer look at recent examples of both community and occupational health studies related to dairy, explore their strengths and limitations, consider the cumulative evidence, and suggest possible next steps.
To step back – Science is based on a system of Observation, Formulation and Testing of Hypotheses to explain and predict and outcome (causal mechanism or mathematical relationship), and depends on replication by other experimenters (peer review).
Producers cannot base decisions about practice on one study – but must consider the body of evidence, strengths and weaknesses and populations studied. Beyond the science Consider practical implications – reasonable, economic, social, political, ethical?
There is a strong body of evidence (more than 35 studies), going back more than a decade, that demonstrates that being raised on a traditional dairy farm is protective for asthma and atopy (allergy). Studies in Europe, North America, South America, and NZ/Australia suggest that this effect is strongest when exposure occurs in utero, and that positive effects can extend into adult life. Specific exposures (contact with cows, drinking raw milk, and high microbial diversity) seem to be more important for asthma but not as consistent for allergic sensitization. atopy . See review by Von Mutius Nature Reviews Immunology 2010.
Mouse models are helping to explain the mechanisms through which microbiome modulates immune responses and allergic inflammation, but long term studies are needed to understand the role of human genetics and timing of exposure.
Study of communities in Yakima Valley – measured settled dust inside and outside of 40 homes. Concentration gradient – higher cow allergen and endotoxin in homes closer to dairies and sprayfields. Concentrations of endotoxin measured in the proximal homes at levels associated with negative respiratory health effects. (measured Eu\U/mg of dust)
Limitations – cross sectional – one time, no info on wind direction and orientation to facility, specific information on facility (# cows etc), use of cow manure at home gardens.
Innate immunity body’s first-line of defense, present from birth Adaptive or acquired immunity develops on exposure and recognition of antigens by the immune system Toll-like receptors shown to play an important roll in both innate and adaptive immune responses Activation pathway of TLR4 in response to Gram negative bacterial endotoxin/LPS has been intensively studied but there are many other immune system pathways that respond to Gram positive bacteria, archea, and other environmental agents. Genetic mutations that affect these pathways may either increase or decrease development of respiratory disease and allergic sensitization.
The recent study of Swedish children in particular has garnered media attention with a statement that pregnant women may benefit from spending time on dairy farms. Lundell and colleagues followed children to the age of 3 years finding that those living on farms had a lower risk of developing asthma and that delayed maturation of immune system B cells among those NOT exposed.
Strengths of study - Weaknesses – relevence for modern farms in US? Genetic and other risk factors. Population, Replication – further human, animal and cell studies.
Recent studies of large modern dairies have found that respiratory disease remains an important problem for dairy workers, contributing to lost time and high turnover. Exposure to high levels of organic dusts generated during milking, moving cows, feeding and other tasks has been associated with increased inflammation and decreased lung function resulting in chronic obstructive pulmonary disease (COPD) and asthma-like diseases. Much research into the cause of respiratory disease in agriculture has focused on the role of endotoxins – a chemical component of Gram-negative bacteria.
Our recent work and others have shown that the exposure response relationship in agricultural workers is modulated by genetic polymorphisms. Effects depend on age at time of exposure.
Inhalation exposure to Gram-positive bacteria and their chemical constituents (e.g. PGN) in dairies is much higher than previously thought, and there is strong in vitro evidence demonstrating their inflammatory effects.
Gao – SNP TLR4 protects vs wildtype, Smit – French case control asthma TLR 2, CD14 atopic asthma – modified by country living
Many new workers adapt to these exposures, and evidence suggests that individual behavior and genetic factors play a key role in explaining why some workers are more susceptible. Our recent work including dairy workers found that Co-exposure to Pesticides, smoking, and TLR4 polymorphisms were effect modifiers on lung function/bioaerosol interaction – - Most recent study populations have included dairy workers but very few studies focused exclusively on exposures and health effects among dairy workers.
Exposure to bioaerosols in combination with self-reported pesticide/herbicide use and in combination with smoking are effect modifiers on cross shift changes in lung function
TLR4 polymorphisms Asp299Gly and Tlr399Ile may influence cross shift changes in lung function for workers exposed to dust and 3-OHFA. However, further study is required due to possible sample interference from the small sample size.
Limitations of Occupational Studies – Few studies simultaneously measured exposure and health effects. Genetics complicated – few studies of multiple genetic polymorphisms along with other potential risk factors including other exposures, behaviors, and diseases.
Exposure to diverse microbiome plays important role in asthma – whether protective or harmful appears dependent on level and timing of exposure, co-risk factors, human genetics.
High levels of organic dusts have been associated with increased inflammation and decreased lung function resulting in chronic obstructive pulmonary disease (COPD) and asthma-like diseases among adult dairy workers.
A growing body of evidence indicates that children living near dairies and other livestock operations with low level exposures at a very young age may be protected against asthma later in life, possibly through priming of the immune system.
This appears to be consistent with the observation that new workers who were raised on farms or have prior farming experience are at lower risk for asthma and asthma like diseases.
Other important disease endpoints and agents to consider in the dairy environment – COPD, heat stress, infectious agents – listeria (blue), E Coli 0157?
Producers need to understand the risks (given current evidence) and balance with reasonable approaches that optimize health of workforce, livestock, consumers and neighbors.
So from a bigger-picture risk management perspective there a number of aspects that producers need to consider.
Although genetics and early exposures appear to be important and this research may lead to protective strategies such as medications that block an over-response to endotoxin – there are no screening or profilactics available now. The ethics of genetic screening and setting exposure guidelines for susceptible workers are being hotly debated. A strong argument has been made that developing guidelines to protect susceptible workers is desirable since it reduces risk for the whole workforce.
Would like to suggest that it would be helpful for producers: to continue to engage with researchers to address research gaps and conduct relevent studies. And to use prudence where feasible – through adopting best practices that promote cow health, worker health, productivity, and community health.
It is worth emphasizing that modern dairy production has already significantly reduced the prevalence of respiratory disease through improved engineering controls/operation design. There are further steps that producers can take to reduce risk of respiratory disease among workers:
Identify locations and tasks that contribute to respiratory exposures
Conduct baseline and annual medical exams to identify existing or developing respiratory problems before they become worse. It is not legal to conduct a pre-hire physical exams, but working with medical providers, workers compensation carriers you may be able to manage job placement.
Focus first on Engineering controls – although in many cases these were not designed with controlling worker exposures there are studies demonstrating that barn ventilation, enclosed/ventilated cabs, parlor washing frequency, feed additives, and bedding materials (Samadi 2012 – found endotoxins lower in barns using sawdust vs. compost. Sand reported to reduce E coli 0157:H7 Westphal 2011). Much more research on cost – effective interventions is needed. We are in first year of study working with producers in Mountain West region to identify and evaluate potential engineering interventions.
Where engineering controls do not exist or are not practical Protective equipment, specifically – N95 dust masks and respirators may be used. Workers must be medically able to wear a respirator, must be fit tested to make sure there are no leaks, and trained. The respirator must also be specific for the hazards including any chemicals.
To be effective any intervention needs to be practical and cost effective. Again we would like to encourage producers to continue to engage with researchers to understand what the science , ant to address knowledge gaps that are most important for sustainability of the industry.
Impact of aerosols on respiratory health of dairy workers and residents living near dairies discussion and implications of recent research
Impact of Aerosols on Respiratory Health
of Dairy Workers and Residents Living
Near Dairies: Discussion and
Implications of Recent Research
Stephen J Reynolds, PhD, CIH, FAIHA
Director High Plains Intermountain Center for Agricultural Health
and Safety, Colorado State University, Ft. Collins, CO
Robert Hagevoort, PhD Dairy Extension Specialist, New Mexico
State University, Clovis, NM
2015 Waste to Worth Confernce
March 31, 2015
Health or disease
Other risk factors?
Association and Causation
• Most convincing evidence for a causal
relation comes from reproducible
experimental demonstration of association.
• Observational studies on human populations
(ethics of experimentation)
o Retrospective (Case History), Prospective
o Mathematical (statistical) models and
agreement on acceptable error
Evidence for Hygiene
Braun-Fahrlander et al. Enviromental
Exposure to Endotoxin and its relation to
asthma in school age children. N Eng J
Illi et al. Protection from childhood asthma
and allergy in Alpine farm environments –
the GABRIEL Advanced Studies. J Allergy
Clin Immunol 2012
Evidence for Hygiene
Ege et al. Gene-environment interaction
for childhood asthma and exposure to
farming in Central Europe. J Allergy Clin
Smit et al. Air pollution from livestock
farms, and asthma, allergic rhinitis, and
COPD among neighboring residents.
Occup Environ Med 2014
Williams et al. Cow allergen (Bos d2) and
endotoxin concentrations are higher in settled dust
of homes proximate to industrial-scale dairy
operations. Nature 2014.
Endotoxin & Innate
Source: Cook et al. 2004
Lundell et al. High Proportion of CD5 B
Cells in Infants Predicts Development of
Allergic Disease. J Immunology 2014.
• Reynolds. Systematic Review of Respiratory
Health Among Dairy Workers J Agromedicine
• Basinas. Sensitization to Common Allergens and
Respiratory Symptoms in Endotoxin Exposed
Workers: a Pooled Analysis JOEM 2012
• Senthilselvan Association of polymorphisms of
toll-like receptor 4 with a reduced prevalence of
hay fever and atopy. Ann Allergy Asthma
• Smit. CD14 and Toll-like receptor Gene
Polymorphisms, Country Living, and
Asthma in Adults . Am J Respir Crit Med
• Gao. Association of Toll-like receptor 2
gene polymorphisms with lung function in
workers in swine operations . Ann Allergy
Asthma Immunol 2013
Reynolds. Pulmonary Function Reductions Among
Potentially Susceptible Subgroups of Agricultural
Workers in Colorado and Nebraska JOEM 2012
Risk Management in face
Liabilities – Community/consumers vs. workplace
Communication and scientific literacy
Cost effective best practices that promote cow
health, productivity, worker health and community
Identify locations and tasks that
contribute to respiratory exposures
Provide baseline and annual medical
Engineering controls – ventilation,
enclosed/ventilated cabs, feed
additives, bedding materials, washing
Protective equipment – N95 dust masks
and respirators (when engineering is