Poultry farmer response to disease outbreaks in smallholder farming systems in southern Vietnam
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Abstract
Avian influenza outbreaks have been occurring on smallholder poultry farms in Asia for two decades. Farmer responses to these outbreaks can slow down or accelerate virus transmission. We used a longitudinal survey of 53 small-scale chicken farms in southern Vietnam to investigate the impact of outbreaks with disease-induced mortality on harvest rate, vaccination, and disinfection behaviors. We found that in small broiler flocks (≤16 birds/flock) the estimated probability of harvest was 56% higher when an outbreak occurred, and 214% higher if an outbreak with sudden deaths occurred in the same month. Vaccination and disinfection were strongly and positively correlated with the number of birds. Small-scale farmers – the overwhelming majority of poultry producers in low-income countries – tend to rely on rapid sale of birds to mitigate losses from diseases. As depopulated birds are sent to markets or trading networks, this reactive behavior has the potential to enhance onward transmission.
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###Reviewer #3:
The article by Delabouglise and collaborators presents a longitudinal analysis of farms in Southeast Asia to understand farmer behaviours in response to disease outbreaks in poultry. The study is original in its design and the results are important for the prevention of avian flu epidemics in the region, as they suggest that smallholder farmers are more likely to sell their poultry to traders following outbreaks, which could contribute to the rapid disease spread. There are important differences in terms of response to outbreaks (harvest, vaccination, etc.) between large and small farms, which suggests that targeted sensitization campaigns and programs are necessary to modify these behaviours. The article is well written, although the discussion needs some work to lay out the limitations of the study and to expand the …
###Reviewer #3:
The article by Delabouglise and collaborators presents a longitudinal analysis of farms in Southeast Asia to understand farmer behaviours in response to disease outbreaks in poultry. The study is original in its design and the results are important for the prevention of avian flu epidemics in the region, as they suggest that smallholder farmers are more likely to sell their poultry to traders following outbreaks, which could contribute to the rapid disease spread. There are important differences in terms of response to outbreaks (harvest, vaccination, etc.) between large and small farms, which suggests that targeted sensitization campaigns and programs are necessary to modify these behaviours. The article is well written, although the discussion needs some work to lay out the limitations of the study and to expand the practical implications of the study in terms of policies or interventions to put in place.
I have a few comments to improve the manuscript:
Introduction:
-I am uncertain about whether the term cohort applies to their study, as the unit of follow-up are farms but they're not following the same individuals (chickens) over time. I would suggest changing the term to longitudinal study.
Methodology:
-How reliable is the classification of outbreaks with and without sudden deaths? Are farmers able to recognize fast the onset of symptoms and then a death within 24h after the onset of those symptoms? I imagine that misclassification can happen, so I would mention this as a potential limitation.
Results:
-Table 2: it would be much more easily interpretable if variables are described fully, with the function used for transformation in brackets. For example, instead of "square root of Nbc", I would include "Number of broiler chickens in the farm (sqrt)", and so on.
Discussion:
-I think the different limitations of the study should be explained and discussed. For instance, 1) the use of a proxy for weight instead of weight itself, 2) potential misclassification of outbreaks (see above), 3) some behaviours may depend on events happening in longer time frames, for example the previous year, but this is not accounted for in the models.
-Also, the harvest of chickens could be greatly influenced by economic needs of the household (a family event, an economic shock, disease, etc.), especially for smallholder farmers in the developing world who may use chicken as a form of cash savings. I am actually surprised that this was not included in the questionnaires, and I think it's an important limitation that should be discussed (and appropriate literature referenced).
-I feel that the discussion lacks insights into practical implications/solutions coming from this study (policies, interventions, etc.). Given the results, what can the government or NGOs or international organizations implement in order to reduce the risk of future outbreaks? This part should be expanded and be more specific.
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###Reviewer #2:
This manuscript addresses an important gap in knowledge of infectious disease emergence and spread within small-scale poultry production systems. The study design allows for analysis of longitudinal epidemiological and human behavioral data, not commonly found in animal health research; the statistical analysis is well thought out and robust. The authors find that farmers with small flocks respond to disease outbreaks with the rapid sale of sick birds to traders, and that despite government-supported programs, there is little uptake of vaccination in this population. Findings point to future areas of research that could inform policy development or better target activities to reduce disease transmission within similar poultry production systems.
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###Reviewer #1:
General assessment:
The manuscript is very well written, easy to follow despite the substantial statistics, and has a clear goal that the authors address with strength. The study is highly relevant in the context of emerging infectious diseases, and addresses one of the main understudied candidate drivers of emergence. The study design allows a thorough analysis of the observed patterns, providing highly useful insights into the potential ways in which avian influenza can spread.
Substantive concerns:
I have no substantive concerns. The longitudinal study seems to have been designed and conducted well, allowing the incorporation of potentially important variables in the statistical models. The authors made great and responsible use of MGAMs, and clearly have an excellent background in statistics. I have no reservations …
###Reviewer #1:
General assessment:
The manuscript is very well written, easy to follow despite the substantial statistics, and has a clear goal that the authors address with strength. The study is highly relevant in the context of emerging infectious diseases, and addresses one of the main understudied candidate drivers of emergence. The study design allows a thorough analysis of the observed patterns, providing highly useful insights into the potential ways in which avian influenza can spread.
Substantive concerns:
I have no substantive concerns. The longitudinal study seems to have been designed and conducted well, allowing the incorporation of potentially important variables in the statistical models. The authors made great and responsible use of MGAMs, and clearly have an excellent background in statistics. I have no reservations or concerns about any aspect of the statistics. In fact I would like to complement the authors on the way in which the methods were described and results were reported, which was done in a clear way despite the large and potentially confusing number of results.
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##Preprint Review
This preprint was reviewed using eLife’s Preprint Review service, which provides public peer reviews of manuscripts posted on bioRxiv for the benefit of the authors, readers, potential readers, and others interested in our assessment of the work. This review applies only to version 1 of the manuscript.
###Summary:
Your manuscript surveyed 53 poultry farms in Southern Vietnam and identified that small scale farmers with lower sized flocks were more likely to rapidly harvest and sell disease birds to mitigate loss of profit. This finding is of great potential importance for developing prevention efforts for introduction of avian influenza into human populations.
The reviewers were all highly complimentary of this paper. They all felt the manuscript was methodologically sound, clearly written, highly original and of …
##Preprint Review
This preprint was reviewed using eLife’s Preprint Review service, which provides public peer reviews of manuscripts posted on bioRxiv for the benefit of the authors, readers, potential readers, and others interested in our assessment of the work. This review applies only to version 1 of the manuscript.
###Summary:
Your manuscript surveyed 53 poultry farms in Southern Vietnam and identified that small scale farmers with lower sized flocks were more likely to rapidly harvest and sell disease birds to mitigate loss of profit. This finding is of great potential importance for developing prevention efforts for introduction of avian influenza into human populations.
The reviewers were all highly complimentary of this paper. They all felt the manuscript was methodologically sound, clearly written, highly original and of substantial public health and policy relevance. Particular noted strengths were appropriate use and description of mixed-effects general additive models, appropriate study design and the inclusion of all raw data for public use.
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