The use of participatory approaches for better ... · The use of participatory approaches for...

The use of participatory approaches for better understanding foot-and-mouth disease

in Cambodia

LIDC seminar 15th April 2013

Timothée Vergne Veterinary Epidemiology, Economics and Public Health Group

Royal veterinary College [email protected]

Introduction

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Introduction

Source: www.thestudentroom.co.uk

http://kitschycoo.blogspot.co.uk

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Introduction

Cambodia

Vietnam

Thailand Lao

Burma

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Introduction

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Introduction

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Introduction

FMD surveillance relies on farmers’ declaration Heavy underreporting Underestimation of the true situation

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Objectives

• From the farmer’s point of view, what is the importance of FMD in Cambodia?

• Can we use participatory approaches for the surveillance of FMD in Cambodia?

• What is the real extend of FMD in the study area?

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Objectives




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What is the importance of FMD for Cambodian farmers?

• Very few studies on the farmer’s perception of FMD in Southeast Asia

• Use of participatory tools for collecting data

• Svay Rieng province

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Cambodia


• Village sampling

• 51 villages

• Selected as randomly as possible

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• First visit

• Chief of the village and Village animal health worker

• Presentation of the objectives of the project

• Collecting general information regarding size of cattle and buffalo population

• Schedule a meeting with 15-20 farmers (second visit)

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• Second visit

• 15-20 farmers (men and women)

• Semi-structured interviews of the group

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• Second visit

• Defining the list of the most frequent diseases they encountered in their village

• Ranking the diseases regarding their general perception (pair-wise ranking)

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• Second visit

• Defining a list of disease impact categories

– Morbidity

– Mortality

– Difficulty of treatment

– Reduced draft power

– Reduced reproduction capacity

– Reduced selling price

– Reduced manure production

– Reduced meat consumption

– Cost of the treatment

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• Second visit

• Weighting each disease impact categories (proportional pilling)

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• Second visit

• For each disease impact category, weighting the relative contribution of each identified disease (proportional pilling)

17 Computation of a Disease Impact Score for each disease


• Second visit

• Further discussions regarding foot-and mouth disease

– Occurrence of the last outbreak

– Management of an outbreak at village level

– Is the help of veterinary authorities required?

– Visit of the village for seeing any potential clinical cases

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• Results

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HS = Hemorrhagic septicemia FMD = Foot and Mouth Disease CSF = Classical Swine Fever BDS = Bloody Diarrhea Syndrom

Global disease impact score for the four most important diseases


• Results

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Detailed disease impact score for the two most important diseases


• Results

• Around 80% of villages said to have experienced FMD cases at least once since 2009

• 50% both in 2009 and 2010

• 20% every year since 2008

• Good agreement between villages concerning the clinical description of FMD

- vesicles in mouth/tongue/gums

- vesicles on feet

- infection of the wounds

- painful legs

- sialorrhea

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• Results

• Farmers try to manage the disease on their own using traditional medicine

• Report to veterinary authorities only if the number of detected clinical cases exceeds a given threshold (from 2 to 30)

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“Ampl”


• Conclusions

• Cambodian farmers seem to be sufficiently aware of FMD clinical signs

• FMD is ranked 2nd in the list of priority (<< HS)

• Weak desire to report outbreaks since FMD entails low direct losses

“We do not really care about FMD since it can always be treated with time, whereas HS cannot”

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Objectives




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Participatory approach as a tool for surveillance?

• Recall

• Around 80% of villages said to have experienced FMD cases at least once since 2009

How many are false positives?

How many are false negatives?

What is the sensitivity of the participatory approach?

What is the specificity of the participatory approach?

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• Serological survey in the same villages

• On cattle and buffaloes

• Born after 1st October 2008 (but older than 5 months)

• Around 20 animals per village

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• Serological survey in the same villages

• Blood samples were analysed by ELISA (DIVA strategy)

National Veterinary Research Institute (Phnom Penh)

• For this analysis, villages were considered as positives if at least one sample reacted positively

• We only considered villages where at least 10 animals have been tested

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Participatory approach: 31 infected and 7 non-infected Serology screening: 25 infected and 13 non-infected


• Bayesian approach

• Multinomial model with 5 parameters:

– Sensitivity and specificity of the participatory approach

– Sensitivity and specificity of the serology screening

– Between-villages prevalence

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Parameters to estimate

Informative priors

Parameter to estimate


• Bayesian approach

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Sensitivity = 0.89 (CI95% 0.60-0.99) Specificity = 0.30 (CI95% 0.10-0.56)

Sensitivity of participatory approach Specificity of participatory approach


• Conclusion

• Participatory approaches are much cheaper than classical approaches for screening a population

• But it leads to heavy overestimations of the number of FMD outbreaks

Presence of other vesicular diseases?

- malignant catarrhal fever

- bovine viral diarrhea…

• Should be used in conjunction with other approaches

• Relevant in the late stages of eradication (cf. rinderpest)

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Objectives




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Capture-recapture analysis using a participatory approach

• Two-source capture-recapture methodology

32 c = number of cases detected by source 2 only

a = number of cases detected by both sources

Infected epidemiological units (N)

a b c

b = number of cases detected by source 1 only

d ???



• Under the assumption of independence between the sources

a/N = (a+b)/N.(a+c)/N

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abccbaN /ˆ



• Underlying assumptions

– Direct independence between the sources

– Indirect independence between the sources

– Only true cases detected by each source

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• Source 1: Official cases reported to veterinary authorities

• 112 infected villages were known by veterinary authorities in 2009

15 officially reported and villages located within a 4km radius

• Source 2: Participatory approach + Serology

• 13 infected villages were detected for 2009

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+


• Results

• 315 (IC95% 117-514) villages of the province experienced clinical cases of

FMD in 2009

50% of the villages

• FMD is still largely enzootic

• FMD is heavily underreported (36%)

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4 108 9


• Conclusion

• Participatory approach was essential to prevent false positives!

• Could not have been used alone

• Participatory approaches are complementary to traditional approaches

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General conclusions

• What have participatory approaches contributed?

• FMD is the second most important disease for Cambodian farmers

• Its apparent prevalence is heavily underestimated

Only 36% of infected villages are known by vet authorities

• Farmers do not report the disease because it entails low direct losses

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This highlights some inconsistencies of international standards FMD has a high impact on international trade FMD is a notifiable disease listed by the OIE But FMD is not a farmers’ important concern…

General conclusions

• What limitations for participatory approaches?

• Relies on farmers’ perception

specificity for identifying outbreaks = 30%

Many false positives!

• Should be used in conjunction with other classical approaches

• Good as a first screening for tracking FMD in the late stages of eradication

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To go further…

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Acknowledgements

Camille Bellet Flavie Goutard Vladimir Grosbois Francois Roger Barbara Dufour Benoit Durand Davun Holl Sorn San Ronello Abila Alexandre Bouchot Helene Ou Eav Chan

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Thank you for your attention

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