Example of

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Surveillance methodology

• Example of
• Classical swine fever

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Surveillance objectives

• Situation of the disease in the country
  (prevalence)
• Detection of all new clinical foci of the disease
  
• Detection of points or zones of viral circulation
• Prove that the country or certain zones are free
  from the disease
• Detect the re-emergence of the disease in a free
  zone
• Protect the national territory of the entry of
  the disease

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In order to ...

• Situation of the disease in the country
  (prevalence)
• In order to take strategic control decision
• Detection of all new clinical foci of the disease
  
• In order to eradicate all clinical foci
• Detection of points or zones of viral
  circulation
• In order to control and eradicate all viral
  circulation
• Prove that the country or certain zones are free
  from the disease
• In order to be recognised as zone or country free
  from CSF
• Detect the re-emergence of the disease in a free
  zone
• In order to maintain the status of country or
  zone free from CSF
• Protect the national territory of the entry of
  the disease
• In order to maintain the status of country or
  zone free from CSF

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But how ?
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Epidemiology of the disease

• Source of virus
• Infected animals
• Infected material
• Infected products
• Expression of the disease
• Clinical forms
• Easy detection
• Sub-clinical forms
• Virus reservoirs
• Piglets born from infected mothers
• Animals vaccinated close to an infection
• Vaccinated animals

6
Origin of contamination

• 1- Contacts with infected animals
• Introduction of infected animals
• Purchase
• Loan or rents Reproducers
• Animals infected in the neighborhoods
• Proximity of a focus
• Proximity of a risk activity
• Market
• Slaughterhouse
• Importer / Trader
• Infected wildlife
• Resurgence of the disease
• Virus reservoirs

7
Origin of contamination

• 2- Consumption of infected products
• Use of waste for feeding
• Access to waste

8
Detection of all new clinical foci of the disease

• Passive surveillance
• Spontaneous declaration of the cases or the
  suspicions
• By the producers
• By the field veterinarians (private or official)
• Technicians of private companies
• Vast training and communication programme
• The only way to obtain early warning

9
Detection of points or zones of viral circulation

• Active surveillance
• Oriented
• High risk points
• High risk farms and villages
• Markets
• Public reproducers
• Points of easy sampling
• Slaughterhouses
• Butcheries and sacrifice point
• Sampling frame
• Action plan in case of positive result
• Identification of the infected premise
• Epidemiological investigation and confirmation of
  the infection

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High risk Criteria

• Foci identified in the past in this place or in
  the neighbourhood
• Low level of biosecurity
• Pigs fed with waste
• Neighbourhood of market, slaughterhouse, roads of
  high transit of pigs
• Absence of vaccination
• High pig turnover
• High level of purchases, sale or importation
• Farm with food factory and marketing

11
Situation of the disease in the country

• Active surveillance
• Transversal survey on sample of population
• Necessary data and decision
• Which population (farms, backyard ??) and
  epidemiological unit
• Geographical extension of the survey
• Awaited prevalence ?
• Precision ?
• How to detect the disease ?
• Antigen / Antibodies / Clinical signs ???

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(No Transcript)
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Infected farm prevalence
Two stages sampling
1. Sample of farms
2. Sample of animals inside The farm
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Necessary data

• Awaited prevalence of infected farms
• In order to determine the number of farms to
  sample
• Fixed for example at 15
• Awaited prevalence of infected animals in an
  infected farm
• In order to determine the number of pigs to
  sample in each farm
• Fixed for example at 15

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Example of DRPopulation of the survey

• CSF eradication programme
• 11 250 producers (N)
• 1 543 673 pigs
• 2005 census
• 5 201 producers
• 549 441 pigs
• Epidemiological unit
• Organized farms
• All backyard pigs of one villages

16
Number of pigs to be sampled in each selected
farm or village

• Awaited prevalence 15 of the animals of the
  epidemiological unit
• Number of animals to sample with 95 probability
  to detect the presence of the disease

17
Prove that the country or certain zones are free
from the disease

• Active surveillance
• International recognition
• Clinical or serological repeated transversal
  survey
• Random sampling
• Statistical criteria
• 95 probability to detect the disease if present
  in 1 of the units
• Absolutely inefficient for early warning

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Detect the re-emergence of the disease in a free
zone

• Passive surveillance

Oriented active surveillance
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Protect the national territory of the entry of
the disease

• Active surveillance
• Oriented
• High risk points
• Border posts
• Sampling frame (systematic)
• Action plan in case of positive result

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Summary of the surveillance methods
Passive surveillance (disease notification
search)? Total population
Active surveillance on representative sample
Prevalence survey
Survey to be recognized free of the disease
Active surveillance on oriented sample
Slaughter-houses
Markets
High risk farms or villages
Reproduc- ers