MAXIMISING EFFICIENCY WITH A SURVEILLANCE STRATEGY FOR FOOT-AND-MOUTH DISEASE DURING AN OUTBREAK IN A PREVIOUSLY FMD-FREE COUNTRY.

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1 MAXIMISING EFFICIENCY WITH A SURVEILLANCE STRATEGY FOR FOOT-AND-MOUTH DISEASE DURING AN OUTBREAK IN A PREVIOUSLY FMD-FREE COUNTRY. Kylee Walker Incursion Investigator and Veterinary Epidemiologist, Ministry for Primary Industries, New Zealand 1

2 New Zealand has never had an outbreak of foot-and-mouth disease, but preparedness planning for responding to an incursion is a high priority for New Zealand s Ministry for Primary Industries because of the devastating effect the disease would have on our country. As part of FMD preparedness in New Zealand, a sampling and diagnostic surveillance strategy was developed to guide rapid and efficient detection of infected farms, through to proof-of-disease-freedom surveillance. MPI Investigation and Diagnostic Centre - Wallaceville 2

3 Reasons for a new surveillance strategy for FMD Our current plan for surveillance, once index case testing established the disease is present, would be based around regular surveillance visits to at-risk properties, to identify clinical signs at their onset. But this is not ideal: Waiting for the advent of clinical signs provides greater periods of virus shedding, and greater spread of infection We have large numbers of sheep as well as deer and goats which may not have overt clinical signs It is resource-heavy to send out vets to all at-risk or surveillance zone properties every 2 nd day for 14 days, whereas with testing most farms would have 1 or 2 visits to confirm or rule-out infection Other advantages: Knowing if antibodies or virus are present on farms could aid epidemiological investigation Will use serology in Proof-of-Freedom phase, so should use during outbreak phase too And now we have better tools available: Advancements in laboratory testing for agent identification (RT-s) means we can identify pre-clinical viraemic animals early detection NAIT animal movement tracking system in NZ allows more informed tracing better idea of risk of spread 3

4 Aim of surveillance strategy The strategy: establishes the appropriate diagnostic testing algorithm, specimen types and sample size numbers to use for different farm situations, allowing rapid deployment of an effective, pre-validated surveillance programme to diagnose infected properties, including pre-clinical ones, with the greatest efficiency, accuracy and speed. The diagnostic surveillance strategy is designed to improve efficiency in an outbreak by streamlining and pre-planning decision-making at the farm and the laboratory. It will reduce reliance on clinical surveillance and enhance pre-clinical diagnosis, hopefully assisting in a faster delimitation of an outbreak and ongoing management. Other advantages would be: assisting good decision making for confirmation or rule-out of infection and avoid unnecessary large-scale culls, to allow the collecting of appropriate samples to describe the epidemiology of the outbreak, which may be used both real-time and retrospectively, and providing guidelines for the farm-level sampling and testing for a proof-of-freedom claim. Information adapted from: Laboratory Testing and Sampling in a Foot and Mouth Disease Response by Farm Type, Kylee Walker, November 2011, MPI Internal Document 4

5 Timeline of response to FMD virus infection in an individual animal, including detectable components for testing Exposure to infective dose Incubation period - Within farm 2-14 days - Between farm 4-14 days - Generally 2-6 days Vesicles rupture Circulating Virus-neutralising antibodies appear antibodies appear Clearance of virus Cattle by 2 weeks Pigs by 3-4 weeks post-infection E D wk 2wk 3wk 4wk Development of detectable viraemia Detection of clinical signs Detectable seroconversion: to SPs to NSPs Detectable component: Cattle Pigs Carriers --> Virus in OP fluid Virus in milk Virus in blood Virus in vesicular tissue Clinical signs --> Antibodies Key: Less likely to observe at this time 6

6 Table 1: Minimum screening sample sizes per farm required by purpose of testing and herd size, when clinical signs are absent. Purpose of visit Property status Property in Protection Zone * 3 At-Risk Place* 3 (<3 days post-exposure) At-Risk Place (4-7 days post-exposure) At-Risk Place (>7 days post-exposure) At-Risk Places (every visit) End of surveillance period (Protection Zone or At-Risk Place) Species Sample type * 1 Required or Optional Dairy cattle Dairy cattle Deer Sheep Goats Camelids Buffalo Tests employed, in order of use * 2 Serum R OP fluid or O Throat, nasal or oral swabs Bulk tank milk and Residue milk R (at every surveillance visit) Serum R OP fluid R Serum R OP fluid or O Throat, nasal or oral swabs Serum R Bulk tank milk R and Residue milk Serum R (if no sentinel * 4 species present) O (cattle, pigs, or listed species with sentinels present) * 5 Herd Size (single management group and species) ml 100ml 100ml 100ml 100ml 100ml 100ml 100ml 100ml 100ml 100ml 100ml * 1 Take 2 serum tubes per animal sampled. OP = oropharyngeal. * 2 on serum calculated with test parameters of 100% Sp and 99% 5% prevalence. Screening serum sample numbers also fit with the requirements for if a minimum 10% prevalence of antibodies is assumed in a clinically-recovered herd. All sample sizes calculated for 95% confidence of detecting 1 infected animal. * 3 Protection Zone: within approximately 3km of any Infected Place. At-Risk Place: Determined by Intelligence and Planning Team to be at-risk because of tracing, spatial proximity or air-borne spread. * 4 Sentinel species are regarded as cattle and pigs, where clinical signs are typically more overtly displayed. * 5 Tests are not validated for these species. 7

7 Table 2: Minimum confirmatory sample sizes per farm required by purpose of testing and herd size, when clinical signs are present. Suspect Infected Places. Purpose of visit Confirmatory testing for herds with clinical signs (Suspect Infected Places) Animals to sample Animals with vesicles Animals with clinical signs as sampling priority Animals with clinical signs (increase numbers if need to sample non-clinicals) Sample type * 1 Vesicular fluid, epithelial tags Required or Optional R (if present) Tests employed * 2 Ag ELISA Serum R SP Ab ELISA NSP Ab ELISA OP fluid O Herd Size (single management group and species) Other management groups/species on a Suspect Infected Place, without clinical signs Animals with clinical signs Epithelium (not directly related to a vesicle) O (if animals culled at the visit) Serum R PrioCheck In series with * 1 Take 2 serum tubes per animal sampled. OP = oropharyngeal. * 2 All sample sizes calculated for 95% confidence of detecting 1 infected animal. Serum sample size based on SP ELISA with test parameters of Se 96.4% and Sp prevalence of antibody-positive animals assumed in a clinically-affected herd, or serial interpretation of PrioCheck 5% prevalence. Serum sample size also accurate for on serum calculated with test parameters of Sp 100% and Se 5% prevalence. Vesicular fluid sample size based on test parameters of Sp 100% and Se 50% prevalence of FMD-infected animals within those with vesicular lesions. OP fluid and epithelium calculated for an assumed prevalence of 30% FMD-infected animals within clinically-affected animals. For rationale on these assumptions, please refer to the main body of text. 8

8 Table 3: Sample sizes per farm required in Proof of Freedom stage. Purpose of visit Sample type * 1 Required or Optional Tests employed * 2 Freedom from Serum R PrioCheck disease surveillance In series with property Herd Size (single management group and species) Freedom from disease surveillance property Serum R Idexx In series with N/A * Follow-up visit to property with positive Ab-ELISA results OP fluid or Throat, nasal or oral swabs O 15 * * 1 Only 1 serum tube required per animal sampled. OP = oropharyngeal. * 2 Serum for 5% prevalence for proof of freedom with 1) PrioCheck NSPp + SP ELISA serial sensitivity of 96.4% and serial specificity of 100%, 2) Idexx NSP + SP ELISA serial sensitivity of 89.3% and serial specificity of 100%. OP fluid or swabs to detect virus carriers at minimum prevalence of 15% (carrier rates 15-50%) with s in parallel or series (combined se 95%, 99.94%; sp 100%, 99.8% respectively). * 3 Use Idexx and PrioCheck NSP ELISAs in parallel before SP ELISA in series, or use PrioCheck NSP in series with SP ELISA, to provide necessary sensitivity this is not attainable in small herds from the screening use of Idexx NSP ELISA. Take samples from all animals in herd of up to 40 animals. * 4 use s in parallel for necessary sensitivity or take 20 samples. 9

9 So how would this work practically? One submission form to rule them all... The purpose of the visit to the property (risk status) is prescribed already by the Planning and Intelligence Team on the laboratory submission form, which also serves as the sampling guidelines for the veterinarian. The veterinarian then assesses whether clinical signs are present or absent on the farm. The sampling guidelines from the tables are presented as a flowchart (separated into clinical signs present or absent) on the pre-specified laboratory submission form, enabling the field veterinarian to easily determine the appropriate samples to take for a particular farm. The same submission form identifies for the Animal Health Laboratory which of the preestablished testing algorithms the samples should follow (by identifying testing stream 1-4), and their priority. The results are reported back, along with the pre-specified farm details through a Diagnostic Interpretation role in the Planning and Intelligence Team, who assess the diagnostic results in context of the farm's epidemiology (including risk status). 10

10 Testing streams 1-4 for Testing Algorithms Purpose of visit Property status Property in Protection Zone * 1 Tests employed, in order of use Testing algorithm order (negative farms proceed past first algorithm) Agent detection priority 1 Serology priority 2 Testing stream 1 At-Risk Place* 2 (<3 days post-exposure) Agent detection only 2 At-Risk Place (4-7 days post-exposure) Agent detection priority 1 Serology priority 2 1 At-Risk Place (>7 days post-exposure) Serology priority 1 Agent detection priority 2 3 End of surveillance period (Protection Zone or At-Risk Place) Confirmatory testing for herds with clinical signs (Suspect Infected Places) * 3 SP Ab ELISA NSP Ab ELISA Serology priority 1 Agent detection priority 2 Serology priority 1 Agent detection priority Other management groups/species on a Suspect Infected Place, without clinical signs PrioCheck In series with Serology priority 1 (but alternate testing algorithm) Agent detection priority 2 4 All sample types other than serum Agent detection only 2 * 1 Protection Zone: within approximately 3km of any Infected Place. * 2 - At-Risk Place: Determined by Intelligence and Planning Team to be at-risk of infection because of tracing, spatial proximity or air-borne spread. * 3 Testing other species of animal (Deer, Sheep, Goats, Camelids, Buffalo) in herds without sentinel species present (which are regarded as cattle and pigs, where clinical signs are typically more overtly displayed). Tests are not validated for these other species. 11

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15 Further work which has used these testing protocols as a base Report on Expected Laboratory Testing Workload in a Foot and Mouth Disease Outbreak in New Zealand, March Professor Roger S Morris, Dr Masako Wada, Bryan O Leary, Dr Kylee Walker, Professor John Wilesmith Projected sample numbers to inform the business case for the sizing of New Zealand's new National Biocontainment Laboratory. Cumulative Outbreak Graphs for Enhanced Risk Model in South Auckland 16

16 Further work to do Establish prioritisation system for which farms' samples to test based on what resources we have. This requires knowledge of the capacity of the laboratory (current and future), which has now been done. Establishing how samples will come into specimen reception and proceed into the appropriate testing algorithm. This is underway now with templates for the laboratory information management system being written, and logistics being worked out. A vaccination policy is under discussion now in New Zealand, if this is implemented, will need to adapt the protocols for DIVA testing. Also as additional tests become available, creating an active system for incorporating them and adapting the protocols. Problems Establishing a practical system for this process to work. The current software we use doesn't support it and a paper-based system would be difficult to maintain. In the event of an outbreak in New Zealand, it is likely that one of the two main islands would be affected predominantly. This means that establishing compartment freedom for one island to resume trade would be a priority along with controlling the epidemic in the other island. In this instance, the sample collection and testing resources required for compartment proof-of-freedom and epidemic control may be demanded simultaneously. 17

17 Acknowledgements In particular, Dr Richard Clough at MPI AHL IDC Wallaceville for the details of the available diagnostics, and the validation work done on them, and helping formulate and adapt the testing algorithms. The scientists at MPI Animal Health Laboratory IDC Wallaceville, in particular the other members of the AHL FMD Preparedness Planning Group, for example Reinhold Kittelberger who is here today, for accommodating this strategy and helping make it achievable! My manager and team of Surveillance and Incursion Investigation (Animals and Marine) at MPI IDC Wallaceville for support and advice. 18