4.2 Collection of sera/specimens for validation of DIVA tests for detection of animals received from SAT virus infection

had occurred in associated feedlots, could provide useful indicators of the prevalence to expect in vaccinated herds in Europe exposed to infection but where no clinical signs are observed. However, since only two farms were studied where no FMD signs had been observed, the number of observations were seen as inadequate.

Recommendation

Further data on intra-herd prevalence in vaccinated herds exposed to infection is needed, and therefore it was recommended that similar studies should be conducted if further opportunities arise, especially in the context of emergency vaccination.

4.2 Collection of sera/specimens for validation of DIVA tests for detection of animals received from SAT virus infections

The context of the study (Reported in Appendix 17) was provided by Donal Sammin; following the Gerzensee (2003) and Çesme (2002) Sessions, to address the lack of suitable sera for validation of NSP tests for detection of antibodies to SAT viruses, the opportunity had arisen to utilize field exposure in Zimbabwe and a contract had been developed with the Zimbabwean authorities. Funding was agreed with the EC (DG-SANCO) through the EUFMD/EC Trust Fund. Together with David Paton, a report was presented on the activities and results, which had been successful in meeting almost all of the objectives; sera had been collected from a high number of animals subsequently shown to be persistently infected with SAT1 or SAT2 virus, and therefore this enabled evaluation of indirect tests including NSP tests, as markers of infection. The results demonstrated that NSP tests have the expected sensitivity for SAT1 and SAT2 and give confidence to the use of NSP tests for these types and therefore do not support inferences from some earlier field studies that NSP tests for SAT infections have a lower sensitivity. In addition, a unique dataset of test results has been obtained on performance of tests which will assist selection of diagnostic tests for detection of carriers.

Dr Paton highlighted the value of the study for collection of samples for validation purposes and cautioned that the herd vaccination/infection status could not be considered similar to vaccination and infection status expected under disease management scenarios in Europe.

He concluded:

1. The study provided useful data on the prevalence of SAT 1 and 2 virus carriers in cattle herds 1-5 months after FMDV infection and on their ease of detection by different virological and serological methods. 2. Virological tests on nasopharyngeal brush swabs scored very few cattle as infected compared to the conventional approach of testing samples obtained with a probang sampling cup. 3. Routine RT-PCR was equivalent to, and optimised RT-PCR more sensitive than, virus isolation for the detection of SAT 1 and SAT 2 FMDV in probang cup samples. 4. SPCE and NSPE tests readily detected animals that had been infected with SAT 1 and SAT 2 FMD viruses. 5. Sensitivity estimates of NSPE for detection of FMDV carriers (75-90%) were very similar to those obtained with experimental sera during the NSPE workshop in Brescia in May 2004. By comparison, the VNT could detect all carriers. 6. Since none of the herds from which virological data were available had been optimally vaccinated and since clinical disease was obvious, the study provides limited insight into the prevalence of carriers likely following subclinical infection in well vaccinated herds.

He recommended that:

1. Final conclusions should wait until the results of all tests, such as antibody detection tests on saliva samples, use of RT-PCR internal standards and completion of data analysis. 2. It would be useful to conduct similar exercises involving herds with a more certain vaccination status and following use of emergency vaccination in a previously disease-free region, and also in areas where disease has occurred in vaccinated pigs and sheep.

Dr De Clercq congratulated those involved and expressed gratitude on behalf of the RG for the valuable samples collected and the results obtained.

Recommendations

1. A further presentation to the group be made after all tests have been completed, which should also provide guidance on use of single or parallel tests for detection of carriers.