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Appendixes

Archive: 1999 Session - Appendix 10

1999 Session of the Research Group of the Standing Technical Committee of EuFMD

 

Serosurveillance for Foot-and-Mouth Disease in Bulgaria (1998)

Yanko Ivanov, Georgi Georgiev, Emilia Veleva

Introduction

The European Commission for FMD was established in 1954 to coordinate the measures for control of the disease in the European countries. At that time the FMD was endemic in many countries in Europe and the general agreement was that due to the high contagiosity of the disease the control was not possible only by national programmes and the coordination of different national measures was essential.

The first step was to reduce the spread of the disease by encouraging all European countries to carry out mass annual vaccinations and in case of outbreaks to slaughter the infected and contact animals.

Most of the countries applied that vaccination/stamping out policy and as a result in the eighties the total number of FMD outbreaks was considerably reduced. Between 1980 and 1990 the mass annual vaccinations in Europe were progressively replaced by zonal and frontier vaccinations. Vaccinations ceased in 1990.

The area known as Thrace, i.e. Turkey west of the Marmara Sea and the adjoining parts of Southern Bulgaria and north-east Greece which has always been of strategic importance in preventing incursions of FMD from the Middle East and South Asia, was the vaccination buffer zone for Europe. The vaccines were supplied by FAO. Vaccinations in Thrace ceased in 1991 when the buffer zone was moved to the Asiatic part of Turkey.

Although the European part of Turkey is considered free of FMD, it is influenced significantly by the epidemiological situation of its Asiatic part which is endemic.

As a result several outbreaks occurred after 1990 in Thrace caused by Middle East FMD virus strains: Bulgaria (1991, 1993, 1996), Greece (1994, 1996), Turkey (1995, 1996). The Turkish veterinary authorities decided to return to vaccination against FMD in Thrace which made the situation in the region more complicated because of the lack of coordination of national measures at regional level.

It is obvious from the above that Turkish Thrace is no more an FMD free area and should be considered a zone of virus migration.

The Bulgarian veterinary legislation concerning the FMD control is based on Directive 85/511/ECC. The Directive requires stamping out of the infected and contact herds whenever outbreaks occur, and establishing of protection zones of 3 km radius around the infected premises, as well as surveillance zones of 10 km radius.

Taking into consideration the potential risk of transboundary spread of FMD from Turkey into Bulgaria in accordance with Directive 85/511/ECC, a 10 km surveillance zone was established in Bulgaria all along the 345 km border line with Turkey.

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Materials and methods

Three of all 28 districts in Bulgaria are bordering Turkey (Burgas, Yambol and Haskovo). There are 42 villages in the 10 km surveillance border zone (Burgas - 15; Yambol - 11; Haskovo - 16).
Blood samples were taken regularly from never vaccinated small ruminants born by non-vaccinated dams with an interval of 21 days from March to November when animals are grazing. The period also coincides with mating and migration of wild animals. The method of sampling was based on calculations that if FMD was introduced in Bulgaria at least 5% of the sheep and goat flocks would have been exposed to the infection and at least 10% of the animals in those flocks would have antibodies to the virus that could be detected by liquid phase blocking ELISA.
The samples were of sufficient size as to provide a 95% confidence that the disease was not present at that prevalence in case of negative results. Serum samples were checked for O1A22 FMD antibodies by liquid phase blocking ELISA [1]. Titres over 1:40 were considered positive.

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Results and Discussion

In 1998 a total of 19 188 samples from 282 sheep/goat flocks within the 10 km surveillance border zone were tested. 54 of all 19 188 samples showed titres over the threshold 1:40 < 1:100. Further testing according to the study protocol clearly demonstrated that the reactions were not due to the presence of specific FMD antibodies in the sera, but to technical errors related to the change of some ELISA components or wrong pippeting and dilutions. Nevertheless, according to the requirements of the contingency plan, the flocks were isolated, clinically inspected and the animals were individually tested. The results were negative for both O1A22. Unfortunately the samples were not checked for antibodies against FMD virus non-structural proteins because of the lack of regaents.
Usually when seropositive animals are established the first questions to be answered by laboratories are: could it be a technical error, what is the titre of the antibodies and against which serotype.
Previous FAO collaborative studies for standardisation of FMD antibody detection demonstrated wide variation between laboratories in the interpretation of reference sera as positive or negative for antibody to FMD virus in spite of the usage of uniform reagents, assays and protocols.

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Recommendations

Having in mind that:

  • Thrace is a region of FMD virus migration;

  • strains other than O1A22 could migrate as well;

  • Turkey is carrying out vaccination while Bulgaria and Greece are not;

  • FMD control requires international collaboration and regional approach;

and with view of the improvement of the measures for efficient FMD control at regional level, the following recommendations may be suggested:
1. The former vaccination buffer zone in Thrace should become a serosurveillance zone.
2. Samples from small ruminants should be taken for serosurveillance by Turkey, Greece and Bulgaria simultaneously and checked for antibodies against FMD virus non-structural proteins in their national laboratories.
3. The samples should be of sufficient size as to provide 95% confidence level.
4. The three countries should use standard ELISA reagents and a protocol for carrying out the tests. 5. The samples showing titres above the threshold should be sent to the WRL for further testing.
6. The WRL should test the samples with priority and inform the three countries about the results.
7. EuFMD commission should organise and coordinate the serosurveillance programme in Thrace.

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