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Evaluation of laboratory tests for sat serotypes of foot-and-mouth disease virus with specimens collected from convalescent cattle in Zimbabwe
  1. D. J. Sammin, MVB, PhD1,
  2. D. J. Paton, MA, VetMB, PhD2,
  3. S. Parida, BVSc, MVSc, PhD2,
  4. N. P. Ferris, BA, MSc, PhD2,
  5. G. H. Hutchings2,
  6. S. M. Reid, BSc, MSc2,
  7. A. E. Shaw, BSc2,
  8. C. Holmes2,
  9. D. Gibson, BSc2,
  10. M. Corteyn2,
  11. N. J. Knowles, MPhil2,
  12. J-F. Valarcher, DVM, PhD2,
  13. P. A. Hamblin2,
  14. L. Fleming, BSc2,
  15. G. Gwaze3 and
  16. K. J. Sumption, MA, VetMB, PhD, EUFMD Secretariat1
  1. 1 Animal Health Service, FAO Headquarters, Viale Delle Terme di Caracalla, 00100 Rome, Italy
  2. 2 FAO World Reference Laboratory for FMD, Institute for Animal Health, Ash Road, Pirbright, Surrey GU24 0NF
  3. 3 Department of Veterinary Field Services and Tsetse Control, Ministry of Lands, Agriculture and Rural Resettlement, PO Box CY52, Causeway, Harare, Zimbabwe
  1. Dr Sammin's present address is CURL, Department of Agriculture and Food Laboratories, Backweston, Celbridge, County Kildare, Ireland
  2. Correspondence to Dr Paton

Abstract

During a field study in Zimbabwe, clinical specimens were collected from 403 cattle in six herds, in which the history of foot-and-mouth disease (fmd) vaccination and infection appeared to be known with some certainty. Five herds had reported outbreaks of disease one to five months previously but clinical fmd had not been observed in the sixth herd. A trivalent vaccine (South African Territories [sat] types 1, 2 and 3) had been used in some of the herds at various times either before and/or after the recent outbreaks of fmd. The primary aim of this study was to evaluate the performance of serological tests for the detection of sat-type fmd virus infection, particularly elisas for antibodies to non-structural proteins (nsps) of fmd virus and solid phase competition elisas (spces) for serotypes sat1 and sat2. Secondary aims were to examine nsp seroconversion rates in cattle that had been exposed to infection and to compare virus detection rates by virus isolation and real-time reverse transcriptase-pcr (rtrt-pcr) tests on both oesophagopharyngeal fluids and nasopharyngeal brush swabbings. In addition, the hooves of sampled animals were examined for growth arrest lines as clinical evidence of fmd convalescence. Laboratory tests provided evidence of fmd virus infection in all six herds; sat2 viruses were isolated from oesophagopharyngeal fluids collected from two herds in northern Zimbabwe, and sat1 viruses were isolated from three herds in southern Zimbabwe. Optimised rtrt-pcr was more sensitive than virus isolation at detecting fmd virus persistence and when the results of the two methods were combined for oesophagopharyngeal fluids, between 12 and 35 per cent of the cattle sampled in the convalescent herds were deemed to be carriers. In contrast, nasopharyngeal swabs yielded only two virus-positive specimens. The overall seroprevalence in the five affected herds varied with the different nsps from 56 per cent to 75 per cent, compared with 81 per cent and 91 per cent by homologous spce and virus neutralisation tests respectively. However, if serological test results were considered only for the cattle in which persistent infection with fmd virus had been demonstrated, 70 to 90 per cent scored seropositive in the different nsps.

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