Evaluation of laboratory tests for sat serotypes of foot‐and‐mouth disease virus with specimens collected from convalescent cattle in Zimbabwe

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.

Development and Evaluation of an Indirect Enzyme-Linked Immunosorbent Assay for Detection of Foot-and-Mouth Disease Virus Nonstructural Protein Antibody using a Chemically Synthesized 2B Peptide as Antigen

“…All of the NSP tests detected more positive reactors in herds A, B, and C than herds D and E. It appears from this that for optimal sensitivity, serosurveillance should be done within 2 months of an outbreak, as late serosurveillance as in herds D and E reduced the efficiency of detection of NSP antibody. The 2B test also detected the highest number (93.3%) of virus carrier animals confirmed by virus isolation and RT-PCR, 14 which is not significantly different (P . 0.05) from the performance of the Cedi test.…”

“…Field sera Four hundred and one sera collected from FMD affected cattle herds in Zimbabwe 14 were analyzed by the 2B ELISA to compare the rate of seroconversion in a field situation between this test and 4 commercial assays 14 i.e., Cedi, …”

“…It was prepared from O1K FMDV infected BHK-21 cells, as previously described. 10 UBI, c, 16 and Svanova d,1 ) used in a previous study 14 were compared to the current results of 2B ELISA using the same field sera. Three tests detect antibodies to viral nonstructural poly peptide 3ABC whereas the UBI test detects antibody to a 3B synthetic peptide.…”

“…8,17 Recently a number of in-house and commercial tests have been developed and evaluated to identify infection in vaccinated livestock, including the presence of viral carrier animals. Use of these tests in experimental vaccinated animals as well as animals from the field 1,12,14 failed to provide a categorical assurance of detecting infection; therefore, there is still a need to develop and validate more sensitive and specific tests that could be used either in their own right, or as the screening or confirmatory method alongside existing NSP tests. The potential for use of a 2B synthetic peptide ELISA for the detection of NSP antibodies in infected animals from an experi-mental vaccine challenge study 12 encouraged us to check the use of other NSP peptides as well as this 2B peptide with further field and experimental samples.…”

Development of a Peptide-Based Immunochromatographic Strip for Differentiation of Serotype OFoot-and-Mouth Disease Virus—Infected Pigs from Vaccinated Pigs

“…2,3,11 Recently, a number of in-house and commercial tests to identify infection within vaccinated livestock (i.e., the presence of viral carrier animals) were developed and evaluated. 4,10,12 These methods are theoretically based on the assumption that semi-purified, inactivated FMDV vaccines mainly consist of capsid (structural) proteins, and so they are less likely to elicit production of antibodies against nonstructural proteins (NSP). An antibody response against NSPs is only related to in vivo virus activity.…”