Development of a chromatographic strip assay for detection of porcine antibodies to 3ABC non-structural protein of foot-and-mouth disease virus serotype O.

A chromatographic strip assay was developed for rapid detection of serum antibodies to non-structural protein of foot-and-mouth disease virus. The assay was based on Escherichia coli-expressed 3ABC non-structural protein and an immunochromatographic technique, which shortened the detection time to about one hour. The sensitivity of the assay was determined to be 96.8% for infected pigs; its specificity was 100% for naïve pigs and 98.8% for vaccinated pigs. In the experimentally infected pigs, anti-3ABC antibodies were detectable from eight days post-infection until the end of the study, 34 days post-infection. The performance of this assay was comparable to that of two commercial ELISA kits, Ceditest FMDV-NS and UBI FMDV NS EIA, and was better than that of CHEKIT FMD-3ABC po. Given its advantages of instant testing and quantitative measurement, this assay has potential as a useful tool for rapid on-farm diagnosis of foot-and-mouth disease.

Genetic variation in open reading frame 5 gene of porcine reproductive and respiratory syndrome virus in Taiwan.

In an effort to understand the genetic variation in porcine reproductive and respiratory syndrome virus (PRRSV) isolates in Taiwan, 40 isolates obtained between 2004 and 2006 were analyzed for their sequences of open reading frame 5. After reverse transcription polymerase chain reaction, the amplified open reading frame 5 fragments were analyzed by restriction fragment length polymorphism and sequence comparison. The results showed that all the Taiwanese isolates belonged to the North American genotype. Multiple patterns obtained from restriction fragment length polymorphism, 83-99% nucleotide similarity and 84-99% deduced amino acid similarity suggested a high level of genetic variation and PRRSV was not a single invasion to Taiwan. Moreover, vaccine-like isolates were isolated from the field, implying that some field isolates might originate from vaccine virus.

Rapid detection and differentiation of wild-type and three attenuated lapinized vaccine strains of classical swine fever virus by reverse transcription polymerase chain reaction.

A simple one-step reverse transcription polymerase chain reaction (RT-PCR) method was developed based on T-rich insertions in the viral genome for simultaneous detection and differentiation of wild type and vaccine strains of Classical swine fever virus (CSFV). The CSFV-specific primers were designed to contain the sequences of the T-rich insertion sites that exist uniquely in the 3' nontranslated regions (3' NTR) of the genome of lapinized CSFV vaccine strains. By using a one-step RT-PCR or a nested PCR followed by an agarose gel electrophoresis or a multicapillary electrophoresis, the wild-type and lapinized vaccine strains of CSFV in clinical samples could be detected and accurately distinguished. These assays can be applied to at least 3 attenuated lapinized vaccine strains, lapinized Philippines Coronel (LPC), hog cholera lapinized virus (HCLV), and Chinese strain (C strain). The detection limit of the wild-type virus was 6.3 TCID(50) (50% tissue culture infective dose)/ml for RT-PCR and 0.63 TCID(50)/ml for nested PCR. In previous studies, notable T-rich insertions of 12-13 nucleotides (nt) were found in the 3' NTR of the genome of lapinized vaccine strains of CSFV. However, this study discovered that 2 T-rich insertions, 42 and 36 nt in length, are present in the viral genome of lapinized vaccine strains LPC/PRK (primary rabbit kidney) and LPC/TS (Tam-Sui), respectively. These T-rich insertions of 12, 36, and 42 nt length increases the size of PCR fragments, which are favorable genetic markers for rapid detection of and differentiation between wild-type and different lapinized vaccine strains of CSFV.