No abstract

The technique of RT-PCR and restriction enzyme analysis was standardized to detect and differentiate Newcastle disease viruses. Digestion of RT-PCR-amplified, F gene sequences encoding for the cleavage activation sites of fusion protein with restriction enzymes AluI, BglI, HaeIII, HinfI, HhaI, RsaI, StyI and TaqI was carried out in order to characterize Newcastle disease viruses of varying pathogenicity. Restriction enzyme digestion of the amplicons by BglI and HhaI could group eight viruses, both field isolates and known vaccine strains, into lentogenic, mesogenic and velogenic pathotypes. By employing this technique directly on a clinical sample, Newcastle disease virus of the lentogenic pathotype could be detected.

The polymorphism of the major histocompatibility complex (MHC) class II DRB gene of riverine buffalo (Bubalus bubalis) was studied. Second exon sequences from the buffalo DRB locus, homologous to the cattle DRB3 gene, were amplified and characterized. A combination of single strand conformation polymorphism (SSCP) and heteroduplex analysis (HA) in a non-denaturing gel was used to identify new DRB second exon sequences. SSCP, HA and finally sequencing allowed the identification of 22 MHC-DRB exon 2 alleles from 25 unrelated Indian river buffalo. These are the first river buffalo DRB second exon sequences reported. A high degree of polymorphism in the sequences encoding the peptide binding regions was observed and some amino acid substitutions were found unique to the river buffalo.

Attempts have been made to characterize infectious bursal disease virus (IBDV) isolates collected from different parts of India during 1993 to 1999. Phylogenetic analysis was performed on a sequence generated by cycle sequencing comprising the variable region of the VP2 gene of 14 isolates. Indian IBDV isolates had divergence of 0.2 to 4.3% at nucleotide and 0 to 2.2% at amino acid levels among themselves. Nine nucleotide changes were found in Indian IBDV field isolates, resulting in the four specific amino acid changes at 222P-A, 256V-I, 294L-I and 299N-S, reported regularly in very virulent isolates. One of the Indian IBDV isolates, UP1/99, had change D to N at position 212 in the first hydrophilic region. The serine-rich heptapeptide sequence 'SWSASGS' was conserved in all the isolates. Phylogenetically, all Indian field isolates were found to be closely related to very virulent IBDV isolates from Europe, Japan, China and Israel.

The RT-PCR technique was adopted to amplify variable region of VP2 gene of infectious bursal disease virus using three different sets of primers. These primers could generate products of 643, 474 and 552 bp sizes. The authenticity of the amplicons was confirmed by their size in agarose gel, restriction enzyme digestion and by nested PCR. Out of total five clinical samples tested, IBD viral genomic RNA could be detected in four by RT-PCR. Restriction enzyme digestion of PCR products with StuI could differentiate clinical samples from an intermediate vaccine strain currently being used in India.