Pathogenic characterization of porcine reproductive and respiratory syndrome virus of Indian origin in experimentally infected piglets

Porcine reproductive and respiratory syndrome (PRRS) is an economically important transboundary viral disease of pigs confronting the swine industry worldwide. This study was aimed to assess the pathogenic potential of PRRS virus belonging to genotype 2 that emerged in India in 2013. Nine 6-week-old piglets were inoculated intranasally with 2 × 10^5.75  TCID₅₀ /ml of PRRSV (Ind-297221/2013). Three piglets were kept as uninfected controls. Blood and nasal swabs were collected daily up to 7 days post-infection (dpi) and on alternate days subsequently. Piglets were necropsied for tissue sample collection either on death or after euthanasia on 7, 14 or 21 dpi (one uninfected control and three PRRSV-infected piglets per interval). The virus caused high fever, typical blue ear, weight loss, respiratory distress, diarrhoea and leucopenia between 2 and 8 dpi. Two infected piglets died (on 3 and 17 dpi) during the course of study. The presence of virus in serum and nasal secretion was observed up to 19 and 17 dpi, respectively, with the maximum load between 4 and 7 dpi. Seroconversion started 6 dpi and the mean PRRSV antibody titre reached up to 640 by 21 dpi. Virus load was highest in tonsils at all the intervals, whereas in spleen and lymph nodes load was higher in later intervals. Major microscopic lesions in PRRSV-infected piglets included moderate to severe interstitial pneumonia, lymphoid depletion in tonsils and lymph nodes (cystic), thymic atrophy, reactive hyperplasia followed by lymphoid depletion in spleen. PRRSV antigen was consistently demonstrated by immunoperoxidase test in the lungs, spleen, tonsils and lymph nodes. Antigen distribution was more widespread on 7 and 14 dpi than on 21 dpi. The findings establish that the Indian PRRSV is highly pathogenic to piglets.

Expression and purification of recombinant H5HA1 protein of H5N1 avian influenza virus in E. coli and its application in indirect ELISA

The PCR amplified HA1 fragment of H5N1 (H5HA1) avian influenza virus (AIV) hemagglutinin gene was cloned into pET28a (+) expression vector and expressed in Rosetta Blue (DE3) pLysS cells. The recombinant H5HA1 (rH5HA1) protein purified by passive gel elution after SDS-PAGE of the inclusion bodies reacted specifically with H5N1 serum in Western blot analysis. A subtype specific indirect enzyme linked immunosorbent assay (iELISA) using the rH5HA1 protein as the coating antigen was developed for detecting antibodies to H5 subtype of AIV. The assay had 89.04% sensitivity and 95.95% specificity when compared with haemagglutination inhibition test. The Kappa value of 0.842 indicated a perfect agreement between the tests. The iELISA developed can be used for serosurveillance of avian influenza in chickens.

Small interfering RNAs targeting viral structural envelope protein genes and the 5ʹ-UTR inhibit replication of bovine viral diarrhea virus in MDBK cells

Bovine viral diarrhea viruses (BVDVs) are important pathogens of cattle that occur worldwide, and for which no antiviral therapy is available. In the present study, the inhibitory effect of small interfering (si) RNAs on bovine viral diarrhea virus 1 (BVDV-1) replication in cultured bovine cells was explored. Four synthetic siRNAs were designed to target structural envelope region genes (Erns, E1, and E2) and one cocktail of siRNA was generated to target the 5ʹ-UTR of the BVDV-1 genome. The inhibitory effects of siRNAs were assessed by determination of infectious viral titer, viral antigen and viral RNA. The siRNA cocktail and three of the synthetic siRNAs produced moderate anti-BVDV-1 effect in vitro as shown by 25%-40% reduction in BVDV-1 antigen production, 7.9-19.9-fold reduction in viral titer and 21-48-fold reduction in BVDV-1 RNA copy number. Our findings suggest that siRNA cocktail targeted at the 5ʹ-UTR is a stronger inhibitor of BVDV-1 replication and the targets for siRNA inhibition can be extended to BVDV-1 structural envelope protein genes.

Genetic and antigenic characterization of bovine viral diarrhoea virus type 2 isolated from cattle in India

Previous studies have shown that bovine viral diarrhoea virus type 1 (BVDV-1) subtype b is predominantly circulating in Indian cattle. During testing for exotic pestiviruses between 2007 and 2010, BVDV-2 was identified by real time RT-PCR in two of 1446 cattle blood samples originating from thirteen states of India. The genetic analysis of the isolated virus in 5' UTR, N(pro), entire structural genes (C, E(rns), E1 and E2), nonstructural genes NS2-3 besides 3' UTR demonstrated that the nucleotide and amino acid sequences showed highest similarity with BVDV-2. The entire 5' and 3' UTR consisted of 387 and 204 nucleotides, respectively, and an eight nucleotide repeat motif was found twice within the variable part of 3' UTR that may be considered as a characteristic of BVDV-2. The phylogenetic analysis revealed that the cattle isolate and earlier reported goat BVDV-2 isolate fall into separate clades within BVDV-2a subtype. Antigenic typing with monoclonal antibodies verified the cattle isolate also as BVDV-2. In addition, cross-neutralization tests using antisera raised against Indian BVDV strains circulating in ruminants (cattle, sheep, goat and yak) displayed significant antigenic differences only between BVDV-1 and BVDV-2 strains. This is the first identification of BVDV-2 in Indian cattle that may have important implications for immunization strategies and molecular epidemiology of BVD.