Large-Scale International Validation of an Indirect ELISA Based on Recombinant Nucleocapsid Protein of Rift Valley Fever Virus for the Detection of IgG Antibody in Domestic Ruminants

Development of a luminex-based assay for the detection of anti-capripoxvirus and rift valley fever virus antibodies in domestic ruminants

The three members of the genus capripoxvirus (CaPV), lumpy skin disease virus (LSDV), sheeppox virus (SPPV), and goatpox virus (GTPV) have common hosts and areas of overlapping geographical distribution with Rift Valley fever virus (RVFV). Hence, to ensure more cost-effective disease surveillance we developed and evaluated a Luminex assay for the simultaneous detection of antibodies against CaPV and RVFV in domestic ruminants. In cattle, the assay had a sensitivity (Se) of 98.7% and a specificity (Sp) of 98.3% in detecting anti-LSDV antibodies; both diagnostic parameters were 100% for the detection of anti-RVFV antibodies in this species. In sheep and goats, Se and Sp were 100% for the detection of anti-SPPV and anti-GTPV antibodies while they were 100% and 98.9%, respectively for the detection of anti-RVFV antibody. The assay did not cross react with anti-parapoxvirus antibodies of cattle, sheep, and goats. This multiplex serological assay offers a practical tool for accurate detection and monitoring of the immunological status of domestic ruminant populations against veterinary and socio-economically important capripox- and phleboviral infections, thus has the potential to aid in the strategic application of vaccination programmes.

Evaluation of commercial ELISA kits' diagnostic specificity for FAST diseases in wild animals

Wild animals, sharing pathogens with domestic animals, play a crucial role in the epidemiology of infectious diseases. Sampling from wild animals poses significant challenges, yet it is vital for inclusion in disease surveillance and monitoring programmes. Often, mass surveillance involves serological screenings using enzyme-linked immunosorbent assay (ELISA) tests, typically validated only for domestic animals. This study assessed the diagnostic specificity of commercially available ELISA tests on 342 wild ruminant serum samples and 100 from wild boars. We evaluated three tests for foot-and-mouth disease: two for Peste des petits ruminants, two for Rift Valley fever and one for Capripox virus. Diagnostic specificity was calculated using the formula True Negative/(False Positive + True Negative). Cohen's kappa coefficient measured agreement between tests. Results showed high specificity and agreement across all tests. Specificity for foot-and-mouth disease (FMD) ranged from 93.89% for Prionics to 100% for IDEXX, with IDvet showing 99.6%. The highest agreement was between FMD IDvet and IDEXX at 97.1%. Rift Valley fever (RVF) tests, Ingezim and IDvet, achieved specificities of 100% and 98.83%, respectively. The optimal specificity was attained by retesting single reactors and inactivating the complement.Contribution: Commercially available ELISA kits are specific for foot-and-mouth disease and similar transboundary animal diseases and can be used for highly specific wild animal testing.

Cloning and phylogenetic analysis of N protein gene from Rift Valley Fever Virus (RVFV)

Rift Valley Fever (RVF) is a mosquito-borne viral zoonosis caused by RVFV in humans and livestock. Currently, there are no approved vaccines or antiviral therapies available. Additionally, in Saudi Arabia, there is a lack of a routine screening system to monitor RVFV in humans and animals which hinders to design and develop the preventive measures as well as the prediction of future outbreaks and the potential re-emergence of RVFV. Hence, we have performed the cloning, sequencing, and phylogenetic analysis, of nucleocapsid (N) protein gene. The sequence analysis showed high similarities with RVFV isolates reported from humans and animals. The highest similarity (99.5%) was observed with an isolate from Saudi Arabia (KU978775-Human) followed by 99.1% with four RVFV isolates (Human and Bovine) from other locations. A total of 51 nucleotides and 31 amino acid variations were observed throughout the N protein gene sequences. The phylogenetic relationship formed closed clusters with other isolates collected from Saudi Arabia. Thus, we report of the cloning, sequencing, and phylogenetic analysis of the RVFV-N protein gene from Saudi Arabia.