Application of recombinant nucleocapsid protein-immunofluorescence assay (IFA) in hospital-based serological surveillance of rift valley fever in humans.
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Date
2025
Authors
Mwansa, Peter Chibale
Journal Title
Journal ISSN
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Publisher
The University of Zambia
Abstract
Rift Valley fever (RVF) is a mosquito-borne viral zoonosis caused by the Rift Valley fever virus (RVFV), a negative-sense RNA virus belonging to the genus Phlebovirus in the family Phenuiviridae. Transmission to humans and animals occurs through mosquito bites (Culex and Aedes spp.), direct contact with infected animal blood or organs, ingestion of contaminated animal byproducts, or inhalation of aerosols from infected animals. In this study, analysis of human serum was conducted at the Virology Laboratory at the University of Zambia in Lusaka. Human serum samples were screened using a locally prepared recombinant Nucleocapsid-based Immunofluorescence Assay (IFA), where Vero E6 cells were transfected with a plasmid encoding the RVFV N gene and cultured on glass slides to express the recombinant protein. After incubation, the cells were fixed, preserved,
and stored for later use. The commercial ID Screen® Rift Valley Fever Competition Multi-species enzyme-linked immunosorbent assay (ELISA) was used as confirmatory test; the tests were analysed according to the manufacturer’s guidelines. From previous studies a prevalence of 9.43% of RVF
antibodies was recorded in Lusaka abattoir workers dealing with cattle, while in Mazabuka district 18.63% tested were sero-positive of RVFV antibodies. However, Zambia has not recorded an outbreak of RVF for over 30 years. The current sero-prevalence and risk factors associated with
RVFV in human populations is not known. This study utilized convenience sampling, obtaining archived human serum samples from selected hospitals. Sample selection was based on availability, patient records, and storage conditions at -30°C. A total of 593 archived human serum samples were
analysed, revealing an overall seroprevalence of 1.7% (10/593) on both IFA and ELISA. Lukulu District Hospital had the highest prevalence 0.84% (5/593); Choma General Hospital and Kanyama Hospital both had 0.34% (2/593), while Kalabo had the lowest 0.17% (1/593). Occupation was
significantly associated with RVF seropositivity (p = 0.000), with farmers accounting for 1.35% (8/593) of cases. The highest seroprevalence was among farmers, individuals from Western Province, and patients attending Lukulu District Hospital. The aim of the study focused on the application of the Recombinant Nucleocapsid Protein (rNP) - IFA for hospital-based serological surveillance of RVFV in humans. IFA was successfully applied for the detection of RVF-specific antibodies in human serum samples, demonstrating high sensitivity and specificity in identifying seropositive cases. These findings highlight the potential of IFA as a valuable method for hospitalbased surveillance for further development of rapid, point-of-care diagnostic tests based on the recombinant RVFV Nucleocapsid protein (NP) could improve early detection in rural or resourcelimited areas.
Description
Thesis of Master of Science in One Health Laboratory Diagnostic Sciences.