Rift Valley Fever Virus: An Overview of the Current Status of Diagnostics

Abstract

Rift Valley fever is a vector-borne zoonotic disease caused by the Rift Valley fever virus (Phlebovirus genus) listed among the eight pathogens included in the Bluepoint list by the WHO. The transmission is mainly vehicled by Aedes and Culex mosquito species. Symptoms of the disease are varied and non-specific, making clinical diagnosis often challenging, especially in the early stages. Due to the difficulty in distinguishing Rift Valley fever from other viral hemorrhagic fevers, as well as many other diseases that cause fever, an early diagnosis of the infection is important to limit its spread and to provide appropriate care to patients. To date, there is no validated point-of-care diagnostic tool. The virus can only be detected in the blood for a brief period, suggesting that molecular methods alone are not sufficient for case determination. For this, it is preferable to combine both molecular and serological tests. The wide distribution of competent vectors in non-endemic areas, together with global climate change, elicit the spread of RVFV to continents other than Africa, making surveillance activities vital to prevent or to limit the impact of human outbreaks and for a rapid identification of positive cases, making diagnosis a key factor for this achievement.

Keywords: Rift Valley fever virus; early diagnosis; molecular diagnostics; serology.

Figure 1

RVFV structure and genome organization. (A) Enveloped RVFV virion comprises nucleoprotein (N) and envelope glycoproteins (Gn and Gc). Viral polymerase (L) and N proteins are associated with the viral genomic segments (RNA, negative or ambisense polarity). (B) Schematic representation of RVFV genome organization. The L segment encodes the viral RNA polymerase; the M segment encodes NSm, Gc, and Gn proteins; and the S segment encodes the N protein and NSs protein (ambisense polarity). Created with Biorender.com.

Figure 2

Epidemiological transmission cycles of RVFV. Created with Biorender.com.

Figure 3

RVF distribution map. Created with Biorender.com.

Figure 4

Viral neutralization assay. Serum to be tested is serially diluted and incubated with a defined quantity of viral particles (1). The virus-serum solutions are added to Vero or BHK cells (2) and incubated for 3/5 days at 37 °C in a humidified atmosphere with 5% CO₂. Finally, the cytopathic effect of viral infection is evaluated through microscopic observation (3). Created with Biorender.com.

Figure 5

Schematic representation of RVFV isolation. The blood or serum sample is collected from infected hosts (1) and inoculated in cell culture (2). After incubation at 28 °C (AP61 cells) or 37 °C (Vero and BHK cells) for 1 h (3), cell monolayers are washed with PBS and fresh medium is added (4). Virus isolation is validated by RT-PCR analysis (5). Created with Biorender.com.