Rift Valley Fever

Most infected individuals remain asymptomatic or develop a mild form of the disease, consisting of fever, muscle and joint pain, weakness, backache, and headache. The clinical picture may resemble meningitis with neck stiffness photophobia, anorexia, and vomiting. Still, symptoms may be difficult to recognize, especially if the epizootic context is unknown and diagnosis may depend on reliable laboratory techniques.

Severe illness consists of ocular disease, meningoencephalitis, and hemorrhagic fever. Ocular symptoms like blurred or decreased vision signify retinal or macular damage, that might spontaneously resolve or become permanent, leading to vision loss. Central nervous system disease manifests as an intense headache, hallucinations, confusion, seizures, lethargy, and coma, with persistence of neurologic deficit, whereas hemorrhagic fever signifies liver damage and manifests as jaundice, melena, hematemesis, menorrhagia, epistaxis or other mucosal hemorrhages, purpuric rash or ecchymosis. 50% of patients with hemorrhagic fever die within one week of symptom onset. Jaundice, neurologic and hemorrhagic forms have a higher incidence of mortality [1] [2]. Central nervous system disease may be followed by permanent neurologic deficits.

Although abortion is the most prominent trait of this disease in animals, pregnant women, newborns, and small children usually are spared from this infection. The reason for this might be that they usually are not exposed to diseased animals and more efforts are made to prevent their exposure to mosquitoes; if other reasons exist, they are yet to be reported.

Rift valley fever (RVF) induces life-long immunity.

Ocular disease becomes apparent 7-21 days after infection and resolves after 10-12 weeks. Encephalitis may be suspected 1-4 weeks after initial general symptoms of the disease appear, while hemorrhages occurring much sooner i.e. 2-4 days following exposure, entail a poor prognosis.

Laboratory techniques used in order to establish the diagnosis include reverse transcriptase-polymerase chain reaction (RT-PCR) [3] [4], virus isolation in cell cultures [5], enzyme-linked immunoassay (ELISA) to detect viral antigens [6] [7], immunoglobulin IgM and IgG [8] and real-time reverse transcription-loop-mediated isothermal amplification assays (RT-LAMP) [9] [10], a new, highly specific and sensitive diagnostic test. Samples should be handled with caution and processed in specialized facilities, as they might be a bio- hazard. The virus is isolated from serum, liver, spleen or brain tissue. Rapid virus identification in severe cases is extremely important as patients need special management.

Immunological viral antigen detection methods include agar gel immunodiffusion and immunostaining on impression smears or on cryostat sections of liver, spleen, and brain, while histopathological examination reveals specific characteristics [11] [12]. Sandwich ELISA for antigen detection (sAg-ELISA) is a new technique to identify the disease and it is less dangerous to laboratory personnel [13] [14].

Antibody detection methods include hemagglutination-inhibition, complement fixation, indirect immunofluorescence which aim to prove seroconversion and virus neutralization test which is considered to be the gold standard [11] [8].

1. Laughlin L, Meegan J, Strausbaugh L. Epidemic Rift Valley fever in Egypt: Observations of the spectrum of human illness. Trans. R. Soc. Trop. Med. Hyg. 1979;73:630–633.
2. Madani T, Al-Mazrou Y, Al-Jeffri M, et al. Rift Valley fever epidemic in Saudi Arabia: Epidemiological, clinical, and laboratory characteristics. Clin. Infect. Dis. 2003;37:1084–1092.
3. Garcia S, Crance J, Billecocq A, et al. Quantitative real-time PCR detection of Rift Valley fever virus and its application to evaluation of antiviral compounds. J. Clin. Microbiol. 2001;39:4456–4461.
4. Ibrahim M, Turell M, Knauert F, Lofts R. Detection of Rift Valley fever virus in mosquitoes by RT-PCR. Mol. Cell. Probes 1997;11:49–53.
5. Anderson G, Saluzzo J, Ksiazek T, et al. Comparison of in vitro and in vivo systems for propagation of Rift Valley fever virus from clinical specimens. Res. Virol. 1989;140:129–138.
6. Meegan J, Le Guenno B, Ksiazek T, et al. Rapid diagnosis of Rift Valley fever: A comparison of methods for the direct detection of viral antigen in human sera. Res. Virol. 1989;140:59–65.
7. Niklasson B, Grandien M, Peters C, Gargan T. Detection of Rift Valley fever virus antigen by enzyme-linked immunosorbent assay. J. Clin. Microbiol. 1983;17:1026–1031.
8. Swanepoel R, Struthers J, Erasmus M, et al. Comparison of techniques for demonstrating antibodies to Rift Valley fever virus. J. Hyg. 1986;97:317–329.
9. Le Roux C, Kubo T, Grobbelaar A, van Vuren P, Weyer J, Nel L. Development and evaluation of a real-time reverse transcription-loop-mediated isothermal amplification assay for rapid detection of Rift Valley fever virus in clinical specimens. J. Clin. Microbiol. 2009;47:645–651.
10. Peyrefitte C, Boubis L, Coudrier D, et al. Real-time reverse-transcription loop-mediated isothermal amplification for rapid detection of Rift Valley fever virus. J. Clin. Microbiol. 2008;46:3653–3659.
11. Gerdes G. Rift Valley Fever. In: Manual of diagnostic yeasts and vaccines for terrestrial animals (mammals, birds and bees), Office International des Epizooties, Paris, 2004;185–194.
12. Swanepoel R, Coetzer J. Rift Valley fever. In: Coetzer J, Tustin R.C. (Eds.), Infectious diseases of livestock, Oxford University Press Southern Africa, Cape Town, 2004;1037–1070.
13. van Vuren P, Paweska J. Laboratory safe detection of nucleocapsid protein of Rift Valley fever virus in human and animal specimens by a sandwich ELISA. J. Virol. Meth. 2009;157:15–24.
14. Pepin M, Bouloy M, Bird B, Kemp A, Paweska J. Rift valley fever virus (Bunyaviridae:Ohlebovirus): an update on pathogenesis, molecular epidemiology, vectors, diagnostics and prevention. Vet Res. 2010;41(6): 61.