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.

• Fever

  24 November 2016 Rift Valley Fever in Niger 29 September 2016 Rift Valley fever in Niger 2 August 2016 Rift Valley fever in China 1 November 2012 Rift Valley fever in Mauritania 12 May 2010 Rift Valley fever in South Africa- update 2 4 May 2010 Rift [who.int]

  Bath, Rift Valley Fever, Diseases of Sheep, (469-473), (2008). [doi.org]

  Rift Valley Fever in Niger External and unpublished WHO Situation Reports. FAO: Rift Valley Fever in Niger: Risk assessment Cdc-pdf [PDF -1.66MB] External, March 2017. [cdc.gov]

  fever virus infection had miscarriages compared with 12 (12%) of 102 women negative for Rift Valley fever virus (p INTERPRETATION: This study is the first to show an association between infection with Rift Valley fever virus and miscarriage in pregnant [ncbi.nlm.nih.gov]

• Anorexia

  The clinical picture may resemble meningitis with neck stiffness photophobia, anorexia, and vomiting. [symptoma.com]

  Nonspecific signs of fever, anorexia, weakness, lymphadenopathy, respiratory signs and hemorrhagic diarrhoea can be seen in young animals. [galvmed.org]

  In young animals, peracute disease causes anorexia, listlessness, collapse and death. Humans develop malarial-like disease. High risk individuals include farmers, veterinarians and abattoir staff. [web.archive.org]

  Clinical Signs Fever Anorexia (poor appetite) Weakness Death in young animals Abortion (may be 100% in the herd) Treatment There is no specific treatment for Rift Valley Fever. [thecattlesite.com]

  The outstanding symptoms were headache, backache, anorexia, prostration and fever. The duration of fever ranged from 2 to 6 days. All the patients recovered without exhibiting any permanent sequelae, but the rapidity of convalescence was variable. [jimmunol.org]

• High Fever

  Clinical signs of RVF · Sudden onset of abortion storms · Up to 100 percent mortality in lambs under five to six days old · High fever, lymphadenitis, nasal and ocular discharges in mature animals · Profuse fetid diarrhoea (often haemorrhagic) · Vomiting [fao.org]

  It is a member of the Phlebovirus genus and causes a high fever and severe disease in infected animals. The virus has an incubation period (the time it takes from infection to first signs and symptoms) of two to six days. [thesun.co.uk]

  The disease is characterized by sudden onset of high fever, severe headache, myalgia, arthralgia, and photophobia in humans [1]. [microbewiki.kenyon.edu]

  Among the 11 confirmed cases, 45.5% (5 of 11) were symptomatic with high fever 100% (5 of 5), jaundice 60% (3 of 5), encephalitis 40% (2 of 5), and macular retinitis with optic disc edema 20% (1 of 5). [ofid.oxfordjournals.org]

  The viral disease was identified for the first time in 1930 in Kenya and is characterized by high fever and abortion in livestock and high neonatal mortality mainly in sheep [ 3 – 6 ]. [bmcvetres.biomedcentral.com]

• Swelling

  Most patients recover 4 to 7 days later, but some end up with one or more severe forms of the infection: Ocular syndrome (legions to the retina causing possible vision loss), meningoencephalitis (brain swelling causing memory loss, hallucinations, and [iamat.org]

  While most people infected with the virus don’t show any sign of the disease, rarely—about 1 percent of cases—an infected person can develop blindness, swelling of the brain, and hemorrhagic fever. In livestock, the virus is much more serious. [climate.gov]

• Biphasic Fever

  The incubation period is 12–36 hr in lambs, and a biphasic fever of up to 108 F (42 C) may develop. Affected animals are listless and reluctant to move or feed and may show signs of abdominal pain. [msdvetmanual.com]

• Generalized Lymphadenopathy

  There is a generalized lymphadenopathy involving the superficial and visceral lymph nodes. These are oedematous with petechial haemorrhages. The spleen may or may not be enlarged with subcapsular haemorrhages. [fao.org]

• Vomiting

  The clinical picture may resemble meningitis with neck stiffness photophobia, anorexia, and vomiting. [symptoma.com]

  Affected animals show: Fever (40-42 C) Anorexia, depression and weakness in adult cattle and lambs, Mucopurulent nasal discharge in sheep and goats, Vomiting, Diarrhea in cattle, Vomiting and jaundice in sheep, Sometimes haemorrhagic diarrhoea in lambs [lrd.spc.int]

  Vomiting and diarrhoea may involve melaena and haematochezia. Tachycardia, cyanosis, petechiation, haemorrhage and clotting defects are haematological consequences of RVF. [web.archive.org]

  With no specific treatment or effective human vaccine, Rift Valley fever can cause blindness and severe hemorrhaging, leading the victim to vomit blood or even bleed to death. [voanews.com]

  Anorexia, injected conjunctivae, nasal discharges, vomiting and other signs are seen but are generally less severe than in young animals. Abortion is a feature, as is diarrhoea. [fao.org]

• Abdominal Pain

  Affected animals are listless and reluctant to move or feed and may show signs of abdominal pain. Mortality in young lambs is high (90%–100%), and animals usually die within 2–3 days. [msdvetmanual.com]

  pain, photosensitivity, anorexia, excessive salivation and decreased milk production. [en.wikivet.net]

• Loss of Appetite

  Sensitivity to light, neck stiffness, vomiting and loss of appetite are also common. [iamat.org]

  Some develop neck stiffness, sensitivity to light, loss of appetite and vomiting, in the early diagnosing process these symptoms can often be confused with meningitis. [thesun.co.uk]

  Some patients develop neck stiffness, sensitivity to light, loss of appetite and vomiting; in these patients the disease, in its early stages, may be mistaken for meningitis. [web.archive.org]

• Nausea

  Humans experience flu-like symptoms, which may include fever, weakness, weight loss, dizziness, headache, nausea, vomiting, and muscle and joint pain. About 1% of those infected experience more severe symptoms. [floridahealth.gov]

• Jaundice

  Jaundice, neurologic and hemorrhagic forms have a higher incidence of mortality. Central nervous system disease may be followed by permanent neurologic deficits. [symptoma.com]

  The necrotic changes induce jaundice and a stage is reached when the liver has a bronze appearance as the congestion, necrotic areas and icterus develop. At later stages the liver will be completely yellow with jaundice. [fao.org]

  Our data reveal an identifiable clinical syndrome suggestive of severe RVF, characterized by fever, large-joint arthralgia, and gastrointestinal complaints and later followed by jaundice, right upper-quadrant pain, and delirium, often coinciding with [ncbi.nlm.nih.gov]

  Affected animals show: Fever (40-42 C) Anorexia, depression and weakness in adult cattle and lambs, Mucopurulent nasal discharge in sheep and goats, Vomiting, Diarrhea in cattle, Vomiting and jaundice in sheep, Sometimes haemorrhagic diarrhoea in lambs [lrd.spc.int]

  In older animals, the liver is enlarged and inflamed, with many foci of necrosis which are bronzed and jaundiced. The gall bladder may also be distended and haemorrhagic. [web.archive.org]

• Tachycardia

  Tachycardia, cyanosis, petechiation, haemorrhage and clotting defects are haematological consequences of RVF. The respiratory disease of RVF is non-specific: Purulent nasal discharge, epistaxis, tachypnoea and dyspnoea. [web.archive.org]

• Cyanosis

  Tachycardia, cyanosis, petechiation, haemorrhage and clotting defects are haematological consequences of RVF. The respiratory disease of RVF is non-specific: Purulent nasal discharge, epistaxis, tachypnoea and dyspnoea. [web.archive.org]

• Tachycardia

  Tachycardia, cyanosis, petechiation, haemorrhage and clotting defects are haematological consequences of RVF. The respiratory disease of RVF is non-specific: Purulent nasal discharge, epistaxis, tachypnoea and dyspnoea. [web.archive.org]

• Myalgia

  The usual presentation is of sudden onset fever, myalgia, biphasic behaviour and gastrointestinal disease. [web.archive.org]

  The disease is characterized by sudden onset of high fever, severe headache, myalgia, arthralgia, and photophobia in humans [1]. [microbewiki.kenyon.edu]

  The symptoms of uncomplicated infections may include fever, headache, generalized weakness, dizziness, weight loss, myalgia and back pain. Some patients also have stiffness of the neck, photophobia and vomiting. [healio.com]

  The usual presentation is of sudden onset fever, myalgia, biphasic behaviour and gastrointestinal disease. [4] Diagnosis Following infection viraemia is often high (though short lived) so the virus can be easily detected in the blood shortly after. [en.wikivet.net]

• Arthralgia

  Our data reveal an identifiable clinical syndrome suggestive of severe RVF, characterized by fever, large-joint arthralgia, and gastrointestinal complaints and later followed by jaundice, right upper-quadrant pain, and delirium, often coinciding with [ncbi.nlm.nih.gov]

  The disease is characterized by sudden onset of high fever, severe headache, myalgia, arthralgia, and photophobia in humans [1]. [microbewiki.kenyon.edu]

  The mild disease course typically presents as an influenza-like illness with abrupt onset of fever, mylagia and arthralgia, and headache. [infectionlandscapes.org]

  Systemic reaction parameters include fever, chills, headache, malaise, myalgia, arthralgia, sore throat, gastric upset, dizziness, photophobia and skin rash. [google.ch]

• Petechiae

  On necropsy, in the viraemic stage, widespread petechiae and ecchymoses on serous surfaces and organs will be seen and extravasated blood present in the body cavities. [web.archive.org]

  The symptoms may include jaundice, hematemesis, melena, a purpuric rash, petechiae and bleeding from the gums. Hemorrhagic fever frequently progresses to frank hemorrhages, shock and death (case fatality rate of up to 50%). [healio.com]

  In all animals, the spleen and peripheral lymph nodes are enlarged and edematous and may show petechiae. [msdvetmanual.com]

  On post mortem during the viraemic stage, widespread petechiae and ecchymoses on serous surfaces and organs will be seen and present in the body cavities. [en.wikivet.net]

• Epistaxis

  […] 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 [symptoma.com]

  The respiratory disease of RVF is non-specific: Purulent nasal discharge, epistaxis, tachypnoea and dyspnoea. Fever, lymphadenopathy, depression and lethargy usually accompany infection. Hepatitis may cause consequent photosensitisation. [web.archive.org]

• Headache

  Most infected individuals remain asymptomatic or develop a mild form of the disease, consisting of fever, muscle and joint pain, weakness, backache, and headache. [symptoma.com]

  The mild symptoms may include: fever, muscle pains, and headaches which often last for up to a week. [en.wikipedia.org]

  On March 9, 2016, a male butcher from Kabale District, Uganda, aged 45 years, reported to the Kabale Regional Referral Hospital with fever, fatigue, and headache associated with black tarry stools and bleeding from the nose. [ncbi.nlm.nih.gov]

  Mild symptoms include hemorrhagic fever, muscle pains and headaches whereas severe symptoms range from loss of sight within weeks of infection to brain inflammation, which can lead to headaches and seizures. ... [allafrica.com]

  The virus also infects humans, commonly causing malaise, fever and headaches; in epidemics in North Africa, encephalitis and death have also occurred. [epi.ufl.edu]

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.