Approach

Diagnosis is made based on history and physical examination. Clinical features for Rift Valley fever virus (RVFV) infection are relatively non-specific. Therefore, exposure history and public health information are critical for interpreting clinical findings and patient-reported symptoms. Often, epidemics of ruminant abortion storms precede recognition of human cases if the exposed livestock reside in a naive area.

RVF is a notifiable disease in both livestock and humans.

History

A history of exposure to mosquitoes in an area with a history of RVFV outbreaks or cases may be revealed. History of animal exposure through livestock handling at home, occupational exposure as a herder or abattoir worker, or through sacrificial slaughtering is critical to diagnosis. Contact with infected animals through care, breeding, or slaughter is a significant risk for transmission. Consuming raw milk, blood, and meat, as well as birthing and handling aborted tissue or fluids from infected animals are also significant risks for exposure.[8][11][12][32][41]

Asymptomatic cases are common. Many patients develop RVF, characterised with non-specific and mild symptoms lasting up to 2 weeks. Symptoms include fever, headache, malaise, myalgia, backache, arthralgia, weakness, nausea, vomiting, abdominal pain, diarrhoea, and jaundice.[1][12][41][48][49][50] Haemolytic anaemia may present as well. Patients may also complain of visual disturbances, such as blurred or loss of vision, and pain behind the eyes.[49][51]

Severe disease occurs in 1% to 10% of patients with RVF.[1][2] Severe disease can occur in the form of ocular disease, meningoencephalitis, or haemorrhagic fever. In one study of miscarriage in pregnant women, one half of febrile women with acute RVFV miscarried at various stages of pregnancy.[3] The appearance of shock, multi-organ failure, and disseminated intravascular coagulation typically indicate poor prognosis, especially when persistent despite supportive care.

Physical examination

Physical examination may reveal visible swelling of the joints as a result of arthralgia or myalgia. Patients may also experience splenomegaly or jaundice.[49]

Opthalmoscopic examination should be performed in all suspected cases. This may reveal ocular lesions, retinal haemorrhages, optic disc oedema, or retinal vasculitis.[51] Decreased visual acuity may be a low cost non-specific indication of RVF disease.[35]

Neurological manifestations, including confusion, dizziness, intense headache, loss of memory, hallucinations, disorientation, vertigo, convulsions, lethargy, or coma are rare.[1] Presence of such symptoms may indicate the onset of meningoencephalitis. Chronic or long-term neurological sequelae have yet to be defined for patients experiencing acute or severe RVF.

Initial investigations

Serological testing is recommended in patients with influenza-like symptoms (e.g., fever and headache) or acute fever and gastroenteritis-like illness (nausea, vomiting, abdominal pain, and diarrhoea) who reside in or have recently travelled from endemic areas, and/or have a history of exposure to livestock or consumption of raw meat, milk, or blood. Serological testing is also recommended in patients with influenza-like symptoms who reside in or have recently travelled from endemic areas, and have had recent mosquito exposure (e.g., recollection of mosquito bites).

Patients suspected of acute RVF should undergo enzyme-linked immunosorbent assay and/or reverse transcriptase-polymerase chain reaction testing, when available. Suspected cases should also be reported to the local Department or Ministry of Health. Often, local Departments of Health require that a patient sample is sent for confirmatory serological testing by plaque reduction neutralisation testing.

FBC, serum electrolyte, serum creatinine, urea, and liver function tests should be performed in patients with suspected RVF. Patients should be monitored closely for the development of severe RVF symptoms (loss of vision, meningismus or neurological signs, mucosal or deep tissue bleeding).

Isolating the virus from biological specimens (e.g., blood, serum, cerebrospinal fluid, or tissue samples) is the optimal test for RVF diagnosis, but is not routinely recommended, as this requires proper biosafety containment facilities (e.g., a BSL-3+ facility).

Use of this content is subject to our disclaimer