History and exam

Key diagnostic factors

common

presence of risk factors

Key risk factors include: occupational exposure, livestock handling through occupational exposure or homestead exposure, consuming raw animal fluids or tissue, genetic polymorphism, advanced age, or mosquito exposure.

fever ≥37.5°C

Presenting symptom in >90% of patients, and is often >39°C with a remitting pattern.[12][40][41][48][50]

Other diagnostic factors

common

headache

Presenting symptom in approximately 90% of patients.[1][12][40][50]

myalgia

Presenting symptom in the majority of patients.[1]​​[40][50] Occurs during acute illness, yet long-term myalgia sequelae are currently uncharacterised and may be possible.[48]

arthralgia

Presenting symptom in the majority of patients.[1]​​[40] Occurs during acute illness, yet long-term arthralgia sequelae are currently uncharacterised and may be possible.[48]

weakness

Presenting symptom in approximately 90% of patients.[1][12][40][50]

backache

Often a presenting symptom along with fever, weakness, and dizziness.[12]

neck stiffness

Commonly grouped with myalgia, pain behind the eyes, or headache.[1][50]

dizziness

Presenting symptom may result from fever, loss of appetite, or dehydration.[12]

chills

Presenting symptom is often resulting from persistent fever.[32]

loss of appetite

General feeling of illness and discomfort may cause loss of appetite in patients.[1][2]

vomiting

Patients should be monitored for haematemesis, which may indicate the onset of haemorrhagic fever or other severe disease symptoms.[1][2][41]

photophobia

Presents as sensitivity to light and may be experienced with pain behind the eyes.[51][52]

pain behind the eyes

Pain may be illustrative of other RVF symptoms (e.g., fever, headache, straining to correct vision impairment).[41][51]

uncommon

vision impairment

Vision impairment, such as scotomas (partial loss of visual field), painless blurred, or decreased vision, as a result of retinal or macular changes may be temporary (when changes are due to uveitis) or permanent (when changes are due to retinitis).[35][40][51][52] Changes in vision should be monitored for progression to retinitis or permanent damage.

retinitis

Occurs in approximately 10% of patients.[1][2] Onset is usually 1 to 3 weeks after initial onset of symptoms, including mild or subclinical presentation. Patients usually experience sudden, progressive retinitis.[51] Usually presents as painless blurred or scotomata. Symptoms typically last 10 to 12 weeks, but may result in permanent loss of vision.[1][2][35][40][41][53] Permanent vision loss is correlated with lesions of the macula in up to 70% of patients. Lesions may include retinal haemorrhages, vitreous reactions, optic disc oedema, and retinal vasculitis.[8][32][51][52]

meningoencephalitis

Occurs in 1% of patients.[1][2][40][50] Onset occurs 1 to 4 weeks after initial symptoms occur. Neurological complications and sequelae may manifest more than 60 days after initial RVF symptom presentation. Key features include intense headaches, loss of memory, hallucinations, confusion, disorientation, vertigo, convulsions, lethargy, and coma. Residual neurological deficit is a common result.[1][2][8][40]

hepatitis

Occurs in 1% of cases.[50] May occur with or precede other complications (e.g., haemorrhage or meningoencephalitis).[1][2]

acute kidney injury

Occurs in 1% of cases. Acute kidney injury may be secondary to hypovolaemia, multiple-organ dysfunction, hepatorenal syndrome, or direct virus-related injury.[1][2][54]

haemorrhagic fever

Occurs in approximately 1% of cases, but has a high mortality rate (up to 65%) for individuals suffering from the haemorrhagic form of RVF.[1][2][8][40][41][48][50] Appears quickly, between 2 to 4 days after the initial onset of RVF. Is often present as haematemesis, melaena, a petechial or purpuric rash, ecchymoses, bleeding from the nose or gums, menorrhagia, or bleeding from venipuncture sites. Hepatitis may also be present, often preceding the haemorrhagic state, and may progress to liver failure.[1][2][40][41]

Risk factors

strong

livestock handling through occupational exposure or homestead exposure

In endemic regions, common occupations include livestock handler, herder, or slaughterhouse worker. It is also common for households or communities to keep livestock. Exposure to animal fluids and carcasses increases risk of exposure to zoonotic infections. Particularly, individuals involved in birthing animals, handling aborted animal tissue and fluids, and slaughtering and skinning animals are at high risk of Rift Valley fever virus (RVFV) transmission.[9][28][30][31][32][33]

History of recurrent abortions and deaths among newborn and young livestock in the region should be analysed for potential RVFV causation.

consuming raw animal fluids or tissue

In areas where RVFV is endemic, consuming raw meat, milk, and animal blood as cultural or ceremonial practice has been shown to increase an individual’s risk of exposure to RVFV.[6][30][32][34][35][36]

genetic polymorphism

An association was found between single nucleotide polymorphism (SNP) genotype, serology, and RVF symptom clusters. The meningoencephalitis symptom phenotype cluster among seropositive patients has been associated with polymorphisms in DDX58/RIG-I and TLR8. Having 3 or more RVF-related symptoms has been significantly associated with polymorphisms in TICAM1/TRIF, MAVS, IFNAR1, and DDX58/RIG-I. SNPs significantly associated with eye disease include 3 different polymorphisms of TLR8 and haemorrhagic fever symptoms associated with TLR3, TLR7, TLR8, and MyD88.[29]

advanced age

Many studies have found that advanced age may increase risk of infection.[8][28][32][37] It has also been suggested that advanced age may increase susceptibility for severe disease.[28]

mosquito exposure

Aedes spp. and Culex spp. have been shown to transmit RVFV in endemic areas.[38][9] Spatial and temporal patterns have been significantly associated with seropositivity in some studies, linking likelihood of flooding or access to bodies of water with mosquito behaviour.[38][9][39] Seropositivity for RVFV is not limited to those who handle livestock, thus mosquito exposure and abatement measures should be considered during the physical examination and health history. It has also been suggested that mosquito saliva enhances viraemia and disease severity.[40]

weak

sex

Some studies suggest that males have a higher risk of infection, whereas others have shown no specific risk associated with sex.[28][31][32][37][41] Further research is needed to determine the true risk associated with sex.

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