History and exam
Key diagnostic factors
common
fever of sudden onset
Can occur in West Nile fever or neuroinvasive disease.
malaise
Can occur in West Nile fever.
myalgia
Can occur in West Nile fever.
arthralgia
Can occur in West Nile fever.
pharyngitis
Can occur in West Nile fever.
anorexia
Can occur in West Nile fever.
abdominal pain
Usually mild to moderate. Right upper quadrant pain suggests hepatitis, whereas epigastric pain suggests that pancreatitis may be present.[41]
visual disturbances
Can occur in West Nile fever. Includes gradual visual blurring and loss, floaters and flashes, and eye pain.[34]
headache
Mild to moderate headache occurs in West Nile fever. Severe headache raises suspicion of West Nile meningitis or West Nile encephalitis.[40]
rash
Rash has been reported in 16% to 27% of patients with West Nile fever (WNF).[45][46] More frequent in WNF than in neuroinvasive disease. Transient (in some cases lasting <24 hours). Morbilliform, maculopapular, non-blanching, and non-pruritic rash on the neck, torso, and extremities, sparing the palms and soles. More frequent in younger than older patients.[47]
lymphadenopathy
Lymphadenopathy is often sub-mental.[41]
conjunctival injection
Seen in West Nile fever as well as neuroinvasive disease.
multi-focal chorioretinal lesions
Clustered in temporal and nasal regions of fundus periphery.[34]
chorioretinitis and inflammatory vitritis
Eye pain or redness, patient sees floating black spots/dots/streaks, light sensitivity, and excessive tearing or blurred vision.
uncommon
seizures
Occur in West Nile encephalitis.[40]
jaundice
Raises suspicion of hepatitis or pancreatitis (which in some cases can cause jaundice).[48]
epigastric tenderness
Raises suspicion of pancreatitis.[49]
mild confusion
Raises suspicion of neuroinvasive disease.[50]
disorientation
Raises suspicion of neuroinvasive disease.[50]
stupor/coma
Raises suspicion of neuroinvasive disease.[50]
neck stiffness
May indicate West Nile meningitis.[40]
Kernig's sign
May indicate West Nile meningitis.[40] There is pain and resistance on attempting to extend the leg at the knee with the thigh flexed at the hip.
Brudzinski's sign
May indicate West Nile meningitis.[40] Neck flexion results in knee and hip flexion.
muscle paralysis
Must distinguish between generalised muscle weakness associated with West Nile fever and flaccid paralysis associated with West Nile poliomyelitis. The paralysis in West Nile poliomyelitis is usually asymmetrical.
Rarely, Guillain-Barre syndrome may develop.[51][52][53] Rhabdomyolysis and myositis have been reported.[42]
parkinsonism
May be seen in West Nile encephalitis or West Nile meningitis. May persist after infection has resolved.[40]
ataxia
May be seen in West Nile encephalitis or West Nile meningitis. May persist after infection has resolved.[40]
myoclonus
May be seen in West Nile encephalitis or West Nile meningitis. May persist after infection has resolved.[40]
tremors
May be seen in West Nile encephalitis or West Nile meningitis. May persist after infection has resolved.[40]
Other diagnostic factors
common
nausea/vomiting
Presence may suggest more severe disease.
generalised muscle weakness
Must distinguish between generalised muscle weakness associated with West Nile fever and flaccid paralysis associated with West Nile poliomyelitis.
splenomegaly
More suggestive of West Nile fever than other viral infections, such as influenza or parainfluenza, that are more common.
retinal haemorrhages
More suggestive of West Nile fever than other viral infections, such as influenza or parainfluenza, that are more common.
uncommon
chest pain, dyspnoea, palpitations
Raises suspicion of myocarditis.[42]
photophobia
May indicate West Nile meningitis.
depression
Seen in neuroinvasive disease.[50]
loss of memory
Seen in neuroinvasive disease. Word-finding difficulties may also occur and persist.[50]
bowel and bladder dysfunction
Can occur in West Nile poliomyelitis.
cranial nerve palsies
Can occur in West Nile poliomyelitis.
Risk factors
strong
living in/visiting areas with high West Nile virus activity
mosquito bites
Outdoor activities between dusk and dawn and having exposed skin while being outdoors increases the risk of mosquito bites, especially in areas where there is significant vegetation or stagnant water.[13]
In temperate regions, mosquito activity and the risk of infection is greatest from the late spring to the late summer/early autumn. In warmer climates, mosquito activity may be year-round.
blood transfusion
Estimated risk of virus transmission ranged from 1.46 to 12.33 per 10,000 donations during the 2002 epidemic.[18]
organ transplant
First documented case of virus transmission through organ transplantation was in 2002. Four cases occurred in Toronto and 4 more in the south-eastern US in 2002.[17][25] Three more cases were reported in New York and Pennsylvania in 2005.[26] Other individual cases have been documented in the US in 2013 and 2018.[9][17]
needle-stick injuries
Virus transmission has occurred through needle-stick injuries.[16]
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