History and exam
Key diagnostic factors
Other diagnostic factors
common
retro-orbital pain
Reported in around 84% of patients with VEEV infection.[5]
altered mental status
In a large outbreak in Venezuela in 1995, around 91% of 313 patients hospitalised with Venezuelan equine encephalitis (VEE) infection presented with altered mental status.[4][27]
Mostly seen in children.[4][27]
Neurological complications appear to be more prevalent among the epizootic VEEV subtypes (IAB and IC) compared with the enzootic subtypes.[4]
uncommon
seizures
Occurs in around 3% of patients with VEEV infection. Mostly seen in children.[4][5][27][32]
The onset of seizures ranges from day 1 to 10 after the onset of fever.[4][5][27][32]
In a large outbreak in Venezuela in 1995, 70.6% of 313 patients hospitalised with encephalitis resulting from VEEV infection presented with seizures.[27]
Neurological complications appear to be more prevalent among the epizootic VEEV subtypes (IAB and IC) compared with the enzootic subtypes.[4]
gastrointestinal bleeding
cough
Reported in around 27% of patients with VEEV infection.[5]
rash
Reported in 1% to 9% of patients; however, also seen in around 25% of patients with dengue fever.[11]
sore throat
Reported in around 16% of patients with VEEV infection.[5]
hemiparesis
Reported in around 11% of hospitalised patients with VEEV infection.[9]
A sign of neurological involvement. The onset of neurological symptoms usually occurs several days into the course of illness.
Neurological symptoms appear to be more prevalent among children (up to 36% of symptomatic children).[9][11][14] Furthermore, neurological complications appear to be more prevalent among the epizootic VEEV subtypes (IAB and IC) compared with the enzootic subtypes.[4]
lethargy, drowsiness, or confusion
A sign of neurological involvement. The onset of neurological symptoms usually occurs several days into the course of illness.
Neurological symptoms appear to be more prevalent among children (up to 36% of symptomatic children).[9][11][14] Furthermore, neurological complications appear to be more prevalent among the epizootic VEEV subtypes (IAB and IC) compared with the enzootic subtypes.[4]
paraesthesias
A sign of neurological involvement. The onset of neurological symptoms usually occurs several days into the course of illness.
Neurological symptoms appear to be more prevalent among children (up to 36% of symptomatic children).[9][11][14] Furthermore, neurological complications appear to be more prevalent among the epizootic VEEV subtypes (IAB and IC) compared with the enzootic subtypes.[4]
ataxia/gait abnormalities
A sign of neurological involvement. The onset of neurological symptoms usually occurs several days into the course of illness.
Neurological symptoms appear to be more prevalent among children (up to 36% of symptomatic children).[9][11][14] Furthermore, neurological complications appear to be more prevalent among the epizootic VEEV subtypes (IAB and IC) compared with the enzootic subtypes.[4]
behavioural abnormalities
Reported in 11% of hospitalised patients with VEEV infection.[9]
A sign of neurological involvement. The onset of neurological symptoms usually occurs several days into the course of illness.
Neurological symptoms appear to be more prevalent among children (up to 36% of symptomatic children).[9][11][14] Furthermore, neurological complications appear to be more prevalent among the epizootic VEEV subtypes (IAB and IC) compared with the enzootic subtypes.[4]
stupor, somnolence, or coma
neck stiffness (nuchal rigidity)
Reported in 10% to 19% of patients with VEEV infection.[11]
A sign of neurological involvement, particularly when an intense headache is also present. The onset of neurological symptoms usually occurs several days into the course of illness.
Neurological symptoms appear to be more prevalent among children (up to 36% of symptomatic children).[9][11][14] Furthermore, neurological complications appear to be more prevalent among the epizootic VEEV subtypes (IAB and IC) compared with the enzootic subtypes.[4]
jaundice
A sign of liver failure. Mentioned in case reports of patients with VEEV infection.[4]
papilloedema
Fundoscopic examination may reveal papilloedema.
Papilloedema indicates neurological involvement. The onset of neurological symptoms usually occurs several days into the course of illness.
Neurological symptoms appear to be more prevalent among children (up to 36% of symptomatic children).[9][11][14] Furthermore, neurological complications appear to be more prevalent among the epizootic VEEV subtypes (IAB and IC) compared with the enzootic subtypes.[4]
Risk factors
strong
living and/or working in or near tropical forests in Central or South America
Particularly in or around areas where an epizootic outbreak is occurring (i.e., involving horses).
In a cross-sectional study carried out in Darién (Panama), working in forests in endemic regions was associated with a higher risk of being seropositive for Venezuelan equine encephalitis (adjusted odds ratio [OR] 3.8, p = 0.01).[26] This was likely mediated by increased exposure to the mosquito vectors (Culex [Melanoconion] species).
In a study carried out in Iquitos (Peru), occupations involving outdoor work (e.g., labourer or lumberjack) in forest areas were found to confer significant risk for VEEV seropositivity (adjusted OR 3.4).[12]
fishing in or near tropical forests in Central or South America
Particularly in or around areas where an epizootic outbreak is occurring (i.e., involving horses).
In a cross-sectional study carried out in Darién (Panama), fishing was associated with a higher risk of being seropositive for Venezuelan equine encephalitis (adjusted OR 10.8, p = 0.001).[26] This was likely mediated by increased exposure to the mosquito vectors (Culex [Melanoconion] species).
age <15 years
Children with VEEV infection are at higher risk for developing neurological complications (e.g., encephalitis) compared with adults.
In a large outbreak in Venezuela in 1995, 92.3% of 313 patients hospitalised with Venezuelan equine encephalitis (VEE) presented with fever, 90.7% with altered mental status, 70.6% with seizures, 55.9% with headache, and 54.6% with vomiting.[27] Among those hospitalised with VEE, 75.7% were under the age of 15 years. Furthermore, an outbreak of epizootic VEEV in Texas (US) found that 10/28 (36%) symptomatic children had central nervous system involvement, compared to 6/51 (12%) adults.[11]
occupational exposure (laboratory)
Aerosolised transmission of VEEV has been documented in the laboratory setting.
Handling high virus concentrations, mouth pipetting, and engaging in activities that generate aerosols (e.g., tissue homogenisation, centrifugation) are risk factors for occupational infection.[1]
weak
bioterrorism
VEEV is considered a potential bioterrorism weapon as it can be produced in large amounts in aerosolised form.
In the US, VEEV (and other alphaviruses) is classified as a Category B agent by the Centers for Disease Control and Prevention (CDC), which is the second highest threat category.
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