Venezuelan Equine Encephalitis Clinical Presentation

Updated: Jun 02, 2021
  • Author: Robert W Derlet, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Patients give a history of exposure to mosquitoes in an area endemic for Venezuelan equine encephalitis. Suspect Venezuelan equine encephalitis and dengue fever in anyone with a febrile illness who has recently traveled in rural areas of Central America or tropical South America.

 Venezuelan equine encephalitis virus infection manifests as influenzalike symptoms approximately 1-6 days after infection. Subclinical infections occur, but the incidence is unknown.

Typical initial symptoms of infection include  fatigue, weakness, malaise, fever, chills, myalgia, lumbosacral pain, nausea, vomiting, and prostration.  Severe headache with or without associated photophobia may also be reported. Fever may abate in a few days, followed by recrudescence the following day. These initial symptoms may be followed by diarrhea and a sore throat.

Most Venezuelan equine encephalitis virus infections in humans are relatively mild, with symptoms lasting 3-5 days.

Children are at particular risk to progress to clinical CNS involvement, especially encephalitis. Symptoms of CNS involvement include disorientation, somnolence, nuchal rigidity, convulsions, inappropriate antidiuretic hormone (ADH) secretion, paralysis, coma, and death.

Most persons have resolution of symptoms after 5 days; however, a subset of infected persons may remain symptomatic for as long as 2 weeks.

Maternal infection may result in fetal demise or abortion. Congenital infection with CNS malformations has been reported.


Physical Examination

In humans, fever is the most common physical finding of Venezuelan equine encephalitis virus infection. Tahcycardia, pharyngitis, conjunctival congestion, facial flushing, and, rarely, lymphadenopathy are among the  physical findings found in mild forms of Venezuelan equine encephalitis. Some patients may progress to exhibit somnolence, photophobia, and mild confusion.

The few patients with Venezuelan equine encephalitis who develop severe neurologic compromise develop significant physical findings, including nuchal rigidity, stupor, delirium, coma, nystagmus, cranial nerve palsies, pathologic reflexes, ataxia, and spastic paralysis. Tremors, abnormal movement disorders, and visual field defects are uncommon.

In equines, signs of infection, including fever, tachycardia, anorexia, and depression, usually appear approximately 2 days after infection. Encephalitis develops in some of these animals within 5-10 days of infection. The animals may show signs of circling, ataxia, and hyperexcitability. Death usually occurs approximately 1 week after infection. The development of encephalitis in equines is related to the magnitude of viremia.