Viral encephalitides, mosquito-borne

Viral encephalitides, mosquito-borne are carried by mosquitoes and cause encephalitis. The group includes Venezuelan equine encephalitis (VEE); St. Louis encephalitis (SLE); Japanese encephalitis (JE); West Nile encephalitis (WNV); Western and Eastern Equine encephalitis (WEE) (EEE).

5,000 (US); 50,000 (Global)
Venezuelan equine encephalitis (VEE); St. Louis encephalitis (SLE); Japanese encephalitis (JE); West Nile encephalitis (WNV); Western and Eastern Equine encephalitis (WEE) (EEE);
Usually 3-14 days; [CCDM, p. 40]
For Japanese encephalitis, <1% of patients infected develop neurological disease. [CDC Travel, p. 249]
"Not transmitted from person to person except rarely by transfusion, and for West Nile virus by organ transplant, breast milk or transplacentally. Install screens in windows and doors in endemic areas. Use DEET-containing mosquito repellants and clothing to cover extremities." [CDC 2007 Guideline for Isolation Precautions]
Nuchal rigidity and seizures may occur. Flaccid or spastic paralysis may appear after the first week. [ID, p. 1291] For St. Louis encephalitis, generalized motor weakness is more common than focal signs. [PPID, p. 2030] Most patients with JE have severe encephalitis. Fatality rates are 25% in regions with intensive care units. 85% of children and 10% of adults have seizures. Movement disorders include opisthotonus, rigidity, tremor, jaw dystonias, and choreoathetosis. Five years after the initial infection, 1/3 of patients still have neurological abnormalities, e.g., seizures, cranial neuropathy, movement disorders, and cortical blindness. Other findings are abdominal pain and leukocytosis. Hematuria, pyuria, and proteinuria were reported in SLE. [PPID, p. 2029] Bilateral brain lesions (thalmus, basal ganglia, and brainstem) are highly specific for JE. Leukopenia may occur in these viral infections. [Guerrant, p. 512-3] Findings in West Nile virus infection may include a maculopapular rash, lymphadenopathy, arthralgia, flaccid paralysis, and chorioretinitis. [Harrison ID, p. 963] Patients with VEE may have conjunctival injection, a biphasic course, and leukopenia. St. Louis encephalitis virus may cause genitourinary effects including hematuria and pyuria. [Cecil, p. 2231, 2233]

These viruses are laboratory hazards (Biosafety Level 3 or 4). "There is a Japanese encephalitis vaccine available in the US. An equine vaccine is available for EEE, WEE and Venezuelan equine encephalitis (VEE)." [CDC: Arboviral encephalitides]

Between 1964 and 2000, 640 cases of WEE and 182 cases of EEE were reported to the CDC. With more than 10,000 cases through 1990, SLE was the most common cause of mosquito-borne encephalitis in the USA before the arrival of WNV in 1999. VEE has caused tens of thousands of cases in Central and South America, and caused about 200 deaths in Venezuela in 1962-1964. About 10,000 horses were killed by VEE in Texas in 1971. WNV caused the following cases/deaths in 2002, 2003, and 2004 respectively: 4156/284, 9862/264, 2539/100. In 2004 in the USA, about 1/2 of the WNV cases were febrile illnesses and about 1/2 were meningitis/encephalitis. The introduction of the JE vaccine in the mid-1960s caused the elimination of most human cases from Japan, Korea, and Taiwan. Throughout Asia, the vaccine led to the reduction of cases from 160,000 in 1966 to 16,000 in 1996. Since 1970, JE cases have increased in Southeast Asia, India, Nepal, and Sri Lanka. The risk for JE infection is highest in rural areas where flooding irrigation is practiced. [PPID, p. 2019-20; CDC WNV website] See "Venezuelan equine encephalitis." See "West Nile virus infection."
Viral culture; IgM antibodies; Paired sera; [CCDM] For Japanese encephalitis, CSF shows pleocytosis (lymphocytic predominance); Virus-specific IgM in CSF by day 4 & in serum by day 7 after symptom onset; Also paired sera; [CDC Travel p. 249, 251]
  • >arthralgia
  • >fatigue, weakness
  • >fever
  • >fever, biphasic or relapsing
  • >myalgia
  • E dysphagia
  • E pharyngitis
  • G abdominal pain
  • G diarrhea
  • G hepatomegaly
  • G nausea, vomiting
  • H anemia
  • H leukocytosis
  • H leukopenia
  • H lymphadenopathy
  • H splenomegaly
  • H thrombocytopenia
  • N confusion, delirium
  • N headache
  • N lethargy
  • N muscle weakness
  • N opisthotonus
  • N seizure
  • N stiff neck
  • O conjunctivitis, acute
  • R cough
  • S papules or plaques
  • S rash (exanthem)
  • U hematuria
  • U pyuria
  • *blindness
  • *brain abscess or lesion
  • *cranial neuropathy
  • *encephalitis
  • *hepatitis
  • *meningitis
  • *myelitis
  • *myocarditis
  • *pancreatitis
  • *paralysis
  • *peripheral neuropathy
  • *pneumonia
  • *stupor, coma
  • *uveitis




Birds and Poultry, Horses, Rodents, Swine, Wild Animals
  • Fail to complete immunizations
  • Travel to endemic area
  • Work in a medical or research lab
"The primary treatment for all arboviral diseases is supportive;" [CCDM, p. 42]
1. (US) Annual number of cases in US = 2 (WEE), 10 (EEE), 10-50 (California), 0-2000 (SLE), rare (VEE), and up to 3000 (WNV); [Cecil, p. 2229t] Guesstimate = 5000/year;
2. (Global) Japanese encephalitis: Estimated 50,000 cases per year with 10,000-15,000 deaths and 50% of patients having permanent neurological sequelae; [WHO website]