West Nile virus infection

West Nile virus infection causes an illness carried by mosquitoes. It is estimated that about 80% of WNV infections are asymptomatic, 20% are "West Nile Fever," and less than 1% are CNS infections.

CASES/YEAR
3,000 (US); 60,000 (Global)
CATEGORY
AGENT TYPE
Viruses
OTHER NAMES
West Nile fever; WNV infection; Kunjin virus (Australasia);
ACUITY
Acute-Severe
INCUBATION
3-12 days
INITIAL SYMPTOMS
Most infections are asymptomatic; Flu-like illness with fever, headache, and myalgia; Other symptoms are nausea/vomiting, diarrhea, and rash; Neurological symptoms in <1% of infected people; [PPID, p. 2029]
PRECAUTIONS
Standard; Install screens in endemic areas.
COMMENTS
FINDINGS:
The febrile illness includes headache, myalgia, arthralgia, and GI symptoms. [CCDM, p. 675] It is estimated that about 80% of WNV infections are asymptomatic, 20% are "West Nile Fever," and less than 1% are CNS infections. Encephalitis usually occurs in people who are older or chronically ill. Flaccid paralysis is less common than meningitis or encephalitis. Paralysis may involve one extremity only; it is associated with pain but not numbness. [www.cdc.gov] The symptoms of West Nile fever are myalgia, fever, rash, lymphadenopathy, headache, weakness, backache, conjunctival injection, and pharyngitis. Other findings observed in outbreaks of WNV infections are confusion, stiff neck, diarrhea, and leukocytosis or leukopenia. Complications include pancreatitis, myocarditis, optic neuritis, radiculitis, myelitis, and hepatitis. [ID, p. 2129] A maculopapular rash occurred in about 50% of patients in one outbreak. Other findings in West Nile fever are hepatomegaly (20% of patients), splenomegaly (10% of patients), liver dysfunction, abdominal pain, cough, and fatigue. Patients with neurological disease may have paralysis, convulsions, ataxia, tremors, and rigidity. [PPID, p. 2029-30] Can cause a syndrome resembling poliomyelitis; [Cecil, p. 2224] West Nile fever: 2-6 days after mosquito bite, patient has fever, headache, arthralgia, and rash (20%) for 2-7 days. [ABX Guide]

EPIDEMIOLOGY:
Transmission by transfusion and percutaneous occupational exposure has been reported. WNV infections are an occupational hazard for people working outside when mosquitoes are biting. Turkey breeder farm workers have become infected with WNV, but the mode of transmission is not known. [www.cdc.gov] Birds are the reservoir for WNV. Other animals that may become infected include horses, dogs, camel, cows, donkeys, water buffalo, sheep, bats chipmunks, squirrels, rabbits, rats, and skunks. [ID, p. 2128] In America, crows and ravens are often infected; death of these birds, at a higher rate than normal, is a sentinel for the presence of West Nile virus. [Cecil, p. 2224]
DIAGNOSTIC
Virus-specific IgM in serum or CSF can be detected in nearly all patients. The IgM persists for about one year. Use paired serum samples. [www.cdc.gov] Use commercially available WNV test kits, but confirm with CDC; [MMWR May 8, 2009]
SCOPE
Worldwide except Antarctica; First detected in Western Hemisphere in 1999 in New York and spread throughout North, Central, and South America; [CCDM, p. 677]
SIGNS & SYMPTOMS
  • >arthralgia
  • >fatigue, weakness
  • >fever
  • >fever, biphasic or relapsing
  • >myalgia
  • E pharyngitis
  • G abdominal pain
  • G diarrhea
  • G hepatomegaly
  • G liver function test, abnormal
  • G nausea, vomiting
  • H leukocytosis
  • H leukopenia
  • H lymphadenopathy
  • H splenomegaly
  • N confusion, delirium
  • N headache
  • N lethargy
  • N muscle weakness
  • N seizure
  • N stiff neck
  • O conjunctivitis, acute
  • R cough
  • S papules or plaques
  • S rash (exanthem)
  • *cranial neuropathy
  • *encephalitis
  • *hepatitis
  • *meningitis
  • *myelitis
  • *myocarditis
  • *pancreatitis
  • *paralysis
  • *peripheral neuropathy
  • *rhabdomyolysis
  • *stupor, coma
  • *uveitis
ANTIMICROBIC

No

VACCINE

No

ENTRY
Needle (Includes Drug Abuse), Scalpel or Transfusion, Skin or Mucous Membranes (Includes Conjunctiva)
VECTOR
Mosquitoes
SOURCE
Animal Tissue
RESERVOIR
Birds and Poultry, Cattle, Goats and Sheep, Dogs, Horses, Rabbits, Rodents, Wild Animals
RISK FACTORS
  • Care for patients (bloodborne pathogen)
  • Handle infected chickens or birds
  • Handle needles or surgical instruments
  • Have a blood transfusion
  • Travel to endemic area
  • Work in a medical or research lab
REFERENCES FOR CASES/YEAR
1. (US) Responsible for the majority of arboviral meningitis and encephalitis since 2002; 1140 neuroinvasive cases (100 deaths) in 2013; [Harrison ID, p. 346] Up to 3000 cases per year; [Cecil, p. 2229t]
2. (Global) Guesstimate: 20 X US cases/yr;