West nile virus natural history: Difference between revisions
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=====West nile meningitis===== | =====West nile meningitis===== | ||
It usually presents with fever and signs of [[meningeal irritation]] like [[headache], | It usually presents with fever and signs of [[meningeal irritation]] like [[headache]], stiffneck, nuchal rigidity and [[photophobia]]. | ||
=====West nile encephalitis===== | =====West nile encephalitis===== | ||
Revision as of 16:09, 11 September 2014
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ammu Susheela, M.D. [2]
Overview
West nile virus is transmitted to human beings by the culex mosquito after feeding on birds which are the reservoir of this virus. After an incubation period of 2-14 day, they can remain asymptomatic or present as west nile fever or as neuroinvasive disease which can be life threatening. The outcome of mild flu like symptoms are excellent while west nile meningitis/encephalitis can have residual neurologic deficits.
Natural history
West Nile Virus (WNV) is a member of Japanese encephalitis antigenic complex of the family Flaviviridae. West nile virus is spread by the bite of mosquito (most commonly Culex pipiens). Birds are the natural reservoir of the virus and the disease is transmitted when a mosquito that feed on the bird bites a human being. The virus can cause severe disease and death in horses.
Incubation period
The incubation period for WNV disease is typically 2 to 6 days but ranges from 2 to 14 days and can be several weeks in immunocompromised people. An estimated 70-80% of human WNV infections are subclinical or asymptomatic. Less than 1% of infected persons develop neuroinvasive disease, which typically manifests as meningitis, encephalitis, or acute flaccid paralysis.
Asymptomatic west nile infection
80% of the people infected by virus are not symptomatic. Most of them are not aware that they have the disease.
West nile fever
Around 20% of the people infected develop west nile fever and can present with any of following symptoms like fever, headache, tiredness, and body aches, nausea, vomiting, occasionally with a skin rash (on the trunk of the body) and swollen lymph glands. It usually presents as flu like disease.
Neuroinvasive disease
The symptoms of severe disease (also called neuroinvasive disease, such as West Nile encephalitis or meningitis or West Nile poliomyelitis) include headache, high fever, neck stiffness, stupor, disorientation,coma,tremors, convulsions, muscle weakness, and paralysis. It is estimated that approximately 1 in 150 persons infected with the West Nile virus will develop a more severe form of disease. Serious illness can occur in people of any age, however people over the age of 50 and some immunocompromised persons (for example, transplant patients) are at the highest risk for getting severely ill when infected with WNV.
West nile meningitis
It usually presents with fever and signs of meningeal irritation like headache, stiffneck, nuchal rigidity and photophobia.
West nile encephalitis
When the infectious process involves the brain parenchyma, west nile encephalitis develops and the patient may have altered level of conciousness, disorientation and focal neurological signs and symptoms due to the neuroinvasion of substantia nigra in brain stem , basal ganglia and cerebellum.
Acute flaccid paralysis
This is due to the selective lesion on anterior spinal cord by west nile virus. The main clinical feature is acute asymmetric flaccid paralysis with minimal or no sensory disturbances.
Possible Complications
Complications from mild West Nile virus infection are very rare.
Complications from severe West Nile virus infection include:
- Permanent muscle weakness (sometimes similar to polio)
- Dysphagia
- Deep venous thrombosis
- Pressure ulcers
- Chorioretinitis (100% specificity for identifying West Nile virus infection in patients with possible West Nile virus encephalitis)[1]
- Hepatitis
- Myocarditis
- Nephritis
- Pancreatitis
- Splenomegaly[2][3][4]
- Brain damage
- Death
Prognosis
- In general, the outcome of a mild West Nile virus infection is excellent.Most patients with non-neuroinvasive WNV disease or WNV meningitis recover completely, but fatigue, malaise, and weakness can linger for weeks or months.
- Patients who recover from WNV encephalitis or poliomyelitis often have residual neurologic deficits. Among patients with neuroinvasive disease, the overall case-fatality ratio is approximately 10%, but it is significantly higher for patients with WNV encephalitis and poliomyelitis than WNV meningitis.
- For patients with severe cases of West Nile virus infection, the outlook is more uncertain. West Nile encephalitis or meningitis may lead to brain damage and death. Approximately 10% of patients with brain inflammation do not survive.
References
- ↑ Abroug F, Ouanes-Besbes L, Letaief M, Ben Romdhane F, Khairallah M, Triki H, Bouzouiaia N. "A cluster study of predictors of severe West Nile virus infection." Mayo Clinic Proceedings 2006; 81: 12-16.
- ↑ Perelman A, Stern J. "Acute pancreatitis in West Nile Fever." American Journal of Tropical Medicine and Hygiene 1974; 23: 1150-1152.
- ↑ Omalu B I, Shakir A A, Wang G, Lipkin W I, Wiley C A. "Fatal fulminant pan-meningo-polioencephalitis due to West Nile virus." Brain Pathology 2003; 13: 465-472
- ↑ Mathiot C C, Georges A J, Deubel V. "Comparative analysis of West Nile virus strains isolated from human and animal hosts using monoclonal antibodies and cDNA restriction digest profiles." Res Virol 1990; 141: 533-543.