West nile virus natural history: Difference between revisions

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{{West nile virus}}
{{West nile virus}}
{{CMG}}; {{AE}} {{Ammu}}
{{CMG}}; {{AE}} {{Ammu}}


==Overview==
==Overview==
West nile virus
WNV is usually transmitted to humans by the ''culex'' mosquito after feeding on infected birds with high-level viremia. Following an [[incubation period]] of 2-14 day, untreated patients can remain asymptomatic or present with West Nile fever or with life-threatening neuroinvasive disease. Common complications of WNV infections include neurological impairment. The prognosis of mild disease is excellent; whereas West Nile [[meningitis]] and [[encephalitis]] may have residual neurologic deficits.


==Natural history==
==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 bite the bird bites a human being. The virus can cause severe disease and death in horses.
WNV is a member of Japanese [[encephalitis]] antigenic complex of the family Flaviviridae. It is transmitted by a mosquito bite, most commonly ''Culex pipiens''. Birds are the natural reservoir of the virus and the disease is generally transmitted to humans when a mosquito that previously fed on a bird with high-level viremia bites a human.<ref name=WHO>{{cite web | title = West Nile Virus | url = http://www.who.int/mediacentre/factsheets/fs354/en/ }}</ref>


====Transmission====
====Incubation Period====
Human infection is most often the result of bites from infected mosquitoes. Mosquitoes become infected when they feed on infected birds, which circulate the virus in their blood for a few days. The virus eventually gets into the mosquito's salivary glands. During later blood meals (when mosquitoes bite), the virus may be injected into humans and animals, where it can multiply and possibly cause illness. The virus may also be transmitted through contact with other infected animals, their blood, or other tissues. A very small proportion of human infections have occurred through organ transplant, blood transfusions and breast milk. There is one reported case of transplacental (mother-to-child) WNV transmission. To date, no human-to-human transmission of WNV through casual contact has been documented, and no transmission of WNV to health care workers has been reported when standard infection control precautions have been put in place. Transmission of WNV to laboratory workers has been reported.
The incubation period for WNV disease is typically 2 to 6 days. It ranges from 2 to 14 days and can be several weeks in immunocompromised patients. An estimated 70-80% of human WNV infections are subclinical or asymptomatic. Less than 1% of infected individuals develop neuroinvasive disease, which typically manifests as [[meningitis]], [[encephalitis]], or acute flaccid paralysis.<ref name=CBC>{{cite web | title = West Nile Virus | url = http://www.cdc.gov/westnile/healthCareProviders/healthCareProviders-ClinLabEval.html }}</ref>


====Incubation period====
====Asymptomatic West Nile Infection====
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.
When left untreated, approximately 80% of the people infected by virus remain asymptomatic.


====Asymptomatic west nile infection====
====West Nile Fever====
80% of the people infected by virus are not symptomatic. Most of them are not aware that they have the disease.
Around 20% of the patients infected with WNV develop West Nile fever and usually present with fever and other constitutional symptoms. If left untreated, the infection generally self-resolves with no complications or sequelae.


====West nile fever====
====Neuroinvasive Disease====
Around 20% of the people infected develop west nile 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.  
Approximately 1 in 150 persons infected with WNV will develop a severe form of disease if left untreated. Serious illness can occur in patients of any age. However, advanced age, systemic diseases such as malignancy and cardiovascular disease, and immunosuppressed patients are considered high risk for developing neuroinvasive disease.


====Neuroinvasive disease====
==Possible complications==
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.
*Complications from mild West Nile virus infection are very rare.
*Complications from severe West Nile virus infection are as follows


=====West nile meningitis=====
====Neurologic complications====
It usually presents with fever and signs of meningeal irritation like headache, stiffneck, nuchal rigidity and photophobia.
*Meningitis
*Encephalitis
*Parkinsonism
*Rhomboencephalitis
*Cerebellar dysfunction
*West nile poliomyelitis <ref name="Neurologic Complications of West Nile Virus">{{Cite web  | last = | first = | title = Neurologic Complications of West Nile Virus |  url = http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/neurology/neurologic-complications-west-nile-virus/ }}</ref>
*Dysphagia
*Permanent motor weakness
*Cranial nerve palsy


=====West nile encephalitis=====
====HEENT complications====
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.
*[[Chorioretinitis]]
*[[Papilledema]]
*[[Hearing loss]]


=====Acute flaccid paralysis=====
====Respiratory complications====
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.
*[[Ataxic breathing]]
*[[Apnea]]


==Possible Complications==
====Vascular 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]]
*[[Deep venous thrombosis]]
*[[Pressure ulcers]]
*[[Pressure ulcers]]
* [[Chorioretinitis]] (100% specificity for identifying West Nile virus infection in patients with possible West Nile virus encephalitis)<ref>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.</ref>
 
====Other visceral organ complications====
* [[Hepatitis]]
* [[Hepatitis]]
* [[Myocarditis]]
* [[Myocarditis]]
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* [[Pancreatitis]]
* [[Pancreatitis]]
* [[Splenomegaly]]<ref>Perelman A, Stern J. "Acute pancreatitis in West Nile Fever." ''American Journal of Tropical Medicine and Hygiene'' 1974; 23: 1150-1152.</ref><ref>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</ref><ref>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.</ref>
* [[Splenomegaly]]<ref>Perelman A, Stern J. "Acute pancreatitis in West Nile Fever." ''American Journal of Tropical Medicine and Hygiene'' 1974; 23: 1150-1152.</ref><ref>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</ref><ref>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.</ref>
* [[Brain damage]]
* [[Death]]


==Prognosis==
==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.
*In general, the prognosis of a mild WNV infection is excellent. Most patients with non-neuroinvasive WNV disease or WNV meningitis recover completely. However, 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.
*Patients who recover from WNV encephalitis often have residual neurologic deficits. Among patients with neuroinvasive disease, the overall case-fatality ratio is approximately 10%. The rate is significantly higher among patients with WNV encephalitis compared to patients with 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==
==References==
{{Reflist|2}}
{{Reflist|2}}

Latest revision as of 19:27, 11 August 2015


Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ammu Susheela, M.D. [2]

Overview

WNV is usually transmitted to humans by the culex mosquito after feeding on infected birds with high-level viremia. Following an incubation period of 2-14 day, untreated patients can remain asymptomatic or present with West Nile fever or with life-threatening neuroinvasive disease. Common complications of WNV infections include neurological impairment. The prognosis of mild disease is excellent; whereas West Nile meningitis and encephalitis may have residual neurologic deficits.

Natural History

WNV is a member of Japanese encephalitis antigenic complex of the family Flaviviridae. It is transmitted by a mosquito bite, most commonly Culex pipiens. Birds are the natural reservoir of the virus and the disease is generally transmitted to humans when a mosquito that previously fed on a bird with high-level viremia bites a human.[1]

Incubation Period

The incubation period for WNV disease is typically 2 to 6 days. It ranges from 2 to 14 days and can be several weeks in immunocompromised patients. An estimated 70-80% of human WNV infections are subclinical or asymptomatic. Less than 1% of infected individuals develop neuroinvasive disease, which typically manifests as meningitis, encephalitis, or acute flaccid paralysis.[2]

Asymptomatic West Nile Infection

When left untreated, approximately 80% of the people infected by virus remain asymptomatic.

West Nile Fever

Around 20% of the patients infected with WNV develop West Nile fever and usually present with fever and other constitutional symptoms. If left untreated, the infection generally self-resolves with no complications or sequelae.

Neuroinvasive Disease

Approximately 1 in 150 persons infected with WNV will develop a severe form of disease if left untreated. Serious illness can occur in patients of any age. However, advanced age, systemic diseases such as malignancy and cardiovascular disease, and immunosuppressed patients are considered high risk for developing neuroinvasive disease.

Possible complications

  • Complications from mild West Nile virus infection are very rare.
  • Complications from severe West Nile virus infection are as follows

Neurologic complications

  • Meningitis
  • Encephalitis
  • Parkinsonism
  • Rhomboencephalitis
  • Cerebellar dysfunction
  • West nile poliomyelitis [3]
  • Dysphagia
  • Permanent motor weakness
  • Cranial nerve palsy

HEENT complications

Respiratory complications

Vascular complications

Other visceral organ complications

Prognosis

  • In general, the prognosis of a mild WNV infection is excellent. Most patients with non-neuroinvasive WNV disease or WNV meningitis recover completely. However, fatigue, malaise, and weakness can linger for weeks or months.
  • Patients who recover from WNV encephalitis often have residual neurologic deficits. Among patients with neuroinvasive disease, the overall case-fatality ratio is approximately 10%. The rate is significantly higher among patients with WNV encephalitis compared to patients with WNV meningitis.

References

  1. ↑ "West Nile Virus".
  2. ↑ "West Nile Virus".
  3. ↑ "Neurologic Complications of West Nile Virus".
  4. ↑ Perelman A, Stern J. "Acute pancreatitis in West Nile Fever." American Journal of Tropical Medicine and Hygiene 1974; 23: 1150-1152.
  5. ↑ 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
  6. ↑ 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.
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