Sandbox ammu WNV EPi

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

Overview

Universal screening for WNV is not recommended. As blood and transplant-related transmissions of the virus have been reported, nucleic acid tests (NAT) may be used to screen for WNV among potential blood and solid organ donors. In blood donation, individual screening is not recommended either. Instead, a "minipool" nucleic acid testing program (MP NAT) is implemented. Positive pools warrant further investigation for individuals. Patients with positive NAT may not donate blood or solid organs for at least 120 days. Re-testing after 120 days is indicated.

Screening

Universal screening for WNV is not recommended. Screening is only recommended for blood and solid organ transplant donors.

Screening donor blood products

Following the discovery of WNV transmission by blood transfusions, WNV blood donor screening is performed using nucleic acid testing (NAT). A "minipool" nucleic acid testing program (MP NAT) is currently implemented to detect WNV viremia among donors. In contrast, serological testing is not feasible for screening purposes because IgM seroconversion may be detectable approximately 5 months following infection. Pools with positive NAT results warrant further investigation for individual screening. Individual patients with positive NAT may not donate blood for at least 120 days.

Screening solid organ transplant donors

Although the only data on human-to-human transmission by organ transplantation is derived from reports that included deceased donors, transmission to recipients may still occur if donors have NAT-negative IgM-positive results. These findings suggest that clearance of the WNV from solid organs may be delayed compared to its clearance from plasma. Accordingly, screening for WNV among transplant donors is recommended using NAT. There is no evidence to demonstrate the optimal time for solid organ donation in cases of positive NAT, but re-testing after 120 days to confirm negative NAT has become common practice. Patients with negative results after 120 days may donate solid organs.

References

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2] Associate Editor(s)-in-Chief: Alejandro Lemor, M.D. [3]

Overview

West Nile fever must be differentiated from other diseases that cause fever, skin rash, myalgias, and back pain, such as other viral infections due to rhinovirus, enterovirus D68, coxsackievirus, influenza, echovirus. Patients with severe WNV infection may present with meningitis, encephalitis, or flaccid paralysis. These diseases must be differentiated from other diseases that cause severe headache, altered mental status, seizures, and paralysis, such as herpes virus encephalitis, enterovirus encephalitis, bacterial encephalitis, metabolic encephalitis, poliomyelitis, and Guillain-Barre syndrome.

Differential Diagnosis

Differential diagnosis of West Nile fever

Differential Diagnosis
Rhinovirus infection
Enterovirus D68 infection
Coxsackievirus infection
Influenza infection
Rocky Mountain spotted fever
Chikungunya virus infection
Dengue fever

Differential diagnosis of severe West Nile virus infection

West Nile Virus Presentation	Differential Diagnosis
West Nile Virus Encephalitis and Meningitis	Herpes simplex virus, coxsackievirus, echovirus, other arbovirus, metabolic encephalopathy, bacterial meningitis, St. Louis encephalitis, eastern equine encephalitis virus, western equine encephalitis, Lyme disease.
West Nile Virus Flaccid Paralysis	Acute poliomyelitis, Guillain-Barre syndrome, stroke, myasthenia gravis

References

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [4]

Overview

On physical examination, patients with WNV infection may have no specific signs. Physical examination findings may range from an isolated fever to signs of severe neurological impairment, meningeal irritation, stupor, and coma.

Physical exam

Most patients with WNV are asymptomatic or experience a mild disease that may often have no signs on physical examination.

Vital signs

• Fever
• Tachycardia
• Tachypnea

Skin

• Macular or papular truncal rash

HEENT

• Papilledema
• Nystagmus
• Lymphadenopathy
• Non exudative pharyngeal erythema

Chest

• Ataxic or apneustic breathing

Abdomen

• Abdominal tenderness
• Splenomegaly
• Vesical fullness

Neurologic

• Altered mental status
• Tremor
• Myoclonus
• Bradykinesia
• Rigidity
• Absent corneal reflex
• Absent gag reflex
• Memory loss
• Sensory loss
• Motor weakness
• Neck stiffness
• Positive Kernig and Brudzinski tests
• Hyperreflexia
• Positive Babinski reflex

References

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [5]; Associate Editor(s)-in-Chief: Ammu Susheela, M.D. [6]

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.

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.

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
• Dysphagia
• Permanent motor weakness
• Cranial nerve palsy

HEENT complications

• Chorioretinitis
• Papilledema
• Hearing loss

Respiratory complications

• Ataxic breathing
• Apnea

Vascular complications

• Deep venous thrombosis
• Pressure ulcers

Other visceral organ complications

• Hepatitis
• Myocarditis
• Nephritis
• Pancreatitis
• Splenomegaly

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.