# Presentation: 076861

## West Nile Virus: Background and Ecology

- First isolated in West Nile district, Uganda, 1937
- Commonly found in humans and birds and other vertebrates in Africa, Eastern Europe, West Asia, and the Middle East, but has not previously been documented in the Western Hemisphere
- Basic transmission cycle involves mosquitoes feeding on birds infected with the West Nile virus
- Infected mosquitoes then transmit West Nile virus to humans and animals when taking a blood meal

## The Japanese Encephalitis Serocomplexof the Family Flaviviridae

- The Japanese Encephalitis Serocomplexof the Family Flaviviridae

## West Nile Virus Outbreaks

- Israel – 1951-1954, 1957, 2000
- France – 1962, 2000
- South Africa – 1974
- Romania – 1996
- Italy – 1997
- Russia – 1999
- United States – 1999-2002

## Spread of West Nile Virus in the U.S. 7/30/02

- Humans

**2001**

**2000**

**1999**

**2002**

- Spread of West Nile Virus in the U.S. 7/30/02

## 1999 - 2002 Verified WNV Surveillance Results Reported to ArboNet

| Year | States | Humans/
Fatalities | Birds | Mosquito
Pools | Horses |
| --- | --- | --- | --- | --- | --- |
| 1999 | 4 | 62/6 | ? | 16 | 25 |
| 2000 | 11 + DC | 21/2 | 4305 | 515 | 63 |
| 2001 | 27 + DC | 66/9 | 7332 | 919 | 731 |
|  2002  | 34 + DC | 89/4 | 1545 | 349 | 66 |

## WNV Case-Patient Demographics & Mortality United States, 1999-2001

|  | 1999-2000 | 2001 |
| --- | --- | --- |
| n | 83 | 66 |
| Age (yr) |  |  |
|     median | 65 | 68 |
|     range | 5 - 90 | 19 - 90 |
| Males | 54% | 65% |
| CFR | 11% | 14% |

**Notes:**
Among the 66 cases that were reported in 2001, the median age was 68 years with a range of 19 to 90 years. In 2001, there were 9 deaths attributed to the WNV infection a case fatality ratio of 14%. As you can see, there is no significant difference in the proportion of males or the CFR between the 1999/2000 cases and the 2001 cases.

## Date of Symptom Onset, West Nile VirusUnited States, 1999-2001

**Notes:**
As of about three weeks ago, we have received reports of 59 cases of WNV illness that occurred in 2001. The first two reported cases were reported from Florida in mid-July and the last reported case occurred in Georgia in the first week of December. Cases occurred over a 22-week period with the peak occurring during the week ending September 1.

## 1999 and 2000 Serosurvey Results 

| Location | Participants | Positives | Seroprevalence (%) |
| --- | --- | --- | --- |
| NYC 1999
Queens | 677 | 19 | 2.6 |
| NYC 2000
Staten Is. | 871 | 4 | 0.46 |
| NYS 2000
Suffolk Co. | 834 | 1 | 0.12 |
| CT 2000
Fairfield Co. | 731 | 0 | 0.0 |

## Clinical Epidemiology

- Incubation period 3 - 14 days
- 20% develop “West Nile fever”
- 1 in 150 develop meningoencephalitis
- Advanced age primary risk factor for severe neurological disease and death

## West Nile Fever: Classic Clinical Description

- Mild dengue-like illness of sudden onset
- Duration 3 - 6 days
- Fever, lymphadenopathy, headache, abdominal pain, vomiting, rash, conjunctivitis, eye pain, anorexia
- Symptoms of West Nile fever in contemporary outbreaks not fully studied

## Symptoms of Hospitalized Patients withWest Nile Virus, New York City, 1999

- 2%

- Lymphadenopathy

- 19%

- Rash

- 27%

- Diarrhea

- 46%

- Change in mental status

- 47%

- Headache

- 51%

- Vomiting

- 53%

- Nausea

- 56%

- Weakness

- 90%

- Fever

## Neurological Presentations of West Nile Virus Infection

- New York City 1999
- Encephalitis/meningoencephalitis 62%
- Meningitis 32%
- Complete flaccid paralysis 10%
- Confused with Guillain-Barre syndrome
- EMG and nerve conduction velocity studies indicating both axonal and demyelinating lesions, with axonal lesions most prominent
- Previous series
- Ataxia, extrapyramidal signs, cranial nerve abnormalities, myelitis, optic neuritis, seizures

## Neurological Presentations of West Nile Virus Infection

- Preliminary data 2002
- Complaints of weakness out of proportion to evidence on physical exam
- Myoclonus nearly a universal finding
- Some patients have Parkinsonian-like signs

## Outcome of West Nile Virus Infection among Hospitalized Patients

- At discharge (NY and NJ, 2000)
- More than half did not return to functional level
- Only one-third fully ambulatory
- At one year (NYC 1999 patients)
- Fatigue 67%, memory loss 50%, difficulty walking 49%, muscle weakness 44%, depression 38%

## Predictors of Death among West Nile Virus-Infected Patients

- Change in level of consciousness
- Encephalitis with severe muscle weakness
- Advanced age
- Possibly diabetes mellitus or immunosuppression

## Treatment

- Supportive treatment
- About 25% require ICU care; 10% mechanical ventilation
- Ribavirin and interferon-a2b
- In-vitro activity in high doses
- One reported comatose patient did not improve
- Worse outcome with ribavirin in open-label trial in Israel – unclear patient selection

## Risk of West Nile Virus Transmission Through Blood Transfusion

- Concern: most WNV infections have no or only mild symptoms, and transient viremia occurs after infection
- Transfusion-transmission of WNV or other related flaviviruses not reported, but plausible
- Mathematical modeling: estimated risk of transfusion-transmission was 2 in 10,000 during NYC outbreak (Transfusion, Aug 2002)
- WNV should be considered in persons who develop unexplained fever, meningitis, or encephalitis after transfusion

## Laboratory Findings from  WNV Outbreaks in New York and Israel

- Total leukocyte count normal or slightly elevated
- Hyponatremia occasionally in patients with encephalitis
- CSF
- Leukocytes 0 - 1782 cells/mm3, mostly lymphocytes
- Protein universally elevated 51 - 899 mg/dL
- Glucose normal
- CT brain:  no evidence of acute disease
- MRI in one-third showed enhancement of leptomeninges, periventricular areas, or both