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West Nile Virus: Surveillance and Clinical Issues Anne Kjemtrup, DVM, MPVM, Ph.D. California Department of Public Health Vector-Borne Disease Section 1.

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Presentation on theme: "West Nile Virus: Surveillance and Clinical Issues Anne Kjemtrup, DVM, MPVM, Ph.D. California Department of Public Health Vector-Borne Disease Section 1."— Presentation transcript:

1 West Nile Virus: Surveillance and Clinical Issues Anne Kjemtrup, DVM, MPVM, Ph.D. California Department of Public Health Vector-Borne Disease Section 1

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3 Sequence of WNV detection events in California relative to human case onset, 2008 Disease Week of Onset Number of human cases JanFebMar AprMay JunJul Aug SepOctNovDec 3/21 1/29 6/20 6/27 4/4 3

4 The Clinical “Pyramid Picture” ~80% Asymptomatic ~20% West Nile fever <1% WNND ~10% of WNND are fatal (<0.1% of total infections) 4

5 West Nile fever ► Typical clinical manifestations ► Fever ► Headache ► Fatigue ► Muscle weakness ► Muscle aches ► Skin rash on trunk of body ► Anorexia ► Duration of illness=3 – 6 days ► Outcome: in general, excellent w/o specific treatment 5

6 *Watson JT et al. Ann Intern Med 2004; 141:

7 West Nile Neuroinvasive Disease ► Aseptic Meningitis (25%-35% WNND cases)  Fever, headache, malaise, muscle weakness  Nausea, vomiting, stiff neck, myalgia, cranial nerve palsies  Outcome generally good ► Encephalitis (60% - 70% WNND cases)  Alternation of consciousness (lethargy  coma), tremors, weakness, brainstem/cranial nerve deficits, cerebellar signs/symptoms  Outcome variable. Fatality-case ratio up to 15%; increases with advanced age. Potential of long-term neurologic deficits in some patients. ► WNV “Poliomyelitis”- a flaccid paralysis syndrome (uncommon).  Acute onset of asymmetric limb weakness or paralysis in absence of sensory loss  Can occur in the absence of fever, headache, or other WNV- associated signs. 7

8 CharacteristicWNF n (%) WNND OR 95% CI Diabetes 9 (7) 12 (20) Age (>64 years) 24 (13) 25 (31) – 5.60 Hypertension 36 (26) 26 (44) – 4.27 Gender (male) 114 (62) 56 (69) Preliminary Univariate Analysis (2006): Risk Factors for Developing WNND vs. WN Fever 8

9 WNV Outcome Picture ► Risk factors for severe disease include increasing age, immunosuppression, diabetes, and hypertension.  Though risk of WNV infection higher in children than adults, risk of WNND in children lower than adults. ► Most WNF patients recover in first few months. For some, problems may linger (subclinical encephalitis? Other risk factors?). ( Encephalitis Outcome Study Shilpa Gavali-Jani, VRDL; Carson et al., CID 2006; Haaland et al EID 2006 ) 9

10 “We’re pretty sure it’s the West Nile virus...” Diagnosis 10

11 West Nile virus Laboratory Testing ► West Nile virus (WNV) testing within the regional public health laboratory network is recommended on individuals with the following:  A. Encephalitis  B. Aseptic meningitis (Note: Consider enterovirus for individuals ≤ 18 years of age)  C. Acute flaccid paralysis; atypical Guillain-Barré Syndrome; transverse myelitis; or  D. Febrile illness ► Illness compatible with West Nile fever and lasting ≥ 7 days ► Must be seen by a health care provider 11

12 West Nile virus Laboratory Testing ► IgM antibody-capture ELISA for serum collected within 8-14 days of illness onset or CSF collected within 8 days of illness onset  IgM in CSF strong suggests CNS infection since IgM does not cross blood-brain barrier. ► Plaque-reduction neutralization test (PRNT) used to distinguish false-positive results or cross reactivity with other arboviruses 12

13 West Nile virus Why test? ► Differentiate from other conditions (enterovirus, other arboviral diseases) ► Forewarn of further complications (e.g. flaccid paralysis) ► Help with treating/dealing with unexplained lingering health issues. Early testing in the febrile phase will help determine acute infection. ► A febrile positive WNV patient may have older family members at risk for serious WNV disease (since often acquired near the place of residence) - in effect functioning as a local sentinel. ► Mosquito control and public health agencies can institute proper control measures to save others from serious disease. ► Testing by local health departments is FREE! 13

14 Treatment ► Supportive Care ► Experimental: Clinical trial of interferon for meningoencephalitis patients underway. 14

15 For More Information: 15

16 Where it all began… West Nile Region of Uganda Mt. Luku Islandmountain Murchison Falls 16


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