ARBOVIRAL DISEASES

Wisconsin Division of Public Health Disease Surveillance Manual (EpiNet, March 2006)

I. IDENTIFICATION

A. CLINICAL DESCRIPTION: Arboviral infection may be asymptomatic or result in a febrile illness of variable severity, sometimes associated with neurologic symptoms ranging from headache to aseptic meningitis and encephalitis. Arboviral encephalitis cannot be distinguished clinically from infection with other neurotropic viruses. Symptoms include fever, headache, confusion or other alterations in sensorium, nausea, or vomiting. Signs may include evidence of elevated intercranial pressure, or meningeal irritation, cranial nerve palsies, paresis or paralysis, altered reflexes or convulsions. Less common neurological syndromes can include cranial and peripheral neuritis/neuropathies, including Guillain-Barré syndrome. Arboviruses causing encephalitis include the following:

1. West Nile virus (WNV)
2. St. Louis encephalitis (SLE)
3. California encephalitis [includes infection with the following viruses: La Crosse (LAC), Jamestown Canyon (JC), Snowshoe Hare (SSH), Trivittatus (TVT), and California viruses (CE)]
4. Eastern equine encephalomyelitis (EEE)
5. Western equine encephalomyelitis (WEE)
6. Powassan encephalitis (POW)
7. Other central nervous system infections transmitted by mosquitoes, ticks, or midges [Venezuelan equine encephalomyelitis (VEE), Cache Valley encephalitis (CV)]

These viruses may also cause non-neuroinvasive syndromes, most commonly manifesting as febrile illnesses (e.g. West Nile Fever). These are non-localized, self-limited illnesses with headache, myalgias, and arthralgias and sometimes accompanied by a skin rash or lymphadenopathy. Although rare, non-neuroinvasive syndromes caused by these viruses may also include myocarditis, pancreatitis or hepatitis. Laboratory confirmation of arboviral illnesses lacking a documented fever does occur, and overlap of the various clinical syndromes is common.

B. CLINICAL CRITERIA FOR DIAGNOSIS:
Clinical cases of arboviral disease are classified according to the following criteria:

• Neuroinvasive disease requires the presence of fever and at least one of the following signs and symptoms, as documented by a physician and in the absence of a more likely clinical explanation:
• Acutely altered mental status (e.g., disorientation, obtundation, stupor, coma) OR
• Other acute signs of central or peripheral neurologic dysfunction (e.g., paresis or paralysis, nerve palsies, sensory deficits, abnormal reflexes, generalized convulsions, abnormal movements) OR
• Pleocytosis (increased white blood cell count) in cerebrospinal fluid (CSF) associated with illness clinically compatible with meningitis (e.g., headache or stiff neck)
• Non-neuroinvasive disease requires the presence of documented fever, as measured by the patient or clinician, the absence of neuroinvasive disease (above), and the absence of a more likely clinical explanation for the illness. Signs and symptoms may include, fever, headache, stiff neck, myalgias, arthralgias, rash, lymphadenopathy, nausea or vomiting.

C. REPORTING CRITERIA: Laboratory evidence (probable OR confirmed*) with a compatible clinical illness.

*The Wisconsin Department of Health and Family Services, Division of Public Health will determine whether the case is classified as probable or confirmed.

D. LABORATORY CRITERIA FOR CONFIRMATION:

Cases of arboviral disease are classified according to the following laboratory criteria:

• Confirmed case :
• Fourfold or greater change in virus–specific serum antibody titer, OR
• Isolation of virus from or demonstration of viral antigen or genomic sequences in tissue, blood, CSF, or other body fluid, OR
• Virus-specific immunoglobulin M (IgM) antibodies in CSF by antibody-capture enzyme immunoassay (EIA), OR
• Virus-specific IgM antibodies demonstrated in serum by antibody-capture EIA AND confirmed by demonstration of virus specific immunoglobulin G (IgG) antibodies in the same or later specimen by another serologic assay (such as neutralization or hemagglutination inhibition).
• (Physicians are encouraged to draw a convalescent blood sample from patients with a single positive IgM serum antibody 2-3 weeks after the first test .)
  
• Probable case :

• Stable (less than or equal to a twofold change), but elevated titer of virus-specific serum antibodies, OR
• Virus-specific serum IgM antibodies detected by antibody-capture EIA but with no available results of a confirmatory test in the same or later specimen.

Comment :
Because serologic cross-reactivity often occurs between closely related arboviruses (especially between SLE and WNV), positive results from a single serologic test can be misleading. It is therefore recommended that an arbovirus panel (which includes testing for WNV, SLE, LAC and EEE) be requested when there is clinical suspicion of arboviral disease, rather than requesting individual tests.

Arboviral transmission varies according to local climatic conditions and West Nile virus-specific IgM antibody can be detectable for more than a year following infection. Therefore, the importance of a recent travel history and thorough serologic testing cannot be overemphasized.

E. WISCONSIN CASE DEFINITION*:

An illness is classified as a case if it meets one or more of the above clinical criteria, AND one or more of the above laboratory criteria, AND occurred when and where there is a high likelihood of vector activity.

*The Wisconsin Department of Health and Family Services, Division of Public Health will make this determination.

II. ACTIONS REQUIRED / PREVENTION MEASURES

A. WISCONSIN DISEASE SURVEILLANCE CATEGORY II: Report to the patient's local health officer on an Acute and Communicable Disease Case Report (DPH 4151) or other means within 72 hours of the identification of a case or suspected case.

B. EPIDEMIOLOGY REPORTS REQUESTED:

1. Acute and Communicable Diseases Case Report (DPH 4151).
2. Arbovirus Infection Follow-up Form (CDES 103).

C. PUBLIC HEALTH INTERVENTIONS:

• Source investigation by LHD to identify mosquito breeding sites near the probable location of the exposure.
• Determine if friends or family <15 years old had similar illness in the previous month (particularly for La Crosse encephalitis).

III. CONTACTS FOR CONSULTATION

A. BCDP / COMMUNICABLE DISEASE EPIDEMIOLOGY SECTION: (608) 267-7321.

B. REGIONAL STAFF: See Epinet Introduction: “REGIONAL OFFICE CONTACTS”.

C. WSLH / VIRAL SEROLOGY: (608) 262-0248.

IV. RELATED REFERENCES

1. "Arboviral Infections" DPH Disease Fact Sheet Series: View a list of all current Communicable Disease Fact Sheets
   
2. Heymann DL, ed. ARTHROPOD-BORNE VIRAL DISEASES. In: Control of Communicable Diseases Manual. 18 th ed. Washington , DC : American Public Health Association, 2004:29-43.
   
3. “Revision of the National Surveillance Case Definition of Diseases Caused by Neurotropic Domestic Arboviruses, Including the Addition to the NNDSS of Non-Neuroinvasive Illness Caused by these Viruses”, Committee of Infectious Disease, Position Statement 04-ID-01, Council of State and Territorial Epidemiologists website (accessed on 12/28/04), http://www.cste.org/ps/2004pdf/04-ID-01-final.pdf.

V. DISEASE TRENDS

Since the first human case of West Nile virus was diagnosed in Wisconsin in 2002, West Nile virus cases have declined. Fifty-two cases were diagnosed in 2002, while there were only 17 cases in 2003 and 12 cases in 2004. There is no way to predict if this trend will continue or if the disease will have periodic increases in activity. The majority of cases of West Nile virus were reported in adults over the age of 50.

Wisconsin averaged approximately 13 cases of La Crosse encephalitis annually between 1999-2004. Sixty-eight percent (51/75) of the reported cases were in children less than 10 years old.

Cases of arboviral disease were reported from June through November with the highest incidence being reported from July through September.

For more information on West Nile virus activity in Wisconsin , please refer to the DHFS website at http://dhfs.wisconsin.gov/communicable/WestNilevirus/.

For national statistics and information about West Nile virus activity, please see the please see the Centers for Disease Control and Prevention website at http://www.cdc.gov/ncidod/dvbid/westnile/index.htm.

For more information on other arboviruses, please see the Centers for Disease Control and Prevention website at http://www.cdc.gov/ncidod/dvbid/arbor/index.htm.