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As of July 1, 2025, Idaho law requires CDH to verify the lawful presence of those applying for public benefits through our agency.

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As of July 1, 2025, Idaho law requires CDH to verify the lawful presence of those applying for public benefits through our agency.

The programs impacted by this change are:
  • Sliding fee discount for medical clinic or counseling services for those not on Medicaid
  • WIC, PAT, and NFP applicants who are not adjunctively eligible for Idaho Medicaid, SNAP, or TAFI

You can review the policy here and then complete the form below to verify your lawful presence online or you can visit one of our CDH offices to confirm in person.

Lawful Presence Online Forms: English | Spanish

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In Health Alert Network, News

Health Advisory: Increased Risk of Severe West Nile Virus and Other Arboviral Diseases in Patients Receiving B Cell-Depleting or B Cell-Modulating Medications

by on August 21, 2026

HEALTH ALERT NETWORK

Health District 4

Advisory for Healthcare Providers

August 21, 2026

Key Actions for Healthcare Providers

  1. Educate patients receiving B cell-depleting or B cell-modulating therapies (particularly anti-CD20 monoclonal antibodies) about their increased risk for severe arboviral disease and the importance of mosquito and tick bite prevention.
  2. Maintain a high index of suspicion for West Nile virus (WNV) and other arboviral infections in immunocompromised patients presenting with fever, meningitis, encephalitis, acute flaccid paralysis, or unexplained neurologic illness during or following mosquito season.
  3. Consider molecular testing (RT-PCR) when arboviral disease is suspected in patients receiving B cell-depleting therapies, as these patients may have delayed or absent antibody responses and may not test positive by serology alone.
  4. Obtain a detailed exposure history, including mosquito exposure, outdoor activities, tick exposure, and recent travel when relevant.
  5. Consult with Idaho Bureau of Laboratories (IBL) at (208) 334-2235 or Central District Health at (208) 327-8625 regarding testing options, particularly for immunocompromised patients with suspected arboviral disease.

Summary

  • West Nile virus (WNV) is the most commonly reported mosquito-borne disease in Idaho.
  • Idaho is currently in peak WNV transmission season. In 2025, Idaho reported nine WNV cases (five neuroinvasive and four non-neuroinvasive). As of August 2026, one neuroinvasive WNV case has been reported. See Idaho’s WNV webpage for current surveillance data.
  • CDC recently issued a Health Advisory regarding severe arboviral disease among patients receiving B cell-depleting or B cell-modulating medications.
  • Patients receiving anti-CD20 monoclonal antibodies are at increased risk for severe neuroinvasive disease, prolonged illness, long-term neurologic sequelae, and death.

West Nile virus is endemic in Idaho and remains the leading cause of domestically acquired arboviral neuroinvasive disease in the United States. Although most infections are asymptomatic, severe neurologic disease can occur, particularly among older adults and immunocompromised individuals. As Idaho enters the late-summer peak transmission period, healthcare providers should be aware of the increased risk of severe arboviral disease among patients receiving B cell-depleting or B cell-modulating therapies.

Background

A growing number of reports of severe arboviral neuroinvasive disease have been associated with patients taking B cell-depleting monoclonal antibodies (mAbs) targeting the CD20 cell surface antigen, in particular. Anti-CD20 mAbs currently approved in the United States include rituximab and biosimilars, ocrelizumab, ofatumumab, ublituximab, obinutuzumab, and ibritumomab tiuxetan. Among published case reports of arboviral neuroinvasive disease in individuals receiving anti-CD20 mAbs, overall mortality was approximately 40%, and most survivors experienced long-term neurologic sequelae. West Nile virus was the most common infecting arbovirus in these reports.

In recent years, a novel clinical presentation of chronic neurodegenerative encephalitis developing over months to years has been described in at least five patients receiving rituximab who were infected with an orthobunyavirus, including Jamestown Canyon virus, Cache Valley virus, or Potosi virus. All patients died.

Diagnosis of arboviral infection in patients receiving anti-CD20 mAbs or other medications that deplete B cells (e.g., anti-CD38 mAbs) or modulate B cell function (e.g., B cell activating factor inhibitors) often requires molecular rather than serologic testing because these patients might not form antibodies against a new infection.

Because no human vaccines or specific antiviral therapies are available for West Nile virus infection, prevention of mosquito bites and early recognition of severe disease remain critical.

 

Clinical Considerations

1. Patient Education and Prevention

Advise patients receiving B cell-depleting or B cell-modulating therapies to:

  • Use EPA-registered insect repellents.
  • Wear long sleeves and pants when outdoors.
  • Avoid mosquito exposure during peak biting times (dawn and dusk).
  • Eliminate standing water around homes.
  • Maintain intact window and door screens.
  • Perform tick checks after outdoor activities.

2. Clinical Evaluation

  • Consider WNV and other arboviral infections in immunocompromised patients with febrile illness, meningitis, encephalitis, acute flaccid paralysis, or unexplained neurologic disease.
  • Recognize that immunocompromised patients may have prolonged incubation periods, atypical presentations, or illness occurring outside the usual arboviral season.
  • Obtain a thorough exposure history, including mosquito, tick, outdoor, and travel exposures.

3. Diagnostic Testing

  • Consider molecular testing (RT-PCR or mNGS) when arboviral infection is suspected in patients receiving B cell-depleting therapies.
  • Delayed or absent antibody responses may result in false-negative serologic tests.
  • Molecular testing is available through some commercial laboratories but not at Idaho Bureau of Laboratories (IBL).
  • WNV IgM testing is available at IBL but should be interpreted cautiously in patients receiving B cell-depleting therapies.
  • For testing consultation, contact IBL at (208) 334-2235 or Central District Health at (208) 327-8625.
  • See the diagnostic testing algorithm for suspected West Nile virus disease for details.

Additional Resources

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