Alabama Department of Public Health
Alabama Emergency Response Technology (ALERT) 
Health Alert Network (HAN)
August 20, 2026
Risk of Severe Arboviral Disease in Patients Receiving B Cell-Depleting or Modulating Medications

The Centers for Disease Control and Prevention (CDC) has issued a health advisory to notify clinicians, public health authorities, and the public about the risk of severe arboviral neuroinvasive disease among patients who are receiving B cell-depleting or B cell-modulating medications, particularly anti-CD20 monoclonal antibodies (mAbs).

Background

Arboviruses are RNA viruses transmitted by biting arthropods, most commonly mosquitoes and ticks. Although most arboviral infections are subclinical, symptomatic arboviral disease typically presents as acute febrile or neurologic illness (e.g., aseptic meningitis, encephalitis, or acute flaccid myelitis). The incubation period typically ranges from days to weeks from arthropod bite to the onset of symptoms and can be longer in immunocompromised persons.

Medications that deplete B cells or modulate B cell function, used to treat B cell malignancies, many autoimmune conditions, and transplant rejection, can increase the risk of severe arboviral disease. B cell-depleting monoclonal antibodies (mAbs) targeting the CD20 cell surface antigen have been associated with a growing number of reports of severe arboviral neuroinvasive disease in patients on these medications. 

The Alabama Department of Public Health (ADPH) encourages health professionals to be aware of this information because the United States had an early and strong start to this year's West Nile virus season and many weeks of the arbovirus transmission season remain.

Recommendations for Clinicians

• When prescribing immunosuppressive medications or caring for patients taking immunosuppressive medication, particularly B cell-depleting mAbs, educate patients about the risk of severe arboviral disease and advise them to take measures to prevent mosquito and tick bites.
• Be aware that patients with an arboviral disease who are immunocompromised can have a prolonged incubation period or an atypical course and might not present with illness during the usual months when mosquitoes and ticks are active.
• Take a thorough exposure and travel history for patients presenting with a febrile or neurologic illness.
• When an arboviral infection is suspected in a patient receiving B cell-depleting mAbs, preferentially order molecular testing (i.e., RT-PCR or mNGS).

For more information, visit: https://www.cdc.gov/han/php/notices/han00532.html.