Authored by Brian Koffman,(MDCM )retired, MSEd
Bottom Line:
West Nile season started early, and CLL weakens immunity even before treatment. Avoiding mosquito bites is your best protection.
Why this matters right now:
The U.S. Centers for Disease Control and Prevention (CDC) has alerted doctors that mosquito-borne (arboviral) illnesses, including West Nile virus, started unusually early this season. The CDC specifically warns that people whose immune systems are weakened, especially those taking medicines that lower or remove B cells, are much more likely to become severely ill, to have lasting problems, or to die from these infections.
Why CLL and SLL themselves weaken the immune system:
Chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) are the same disease affecting B cells, the cells that make antibodies. Even if a person has never been treated, and even in active surveillance (aka “watch and wait”), the immune system does not work normally:
• Antibody levels (immunoglobulins) are often low, a condition called hypogammaglobulinemia.
• T cells, natural killer cells, and infection-fighting white cells also work poorly.
• These problems tend to worsen slowly over time and make vaccines less effective.
This reason is why infection is one of the most common serious complications of CLL / SLL. Being “untreated” does not mean “not immunocompromised.”
How anti-CD20 antibodies can add to the risk:
Anti-CD20 antibodies (rituximab, obinutuzumab): These remove cancerous and healthy B cells for many months — sometimes a year or longer after the last dose. Antibody levels can stay low. In reported cases of West Nile and similar viruses in people on these drugs, illness was frequently severe, involved the brain and spinal cord, and can be fatal.
Another important warning: in people on B cell–depleting drugs, the usual blood antibody test for West Nile virus can be falsely negative, because the body cannot make antibodies. Diagnosis may require a different test (PCR). Mention any recent anti-CD20 treatment to every clinician who evaluates a fever.
Oral targeted drugs have not been shown to raise West Nile risk on their own. But keep in mind that they, especially venetoclax, are almost always given together with rituximab or obinutuzumab. Ask your care team whether an antibody is or was part of your treatment.
How to avoid mosquito bites:
There is no vaccine and no proven treatment for West Nile virus in people, so avoiding bites is the only real protection.
• Use an EPA-registered insect repellent every time you go outdoors. Look for DEET, picaridin, IR3535, or oil of lemon eucalyptus. Apply over sunscreen and reapply as directed on the label. Products such as citronella, cedar, or peppermint oils have not been shown to work.
• Cover up. Long-sleeved shirts, long pants, and socks. Loose, light-colored clothing is more comfortable in heat.
• Treat clothing and gear with permethrin (never apply permethrin to skin) for extra protection during outdoor work or travel.
• Limit time outdoors from dusk to dawn, when the Culex mosquitoes that spread West Nile virus bite most.
• Keep mosquitoes out of the house. Repair window and door screens and use air conditioning when available.
• Empty standing water weekly around the home: flowerpot saucers, buckets, tires, birdbaths, gutters, kiddie pools, pet bowls, and trash containers. Mosquitoes need only a bottle cap of water to breed.
• Check local alerts. Many counties post mosquito spraying and West Nile activity reports; be extra careful when local activity is reported.
When to call your care team:
Contact your hematology or oncology team if you develop any of the following during mosquito season:
• Fever, chills, severe headache, or body aches
• Confusion, unusual sleepiness, or difficulty concentrating
•Stiff neck, tremor, or trouble with balance or walking
• New weakness in an arm or leg
More information:
Check out the CDC Health Alert Network advisory and CDC mosquito bite prevention page for more helpful information.
