Mosquitoes and ticks can pick up certain viruses and bacteria that they can pass to humans. Typically, they get it from another animal or person. They then spread that disease from one animal or person to another through their bite. In the United States, both mosquitoes and ticks can spread illnesses. These illnesses are called vector-borne diseases. and ticks spread illnesses such as West Nile virus, dengue, and Lyme disease.
Anyone can be bitten, but people with weakened immune systems, including many people with cancer, face a higher risk of severe illness if infected. Fortunately, most of these diseases can be avoided with a few consistent prevention habits.
What are vector-borne diseases?
A vector-borne disease is an illness spread by the bite of an infected mosquito, tick, or other insect. Mosquitoes can spread viruses such as West Nile virus, dengue, and Zika. Ticks can spread bacteria and other organisms that cause Lyme disease, Rocky Mountain spotted fever, and several other conditions. These viruses spread by insects are sometimes called arboviruses, a term that simply means a virus carried by an arthropod, such as a mosquito or tick.
What raises your risk?
Everyone who spends time outdoors is at some risk of being bitten. A few factors affect how likely you are to be bitten or to get seriously ill if infected:
Location and season. Ticks are most active from April through September in the United States, with additional peaks in spring and fall depending on the region. Mosquitoes are active during warmer months, and mosquito-borne virus activity tends to peak from July through October.
Outdoor activity. Spending time in grassy, brushy, or wooded areas increases contact with ticks. Being outdoors at dawn, dusk, or nighttime increases contact with many mosquito species.
Travel. Traveling to regions where malaria or other vector-borne diseases are common raises exposure risk.
Immune system status. People with weakened immune systems, including many people being treated for cancer, are more likely to develop severe illness if they are infected.
How to prevent mosquito and tick bites
Before going outside:
Use an EPA-registered insect repellent, applied as directed on the label.
Wear loose-fitting, long-sleeved shirts and pants.
Treat clothing and outdoor gear with a product containing 0.5% permethrin, an insecticide made for fabric rather than skin.
Around your home:
Empty containers of standing water, since mosquitoes lay eggs in even small amounts of water.
Use window and door screens or air conditioning to keep mosquitoes outside.
Avoid walking through tall grass, brush, or leaf litter, where ticks tend to wait for a host.
After coming inside:
Check your body and clothing for ticks.
Remove any attached tick as soon as possible.
Shower within two hours of coming indoors to wash off unattached ticks and make checking easier.
Tumble dry clothes on high heat for 10 minutes to kill any remaining ticks.
If traveling: Ask your healthcare provider about additional precautions, including preventive medicine, if you are traveling somewhere malaria is present.
Special considerations for people with cancer
People being treated for cancer, especially those on immune-suppressing therapies, need to take these precautions seriously. The Centers for Disease Control and Prevention has noted that certain cancer treatments, including a category of drugs called B-cell depleting monoclonal antibodies, are linked to a higher risk of severe illness and death from mosquito- and tick-borne viruses. These drugs work by lowering the number of B cells, a type of immune cell that helps the body produce antibodies to fight infection.
TBecause these treatments can blunt the antibody response. That means, standard blood tests may not reliably detect an infection in someone taking these medications. Diagnosis often requires a different type of laboratory test that looks for the virus's genetic material directly. There is also no specific antiviral treatment for most of these infections once someone becomes ill, which makes prevention especially important.
If you are undergoing cancer treatment:
Talk to your oncology team about your personal risk and any extra precautions they recommend.
Follow the bite-prevention steps above closely during mosquito and tick season.
Seek medical care promptly if you develop a fever along with confusion, tremors, or other neurological symptoms after spending time outdoors, and mention any recent outdoor activity or travel to your care team.
An interesting connection between mosquito bite infections and cancer is being studied
Researchers have also been studying whether infections spread by mosquitoes might play a role in cancer development itself, separate from the risks described above. The clearest example involves malaria, a mosquito-borne infection that, in parts of Africa where it is constantly present, has been linked to a childhood cancer called Burkitt lymphoma. Scientists believe malaria may reactivate a common virus called Epstein-Barr virus, which appears to contribute to this cancer.
Other theories establish that mosquitoes could be transmitting cancer cells or bite reactions triggering cancer, however, these theories are not proven scientifically and remain as hypotheses rather than established findings. Researchers have called for more study in this area, but for now, mosquito-borne infections are understood mainly as a cause of acute illness rather than a confirmed cancer risk.
Remember that these diseases can be preventable
Mosquitoes and ticks spread a range of illnesses, some of which can be serious.
Repellent, protective clothing, and checking for ticks after being outdoors are effective, low-cost prevention steps.
People with cancer, particularly those on immune-suppressing treatments, face a higher risk of severe illness and should take extra precautions and report symptoms early.
Research into whether mosquito-borne infections contribute to cancer directly is ongoing but not yet conclusive.
Sources
Centers for Disease Control and Prevention. How to Prevent Mosquito and Tick Bites
Centers for Disease Control and Prevention. Clinical Guidance for Vector-Borne Viral Diseases in People Who Are Immunocompromised
Mosquitoes, Infectious Diseases, and Cancer: A Connection to Study?
