IDPH Health Alert July 14, 2026
Summary and Action Items
As summer progresses, with warmer weather and increased outdoor activity, Illinois is now entering peak tick and mosquito season. Healthcare providers are asked to maintain heightened suspicion for vector borne diseases (VBDs) when evaluating patients with compatible symptoms and recent outdoor travel exposures. Early recognition and treatment remain essential for reducing morbidity.
Background
Illinois continues to see significant activity from both tick‑ and mosquito‑borne diseases, and prior years’ case counts demonstrate that these illnesses are an ongoing public health concern across the state. Each year, Illinois reports hundreds of cases of diseases spread by mosquitoes and ticks, with seasonal increases typically beginning in late spring and continuing through early fall. West Nile virus remains the most frequently reported mosquito‑borne illness in Illinois, along with Lyme being the most frequently reported tick-borne illness. WNV had a reported provisional count of 150 cases with 10 deaths, and Lyme had a reported provisional count of 440 cases in 2025.
Fluctuations in weather conditions, including warmer temperatures and increased rainfall, can create favorable environments for mosquito and tick populations, increasing the likelihood of human exposure. The expanding range of several tick species, including the blacklegged tick, has also contributed to rising case counts and more widespread risk in areas of the state where these illnesses were previously uncommon.
Transmission
The bite of an infected mosquito or tick can transmit the associated vector-borne pathogen to humans. Rarer possible modes of exposure include blood transfusions, organ or tissue transplants, and possibly laboratory exposure. For more information on transmission of vector-borne diseases, refer to our educational resources linked on our IDPH website. The Illinois Tick Surveillance Map identifies established tick populations throughout Illinois known to transmit pathogens that may cause human illness. Resources linked below.
Symptoms
In many cases, the symptoms of VBDs are similar and include fever, rash, headache, arthralgia, myalgia, and neurologic symptoms. Some specific VBDs may have highly distinct symptoms that are not seen in other illnesses. For example, a Bull’s Eye (EM) rash is a unique characteristic of a tickborne Lyme infection. Neurologic presentations such as meningitis, encephalitis, or flaccid paralysis can be seen when considering arboviral WNV infection for mosquito borne illness.
Testing
Commercial testing should be used for diagnosis of tick/mosquito-borne diseases. The Illinois Department of Public Health labs do not perform routine testing for VBD specimens, with the exception of Malaria. Specifically for Malaria, specimens need to be confirmed and speciated when not done at the commercial laboratory. Health care providers must contact their LHDs to request authorization for confirmation testing of specimens that have not been speciated or when cross-reactivity in serologic testing has occurred. Additionally, local public health departments can help coordinate confirmatory testing in patients with a low pretest probability or in rare situations when a patient’s clinical presentation is strongly consistent with a tick‑ or mosquito‑borne illness, but routine diagnostic tests for the most common pathogens have been negative or inconclusive. Additionally, Heartland, Bourbon, and Powassan viruses should be considered in patients treated for tickborne illness that show no clinical response to treatment.
Reporting
Healthcare professionals are required to report nationally notifiable VBDs through their local health departments, as outlined in Illinois Administrative Code: Section 690.200. In addition to full patient demographic and clinical information, travel history (with departure and return dates) and exposure history should be reported to the respective LHDs.
Prevention
IDPH encourages providers to discuss prevention measures with their patients. Preventing tick and mosquito bites is the best approach to avoid contracting VBDs. More information can be found on the IDPH Vector control page and the CDC Division of Vector-Borne Diseases website.
Contact
For additional information regarding human vector-borne disease surveillance, local health departments should contact the Vector-borne Disease Surveillance program in the IDPH Communicable Disease Control Section at 217-782-2016.
Resource Links
Tickborne Illinesses in Illinois
For additional information on vector-borne diseases, visit the following links:
CDC Tickborn Diseases of the United States: A Reference Maunal for Healthcare Providers
CDC Division of Vector-Borne Disease (DVBD) A-Z Topics Index
Date Issued: July 14, 2026
Author: IDPH Communicable Disease Section
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