The Delaware Division of Public Health (DPH) is sending this health advisory to notify health care providers of the first detection of Powassan virus in a tick in Delaware. The tick was collected in June 2024 in New Castle County and the positive test results were reported to DPH in February 2026. Although there are no confirmed human cases of Powassan virus disease reported to DPH to date, the purpose of this health advisory is to alert clinicians to consider testing for Powassan virus in patients presenting with unexplained encephalitis, meningitis, or high fever (≥100.4 degrees F or 38 degrees C) during the late spring, summer, and early fall.

Summary
•  Powassan virus disease is a rare but serious arboviral illness transmitted through the bite of an infected Ixodes spp. tick. 
•  Signs and symptoms include fever, headache, vomiting, weakness, confusion, seizures, and memory loss. Symptoms can begin anytime from one week to one month after the tick bite and long-term neurological problems may occur. 
• There is no specific treatment, but people with severe Powassan virus disease often need to be hospitalized. 
• Health care providers should consider the diagnosis of Powassan virus disease in patients with meningitis, encephalitis, or other non-specific febrile illness, especially if the patient has a history of tick exposure or bite and tested negative for more common causes of meningitis and encephalitis.
• Powassan virus disease is reportable in Delaware. All suspect cases and positive laboratory reports should be reported to DPH by emailing reportdisease@delaware.gov, by calling the Office of Infectious Disease Epidemiology at 1-888-295-5156, or electronically through the Delaware Eila Insight (DELI) Disease Surveillance System (for providers who have registered in the provider portal).

Background
Powassan virus is transmitted by the bite of an infected Ixodes spp. tick. Three species of ticks are known to carry Powassan virus: the blacklegged/deer tick (Ixodes scapularis), the groundhog/woodchuck tick (Ixodes cookei), and the squirrel tick (Ixodes marxi). Delaware is home to all three of these species of ticks, but squirrel and woodchuck ticks rarely bite humans. The blacklegged tick will bite humans and is also the primary vector of Lyme disease and several other tick-borne pathogens.

In February 2026, DPH was notified that a blacklegged tick from New Castle County (collected in June 2024) was positive for Powassan virus, marking the first detection of a Powassan virus-positive tick from Delaware.

While tick-borne diseases like Lyme disease require an infected blacklegged tick to be attached for over 24 hours to transmit the disease, studies have shown significantly less time may be needed to transmit Powassan virus. Powassan virus can rarely be transmitted through infected blood transfusions.

Clinical Characteristics 
Most people infected with Powassan virus are asymptomatic. Illness, if it develops, appears one week to one month after the tick bite. Symptoms are typical of neuroinvasive arboviral disease and include but are not limited to fever, headache, vomiting, weakness, altered mental status, confusion, loss of coordination, speech difficulties, memory loss, encephalitis, and meningitis. Infection can be fatal in about 10% of neuroinvasive cases. Non-neuroinvasive Powassan virus disease has been documented and manifests as a febrile flu-like illness. 

Diagnosis
Powassan virus cannot be clinically distinguished from other arboviral diseases without diagnostic laboratory testing. The most common diagnostic approach is detection of Powassan virus-specific IgM antibodies in serum or cerebrospinal fluid (CSF). Diagnostic testing for Powassan virus is not widely available at commercial labs and as of March 2026, is not available at the Delaware Public Health Laboratory (DPHL). However, DPH can assist providers with sending samples to DPHL to ship to the Centers for Disease Control and Prevention for testing with prior DPH approval. Patients who are hospitalized with meningitis or encephalitis have a presumed infectious cause of illness, and are negative or concurrently tested for more common causes of meningitis and encephalitis like West Nile virus, Lyme disease, herpes, and varicella may be approved for testing. For testing approval, contact the DPH Office of Infectious Disease Epidemiology at 1-888-295-5156 and provide patient information (name, address, date of birth), information about their illness (date of onset, clinical presentation), tick exposure, and travel history three months prior to the date of symptom onset. 

Recommendations for Prevention
The best way to prevent Powassan virus disease is to prevent tick bites. Effective strategies include:
• Wear light-colored clothing when outdoors to help you spot ticks more easily.
• Tuck pant legs into socks so ticks cannot crawl up the inside of the pants.
• Use Environmental Protection Agency (EPA) registered insect repellents containing DEET (up to 30%), picaridin, or oil of lemon eucalyptus (OLE).
• Pre-treat clothing and gear with permethrin-based repellents to protect against tick bites for at least two weeks without reapplication. Permethrin can be used to treat boots, clothing, and camping gear and it remains protective through several washings. Alternatively, you can buy permethrin-treated clothing and gear.
• Tumble dry clothing and gear on high heat for at least 60 minutes after spending time in areas where ticks live.
• When outdoors, stay on the center of trails. Ticks crawl on the tips of grasses and shrubs and crawl on people and animals when they brush against the vegetation. Ticks do not jump, fly, or fall from trees.
• Manage areas where tick lives:
  o Mow lawns and trails frequently.
  o Remove leaves and brush.
  o Create a barrier of wood chips or rocks between mowed lawns and woods. 

Recommendations for Management
There is no specific treatment for Powassan virus disease. Care for patients is typically supportive and may include intravenous fluids and respiratory support.

Reporting 
Powassan virus disease is reportable in Delaware. All suspect cases and positive laboratory reports should be reported immediately to DPH by emailing reportdisease@delaware.gov, by calling the Office of Infectious Disease Epidemiology at 1-888-295-5156, or by sending electronically through the Delaware EpiLab Insight (DELI) Disease Surveillance System.