A Tick-Borne Disease With No Warning Rash Is Spreading Across the U.S.

As summer progresses, small ticks are actively spreading diseases, many of which are unfamiliar to most Americans. Some healthcare professionals are deeming one of these conditions a significant public health risk, drawing comparisons to Lyme disease.

“It’s a fact that reports of diseases caused by mosquitoes and ticks—generally referred to as ‘vector-borne’ diseases—are rising. This might be partly due to shifts in regional climates and the expansion of insect and tick habitats,” explained Dr. Natasha Wyndham Hanners, an infectious disease expert at Children’s Health and an Assistant Professor at UT Southwestern Medical Center. “Additionally, increased global travel and advanced diagnostic methods are revealing the emergence of previously unknown pathogens or those that are new to certain areas.”

This warning comes as research shows that a group of tick-borne viruses known as orthonairoviruses can evade the human immune system. Public health officials are closely monitoring the spread of ticks that carry harmful new pathogens throughout North America.

Together, these findings suggest a changing landscape for tick-borne illnesses in the U.S.

Three Tick-Borne Threats to Know

• Anaplasmosis: This bacterial infection is spread by the blacklegged deer tick. Symptoms include fever, headache, chills, and muscle aches. However, unlike Lyme disease, it doesn’t create a distinctive bull’s-eye rash, making it easy for both patients and doctors to overlook unless blood tests are performed.
• Orthonairoviruses: This family of tick-borne viruses features the Crimean-Congo hemorrhagic fever virus, which poses considerable danger due to its potential to cause severe hemorrhagic disease in humans. Recent studies indicate these viruses possess proteins that can effectively strip the immune system of warning signals, allowing them to escape detection.
• Nairoviruses: A broader and emerging class of what is labeled “tick-borne pathogens.” Researchers have identified a nairovirus, called PCTNV, in the Pacific Coast tick within the U.S. Although it hasn’t been confirmed in humans yet, lab tests indicate that its immune-evading enzyme is particularly potent, raising concerns about possible human exposure.

The Virus That Hides From the Immune System

A study from the University of California, Riverside, recently highlighted how orthonairoviruses can block the body from detecting infections. The researchers focused on certain viral proteins known as ovarian tumor domain proteases (OTUs), which can eliminate small immune-signaling molecules like ubiquitin and ISG15 from human cells. Typically, these molecules sound the alarm that an infection is present, but if OTUs are removing them, the alarm never rings, and consequently, the immune response is never triggered.

Tests conducted by the researchers involved enzymes from four species of nairoviruses, including three newly discovered viruses found in patients in Asia alongside PCTNV, which is associated with North America’s Pacific Coast tick.

This particular tick-borne enzyme was notably effective at stripping immune signals, suggesting that PCTNV might have a distinct ability to bypass human defenses.

With the Pacific Coast tick already known to bite humans and transmit Rocky Mountain spotted fever, this finding raises concerns about the potential for exposure to PCTNV among West Coast residents, although more research is necessary to verify if human exposure is actually occurring.

“This study underscores the need for increased awareness, not just regarding tick bites, but also the specific types of ticks involved, as they may carry diseases outside our typical range of expectation,” Scott Pegan, the corresponding author of the study, commented.

In addition to the rise of nairoviruses, anaplasmosis, which is spread by the blacklegged deer tick, is extending into new areas.

“Anaplasmosis is concerning because it is carried by the common deer tick, which is the blacklegged tick, yet it doesn’t come with the recognizable Lyme disease rash,” observed Craig Bober, a primary care physician at Inspira Health in New Jersey. “While Lyme disease gets a lot of attention, deer ticks can also transmit infections like anaplasmosis and babesiosis, which can cause similar symptoms like fever, headache, chills, and muscle aches without that tell-tale rash.”

“Since symptoms of these infections often overlap with those of Lyme disease, it’s essential to conduct blood tests to determine the right treatment approach.”

Clinical teams are also keeping an eye on the Asian longhorned tick, first identified in the U.S. in 2017 and currently found in states such as New Jersey and Pennsylvania. This tick, known for its ability to reproduce without mating, is also a carrier of SFTS. While human infections in the U.S. are still rare, experts believe its rapid spread necessitates increased public awareness.

How to Protect Yourself

Healthcare providers advise that those spending time outdoors should wear long sleeves and tuck their pants into their socks, along with using EPA-registered repellents that contain DEET, picaridin, or IR3535. They also recommend treating clothing and gear with permethrin.

Moreover, it’s advisable to shower within two hours of returning indoors to rinse off any unattached ticks, and to check the whole body—especially the scalp, behind the ears, underarms, and behind the knees. If a tick is found attached, it’s best to grasp it with fine-tipped tweezers as close to the skin as possible, pulling straight out. Afterward, clean the bite area promptly. If symptoms develop, seeking medical advice quickly is recommended.

Reference

Gonzalez, D. S., et al. (2026). Insights into the Structure and Function of the OTU Protease Virulence Factors from Emerging Human Nairoviruses. ACS Infectious Diseases. https://doi.org/10.1021/acsinfecdis.6c00320.