Soft Ticks and Tick-Borne Relapsing Fever

Quick answer

Soft ticks (Ornithodoros species) are leathery ticks that live in rodent nests, often inside the walls of rustic cabins in western mountains. They feed at night for less than half an hour, and the bites are painless. In the U.S. they can spread tick-borne relapsing fever, which CDC now calls soft tick relapsing fever. They do not spread Lyme disease.

What soft ticks look like

Soft ticks look different from hard ticks like the blacklegged tick. The Merck Veterinary Manual describes them:

• Body: leathery and soft, with no hard shield (scutum) on the back. Males and females look alike, though females are bigger.
• Head: in nymphs and adults, the mouthparts sit on the underside of the body, so you cannot see the “head” from above.
• Size: small. Arizona’s health department describes the relapsing fever tick as about 3 mm long.
• Life span: long. Arizona health officials say these ticks can live 10 to 20 years.

People almost never see them. Compare them with hard ticks in our types of ticks guide.

Where soft ticks live in the US

CDC says STRF in the U.S. occurs mostly in mountainous areas of western states and in parts of Texas. A CDC report on 2012 to 2021 found 251 cases in 11 states. California, Washington, Colorado and Oregon accounted for more than three-quarters of them.

• O. hermsi lives in western mountain forests. Mono County, California, public health says it is found in coniferous forests at about 1,500 to 8,000 feet.
• O. turicata is found in the south-central U.S., often near caves, especially in central Texas.

The cabin connection: these ticks live in rodent nests, including nests in a cabin’s walls or under its floors. In the CDC report, about three out of four western cases with a known exposure were linked to staying in cabins, and most patients were visitors.

When they bite

CDC says exposure is most common in summer. In the 2012 to 2021 report, 71% of western cases happened between June and September. But winter cases happen too: CDC and Mono County note that lighting a fire to warm a cabin can wake up ticks resting in the walls.

O. hermsi comes out at night and feeds while people sleep. When rodents are scarce or nests are disturbed, hungry ticks may turn to people, Arizona health officials say.

Tick-borne relapsing fever

Per CDC, symptoms start 4 to 21 days after exposure (about a week is typical) and can include:

• high fever, chills and drenching sweats
• headache
• muscle and joint aches
• nausea, vomiting and dizziness

The pattern is what gives it its name: about 3 days of fever, about 7 days without fever, then fever again. Without antibiotics, CDC says the cycle can repeat several times. In the CDC case report, more than half of patients were hospitalized, and no deaths were reported. CDC notes it can be dangerous in pregnancy and for newborns.

Lyme connection: relapsing fever bacteria are Borrelia, like Lyme bacteria, but cause a different illness. CDC’s provider manual notes that relapsing fever blood tests can cross-react with Lyme tests. Treatment is with antibiotics chosen by your provider. CDC’s manual advises watching patients after the first treatment for a Jarisch-Herxheimer reaction.

Relapsing fever from hard ticks is a separate illness; see Borrelia miyamotoi and our co-infections guide.

Soft tick bites

Hard ticks often stay attached for a day or more, so tick checks help. Soft ticks feed briefly at night and drop off, so you probably will not find one, and a tick check is not enough protection in a cabin. If you do find any tick attached, our tick bite guide explains what to do.

Prevention

CDC and state health departments focus on rodents:

1. Avoid sleeping in rodent-infested buildings. Look for droppings, nesting material, gnaw marks and a stale smell.
2. If you must stay, move beds away from walls, keep bedding off the ground, and avoid sleeping on the floor.
3. Renting? Tell the owner if you find signs of rodents.
4. Cabin owners: keep rodents out and hire a licensed pest control professional to remove nests and treat cracks and crevices. Don’t remove nests yourself; CDC warns rodent contact can spread other diseases, such as hantavirus.
5. In caves or near burrows, wear long sleeves and pants and avoid skin contact with cave floors.
6. Use repellent. CDC suggests EPA-registered insect repellent on skin or clothing, or permethrin-treated clothing and gear.

For the outdoor ticks that spread Lyme, see ticks that carry Lyme disease and Step 1 of How to beat Lyme: Prevent it.

At a glance

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