The genus Borrelia contains numerous species of spiral-shaped bacteria, many of which are known to cause Lyme disease – the most common vector-borne disease in the U.S. However, there are several other Borrelia species that cause similar but biologically distinct infections known as Relapsing Fever. Relapsing Fever Borreliosis can be spread by lice or ticks; this article will focus on Tick-Borne Relapsing Fever (TBRF).
The CDC currently recognizes three common Borrelia species that cause TBRF in the U.S., with a fourth species – Borrelia miyamotoi – recently gaining more mainstream attention. However, these are just a handful of the several species of TBRF-causing bacteria.
Read on to learn more about the different species of Relapsing Fever Borrelia, what kinds of ticks spread them, and what this means for diagnosis and treatment.
The Different Types of Relapsing Fever Borrelia
Tick-Borne Relapsing Fever Borrelia
Tick-Borne Relapsing Fever is a type of Borreliosis that is spread by ticks, as opposed to the Relapsing Fever Borreliosis spread by body lice (more on that later). It’s not uncommon for people who believe they have Lyme disease, but go on to receive negative test results on a Lyme test, to actually be infected with TBRF, which shares some symptoms with Lyme.
TBRF and Soft Ticks
One major difference between TBRF and Lyme disease is that TBRF in the U.S. is more commonly spread by soft ticks – from the genus Orithorodos – than hard ticks – from the genus Ixodes, the same ticks that spread Lyme.
Soft ticks are usually softer-bodied and lack the hard shell around the mouthparts that are characteristic of hard ticks. Soft ticks also feed much more quickly than hard ticks, making it possible to contract TBRF from a soft tick bite in under 15 minutes. Finally, instead of waiting on leaves or blades of grass for hosts to walk by in a practice known as “questing,” soft ticks often hide in rodent burrows and feed on hosts while they sleep.
Below, Borrelia species are broken down by tick type.
Soft Tick Species of Relapsing Fever Borrelia
1. B. hermsii
B. hermsii is the most common cause of TBRF in the U.S., according to the CDC. It was first described in 1942 and is spread by the Orithodoros hermsi soft tick, found at high altitudes and most closely associated with ground or tree squirrels and chipmunks.
2. B. parkerii
Also first described in 1942, B. parkerii is also common in the U.S., where it is spread by the Orithodoros parkeri soft tick. This tick is common at lower altitudes and associated with caves as well as burrowing rodents and some owls.
3. B. turicatae
B. turicatae is spread by the Orithodoros parkeri soft tick, which is common in caves and small animal burrows in the Southwest U.S. B. turicatae was first described in 1933.
4. Other soft tick species
Some other known species of TBRF Borrelia throughout the world include:
- B. coriaceae (North America) – named after the Orithodoros coriaceus tick
- B. hispanica (Europe, Africa, Middle East, Asia)
- B. persica (Middle East, Asia)
- B. crocidurae (Africa)
- B. latyshervi (Middle East, Asia)
- B. duttoni (Africa)
- B. tillae (Africa)
- B. graingeri (Africa)
- B. venezuelensis (Central & South America)
- B. mazotti (Central & South America)
- B. dugesi (Central & South America)
Hard Tick Species of Relapsing Fever Borrelia
B. miyamotoi
B. miyamotoi is a relatively newly discovered species of Relapsing Fever Borrelia. First discovered in Japan in 1995, the earliest human B. miyamotoi infections were identified in Russia in 2011 and later in the U.S. in 2013.
The threat of B. miyamotoi disease
What makes B. miyamotoi different from other species of Relapsing Fever Borrelia is that it is not spread by soft ticks, but instead by hard ticks. Specifically, it has been found in the Eastern blacklegged or “deer” ticks and the Western blacklegged tick – the same species of ticks that spread Lyme disease.
Another important difference is that baby ticks can be infected with B. miyamotoi by their mothers. Unlike the bacteria that cause other tick-borne diseases, which are usually transmitted from mammals to ticks, adult ticks can transmit B. miyamotoi to baby ticks via what’s known as transovarial transmission.
The CDC calls this infection B. miyamotoi disease. However, symptoms of infection by B. miyamotoi can resemble the symptoms of TBRF spread by soft ticks. It’s important for those displaying tick-borne disease symptoms to get tested for B. miyamotoi.
B. miyamotoi disease is not currently reportable to the CDC.
Louse-Borne Relapsing Fever Borrelia
There is one known species of Relapsing Fever Borrelia spread from human to human by the body louse: B. recurrentis. This species was discovered as early as 1874, and since then the body louse has been the only known vector. B. recurrentis usually only shows up in situations of overcrowding, such as during wartime or humanitarian crises.
As with Lyme Borrelia, it is possible the scientific community will continue to discover new species of Relapsing Fever Borrelia. To learn about the different species of Lyme Borrelia, check out the Tick Talk blog An Overview of the Types of Borrelia That Cause Lyme Disease.
Getting Diagnosed
Just like with Lyme disease, doctors will consider your lab test results alongside your symptoms in order to make a diagnosis of TBRF. These symptoms can show up within approximately 7 days of the tick bite and include:
- Headache
- Muscle and joint aches
- Recurring high fever (e.g., 103 degrees F) that shows up within a week of the tick bite, lasts for about 3 days, then returns after another 7 days, and so on
It’s important to note that not all TBRF infections result in relapsing fevers. In fact, some patients never have a fever at all. It is entirely possible to have no fever and still have a TBRF infection. If you are experiencing Lyme-like symptoms but have received negative Lyme test results, you may want to consider the possibility of a TBRF infection.
Treating tick-borne illnesses like Lyme and TBRF requires early, accurate detection – otherwise, when left untreated, these diseases can become chronic and debilitating. Check out the TBRF testing available at IGeneX today.
