Relapsing fevers are bacterial infections that can cause recurrent fevers, headache, muscle and joint pain, and nausea. They are caused by bacteria of the genus Borrelia.

There are three types of relapsing fever:

• Tick-borne rel apsing fever is caused by Borrelia dutoni and other species transmitted by leather ticks
• Borrelia miyamotoi Lyme disease is caused by Borrelia miyamotoi and differs from tick-borne relapsing fever in part because shield ticks transmit the pathogen
• Louse relapsing fe ver is a notifiable infectious disease caused by Borrelia recurrentis

Tick-borne relapsing fever occurs in isolated areas around the world, including Spain and Portugal, the mountainous regions of North America, the high plains of Mexico, Central and South America, Central Asia, and much of Africa.

Historically, relapsing louse fever occurred most frequently among slum dwellers, prisoners, and persons living in impoverished, crowded, and unsanitary conditions. In the 20th century, large outbreaks of louse relapsing fever occurred in Eastern Europe, the Balkans, the former Soviet Union, and Africa in association with wars and famine. Due to improvements in living standards, the geographic spread of louse relapsing fever has decreased. Currently, isolated cases and outbreaks occur in Ethiopia, Somalia, Eritrea, and Sudan, primarily in war zones and refugee camps. Cases have also been reported in the rural Andean community in Peru and in northern China. In Europe, homeless people and migrants are among the risk groups for lice-borne diseases.

Borrelia miyamotoi has been detected in ticks in numerous countries in Europe, including Russia, in the United States, and in Japan. By 2022, 504 human cases of Borrelia miyamotoi Lyme disease have been identified in the Northern Hemisphere.

Rodents are the hosts of tick-borne relapsing fever borrelia. Leather ticks are a major reservoir, as they can maintain the Borrelia for many years.

Louse relapsing fever: humans are hosts of the pathogen Borrelia recurrentis.

Borrelia miyamotoiLyme disease: Small rodents and specific bird species are thought to be the hosts of Borrelia miyamotoi.

Tick-borne relapsing fever is transmitted to humans by ticks of the genus Ornithodoros of the leather tick family. The causative agent of tick-borne relapsing fever is transmitted from person to person by the body louse Pediculus human us humanus. Transmission to humans occurs only when the louse is crushed while sucking blood, such as by scratching. The pathogen Borrelia miyamotoi is transmitted by shield ticks of the genus Ixodes.

Characteristic of tick-borne relapsing fever is sudden onset of high fever (> 39-40 °C) lasting three to six days. Other symptoms include headache, muscle and joint pain, and nausea. Symptoms may recur without antibiotic treatment, and a temporal pattern emerges. The number of episodes varies widely (0-15) and they usually become shorter and milder each time. The interval between fever episodes ranges from four to 14 days.

Symptoms of relapsing lice fever usually occur quite abruptly. There is high fever, general malaise, chills and sweats, headache, muscle and joint pain, and nonspecific gastrointestinal symptoms. Neurologic complications and vision impairment, as well as skin and mucosal, cardiac, and respiratory symptoms may also occur. The disease can be very severe and leads to death in 10% to 40% symptomatic cases without adequate treatment.

The most common symptoms of Borrelia miyamotoi Lyme disease are fever, chills, and headache, as well as joint pain and fatigue. B. miyamotoi infections have been described mainly in immunocompromised individuals.

The recommended therapy for tick relapsing fever is the antibiotics tetracycline or doxycycline. For lice relapsing fever, a single course of antibiotics is effective in most cases. Prolonged treatment is usually given to minimize the likelihood of recurrence. Borrelia miyamotoi infections are treated with the antibiotic doxycycline for two to four weeks. Amoxicillin and ceftriaxone have also been used successfully.

A vaccine is not currently available. Essential to the prevention of tick-borne relapsing fever and Borrelia myamotoi Lyme disease is the avoidance of tick bites. Primary prevention of lice relapsing fever is based on measures to avoid infestation with body lice.

There are no known cases of tick-borne and louse-borne relapsing fever acquired in Austria (autochthonous). Cases of tick and lice relapsing fever detected in Austria in recent years were without exception imported diseases. In Austria, the presence of Borrelia miyamotoi in ticks has been documented. Isolated cases of Borrelia myamotoi borreliosis originating in Austria have also been detected.

Tick-borne relapsing fever

Route of Infection: After blood feeding on infected rodents, Borrelia spreads to all tissues of the leather tick, including the ovaries (responsible for transovarian transmission), salivary glands, and excretory organs. Ticks are capable of maintaining Borrelia throughout their life span (5-10 years). Leather ticks differ from shield ticks (which transmit babesia, among other diseases) in two characteristics: 1) the bite of leather ticks is short-lived, usually less than half an hour; 2) leather ticks do not forage for prey in tall grass or brush. Instead, they live in rodent burrows and feed on rodents as needed while they sleep. Humans typically come into contact with these ticks when they spend the night in rodent-infested cabins.

Symptoms: Neurologic symptoms (2%) are caused primarily by B. duttoni and B. turicatae and include delirium, facial paralysis, meningitis, and radiculopathy (irritation/damage to a nerve root). In infants and pregnant women, the course of the disease can be more protracted and severe, leading to low birth weight, premature birth, spontaneous abortion, and neonatal death. Although there is a theoretical risk that tick-borne relapsing fever will result in death, reports of deaths are rare (0-8%), with the highest rates occurring in patients who develop a Jarisch-Herxheimer reaction, an immunologic response of the organism, during treatment. This manifests itself as general malaise, headache, fever, sweating, seizures, tachycardia (increased heart rate) and hypotension (decrease in blood pressure), among other symptoms, and lasts for a few hours.

Diagnosis: During primary infestation, detection of the bacteria on thin or thick blood smears is possible with dark-field microscopy or conventional staining. Molecular methods are sensitive and are becoming more common. They offer the possibility of species identification, even on samples with very low loads.

Lice relapsing fever

The pathogen Borrelia recurrentis is transmitted from person to person by the body louse Pediculus humanus human us. The louse ingests the pathogen from infected individuals, but the salivary glands and digestive tract of the louse are not affected by the borrelia. Therefore, transmission to humans only occurs when the louse is crushed while sucking blood, such as by scratching. This releases the pathogen and it is able to penetrate the human organism through intact skin and mucous membrane. If the louse can finish its blood meal undisturbed and leave its host, there is also no transmission of lice relapse fever.

The symptoms of lice relapsing fever usually appear quite abruptly. There is high fever, general malaise, chills and sweats, headache, muscle and joint pain, and nonspecific gastrointestinal symptoms. Neurologic complications and vision impairment, as well as skin and mucosal, cardiac, and respiratory symptoms (cardio-respiratory symptoms), may also occur. Patient:ins may have an enlarged liver and spleen. Symptoms increase in intensity over approximately five days and subsequently subside as the pathogen disappears from the blood. After this initial regression, the pathogen reappears in the blood and symptoms begin again. The relapse extends over several days to weeks, although untreated patients usually experience fewer than ten relapses. The disease can be very severe and leads to death in 10% to 40% of symptomatic cases without adequate treatment; with treatment, the death rate drops to 2% to 5%

Head lice, Pediculus humanus capitis, are also infected with Borrelia recurrentis, but their role as vectors has not been established. Differential diagnoses of lice recurrent fever are: Malaria, typhoid fever, viral hemorrhagic fever, leptospirosis, tick-borne relapsing fever, nontyphoid salmonellosis, meningococcal septicemia, and meningitis. Infection provides only partial protection due to variations in antigens among Borrelia strains. Louse relapsing fever can be severe, with a mortality rate of 30% to 70% during outbreaks.