Factsheet: Louse-borne relapsing fever

The pathogen  

• Louse-borne relapsing fever is caused by the spirochaete Borrelia recurrentis.
• Borrelia recurrentis, like other Borrelia species, has a linear chromosome of 1Mb and five or six plasmids that vary in size from 11 to 192kb. Borreliae are helical, 8 to 30 µm long and 0.2 to 0.5 µm in diameter, are motile and have 8 to 30 flagella.
• Borrelia recurrentis is closely related to Borrelia duttonii the causative agent of tick-borne relapsing fever.

Clinical features and sequelae 

• The incubation period is usually between four and eight days (range: 2–15).
• The symptoms are associated with circulation of bacteria in the blood.
• The onset of symptoms is usually sudden. Symptoms include high fever, general malaise, chills and sweats, headache, meningism, myalgia/arthralgia and non-specific gastrointestinal symptoms (nausea and vomiting).
• Mycocutaneous symptoms include conjunctival injection, scattered petechiae and erythematous rash.
• Cardio-respiratory symptoms such as tachycardia, mild tachypnea and non-productive cough can occur.
• Patients may present with hepatomegaly and splenomegaly, with risk of splenic rupture.
• Neurological and ocular complications can occur: meningoencephalitis, meningitis, neuropathies and cranial-nerve palsy, iritis and acute opthalmitis.Haemorrhage is a common complication with epistaxis, blood-tinged sputum and even central nervous system or gastrointestinal haemorrhage.
• The symptoms increase in intensity over five days on average (range: 2–7), then subside as the pathogenic agent disappears from the blood.
• After a first remission, spirochaetes reappear in the blood and symptoms recur. The relapse occurs over several days to weeks, but fewer than 10 relapses are usually observed among untreated patients.
• Differential diagnosis: malaria, typhoid fever, viral haemorrhagic fever, leptospirosis, typhus, tick-borne relapsing fever, non-typhoidal salmonellosis, meningococcal septicaemia and meningitis.
• Infection confers a partial immunity due to antigenic variation of Borrelia strains.
• The disease can be severe and death occurs in 10% to 40% symptomatic cases in the absence of appropriate treatment, and in 2% to 5% of treated patients.

Epidemiology 

• Historically, the disease has been most common among slum dwellers, prisoners and persons living in impoverished overcrowded and unhygienic conditions.
• In the first half of the twentieth century, major outbreaks of louse-borne relapsing fever occurred in Eastern Europe, the Balkans, the former Soviet Union and Africa, linked with periods of war and famine.
• The geographical distribution of LBRF has declined due to improvements in living standards. Currently, the disease is primarily found in limited endemic foci in Ethiopia but also in Somalia and Sudan. The disease has also been recorded in the rural Andean community in Peru and in northern China.
• Antibodies to Borrelia recurrentis were detected in homeless populations in Marseille in 2002, suggesting that a small, unnoticed outbreak occurred in this particular homeless population.

Transmission 

• Borrelia recurrentis is transmitted from human to human by the body louse Pediculus humanus humanus. Head lice, Pediculus humanus capitis, have been found to be infected, but their role as vector has not been established.
• When feeding on an infected human, the body louse will ingest Borrelia recurrentis. The spirochaetes that survive in the midgut of the louse migrate to the haemocoel where they multiply. From the sixth day after an infective blood meal, spirochaetes become increasingly abundant in the haemocoel of the vector. 
• Transmission occurs when the louse is crushed and the infected haemocoel is released onto the human skin. Borrelia recurrentis is able to penetrate intact mucosa and skin. The transmission invokes the death of the louse, hence an individual louse can only infect one person. Consequently, louse-borne relapsing fever outbreaks are dependent on high louse densities in human populations.
• On average a mature body louse will live for 20–30 days.

Diagnostics 

• The diagnostic test of choice is the direct identification of spirochaetes in the blood.
• Borrelia are spirochaetes that can be identified on stained blood films (Giemsa), especially during the symptomatic febrile phase. The microorganism can be found during examination of stained blood films taken for malaria diagnosis. Bacteria are visible with dark-field or phase contrast microscopy as well.
• Culture is possible on specific media. Serology is unstandardised and not used for diagnostic purposes.
• Nucleic acid detection is carried out in research settings and can be used to support the clinical diagnosis.
• The leucocyte count is often low and thrombocythaemia is usually observed.

Case management and treatment 

• A single dose of antibiotic is effective in the majority of cases of louse-borne relapsing fever but a longer treatment course is usually applied to minimise the probability of recurrence.
• Antibiotics of choice are tetracycline, penicillin G, erythromycin or chloramphenicol.
• A potential severe or fatal Jarisch–Herxheimer reaction can be induced by antibiotic treatment of louse-borne relapsing fever, requiring the close monitoring of patients under antibiotic treatment. This reaction is often observed a few hours after the first antibiotic treatment and follows two successive phases: the chill phase (rigours, high fever, anxiety or confusion, increasing metabolic rate) and the flush phase (decrease in temperature, drenching sweat, and significant decrease in arterial pressure and myocardial dysfunction requiring supportive care for monitoring fluid balance and arterial/venous pressure).

Infection control, personal protection and prevention 

• Primary prevention of louse-borne relapsing fever relies on measures to avoid infestation with body lice.
• Body lice infestations are linked to low socioeconomic status, over-crowding and poor personal hygiene. In Europe, populations at risk for such infestations, and hence louse-borne diseases, include the homeless and migrants. 
• Body lice are transmitted primarily by direct contact with an infested person, transmission of the body lice also occurs through fomites, like clothes or bedding. Lice multiply rapidly and a population can increase by 11% per day.
• Body lice are highly susceptible to cold and desiccation. They are found on clothing close to the human skin. Discarding infected clothes is an effective way to control the infestation. If this is not possible, clothes should be washed at a temperature of 60 degrees Celcius or above.
• In outbreak situations, dusting powder with an appropriate insecticide has been applied to obtain a rapid decrease of infested persons with some lasting benefits.
• Few cases of LBRF transmission through blood transfusion have been reported. Data on survival and persistence of Borrelia recurrentis in donated blood are lacking. Transmission through organs or cells and tissues has not been reported. Due to possible transmission through substances of human origin, infected donors should be deferred until signs and symptoms have subsided and a course of treatment has been completed. Donation of cells and tissues from deceased donors with louse-borne relapsing fever is not recommended.

List of references