Epidemic relapsing fever

Definition

A louse-borne form of relapsing fever caused by Borrelia recurrentis, transmitted person-to-person via the human body louse Pediculus humanus humanus rather than through arthropod vectors with natural reservoirs in wild animals. The pathogen is acquired when crushed lice or their feces contaminate abraded skin or mucous membranes; the lice themselves are not infectious via bite. Epidemic relapsing fever historically accompanied war, famine, and displacement, producing explosive outbreaks with high mortality, and remains endemic in the Horn of Africa. The term distinguishes this human-restricted, louse-borne cycle from endemic (tick-borne) relapsing fevers maintained in zoonotic reservoirs.

Etymology

From Greek epidemia ('upon the people') + Latin relapsus ('to slip back'), referring to the recurrent fever paroxysms and the explosive, crowded human outbreaks characteristic of this form.

Example

During the 2015–2016 refugee crisis in Ethiopia, crowded conditions with poor sanitation triggered an outbreak of epidemic relapsing fever: body lice proliferated on displaced populations, and crushing lice while scratching allowed B. recurrentis to enter through skin lesions, producing the spirochetemia and fever relapses typical of the disease.

Synonyms

• louse-borne relapsing fever
• LBRF

Related Terms

• Pediculus humanus
• Borrelia recurrentis
• endemic relapsing fever
• vector-borne disease
• spirochete
• Epidemic typhus
• body louse

Usage Notes

Distinguish carefully from endemic relapsing fever: epidemic/louse-borne forms lack an animal reservoir and persist only through continuous human-to-human transmission, whereas endemic forms involve Ornithodoros soft ticks and various Borrelia species cycling between ticks and wild mammals (rodents, bats, etc.). The absence of transovarial transmission in lice means the louse is a mechanical vector and short-term carrier, not a biological reservoir. Clinicians and epidemiologists use 'epidemic' specifically for B. recurrentis outbreaks; other Borrelia species causing relapsing fever are tick-borne and termed 'endemic' regardless of outbreak size.