Relapsing fever

Definition

A vector-borne infectious disease caused by spirochete bacteria of the genus Borrelia, characterized by recurrent episodes of high fever separated by asymptomatic intervals. The disease is transmitted to humans and other mammals through the bites of infected lice (Pediculus humanus, body louse-borne epidemic relapsing fever) or soft-bodied ticks of the genus Ornithodoros (endemic relapsing fever), with hard-bodied ticks (Ixodidae) implicated in some transmission cycles. The relapsing pattern reflects antigenic variation in Borrelia surface proteins that allows the bacteria to evade host immune responses.

Etymology

From Latin relapsus (fallen back, slipped back) + febris (fever), describing the characteristic return of fever after apparent recovery

Example

In East African highlands, Ornithodoros moubata soft ticks transmit Borrelia duttonii to humans sleeping in traditional huts, causing endemic relapsing fever with febrile episodes lasting 2–7 days and afebrile intervals of roughly 7 days.

Synonyms

• borreliosis (loose, broader)
• recurrent fever (archaic)

Related Terms

• Borrelia
• vector-borne disease
• Ornithodoros
• Pediculus humanus
• spirochete
• Lyme disease
• tick-borne disease
• louse-borne disease
• antigenic variation

Usage Notes

Distinguish from Lyme disease, also caused by Borrelia but transmitted by hard-bodied Ixodes ticks and lacking the characteristic relapsing fever pattern. The term 'relapsing fever' without modifier usually refers to louse-borne epidemic disease; 'endemic relapsing fever' or 'tick-borne relapsing fever' specifies the tick-transmitted form. Soft ticks (Argasidae) are the primary vectors for endemic disease, whereas hard ticks (Ixodidae) play a secondary role in some regions. The disease is of particular concern in resource-limited settings where louse infestations are common and diagnostic capacity is limited.