Borrelia recurrentis - Relapsing Fever, Pathogenesis, Host Immunity, Reservoir, Source, Transmission

Pathogenesis of relapsing fever caused by Borrelia recurrentis

Borrelia recurrentis is responsible for louseborne or epidemic-relapsing fever. It is transmitted from the louse Pediculus humanus sub spp humanus and humans are the only reservoirs.

Borrelia recurrentis penetrates the stem, reaches blood circulation, and invades various organs of the body. After the invasion of blood by Borrelia recurrentis, Borrelia-specific IgM Ab agglutinates Borrelia recurrentis and causes complement-mediated lysis. Hence, Borrelia is cleared from the bloodstream.

Borrelia recurrentis bonds to c4b binding protein and factor H (major regulators of Ab mediated complement pathway) leading to serum resistance. If present in internal tissues, they alter their serotype-specific outer proteins through gene rearrangement and exhibit new Ag. IgM produced against old Ag is now not effective.

Again host produces specific Ab against new Ag and clears the organism from circulation Development of humoral immunity recovers the patients, but only after a number of relapses.

Host immunity of Borrelia recurrentis

The development of specific humoral host immunity against Borrelia recurrentis contributes to recovery after a number of relapses.

Reservoir, Source, Transmission of Borrelia recurrentis infection

Epidemic relapsing fever

Humans are the only reservoir of epidemic relapsing fever caused by Borrelia recurrentis. The human body louse is the vector of disease.

Borrelia recurrentis is found in the hemolymph of the lice. They are not excreted in the saliva or feces of the lice. The pathogen is not transmitted by the bite of the lice but by the lice being crushed and rubbed into the absorbed skin.

Endemic tick-borne relapsing fever

Endemic tick-borne relapsing fever is a zoonotic disease transmitted from animals to humans, rodents, and small mammals.

Soft ticks are the main vectors. Since it is disseminated in the whole tick body, B. recurrentis are found in saliva and excreta and transmission takes place via the bite of the infected tick.

In ticks, Borrelia recurrentis produces a disseminated infection and becomes a reservoir by transovarial transmission.