Laboratory Diagnosis - Borrelia recurrentis infections

Laboratory Diagnosis

◗ Specimen

Blood collected from a patient during fever, but not from afebrile patient, is a useful specimen.

◗ Microscopy

A wet mount preparation of the blood examined by dark-field or phase contrast microscopy is a useful method for direct observation of Borrelia. The organisms are identified by their dashing movements. Borrelia organisms can also be demonstrated in peripheral blood smear stained with Giemsa or Wright stains. Staining is the most sensitive method for diagnosis of 70% or more patients of louse-borne relapsing fever.

◗ Culture

Cultures are not carried out routinely for isolation of Borrelia from clinical specimens. This is because Borrelia organisms have complex nutritional requirements for their growth and they grow very slowly on these media.

◗ Animal inoculation

Animal inoculation is a more sensitive method. This test is per-formed by inoculating a mouse intraperitoneally with 1–2 mL of blood from the infected patient. The blood is collected from the tail vein of the mice after 1–10 days. Blood is examined for the presence of Borrelia daily for 2 weeks.

◗ Serodiagnosis

B. recurrentis causing relapsing fever undergoes antigenic phasevariation; hence, serological tests are not useful in the diagnosis of the condition.