Abstract
Leptospira are the causative agent of leptospirosis, one of the most widespread zoonotic diseases. Despite being one of the most globally significant zoonotic diseases, leptospirosis is understudied and underreported resulting in the World Health Organization (WHO) labelling it as a neglected zoonotic disease. Leptospirosis follows a biphasic pattern of illness where two distinct phases can be observed, the acute/leptospiraemic phase and the immune phase. During the leptospiraemic phase, affected individuals present with non-specific, flu-like clinical manifestations such as febrile illness, nausea/vomiting, headaches and myalgia. Acute leptospirosis is typically self-limiting, however, 10% of cases progress to severe leptospirosis where host immune responses cause tissue damage to infected organs, which may result in (multi-)organ failure.
Currently there are a number of techniques used to diagnose leptospirosis, however, the Leptospira organism and the clinical course of leptospirosis provide challenges for diagnostic tests. Due to the fastidious and slow growing nature of Leptospira, cultures take several weeks to form and this test has an estimated sensitivity of 10%. Microscopic agglutination tests (MAT) are currently considered the reference standard, however, as a serological test it is reliant on host antibody production. The issue is that antibody production requires time and is frequently not detectable until the patient has recovered or progressed to severe leptospirosis. Leptospira housekeeping genes or virulence genes can be targeted using qPCR to diagnose leptospirosis. This provides an important adjunct to serologic diagnostic tests for detection of leptospirosis early in the illness. Of these the LipL32 virulence gene is an ideal target because it is highly conserved across all pathogenic Leptospira strains and absent in all other non-pathogenic strains.
Leptospirosis has been shown to be a major cause of febrile illness in Tanzania, but due to limitations of MAT, the incidence may be underestimated. This study aims to investigate if the systematic application of LipL32 qPCR will identify additional cases that were missed by MAT. To do this, I set up a qPCR assay and then systematically tested clinical samples from Northern Tanzania. This study could provide important epidemiological information about leptospirosis in Northern Tanzania, an understudied region, which would facilitate the swift detection of leptospirosis cases and enhance public health responses. The LipL32 qPCR assay showed 100% specificity and a LoD/LoQ of 1x10-1 genome copies/µL but limited clinical sensitivity (2.78%) when applied to serum samples from Tanzania.