Project coordination
Laboratório de Hanseníase Fundação Oswaldo Cruz/ FIOCRUZ (Brazil)

Partners
Fundação Afredo da Mata (Brazil)
Universidade Federal de Juiz de Fora (Brazil)
Ludwig-Maximilians University (Germany)

Aim: There are no diagnostic tests that could predict whether or not a “contact” will develop the disease. This project investigated the possible use of M.leprae DNA detection as a early detection method in over 1600 household contacts of leprosy patients. 

Full project title:
Evaluation of the qPCR in household contact monitoring

Final project summary:
Early diagnosis remains one of the greatest challenges in leprosy control. Because there is no single highly accurate diagnostic test for leprosy, diagnosis depends largely on clinical examination. As a result, many patients are only diagnosed after the disease has progressed and symptoms such as nerve impairment have become apparent. This contributes to ongoing transmission and a persistently stable number of new cases.

Household contacts of people affected by leprosy are known to have the highest risk of developing the disease. However, there are currently no reliable markers to predict which contacts are most likely to progress to leprosy. This study investigated whether two laboratory tests—quantitative polymerase chain reaction (qPCR) and anti-PGL-I serology—could help identify contacts at increased risk and improve early diagnosis.

The study followed household contacts attending a reference centre in Rio de Janeiro, Brazil, between 2011 and 2018. In total, 2,437 household contacts were examined. During the first contact surveillance visit, 54 individuals (2.2%) were diagnosed with leprosy through clinical examination. Among the remaining contacts, 25 people presented with skin lesions that were difficult to diagnose. These individuals underwent further investigation using skin biopsy, histopathology, and qPCR testing. Laboratory investigations confirmed leprosy in eight individuals, while the remaining seventeen were diagnosed with other dermatological conditions.

To evaluate the ability of qPCR and anti-PGL-I serology to predict disease progression, a cohort of 955 apparently healthy household contacts recruited between 2011 and 2015 was followed for a minimum of three years and a maximum of seven years. Samples collected included slit-skin smears from the ear lobes for qPCR analysis and blood samples for anti-PGL-I testing.

During follow-up, only five of the 955 contacts (0.5%) developed leprosy. Although a positive qPCR result from ear-lobe samples was associated with an increased relative risk of developing the disease, the test showed low sensitivity. Only one of the five contacts who later developed leprosy had tested positive by qPCR at enrolment. These findings suggest that qPCR performed on ear-lobe slit-skin smears is not suitable as a predictive marker for disease progression among household contacts.

The study also assessed the prevalence of Mycobacterium leprae DNA and anti-PGL-I antibodies among household contacts. Nine percent of contacts tested positive by qPCR, while 12% tested positive for anti-PGL-I antibodies. However, only a small proportion tested positive with both methods. It was not possible to assess the predictive value of anti-PGL-I serology, as none of the contacts who later developed leprosy had tested positive at enrolment.

Although qPCR on ear-lobe samples was not useful for predicting future disease, the study demonstrated an important role for qPCR in supporting diagnosis. Among contacts with suspicious skin lesions, qPCR on skin biopsy samples proved valuable as an additional diagnostic tool alongside histopathological examination. Half of the contacts whose lesions were ultimately confirmed as leprosy tested positive by qPCR, and a positive qPCR result in skin tissue was strongly associated with a diagnosis of leprosy.

The introduction of qPCR into routine practice at the FIOCRUZ clinic also appeared to improve the identification of existing but previously unconfirmed cases among household contacts. Between 2011 and 2018, laboratory testing helped confirm eight additional leprosy cases that might otherwise have remained undiagnosed. This increased the detection of co-prevalent cases—contacts who already had leprosy at the time of screening—and was accompanied by a reduction in the proportion of new cases detected during later follow-up.

The study also identified age as an important factor associated with progression to leprosy. Older household contacts, particularly those over 60 years of age, were found to have a higher risk of developing the disease during follow-up, suggesting that this group may benefit from closer surveillance.

Overall, the findings indicate that routine qPCR testing of ear-lobe slit-skin smears should not be used to predict leprosy risk among household contacts. However, qPCR can be a valuable diagnostic aid when contacts present with suspicious skin lesions, particularly when used alongside histopathological examination of skin biopsy samples. The results also highlight the importance of continued contact surveillance, with particular attention to older household contacts who may be at increased risk of developing leprosy.

Impact

Barbieri, R. R., Manta, F. S., Moreira, S. J., Sales, A. M., Nery, J. A., Nascimento, L. P., ... & Moraes, M. O. (2019). Quantitative polymerase chain reaction in paucibacillary leprosy diagnosis: A follow-up study. PLoS neglected tropical diseases, 13(3), e0007147.

Manta, F. S., Barbieri, R. R., Moreira, S. J., Santos, P. T., Nery, J. A., Duppre, N. C., ... & Moraes, M. O. (2019). Quantitative PCR for leprosy diagnosis and monitoring in household contacts: A follow-up study, 2011–2018. Scientific reports, 9(1), 16675.