Approximately 75% of the emerging infectious diseases and 60% of all human diseases are zoonotic in nature, i.e. they are are caused due to the spread of infection between animals and humans. Leptospirosis, a zoonotic disease is a bacterial infection caused by the pathogen spirochetes and reports an estimated 1.03 million cases and 58,900 deaths each year. Leptospira contains 250 antigenically diverse species and due to these distinct variations in the bacteria --called serovars, creating a cross-protective vaccine against the disease is challenging. Natural immunity against a particular strain of Leptospira doesn’t necessarily ensure a mutual protection against the other serovars of the disease. Given the severity of the cases which occur it is often a misdiagnosed and under-explored disease.
The Regional Medical Research Center and Bharathidasan University conducted a study in three Primary Health Care (PHC) centers of South Andaman district where Leptospirosis has been an important public health issue since 1988. The study aimed at assessing the long-term clinical course and the level and duration of antibody persistence against various strains of Leptospira through natural infection. Patients reporting common symptoms of Leptospirosis were tested through a positive blood culture and sero-diagnosis (diagnosis conducted on blood serum) was conducted through the microscopic- agglutination test (MAT) to confirm the presence of the disease. In order to understand the level and duration of antibody persistence across diverse serovars, blood samples were collected from a sub-sample of positively tested patients at the time of reporting of symptoms and during convalescence at 2-3 weeks post diagnosis. In addition, blood samples were collected at various intervals between the duration of 1-48 months and were also subjected to MAT and blood culture tests to understand the long term clinical course of the disease. The results of this study could yield critical information with regard to the pathology and course of the disease post a natural infection. It could also help us understand the possibility of cross-protection amongst certain serovars in an endemic population leading to the creation of an effective vaccine to combat this epidemic disease.