**1. Introduction**

Leptospirosis is a worldwide but more neglected zoonotic disease that usually affects humans and animals around the world [1–3] with case records 350,000 annually [4]. Death occurs from 10 to 50% in severe infection cases [5]. Pathogenic *Leptospira* are bacteria that cause the disease through penetration into the mucous membrane or damaged skin of the host [6]and then transfer to the proximal tubule of the kidneys [7]. Infected animals remain asymptomatic and secrete infectious organisms in urine throughout their lifetime [8]. *Leptospira* are excreted in the urine for weeks, months, or longer [9]. It pollutes moist soil, farm land, and rivers. Infection occurs when a person or animal is in intimate contact with a contaminated climate or infected urine of host [6]. The famous *Leptospira* carriers are wild, domestic, and some other mammalian species [10]. Occurrence of leptospirosis in humans is also associated with high temperature, high humidity, and basic hygienic conditions [11, 12]. Human leptospirosis is biphasic, with the general symptoms of pyrogens associated with acute or leptospiremic phase, continuing for about 1 week, and subsequent of

recovery or immunization which is defined by antibody production [13]. In the past few decades, leptospirosis has become an infectious disease of urban environments especially in industrialized and developing countries. Rural areas are also affected with high mortality due to delay in diagnosis and lack of infrastructure with adequate clinical suspicion and other unknown causes like inherent pathogenicity of *Leptospira* strains [8]. Leptospirosis is very common in tropical and subtropical areas where people are very close to animals. Warm and humid environment favors in distribution and survival of pathogen [14]. Sporadic cases are reported throughout the year with incidence ranges from 0.1 to 10 per 100,000 people; and during the epidemic, it can reach over 50 per 10,000 people. Most cases are reported in Sri Lanka, India, Indonesia, Maldives, and Thailand. In the past, Sri Lanka (2008), Jakarta (2003), and Mumbai (2005) have been reported as epidemic areas of Southeast Asia [10]. The molecular classification of *Leptospira* in different species is described on DNA correlation base [3, 15]. The genome of *Leptospira* consists of two round chromosomes whose entire sequence has been established recently [8, 16]. The genome is larger than the genomes of other spirochetes, which shows the viability of *Leptospira* in different harsh environments [17]. Symptoms usually appear suddenly after an incubation period of 2–20 days, with a duration of 14 days at least. About 10% of patients diagnosed with leptospirosis having signs like Weil's disease, which manifests itself as jaundice, kidney failure, and hemorrhagic in pulmonary arteries [18]. Leptospirosis is usually related to headache, fever with muscular pain in both adults and children. Drowsiness, vomiting, abdominal pain, diarrhea, cough, photophobia, arthralgia, and constipation may also occur [19].
