In the present study a substantial proportion (24.7%) of the study cohort not only showed seropositivity for anti-Leptospira antibodies, but the majority (21.7% of study cohort and 88% of positive cases) were also IgM seropositive. In contrast, only a small proportion (3%) of participants were IgG seropositive, indicating previous exposure. IgG antibodies persist for many years following infection and their presence does not necessarily indicate current or active infections [19], but rather recovery from infection acquired at some earlier time. Therefore, the significant IgM seroprevalence (21.7%), particularly amongst Rohingyas and Pakistani refugees, indicated that exposure to Leptospira was most likely acquired after entry to Malaysia, rather than prior to leaving their country of origin.
Malaysia is not a signatory party to the 1951 Refugee Convention that relates to the Status of Refugees and its 1967 Protocol, that safeguards the fundamental rights of refugees, regulates their status, and requires their essential needs to be provided in those countries offering asylum. Therefore, there is no legal framework to register, document and recognize the status of refugees and their rights in this country. These communities are totally excluded from the government system and thus vulnerable to detention and exploitation, especially individuals without the possession of UNHCR identification cards. Many live in squatter homes and overcrowded flats with poor waste management and sanitation, conditions that create an ideal environment for rodents to thrive in. Consequently, there is an elevated risk of transmission of rodent-borne zoonotic infections such as leptospirosis. This disease is endemic in the Asian-Pacific region where poor socioeconomic, and behavioral conditions facilitate its incidence and prevalence [20] and are also responsible for mortality in the case of some Burmese refugees at the Juru Detention Centre in Penang [21, 22].
The highest IgM seroprevalence was recorded among subjects who routinely ate food by hand and owned pets, whether rats were or were not present in their living quarters, and both are clearly risk factors in the study cohort. Wild and domesticated mammals including pet cats and dogs have been implicated in the transmission of leptospirosis [23] by acting as maintenance and incidental hosts for some serovars. Both feline and canine hosts are likely to interact frequently with wild rodents thereby providing an important link in the chain of transmission and this was confirmed with presence of two pathogenic Leptospira serovars recovered from urine and kidney samples from 150 local stray dogs [24]. Pet owners are more likely to experience scratching of the skin during physical contact with pets, which in turn may serve as a point of entry for infectious agents, as confirmed in studies where pets were responsible for numerous severe cases of human leptospirosis [25, 26].
There was also a strong sex-linked effect on IgM seroprevalence, which was higher among female, compared with male subjects, whether or not they ate by hand or utilized footwear. The female bias in IgM seroprevalence is consistent with studies on hospital patients [27,28,29], whereas conversely Kawaguchi et al. found higher levels of infection in male hosts [30]. Leptospirosis infections are more likely to take place during outdoor activities through contact with soil and water contaminated with animal urine [8]. It is possible that more females are involved in outdoor activities where rodent populations are high, and when combined with eating by hand (Fig. 1B) this may explain to some extent female bias in IgM seroprevalence. Therefore, sex bias in the incidence and prevalence of leptospirosis among deprived populations is more likely explained by differences in environmental, recreational and travel-related activities between sexes rather than being directly attributable to host sex per se [31].
Age was initially identified as a risk factor for IgG seroprevalence in our preliminary analyses (Table 1), and also when other factors had been taken into account in multifactorial models, but statistical analysis failed to identify age as a risk factor for IgM seroprevalence. Nevertheless, there was some indication of higher IgM seroprevalence among teenage children, who are likely to be the most active sector of any population. Moreover, if they do not wear footwear, they are likely to make direct or indirect contact with contaminated urine, carcasses of infected animals and the reservoir hosts. Based on our observations, both the Rohingya and Pakistani communities commonly lives in buildings associated with bad sanitation and poor waste management which allow the rat populations to thrive, thus contributing to the risk of contracting leptospirosis [32, 33].
Indeed, the presence of rats in living quarters was identified as a risk factor for IgM seroprevalence in the initial preliminary statistical models, and subsequently in the multifactorial model, as a component of the interaction with pet ownership and method of eating food. Values for IgM seroprevalence were marginally higher among those who lived in accommodation where rats were present. Overcrowding and poverty have been implicated in rodent-borne transmission of leptospirosis in Bangladesh [34]. Furthermore, a recent study by Sahimin et al. reported the seroprevalence of anti-Leptospira IgG and IgM antibodies amongst urban residents of low-cost flats in Kuala Lumpur [15] whereas Benacer et al. identified two pathogenic Leptospira serovars; L. borgpetersenii serovar Javanica and L. interrogans serovars Bataviae in urban rat populations in Peninsular Malaysia [35]. These studies, together with the present, therefore highlight poor hygiene practices, inadequate sanitation and the presence of rodents as major risks for leptospirosis infections in Malaysian urban communities [15].
Eating style was another risk factor associated with the raised IgM in the current study. Hand hygiene is known to be important as transmission of leptospirosis can take place through skin penetration [8]. This is particularly relevant for those involved in water recreational water activities, which constitute an important risk factor for the transmission of leptospirosis. Many articles have reported that following exposure to contaminated water and soil during recreational activities, such as jungle hiking, water rafting, swimming and other related water activities, there is an increased risk of acquiring leptospirosis [36,37,38,39]. Water recreation visits were initially found to be associated with anti-Leptospira IgM in the current work, but not when other factors had not been taken into account in the multifactorial analysis. Nevertheless, as reported elsewhere, outbreaks of leptospirosis related to water recreational activities have shown the capacity of pathogenic Leptospira species to live in water for prolonged periods of time, thereby increasing the possibility of infecting a susceptible host [40]. This aquatic route of transmission therefore represents indirect transmission of leptospirosis from animals to humans.
Clinical symptoms often associated with leptospirosis include headaches, fever, jaundice, chills, muscle pain or myalgia, abdominal discomfort, and diarrhea, but in the refugee community from the Klang Valley, none of these symptoms were associated with anti-Leptospira IgG and IgM. Multifactorial models correlating clinical symptoms with IgG seroprevalences showed that refugees without fevers or headaches had higher levels of IgG. The latter were more likely to be due to past acute infections with IgG dependent immunity still being expressed. On the other hand, leptospirosis can also be asymptomatic especially in areas with high transmission rates [41], resulting in the disease being critical in later stages when kidneys, lungs and the heart cease to function [42]. Infection with Leptospira can typically manifest itself in a range of nonspecific clinical symptoms such as acute febrile illness with fever, myalgia, arthralgia and headaches [43,44,45]. Consequently, the infection is frequently misdiagnosed and underreported [46, 47] especially as symptoms also mimic influenza and dengue fever [48,49,50,51]. In more severe cases hemorrhages and multi-organ failure can occur and potentially can be fatal [46].
Overall, the evidence from this study highlighted that many of the participants with past leptospirosis infection most probably acquire the disease due to bad living environmental condition and their lifestyle behaviour that have exposed them to contaminated urine from infected animal reservoirs. This study also suggests that most of the participants may only have limited knowledge on the transmission of the disease.
Moving forward there is a need to look at approaches in delivering awareness of disease transmission to the community to prevent the occurrence leptospirosis outbreak. This can be made through the empowerment of the community via community engagement activities such as wellness program and clean-up activities. However, the delivery of the information must be in their respective languages to enhance better understanding.
Nevertheless, there may be some biases as there were several limitations to the study. Firstly, this study was conducted with a specific cohort group i.e., students and secondly this screening was conducted as a cross sectional study thus, not able to represent the whole refugee community.
