Biodiversity and leptospirosis risk: A case of pathogen regulation?

School of Population Health, Level 2 Public Health Building, University of Queensland, Herston Qld 4006, Australia.
Medical Hypotheses (Impact Factor: 1.07). 06/2011; 77(3):339-44. DOI: 10.1016/j.mehy.2011.05.009
Source: PubMed


Well balanced ecosystems have an essential role in disease regulation, and consequently their correct functioning is increasingly recognised as imperative for maintaining human health. Disruptions to ecosystems have been found to increase the risk of several diseases, including Hantavirus, Lyme disease, Ross River virus, malaria and Ciguatera fish poisoning. Leptospirosis is a globally important emerging zoonosis, caused by spirochaete bacteria, borne by many mammalian hosts, and also transmitted environmentally. We propose that leptospirosis incidence in humans is also linked to ecosystem disruption, and that reduced biodiversity (the diversity of species within an ecological community) may be associated with increased leptospirosis incidence. To investigate this hypothesis, the relationship between biodiversity levels of island nations and their annual leptospirosis incidence rates (adjusted for GDP per capita) was examined by linear correlation and regression. Supportive, statistically significant negative associations were obtained between leptospirosis incidence and (a) total number of species (r2=0.69, p<0.001) and (b) number of mammal species (r2=0.80, p<0.001) in univariate analysis. In multivariable analysis only the number of mammal species remained significantly associated (r2=0.81, p=0.007). An association between biodiversity and reduced leptospirosis risk, if supported by further research, would emphasise the importance of managing the emergence of leptospirosis (and other infectious diseases) at a broader, ecosystem level.

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    • "In Fiji, leptospirosis was identified as one of the four priority climate-sensitive diseases of major public health concern[11]islands as particularly high-risk settings[2]. Apart from the tropical climate and high frequency of extreme weather events[3], factors that could contribute to the high risk of leptospirosis on tropical islands include the low biodiversity and delicate ecosystems that make islands vulnerable to invasive species such as rodents[12]; the outdoor lifestyle and associated intense exposure to the environment; and close contact with subsistence livestock animals[2,4]. Climate change is projected to increase the severity of extreme weather events including increased rainfall and flooding in the Pacific Islands[10], and such events have been associated with increased leptospirosis transmission and outbreaks around the world[[MHMS]). "
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    ABSTRACT: Leptospirosis is an important zoonotic disease in the Pacific Islands. In Fiji, two successive cyclones and severe flooding in 2012 resulted in outbreaks with 576 reported cases and 7% case-fatality. We conducted a cross-sectional seroprevalence study and used an eco-epidemiological approach to characterize risk factors and drivers for human leptospirosis infection in Fiji, and aimed to provide an evidence base for improving the effectiveness of public health mitigation and intervention strategies. Antibodies indicative of previous or recent infection were found in 19.4% of 2152 participants (81 communities on the 3 main islands). Questionnaires and geographic information systems data were used to assess variables related to demographics, individual behaviour, contact with animals, socioeconomics, living conditions, land use, and the natural environment. On multivariable logistic regression analysis, variables associated with the presence of Leptospira antibodies included male gender (OR 1.55), iTaukei ethnicity (OR 3.51), living in villages (OR 1.64), lack of treated water at home (OR 1.52), working outdoors (1.64), living in rural areas (OR 1.43), high poverty rate (OR 1.74), living <100m from a major river (OR 1.41), pigs in the community (OR 1.54), high cattle density in the district (OR 1.04 per head/sqkm), and high maximum rainfall in the wettest month (OR 1.003 per mm). Risk factors and drivers for human leptospirosis infection in Fiji are complex and multifactorial, with environmental factors playing crucial roles. With global climate change, severe weather events and flooding are expected to intensify in the South Pacific. Population growth could also lead to more intensive livestock farming; and urbanization in developing countries is often associated with urban and peri-urban slums where diseases of poverty proliferate. Climate change, flooding, population growth, urbanization, poverty and agricultural intensification are important drivers of zoonotic disease transmission; these factors may independently, or potentially synergistically, lead to enhanced leptospirosis transmission in Fiji and other similar settings.
    Full-text · Article · Jan 2016 · PLoS Neglected Tropical Diseases
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    • "Thus, a higher percentage of ticks that bite humans are infectious, linking biodiversity loss directly to disease emergence (Ostfeld and Keesing, 2000). It is tempting to generalise from this example that biodiversity conservation is protective against infectious disease emergence, and many other examples indeed support that this is the case (Ostfeld, 2009), chiefly for arthropod mediated infections, but also for directly transmitted zoonoses (Derne et al., 2011). However, a recent review article (Randolph and Dobson, 2012) and meta-analysis (Salkeld et al., 2013) have seriously questioned the generalisability of the statement " biodiversity protects against disease " (Randolph and Dobson, 2012). "
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    ABSTRACT: It is well known that the degradation of ecosystems can have serious impacts on human health. There is currently a knowledge gap on what impact restoring ecosystems has on human health. In restoring ecosystems there is a drive to restore the functionality of ecosystems rather than restoring ecosystems to ‘pristine’ condition. Even so, the complete restoration of all ecosystem functions is not necessarily possible. Given the uncertain trajectory of the ecosystem during the ecosystem restoration process the impact of the restoration on human health is also uncertain. Even with this uncertainty, the restoration of ecosystems for human health is still a necessity.
    Full-text · Article · Jan 2015 · Science of The Total Environment
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    • "This observation contrasts with that of Redetzke and McCann (1980), who found a density-dependent relationship. Leptospira maintenance and transmission in Janos may depend on several factors, including temperature, frequency of droughts and rainy periods, and the accessibility of humid environments for Leptospira survival and reproduction (Derne et al. 2011). "
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    ABSTRACT: Abstract Interest in the study of infectious diseases of wildlife has grown in recent decades and now focuses on understanding host-parasite dynamics and factors involved in disease occurrence. The black-tailed prairie dog (Cynomys ludovicianus) is a useful species for this type of investigation because it lives in heterogeneous landscapes where human activities take place, and its populations are structured as a metapopulation. Our goal was to determine if colony area, density, and proximity to human settlements are associated with prevalence of antibodies to Leptospira interrogans in black-tailed prairie dogs of northwestern Chihuahua State, Mexico. We captured 266 prairie dogs in 11 colonies in 2009 and analyzed 248 serum samples with the microscopic agglutination test (MAT) for antibody to any of the 12 pathogenic serovars of L. interrogans. Serologically positive test results for only serovars Bratislava, Canicola, Celledoni, and Tarassovi were considered for statistical analysis. Almost 80% of sera were positive for at least one pathogenic serovar (MAT titer ≥1∶80). The highest recorded antibody prevalences were to serovars Bratislava and Canicola. Correlation analysis showed a negative relationship between L. interrogans antibody prevalence and colony area (r = -0.125, P<0.005), suggesting that animals living in larger colonies were at a lower risk than those in smaller colonies. The correlation between the serovar Canicola and distance was negative (r = -0.171, P<0.007), and this relationship may be explained by the presence of domestic dogs associated with human dwellings. This is the first study of Leptospira spp. antibody prevalence in prairie dogs, and it provides valuable insights into the dynamics of leptospirosis in threatened wildlife species. Further studies are needed to evaluate the impact of Leptospira serovars in metapopulations of prairie dogs and other domestic and wild mammals in grassland communities.
    Full-text · Article · Nov 2014 · Journal of wildlife diseases
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