Rodent Abundance Dynamics and Leptospirosis Carriage in an Area of Hyper-Endemicity in New Caledonia

Abstract

BackgroundWidespread but particularly incident in the tropics, leptospirosis is transmitted to humans directly or indirectly by virtually any Mammal species. However, rodents are recognized as the most important reservoir. In endemic regions, seasonal outbreaks are observed during hot rainy periods. In such regions, hot spots can be evidenced, where leptospirosis is “hyper-endemic”, its incidence reaching 500 annual cases per 100,000. A better knowledge of how rodent populations and their Leptospira prevalence respond to seasonal and meteorological fluctuations might help implement relevant control measures.Methodology/Principal FindingsIn two tribes in New Caledonia with hyper-endemic leptospirosis, rodent abundance and Leptospira prevalence was studied twice a year, in hot and cool seasons for two consecutive years. Highly contrasted meteorological situations, particularly rainfall intensities, were noted between the two hot seasons studied. Our results show that during a hot and rainy period, both the rodent populations and their Leptospira carriage were higher. This pattern was more salient in commensal rodents than in the sylvatic rats.Conclusions/SignificanceThe dynamics of rodents and their Leptospira carriage changed during the survey, probably under the influence of meteorology. Rodents were both more numerous and more frequently carrying (therefore disseminating) leptospires during a hot rainy period, also corresponding to a flooding period with higher risks of human exposure to waters and watered soils. The outbreaks of leptospirosis in hyper-endemic areas could arise from meteorological conditions leading to both an increased risk of exposure of humans and an increased volume of the rodent reservoir. Rodent control measures would therefore be most effective during cool and dry seasons, when rodent populations and leptospirosis incidence are low.

Experimental Hamster Infection with a Strain of Leptospira borgpetersenii Ballum Isolated from a Reservoir Mouse in New Caledonia

“…5,6 In New Caledonia, leptospires of the Ballum serogroup are involved in less than 5% of human cases, 7 with mice comprising the main asymptomatic carrier of this serogroup. 8 Herein, using histological and molecular techniques, we characterized both severe acute and chronic infections in the golden Syrian hamster with the strain B3-13S of L. borgpetersenii serogroup Ballum, isolated from a wild mouse captured in New Caledonia. and was subsequently characterized as L. borgpetersenii belonging to serogroup Ballum.…”

“…and was subsequently characterized as L. borgpetersenii belonging to serogroup Ballum. 8 Bacteria were cultured in a liquid EMJH medium as previously described. 9 Cell concentration was determined using a Petroff-Hausser counting chamber (Hausser Scientific, Horsham, PA).…”

“…8,12 The serogroup Ballum, the principal reservoir of which is mice, is increasingly reported in human infection. 5,6 Here, we characterized the virulence of a Ballum strain B3-13S, which was isolated from a wild mouse captured in New Caledonia, using hamster model.…”

Upsurge of Rodents’ Population in a Rural Area of Northeastern Iran Raised Concerns about Rodent-borne Diseases

“…Reports from various countries show that the outburst of rodents' populations can lead to outbreaks or increase of some zoonotic diseases. For example, an increase in rodents' populations in New Caledonia following a heavy rainfall led to an outbreak of leptospirosis [28]. Climate change was implicated as the cause of increased rodents' populations in China during 2005 to 2012, which was followed by an outbreak of hemorrhagic fever with renal syndrome.…”

Leptospirosis: Time to move to molecular epidemiology

“…Molecular techniques were also used for characterizing uncultured Leptospira from clinical (Agampodi et al, 2013) or animal (Perez et al, 2011) specimens or even from the environment (Ganoza et al, 2006;Viau and Boehm, 2011). However, reconciling the historical serological knowledge with this modern molecular epidemiology data is a real need until animal reservoir studies also move to molecular approaches, but remains very challenging.…”