Human leptospirosis in Seychelles: A prospective study confirms the heavy burden of the disease but suggests that rats are not the main reservoir

Abstract

BackgroundLeptospirosis is a bacterial zoonosis caused by pathogenic Leptospira for which rats are considered as the main reservoir. Disease incidence is higher in tropical countries, especially in insular ecosystems. Our objectives were to determine the current burden of leptospirosis in Seychelles, a country ranking first worldwide according to historical data, to establish epidemiological links between animal reservoirs and human disease, and to identify drivers of transmission.MethodsA total of 223 patients with acute febrile symptoms of unknown origin were enrolled in a 12-months prospective study and tested for leptospirosis through real-time PCR, IgM ELISA and MAT. In addition, 739 rats trapped throughout the main island were investigated for Leptospira renal carriage. All molecularly confirmed positive samples were further genotyped.ResultsA total of 51 patients fulfilled the biological criteria of acute leptospirosis, corresponding to an annual incidence of 54.6 (95% CI 40.7–71.8) per 100,000 inhabitants. Leptospira carriage in Rattus spp. was overall low (7.7%) but dramatically higher in Rattus norvegicus (52.9%) than in Rattus rattus (4.4%). Leptospira interrogans was the only detected species in both humans and rats, and was represented by three distinct Sequence Types (STs). Two were novel STs identified in two thirds of acute human cases while noteworthily absent from rats.ConclusionsThis study shows that human leptospirosis still represents a heavy disease burden in Seychelles. Genotype data suggests that rats are actually not the main reservoir for human disease. We highlight a rather limited efficacy of preventive measures so far implemented in Seychelles. This could result from ineffective control measures of excreting animal populations, possibly due to a misidentification of the main contaminating reservoir(s). Altogether, presented data stimulate the exploration of alternative reservoir animal hosts.

Recent findings related to immune responses against leptospirosis and novel strategies to prevent infection

“…Indeed, several studies show that leptospirosis more often affects men, with a possible bias consecutive to the practice of activities associated with an increased risk of leptospiral infection [58]. Although prevalence of anti-Leptospira antibodies in both genders was shown to be equivalent regardless of the geographic region influence [59,60], thereby suggesting an equal incidence of infection, thorough epidemiological studies show that males are more often hospitalized and more susceptible to development of severe disease than women [61,62]. Interestingly, an increased male susceptibility was recently reported in a sub-lethal infection model in hamsters, in which males were more prone to develop pulmonary haemorrhage than females [63].…”

Pathogenic Leptospira and their animal reservoirs: testing host specificity through experimental infection

“…Rodents are considered as important reservoirs of Leptospira, and have hence been investigated in a number of environmental settings 4-7. Molecular typing of Leptospira hosted by rats from Reunion Island and Seychelles have revealed the dominance of a single species, L. interrogans, represented by three Sequence Types (STs), two of them being reported in different locations worldwide 4,5 . The very limited diversity of these rat-borne leptospires together with cosmopolitan lineage distribution support a recent introduction of L. interrogans in these oceanic islands, possibly concomitant with rat introduction.…”

Complete Genome Sequences of Three Leptospira mayottensis Strains from Tenrecs That Are Endemic in the Malagasy Region

“…This zoonosis is estimated to cause more than one million human cases and 58,900 deaths each year ( 1 ). Disease incidence is highest on tropical islands, notably in the southwestern Indian Ocean, where investigations carried out under a One Health framework have revealed distinct transmission chains in the different islands ( 2 – 5 ), including the occurrence of Leptospira mayottensis , a pathogenic Leptospira species recently recognized as new to science ( 6 ). Representatives of L. mayottensis (formerly known as Leptospira borgpetersenii group B) were originally isolated from human acute cases ( 7 ) and later identified in tenrecs ( 2 , 5 , 8 ), a diversified family of mammals endemic to Madagascar ( 9 , 10 ).…”

“…Three L. mayottensis strains were isolated in the field from two tenrec species, namely, Tenrec ecaudatus on Mayotte (MDI222 and MDI272) ( 2 ) and Microgale dobsoni on Madagascar (VS2413) ( 5 ). Frozen isolates were thawed in liquid Ellinghausen-McCullough-Johnson-Harris (EMJH) medium containing albumin fatty acid supplements (AFAS) ( 3 ), and they were further subcultured in EMJH supplemented with AFAS, 1% fetal calf serum, and 8% rabbit serum. DNA was extracted with the EZ1 virus minikit v.2.0 (Qiagen, Germany), and sequencing was performed on PacBio platforms.…”

“…Human leptospirosis on Mayotte is peculiar because it is associated with four distinct bacterial species, including L. mayottensis ( 14 ), and characterized by a relatively low fatality rate (0.9%) ( 15 ). The epidemiology is clearly distinct in the neighboring Seychelles and on Reunion Island, where L. interrogans is overwhelmingly dominant and fatality rates are higher (11.8% in the Seychelles and 3 to 5% on Reunion Island) ( 3 , 4 , 16 ). An attenuated virulence of Leptospira species prevailing on Mayotte, including L. mayottensis , may be at least in part responsible for this contrasted regional epidemiology.…”