Describing fine spatiotemporal dynamics of rat fleas in an insular ecosystem enlightens abiotic drivers of murine typhus incidence in humans.

Murine typhus is a flea-borne zoonotic disease that has been recently reported on Reunion Island, an oceanic volcanic island located in the Indian Ocean. Five years of survey implemented by the regional public health services have highlighted a strong temporal and spatial structure of the disease in humans, with cases mainly reported during the humid season and restricted to the dry southern and western portions of the island. We explored the environmental component of this zoonosis in an attempt to decipher the drivers of disease transmission. To do so, we used data from a previously published study (599 small mammals and 175 Xenopsylla fleas from 29 sampling sites) in order to model the spatial distribution of rat fleas throughout the island. In addition, we carried out a longitudinal sampling of rats and their ectoparasites over a 12 months period in six study sites (564 rats and 496 Xenopsylla fleas) in order to model the temporal dynamics of flea infestation of rats. Generalized Linear Models and Support Vector Machine classifiers were developed to model the Xenopsylla Genus Flea Index (GFI) from climatic and environmental variables. Results showed that the spatial distribution and the temporal dynamics of fleas, estimated through the GFI variations, are both strongly controlled by abiotic factors: rainfall, temperature and land cover. The models allowed linking flea abundance trends with murine typhus incidence rates. Flea infestation in rats peaked at the end of the dry season, corresponding to hot and dry conditions, before dropping sharply. This peak of maximal flea abundance preceded the annual peak of human murine typhus cases by a few weeks. Altogether, presented data raise novel questions regarding the ecology of rat fleas while developed models contribute to the design of control measures adapted to each micro region of the island with the aim of lowering the incidence of flea-borne diseases.

Low seroprevalence of hepatitis E on Reunion island.

OBJECTIVE: Hepatitis E virus (HEV) has been scarcely investigated in the Indian Ocean. Following a nationwide serosurvey among blood donors, we conducted a population-based serosurvey to assess the magnitude of HEV exposure on Reunion Island. METHODS: Four hundred and sixty-six archived frozen human sera from the 2009 CoPanFlu-RUN cohort were analysed using the Wantai HEV IgG enzyme immunoassay. HEV seropositivity was defined as an IgG titre ≥5 UI/ml. Raw and weighted seroprevalences were assessed to account for the discrepancy between the CoPanFlu-RUN subset and the general community. Prevalence proportion ratios (PPR) were measured using log-binomial models. RESULTS: The raw and the weighted seroprevalences of HEV were 9.01% (95% CI 6.41-11.61) and 6.73% (95% CI 4.47-8.98), respectively. The presence of HEV IgG antibodies was associated with increasing age (P < 0.001). In a survey-adjusted model minimizing the sampling bias and adjusting for age, males were more likely to be seropositive than females (adjusted PPR 2.59, 95% CI 1.07-6.25). Seropositivity was spatially heterogeneous across the island (P < 0.01). Living in the neighbourhood of a pig farm within a low to intermediate slope area was associated with seropositivity in several models adjusting for age, gender, altitude of residency and interaction between slope and pig farms. CONCLUSION: Reunion Island is a low endemic area for HEV exposure. Despite limitations related to the retrospective study design, our findings confirm the roles of cumulative lifetime exposure and male gender in HEV exposure. The risk associated with neighbouring pig farms might also suggest environmental contamination in this setting.

Seroprevalence of Coxiella burnetii (Q fever) Exposure in Humans on Reunion Island.

After the documentation of sporadic cases of Q fever endocarditis, we conducted a serosurvey to assess Coxiella burnetii exposure on Reunion Island. Two hundred forty-one stored frozen human sera were analyzed using an immunofluorescence assay. The weighted seroprevalence of Q fever was of 6.81% (95% confidence interval, 4.02%-9.59%). Despite the absence of infection in youths <20 years of age, exposure was not driven by age or by gender. There was a spatial disparity in exposure across the island, with higher prevalence being reported in regions where ruminant farms are present. The seroprevalence pattern suggests that Q fever is endemic on Reunion Island.

Seroprevalence of typhus group and spotted fever group Rickettsia exposures on Reunion island.

OBJECTIVE: Murine typhus has been increasingly reported on Reunion island, Indian ocean, following documentation of eight autochthonous infections in 2012-2013. We conducted a serosurvey to assess the magnitude of the seroprevalence of rickettsioses in the population. Two hundred and forty-one stored frozen sera taken from the 2009 Copanflu-RUN cohort were analysed using an immunofluorescence assay allowing to distinguish typhus group (TGR) and spotted fever group Rickesttsiae (SFGR). Seropositivity was defined for a dilution titre of Rickettsia IgG antibodies ≥ 1:64. Seroprevalence was weighted to account for the discrepancy between the Copanflu-RUN subset and the general population, as to infer prevalence at community level. Prevalence proportion ratios (PPR) were measured using log-binomial models. RESULTS: The weighted seroprevalences of typhus group rickettsioses and spotted fever group rickettsioses were of 12.71% (95% CI 8.84-16.58%) and 17.68% (95% CI 13.25-22.11%), respectively. Pooled together, data suggested that a fifth of the population had been exposed at least to one Rickettsia group. Youths (< 20 years) were less likely seropositive than adults (adjusted PPR 0.13, 95% CI 0.01-0.91). People living in the western dryer part of the island were more exposed (adjusted PPR 2.53, 95% CI 1.07-5.97). Rickettsioses are endemic on Reunion island and circulated before their first identification as murine typhus in year 2011. Surprisingly, since isolation of Rickettsia africae from Amblyomma variegatum in year 2004 or isolation of Rickettsia felis from Amblyomma loculosum, no autochthonous cases of African tick-bite fever or flea-borne spotted fever has yet been diagnosed.

Molecular Evidence of Drug-Resistant Tuberculosis in the Balimo Region of Papua New Guinea.

Papua New Guinea (PNG) has a high burden of tuberculosis (TB), including drug-resistant TB (DR-TB). DR-TB has been identified in patients in Western Province, although there has been limited study outside the provincial capital of Daru. This study focuses on the Balimo region of Western Province, aiming to identify the proportion of DR-TB, and characterise Mycobacterium tuberculosis (MTB) drug resistance-associated gene mutations. Sputum samples were investigated for MTB infection using published molecular methods. DNA from MTB-positive samples was amplified and sequenced, targeting the rpoB and katG genes to identify mutations associated with rifampicin and isoniazid resistance respectively. A total of 240 sputum samples were collected at Balimo District Hospital (BDH). Of these, 86 were classified as positive based on the results of the molecular assays. For samples where rpoB sequencing was successful, 10.0% (5/50, 95% CI 4.4⁻21.4%) were considered rifampicin-resistant through detection of drug resistance-associated mutations. We have identified high rates of presumptive DR-TB in the Balimo region of Western Province, PNG. These results emphasise the importance of further surveillance, and strengthening of diagnostic and treatment services at BDH and throughout Western Province, to facilitate detection and treatment of DR-TB, and limit transmission in this setting.

A systematic review of human and animal leptospirosis in the Pacific Islands reveals pathogen and reservoir diversity.

BACKGROUND: The Pacific Islands have environmental conditions highly favourable for transmission of leptospirosis, a neglected zoonosis with highest incidence in the tropics, and Oceania in particular. Recent reports confirm the emergence and outbreaks of leptospirosis in the Pacific Islands, but the epidemiology and drivers of transmission of human and animal leptospirosis are poorly documented, especially in the more isolated and less developed islands. METHODOLOGY/PRINCIPAL FINDINGS: We conducted a systematic review of human and animal leptospirosis within 25 Pacific Islands (PIs) in Polynesia, Melanesia, Micronesia, as well as Easter Island and Hawaii. We performed a literature search using four international databases for articles published between January 1947 and June 2017. We further included grey literature available on the internet. We identified 148 studies describing leptospirosis epidemiology, but the number of studies varied significantly between PIs. No data were available from four PIs. Human leptospirosis has been reported from 13 PIs, with 63% of all studies conducted in Hawaii, French Polynesia and New Caledonia. Animal leptospirosis has been investigated in 19 PIs and from 14 host species, mainly pigs (18% of studies), cattle (16%) and dogs (11%). Only 13 studies provided information on both human and animal leptospirosis from the same location. Serology results were highly diverse in the region, both in humans and animals. CONCLUSIONS/SIGNIFICANCE: Our study suggests that, as in other tropical regions, leptospirosis is widespread in the PIs while showing some epidemiological heterogeneity. Data are scarce or absent from many PIs. Rodents, cattle, pigs and dogs are all likely to be important carriers, but the relative importance of each animal species in human infection needs to be clarified. Epidemiological surveys with appropriate sampling design, pathogen typing and data analysis are needed to improve our understanding of transmission patterns and to develop effective intervention strategies.

Biogeography of Leptospira in wild animal communities inhabiting the insular ecosystem of the western Indian Ocean islands and neighboring Africa.

Understanding the processes driving parasite assemblages is particularly important in the context of zoonotic infectious diseases. Leptospirosis is a widespread zoonotic bacterial infection caused by pathogenic species of the genus Leptospira. Despite a wide range of animal hosts, information is still lacking on the factors shaping Leptospira diversity in wild animal communities, especially in regions, such as tropical insular ecosystems, with high host species richness and complex biogeographical patterns. Using a large dataset (34 mammal species) and a multilocus approach at a regional scale, we analyzed the role of both host species diversity and geography in Leptospira genetic diversity in terrestrial small mammals (rodents, tenrecs, and shrews) and bats from 10 different islands/countries in the western Indian Ocean (WIO) and neighboring Africa. At least four Leptospira spp. (L. interrogans, L. borgpetersenii, L. kirschneri, and L. mayottensis) and several yet-unidentified genetic clades contributed to a remarkable regional Leptospira diversity, which was generally related to the local occurrence of the host species rather than the geography. In addition, the genetic structure patterns varied between Leptospira spp., suggesting different evolutionary histories in the region, which might reflect both in situ diversification of native mammals (for L. borgpetersenii) and the more recent introduction of non-native host species (for L. interrogans). Our data also suggested that host shifts occurred between bats and rodents, but further investigations are needed to determine how host ecology may influence these events.

Molecular diagnosis of suspected tuberculosis from archived smear slides from the Balimo region, Papua New Guinea.

BACKGROUND: Tuberculosis (TB) is a serious health problem in Papua New Guinea (PNG) with an estimated 30000 new cases and 3800 deaths each year. In the Balimo region of the Western Province, diagnosis relies on clinical manifestations and on the microscopic detection of acid-fast bacilli (AFB) in sputum smears, a technique with limited sensitivity. METHODS: A molecular diagnosis assay targeting DNA extracted from archived sputum smear slides collected from the Balimo region (2012-2014) was conducted, without the need for a viable culture. The presence of Mycobacterium sp on 1162 slides prepared from 345 sputum samples was assessed using a real-time PCR (qPCR) approach. RESULTS: The qPCR technique identified the presence of mycobacteria in 35.4% of the smear slides and 59.7% of the tested sputum samples. Poor agreement was observed between the two diagnosis methods (smear AFB microscopy versus qPCR), with 100 AFB-positive sputum samples compared to 206 qPCR-positive sputum samples overall. Treatment was initiated in 90.2% of the smear-positive cases. Unnecessary treatment of 'false-positive' TB cases (AFB-negative/qPCR-negative) was very low (8.6%) and was even lower when the nine patients diagnosed with extrapulmonary TB were excluded from the analysis. However, the prevalence of false-negatives (AFB-negative/qPCR-positive) was high (28.5%). CONCLUSIONS: Undetected smear-negative TB is occurring in the Balimo region of PNG, as well as some unnecessary empirical treatment. Molecular methods of diagnosis could greatly reduce the frequency of inappropriate clinical assessment, as well as providing point-of-care diagnosis. This may provide substantial patient and programmatic benefits, including lowering the economic burden on patients from rural areas seeking medical diagnosis in Balimo.

Advances and challenges in barcoding pathogenic and environmental Leptospira.

Leptospirosis is a zoonotic bacterial disease of global importance. A large spectrum of asymptomatic animal hosts can carry the infection and contribute to the burden of human disease. Environmental sources of human contamination also point to the importance of a hydrotelluric reservoir. Leptospirosis can be caused by as many as 15 different pathogenic or intermediate Leptospira species. However, classification of these bacteria remains complicated through the use of both serological and genetic classification systems that show poor correlation. With the advent of molecular techniques, DNA-based barcoding offers a conceptual framework that can be used for leptospirosis surveillance as well as source tracking. In this review, we summarize some of the current techniques, highlight significant successes and weaknesses and point to the future opportunities and challenges to successfully establish a widely applicable barcoding scheme for Leptospira.

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

BACKGROUND: Leptospirosis 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. METHODS: A 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. RESULTS: A 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. CONCLUSIONS: This 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.

Leptospira diversity in animals and humans in Tahiti, French Polynesia.

BACKGROUND: Leptospirosis is a highly endemic bacterial zoonosis in French Polynesia (FP). Nevertheless, data on the epidemiology of leptospirosis in FP are scarce. We conducted molecular studies on Leptospira isolated from humans and the potential main animal reservoirs in order to identify the most likely sources for human infection. METHODOLOGY/PRINCIPAL FINDINGS: Wild rats (n = 113), farm pigs (n = 181) and domestic dogs (n = 4) were screened for Leptospira infection in Tahiti, the most populated island in FP. Positive samples were genotyped and compared to Leptospira isolated from human cases throughout FP (n = 51), using secY, 16S and LipL32 sequencing, and MLST analysis. Leptospira DNA was detected in 20.4% of rats and 26.5% of pigs. We identified two Leptospira species and three sequence types (STs) in animals and humans: Leptospira interrogans ST140 in pigs only and L. interrogans ST17 and Leptospira borgpetersenii ST149 in humans and rats. Overall, L. interrogans was the dominant species and grouped into four clades: one clade including a human case only, two clades including human cases and dogs, and one clade including human cases and rats. All except one pig sample showed a unique L. interrogans (secY) genotype distinct from those isolated from humans, rats and dogs. Moreover, LipL32 sequencing allowed the detection of an additional Leptospira genotype in pigs, clearly distinct from the previous ones. CONCLUSIONS/SIGNIFICANCE: Our data confirm rats as a major potential source for human leptospirosis in FP. By contrast to what was expected, farm pigs did not seem to be a major reservoir for the Leptospira genotypes identified in human patients. Thus, further investigations will be required to determine their significance in leptospirosis transmission in FP.

The risk of global epidemic replacement with drug-resistant Mycobacterium tuberculosis strains.

OBJECTIVES: Multidrug-resistant tuberculosis (MDR-TB) is a threat to tuberculosis (TB) control. To guide TB control, it is essential to understand the extent to which and the circumstances in which MDR-TB will replace drug-susceptible TB (DS-TB) as the dominant phenotype. The issue was examined by assessing evidence from genomics, pharmacokinetics, and epidemiology studies. This evidence was then synthesized into a mathematical model. METHODS: This model considers two TB strains, one with and one without an MDR phenotype. It was considered that intrinsic transmissibility may be different between the two strains, as may the control response including the detection, treatment failure, and default rates. The outcomes were explored in terms of the incidence of MDR-TB and time until MDR-TB surpasses DS-TB as the dominant strain. RESULTS AND CONCLUSIONS: The ability of MDR-TB to dominate DS-TB was highly sensitive to the relative transmissibility of the resistant strain; however, MDR-TB could dominate even when its transmissibility was modestly reduced (to between 50% and 100% as transmissible as the DS-TB strain). This model suggests that it may take decades or more for strain replacement to occur. It was also found that while the amplification of resistance is the early cause of MDR-TB, this will rapidly give way to person-to-person transmission.

Gut microbiota disturbance during helminth infection: can it affect cognition and behaviour of children?

BACKGROUND: Bidirectional signalling between the brain and the gastrointestinal tract is regulated at neural, hormonal, and immunological levels. Recent studies have shown that helminth infections can alter the normal gut microbiota. Studies have also shown that the gut microbiota is instrumental in the normal development, maturation and function of the brain. The pathophysiological pathways by which helminth infections contribute to altered cognitive function remain poorly understood. DISCUSSION: We put forward the hypothesis that gastrointestinal infections with parasitic worms, such as helminths, induce an imbalance of the gut-brain axis, which, in turn, can detrimentally manifest in brain development. Factors supporting this hypothesis are: 1) research focusing on intelligence and school performance in school-aged children has shown helminth infections to be associated with cognitive impairment, 2) disturbances in gut microbiota have been shown to be associated with important cognitive developmental effects, and 3) helminth infections have been shown to alter the gut microbiota structure. Evidence on the complex interactions between extrinsic (parasite) and intrinsic (host-derived) factors has been synthesised and discussed. While evidence in favour of the helminth-gut microbiota-central nervous system hypothesis is circumstantial, it would be unwise to rule it out as a possible mechanism by which gastrointestinal helminth infections induce childhood cognitive morbidity. Further empirical studies are necessary to test an indirect effect of helminth infections on the modulation of mood and behaviour through its effects on the gut microbiota.

Human Leptospirosis on Reunion Island, Indian Ocean: Are Rodents the (Only) Ones to Blame?

BACKGROUND: Although leptospirosis is a zoonosis of major concern on tropical islands, the molecular epidemiology of the disease aiming at linking human cases to specific animal reservoirs has been rarely explored within these peculiar ecosystems. METHODOLOGY/PRINCIPAL FINDINGS: Five species of wild small mammals (n = 995) as well as domestic animals (n = 101) were screened for Leptospira infection on Reunion Island; positive samples were subsequently genotyped and compared to Leptospira from clinical cases diagnosed in 2012-2013 (n = 66), using MLST analysis. We identified two pathogenic species in human cases, namely Leptospira interrogans and Leptospira borgpetersenii. Leptospira interrogans was by far dominant both in clinical samples (96.6%) and in infected animal samples (95.8%), with Rattus spp and dogs being its exclusive carriers. The genetic diversity within L. interrogans was apparently limited to two sequence types (STs): ST02, identified among most clinical samples and in all rats with complete MLST, and ST34, identified in six humans, but not in rats. Noteworthy, L. interrogans detected in two stray dogs partially matched with ST02 and ST34. Leptospira borgpetersenii was identified in two clinical samples only (3.4%), as well as in cows and mice; four haplotypes were identified, of which two seemingly identical in clinical and animal samples. Leptospira borgpetersenii haplotypes detected in human cases were clearly distinct from the lineage detected so far in the endemic bat species Mormopterus francoismoutoui, thus excluding a role for this volant mammal in the local human epidemiology of the disease. CONCLUSIONS/SIGNIFICANCE: Our data confirm rats as a major reservoir of Leptospira on Reunion Island, but also pinpoint a possible role of dogs, cows and mice in the local epidemiology of human leptospirosis. This study shows that a comprehensive molecular characterization of pathogenic Leptospira in both clinical and animal samples helps to gaining insight into leptospirosis epidemiology within a specific environmental setting.

Use of big data in the surveillance of veterinary diseases: early detection of tick paralysis in companion animals.

BACKGROUND: Tick paralysis, resultant from envenomation by the scrub-tick Ixodes holocyclus, is a serious threat for small companion animals in the eastern coast of Australia. We hypothesise that surveillance systems that are built on Internet search queries may provide a more timely indication of high-risk periods more effectively than current approaches. METHODS: Monthly tick paralysis notifications in dogs and cats across Australia and the states of Queensland (QLD) and New South Wales (NSW) were retrieved from Disease WatchDog surveillance system for the period 2011-2013. Internet search terms related to tick paralysis in small companion animals were identified using Google Correlate, and corresponding search frequency metrics were downloaded from Google Trends. Spearman's rank correlations and time series cross correlations were performed to assess which Google search terms lead or are synchronous with tick paralysis notifications. RESULTS: Metrics data were available for 24 relevant search terms at national level, 16 for QLD and 18 for NSW, and they were all significantly correlated with tick paralysis notifications (P < 0.05). Among those terms, 70.8, 56.3 and 50 % showed strong Spearman's correlations, at national level, for QLD, and for NSW respectively, and cross correlation analyses identified searches which lead notifications at national or state levels. CONCLUSION: This study demonstrates that Internet search metrics can be used to monitor the occurrence of tick paralysis in companion animals, which would facilitate early detection of high-risk periods for tick paralysis cases. This study constitutes the first application of the rapidly emerging field of Internet-based surveillance to veterinary science.

Rickettsia and Bartonella species in fleas from Reunion Island.

Rickettsia felis, Rickettsia typhi, and Bartonella DNA was detected by molecular tools in 12% of Rattus rattus fleas (Xenopsylla species) collected from Reunion Island. One-third of the infested commensal rodents captured during 1 year carried at least one infected flea. As clinical signs of these zoonoses are non-specific, they are often misdiagnosed.

Fleas of small mammals on Reunion Island: diversity, distribution and epidemiological consequences.

The diversity and geographical distribution of fleas parasitizing small mammals have been poorly investigated on Indian Ocean islands with the exception of Madagascar where endemic plague has stimulated extensive research on these arthropod vectors. In the context of an emerging flea-borne murine typhus outbreak that occurred recently in Reunion Island, we explored fleas' diversity, distribution and host specificity on Reunion Island. Small mammal hosts belonging to five introduced species were trapped from November 2012 to November 2013 along two altitudinal transects, one on the windward eastern and one on the leeward western sides of the island. A total of 960 animals were trapped, and 286 fleas were morphologically and molecularly identified. Four species were reported: (i) two cosmopolitan Xenopsylla species which appeared by far as the prominent species, X. cheopis and X. brasiliensis; (ii) fewer fleas belonging to Echidnophaga gallinacea and Leptopsylla segnis. Rattus rattus was found to be the most abundant host species in our sample, and also the most parasitized host, predominantly by X. cheopis. A marked decrease in flea abundance was observed during the cool-dry season, which indicates seasonal fluctuation in infestation. Importantly, our data reveal that flea abundance was strongly biased on the island, with 81% of all collected fleas coming from the western dry side and no Xenopsylla flea collected on almost four hundred rodents trapped along the windward humid eastern side. The possible consequences of this sharp spatio-temporal pattern are discussed in terms of flea-borne disease risks in Reunion Island, particularly with regard to plague and the currently emerging murine typhus outbreak.

Deciphering arboviral emergence within insular ecosystems.

The spatial dynamics of zoonotic arthropod-borne viruses is a fashionable though challenging topic. Inter-human local transmission of a given arbovirus during an outbreak and its spread over large distances are considered as key parameters of emergence. Here, we suggest that insular ecosystems provide ideal natural "laboratory" conditions to uncouple local transmission from long distance spread, and differentiate these two processes. Due to geographic isolation, often-limited land surface area and relatively homogenous ecosystems, oceanic islands display low species richness and often-high levels of endemism. These aspects provide the means for comprehensive entomological surveys and investigations of original host/pathogen interactions. In addition, islands are interconnected through discrete anthropogenic and non-anthropogenic exchanges: whilst islands maintain a substantial level of human and domestic animal exchange with other neighbouring or distant territories, they also comprise dispersal and migratory pathways of volant organisms (insects, birds and bats). Hence, both anthropogenic and non-anthropogenic exchanges in island systems are easier to identify and investigate than in continuous, continental systems. Finally, island ecosystems tend to be notably simpler, more prone to invasive taxa and, therefore, easier to document the colonization or displacement of vector species. These different aspects are presented and overlaid upon the spread of arboviruses within two distinct insular systems: islands of Polynesia and the south-western Indian Ocean. The former have been repeatedly affected by Dengue fever epidemics, while the latter recently suffered four successive epidemics, probably of east African origin, three of which involved the emerging viruses Chikungunya, Rift Valley and Dengue fever. Here, we review some new insights into arboviral spread and evolution associated with investigations that followed these epidemics, as well as several aspects that make insular ecosystems favourable to the investigation of arboviral transmission and spread.

Pandemic influenza due to pH1N1/2009 virus: estimation of infection burden in Reunion Island through a prospective serosurvey, austral winter 2009.

BACKGROUND: To date, there is little information that reflects the true extent of spread of the pH1N1/2009v influenza pandemic at the community level as infection often results in mild or no clinical symptoms. This study aimed at assessing through a prospective study, the attack rate of pH1N1/2009 virus in Reunion Island and risk factors of infection, during the 2009 season. METHODOLOGY/PRINCIPAL FINDINGS: A serosurvey was conducted during the 2009 austral winter, in the frame of a prospective population study. Pairs of sera were collected from 1687 individuals belonging to 772 households, during and after passage of the pandemic wave. Antibodies to pH1N1/2009v were titered using the hemagglutination inhibition assay (HIA) with titers ≥ 1/40 being considered positive. Seroprevalence during the first two weeks of detection of pH1N1/2009v in Reunion Island was 29.8% in people under 20 years of age, 35.6% in adults (20-59 years) and 73.3% in the elderly (≥ 60 years) (P<0.0001). Baseline corrected cumulative incidence rates, were 42.9%, 13.9% and 0% in these age groups respectively (P<0.0001). A significant decline in antibody titers occurred soon after the passage of the epidemic wave. Seroconversion rates to pH1N1/2009 correlated negatively with age: 63.2%, 39.4% and 16.7%, in each age group respectively (P<0.0001). Seroconversion occurred in 65.2% of individuals who were seronegative at inclusion compared to 6.8% in those who were initially seropositive. CONCLUSIONS: Seroincidence of pH1N1/2009v infection was three times that estimated from clinical surveillance, indicating that almost two thirds of infections occurring at the community level have escaped medical detection. People under 20 years of age were the most affected group. Pre-epidemic titers ≥ 1/40 prevented seroconversion and are likely protective against infection. A concern was raised about the long term stability of the antibody responses.