Parasite-Parasite Interactions in the Wild: How To Detect Them?

International audienceInter-specific interactions between parasites impact on parasite intra-hostdynamics, host health, and disease management. Identifying and understandinginteraction mechanisms in the wild is crucial for wildlife disease management.It is however complex because several scales are interlaced. Parasite–parasite interactions are likely to occur via mechanisms at the within-host level,but also at upper levels (host population and community). Furthermore, interactionsoccurring at one level of organization spread to upper levels throughcascade effects. Even if cascade effects are important confounding factors, weargue that we can also benefit from them because upper scales often provide away to survey a wider range of parasites at lower cost. New protocols andtheoretical studies (especially across scales) are necessary to take advantage ofthis opportunity

Biogeography of the two major arbovirus mosquito vectors, Aedes aegypti and Aedes albopictus (Diptera, Culicidae), in Madagascar

Background: In the past ten years, the Indian Ocean region has been the theatre of severe epidemics of chikungunya and dengue. These outbreaks coincided with a high increase in populations of Aedes albopictus that outcompete its sister taxon Aedes aegypti in most islands sampled. The objective of this work was to update the entomological survey of the two Aedes species in the island of Madagascar which has to face these arboviroses. Methods: The sampling of Aedes mosquitoes was conducted during two years, from October 2007 to October 2009, in fifteen localities from eight regions of contrasting climates. Captured adults were identified immediately whereas immature stages were bred until adult stage for determination. Phylogenetic analysis was performed using two mtDNA genes, COI and ND5 and trees were constructed by the maximum likelihood (ML) method with the gene time reversible (GTR) model. Experimental infections with the chikungunya virus strain 06.21 at a titer of 107.5 pfu/mL were performed to evaluate the vector competence of field-collected mosquitoes. Disseminated infection rates were measured fourteen days after infection by immunofluorescence assay performed on head squashes. Results: The species Aedes aegypti was detected in only six sites in native forests and natural reserves. In contrast, the species Aedes albopictus was found in 13 out of the 15 sites sampled. Breeding sites were mostly found inman-made environments such as discarded containers, used tires, abandoned buckets, coconuts, and bamboo cuts. Linear regression models showed that the abundance of Ae. albopictus was significantly influenced by the sampling region (F = 62.00, p < 2.2 × 10-16) and period (F = 36.22, p = 2.548 × 10-13), that are associated with ecological and climate variations. Phylogenetic analysis of the invasive Ae. albopictus distinguished haplotypes from South Asia and South America from those of Madagascar, but the markers used were not discriminant enough to discern Malagasy populations. The experimental oral infection method showed that six Ae. albopictus populations exhibited high dissemination infection rates for chikungunya virus ranging from 98 to 100%. Conclusion: In Madagascar, Ae. albopictus has extended its geographical distribution whereas, Ae. aegypti has become rare, contrasting with what was previously observed. Changes are predominantly driven by human activities and the rainfall regime that provide suitable breeding sites for the highly anthropophilic mosquito Ae. albopictus. Moreover, these populations were found to be highly susceptible to chikungunya virus. In the light of this study, Ae. albopictus may have been involved in the recent outbreaks of chikungunya and dengue epidemics in Madagascar, and consequently, control measures should be promoted to limit its current expansion.Rôle des moustiques Culicidae, de leurs communautés microbiennes et des réservoirs vertébrés, dans la transmission des arbovirus à Madagasca

True versus False Parasite Interactions: A Robust Method to Take Risk Factors into Account and Its Application to Feline Viruses

International audienceBACKGROUND: Multiple infections are common in natural host populations and interspecific parasite interactions are therefore likely within a host individual. As they may seriously impact the circulation of certain parasites and the emergence and management of infectious diseases, their study is essential. In the field, detecting parasite interactions is rendered difficult by the fact that a large number of co-infected individuals may also be observed when two parasites share common risk factors. To correct for these "false interactions", methods accounting for parasite risk factors must be used. METHODOLOGY/PRINCIPAL FINDINGS: In the present paper we propose such a method for presence-absence data (i.e., serology). Our method enables the calculation of the expected frequencies of single and double infected individuals under the independence hypothesis, before comparing them to the observed ones using the chi-square statistic. The method is termed "the corrected chi-square." Its robustness was compared to a pre-existing method based on logistic regression and the corrected chi-square proved to be much more robust for small sample sizes. Since the logistic regression approach is easier to implement, we propose as a rule of thumb to use the latter when the ratio between the sample size and the number of parameters is above ten. Applied to serological data for four viruses infecting cats, the approach revealed pairwise interactions between the Feline Herpesvirus, Parvovirus and Calicivirus, whereas the infection by FIV, the feline equivalent of HIV, did not modify the risk of infection by any of these viruses. CONCLUSIONS/SIGNIFICANCE: This work therefore points out possible interactions that can be further investigated in experimental conditions and, by providing a user-friendly R program and a tutorial example, offers new opportunities for animal and human epidemiologists to detect interactions of interest in the field, a crucial step in the challenge of multiple infections

Unknown age in health disorders: A method to account for its cumulative effect and an application to feline viruses interactions.

Remerciements ECOFECTInternational audienceParasite interactions have been widely evidenced experimentally but field studies remain rare. Such studies are essential to detect interactions of interest and access (co)infection probabilities but face methodological obstacles. Confounding factors can create statistical associations, i.e. false parasite interactions. Among them, host age is a crucial covariate. It influences host exposition and susceptibility to many infections, and has a mechanical effect, older individuals being more at risk because of a longer exposure time. However, age is difficult to estimate in natural populations. Hence, one should be able to deal at least with its cumulative effect. Using a SI type dynamic model, we showed that the cumulative effect of age can generate false interactions theoretically (deterministic modeling) and with a real dataset of feline viruses (stochastic modeling). The risk to wrongly conclude to an association was maximal when parasites induced long-lasting antibodies and had similar forces of infection. We then proposed a method to correct for this effect (and for other potentially confounding shared risk factors) and made it available in a new R package, Interatrix. We also applied the correction to the feline viruses. It offers a way to account for an often neglected confounding factor and should help identifying parasite interactions in the field, a necessary step towards a better understanding of their mechanisms and consequences

Woody Plant Traits and Life-History Strategies across Disturbance Gradients and Biome Boundaries in the Hluhluwe-iMfolozi Park

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When females trade grooming for grooming: testing partner control and partner choice models of cooperation in two primate species

International audienceWe tested predictions following from the biological market paradigm using reciprocated grooming sessions among the adult females in a sooty mangabey, Cercocebus atys, group with 35 females (Ivory Coast) and in two groups of vervet monkeys, Chlorocebus aethiops (South Africa) with four and seven females, respectively. Closely ranked females often groomed frequently. The exchanges within such dyads were generally characterized by time matching, but the subordinates groomed for longer than their dominant partners. The reciprocal nature of over 90% of the grooming sessions allowed us to investigate 'partner control' strategies such as 'parcelling' and 'raising the stakes'. Females of both species neither parcelled nor gradually invested more grooming in the course of sessions. Rather, the longer bouts of a grooming session were usually at the beginning of the session and the length of the first bout reliably predicted the length of the whole session for frequently grooming partners. Furthermore, we compared potential trust-building behaviour (or 'strategies') in frequent and infrequent grooming partners. We found that infrequent groomers of both species showed no signs of trust building and that the first bout they invested in a grooming session did not predict the session length. We conclude that each female has a good knowledge of her value as a grooming partner within each dyad and knows how much she has to invest to receive a satisfactory amount of grooming within the same session

Observed (O) and expected (E) frequencies under the independence hypothesis considering risk factors.

<p>Observed (O) and expected (E) frequencies under the independence hypothesis considering risk factors.</p

Pearson's chi-square tests, corrected chi-square tests and logistic regressions for the search of viruses' interactions.

<p>Pearson's chi-square tests, corrected chi-square tests and logistic regressions for the search of viruses' interactions.</p