Lacerda, M. V. G. d. | Search bioRxiv

bioRxiv2025

Navigating parasite antigen genetic diversity in the design of Plasmodium vivax serological exposure markers for malaria

BackgroundPlasmodium vivax poses a major obstacle to malaria elimination because it can lie dormant in the liver for weeks or months before reactivating and causing a relapse of infection. These dormant forms (hypnozoites) cannot be detected using standard diagnostics, but recent P. vivax exposure and by proxy, hypnozoite carriage, can be inferred using antibody-based tests (serological markers). In this study, we examined how genetic variation in P. vivax affects the utility of these antibody markers, and whether redesigned antigens could improve performance. MethodsWe analysed global P. vivax genetic data to assess variation in leading serological markers. Based on this, we produced new antigen versions (haplotypes) that better reflect global sequence diversity, compared to the commonly used reference strain (Sal-1). Antibody responses against these new constructs were then tested using samples from well-characterised cohorts in Brazil and Thailand. Antibody levels were assessed in relation to how recently participants had a qPCR-detectable blood-stage P. vivax infection. We compared the ability of the haplotypes and reference constructs to correctly identify individuals infected within the prior 9-months. FindingsExtensive genetic diversity was identified in two P. vivax antigens, DBPII and MSP5. Several antigens had large numbers of circulating haplotypes globally, with the percentage with similar sequence identity to the reference Sal-1 ranging from 0.4% (MSP5) to 99% (S16). Two antigens exhibited strong differences in immunogenicity by region and construct (RBP2a and DBPII). However, for most proteins (5 out of 8), these differences had little impact on the accuracy of identifying recent exposure. In cases where performance was affected (e.g. RBP2a), this could be overcome by adding multiple antigens into the classification model. InterpretationEven highly diverse antigens can be effective serological exposure markers. Our findings highlight the importance of testing the impact of genetic diversity when designing serological tests and suggest practical strategies, such as using a mix of antigens, to ensure consistent performance across regions.

microbiology↗

bioRxiv2024

Forest edge landscape context affects mosquito community composition and risk of pathogen emergence

Forest edges, where humans, mosquitoes, and wildlife interact, may serve as a nexus for zoonotic arbovirus exchange. Although often treated as uniform interfaces, the landscape context of edge habitats can greatly impact ecological interactions. Here, we investigated how the landscape context of forest edges shapes mosquito community structure in an Amazon rainforest reserve near the city of Manaus, Brazil, using hand-nets to sample mosquitoes at three distinct forest edge types. Sampling sites were situated at edges bordering urban land cover, rural land cover, and natural treefall gaps, while sites in continuous forest served as controls. Community composition differed substantially among edge types, with rural edges supporting the highest species diversity. Rural edges also provided suitable habitat for forest specialists, including key sylvatic vectors, of which Haemagogus janthinomys was the most abundant species sampled overall. Our findings emphasize the importance of landscape context in assessing pathogen emergence risk at forest edges.

ecology↗

bioRxiv2018

Natural avirulent Shigella boydii strain in the Brazilian Amazon lacks major virulence genes and present Type II, Type III and Type VI Secretion Systems

BackgroundAmong Shigella species, Shigella boydii has always displayed a smaller role to the overall Shigella burden, frequently placed at third in epidemiological studies and described as restricted to Southeast Asia. Here we characterize an S. boydii isolated from an epidemiological study enrolling 1,339 Brazilian children from the Amazon region, in which Shigella species solely was the fourth cause of bacterial diarrhea. S. boydii strain 183 was isolated from rotavirus co-infected children with acute diarrhea. Here we aimed to characterize this strain regarding virulence and, immune response in a pulmonary model.\n\nMethodsAn in vitro HEp-2 epithelial cell invasion assay was used to compare the invasive phenotype of S. boydii strain 183 with clinical and highly virulent S. flexneri strain, both isolated from Brazilian children. A murine pulmonary model was performed to assess lung damage by histopathological analysis. mRNA expression of immune response key genes was retrieved by multiplex real-time PCR and correlations were obtained by network analysis. Broad genome analysis was performed to confirm S. boydii identity and define its virulence profile.\n\nResultsS. boydii strain 183 showed fewer invasion rates in vitro and tissue damage in vivo as compared to virulent S. flexneri 201. When compared to a survival challenge in mice, S. boydii had 100% survival against 10% of virulent S. flexneri. Overall, mRNA immune gene expression suggests a protective response against S. boydii strains 183, in contrast to the inflammatory response induced by the virulent S. flexneri strain 201. Network analysis with S. boydii strain 183 displayed IFN-{gamma} protagonism, contrasting with the correlations centralized on TNF- by the virulent S. flexneri strain 201. The genome showed a lack of effector proteins and enterotoxins in S. boydii strain 183, and sequencing analysis of Ipa invasins revealed mutations at functional sites. This avirulent S. boydii strain 183 presents the Type II Secretion System, T6SS, in addition to T3SS.\n\nConclusionsIn addition to causing no disease, S. boydii strain 183 lacks effector proteins and enterotoxins. The presence of T6SS additional secretion system could provide an advantage to establish this strain among commensal bacteria.\n\nAUTHOR SUMMARYThe Shigella genus is a human pathogen responsible to shigellosis and remains one of the significant causes of morbidity and mortality in children under five years old. This genus has four species, Shigella flexneri, Shigella sonnei, Shigella boydii, and Shigella dysenteriae. S. flexneri and S. sonnei are the most common in the worldwide infections; S. dysenteriae is rarely found, and S. boydii is responsible for 1% of the infections and is known to be restricted to Southeast Asia. Once S. boydii have a relatively small role in global Shigella disease, there are few studies regarding its virulence and mechanisms. Here we characterize an S. boydii isolated from Brazilian children from the Amazon region, and aimed to describe this strain regarding virulence. It is known that Shigella species use the Type 3 Secretion System (T3SS) to invade and colonize the human intestine. We found in S. boydii the presence of Type 2 Secretion System (T2SS), Type 6 Secretion System (T6SS), in addition to the T3SS. The T6SS have been described in S. sonnei only, granting a competitive advantage against S. flexneri mixed cultures. The presence of T6SS additional secretion system could provide a benefit to establish this strain among commensal bacteria.

microbiology↗