Showing papers by "Van-Mai Cao-Lormeau published in 2018"

Unexpected outbreaks of arbovirus infections: lessons learned from the Pacific and tropical America

Abstract: Summary Pandemic arboviruses have emerged as a major global health problem in the past four decades. Predicting where and when the next arbovirus epidemic will occur is a challenge, but history suggests that arboviral black swan events (epidemics that are difficult to predict and that have an extreme effect) will continue to occur as urban growth and globalisation expand. We briefly review unexpected arbovirus epidemics that have occurred in the past 50 years, with emphasis on the American and Pacific regions, to illustrate their unpredictability, and to highlight the need for improved global preparedness, including laboratory-based surveillance, prevention, and control programmes.

Using paired serology and surveillance data to quantify dengue transmission and control during a large outbreak in Fiji

Abstract: Dengue is a major health burden, but it can be challenging to examine transmission and evaluate control measures because outbreaks depend on multiple factors, including human population structure, prior immunity and climate. We combined population-representative paired sera collected before and after the 2013/14 dengue-3 outbreak in Fiji with surveillance data to determine how such factors influence transmission and control in island settings. Our results suggested the 10-19 year-old age group had the highest risk of infection, but we did not find strong evidence that other demographic or environmental risk factors were linked to seroconversion. A mathematical model jointly fitted to surveillance and serological data suggested that herd immunity and seasonally varying transmission could not explain observed dynamics. However, the model showed evidence of an additional reduction in transmission coinciding with a vector clean-up campaign, which may have contributed to the decline in cases in the later stages of the outbreak.

Re-visiting the evolution, dispersal and epidemiology of Zika virus in Asia.

Abstract: Based on serological evidence and viral isolation, Zika virus (ZIKV) has circulated for many years relatively benignly in a sylvatic cycle in Africa and an urban cycle in South East Asia (SEA). With the recent availability of limited but novel Indian ZIKV sequences to add to the plethora of SEA sequences, we traced the phylogenetic history and spatio-temporal dispersal pattern of ZIKV in Asia prior to its explosive emergence in the Pacific region and the Americas. These analyses demonstrated that the introduction and dispersal of ZIKV on the Pacific islands were preceded by an extended period of relatively silent transmission in SEA, enabling the virus to expand geographically and evolve adaptively before its unanticipated introduction to immunologically naive populations on the Pacific islands and in the Americas. Our findings reveal new features of the evolution and dispersal of this intriguing virus and may benefit future disease control strategies.

Seroprevalence of Dengue and Chikungunya Virus Antibodies, French Polynesia, 2014-2015.

Abstract: We investigated dengue and chikungunya virus antibody seroprevalence in French Polynesia during 2014–2015. Dengue virus seroprevalence was ≈60% among schoolchildren and >83% among the general population; chikungunya virus seroprevalence was <3% before and 76% after Zika virus emergence (2013). Dengue virus herd immunity may affect Zika virus infection and pathogenesis.

Zika Virus Infection during Pregnancy and Effects on Early Childhood Development, French Polynesia, 2013-2016.

Abstract: Congenital Zika virus syndrome consists of a large spectrum of neurologic abnormalities seen in infants infected with Zika virus in utero. However, little is known about the effects of Zika virus intrauterine infection on the neurocognitive development of children born without birth defects. Using a case-control study design, we investigated the temporal association of a cluster of congenital defects with Zika virus infection. In a nested study, we also assessed the early childhood development of children recruited in the initial study as controls who were born without known birth defects,. We found evidence for an association of congenital defects with both maternal Zika virus seropositivity (time of infection unknown) and symptomatic Zika virus infection during pregnancy. Although the early childhood development assessment found no excess burden of developmental delay associated with maternal Zika virus infection, larger, longer-term studies are needed.

Zika virus outbreak in the Pacific: Vector competence of regional vectors.

Abstract: Background In 2013, Zika virus (ZIKV) emerged in French Polynesia and spread through the Pacific region between 2013 and 2017. Several potential Aedes mosquitoes may have contributed to the ZIKV transmission including Aedes aegypti, the main arbovirus vector in the region, and Aedes polynesiensis, vector of lymphatic filariasis and secondary vector of dengue virus. The aim of this study was to analyze the ability of these two Pacific vectors to transmit ZIKV at a regional scale, through the evaluation and comparison of the vector competence of wild Ae. aegypti and Ae. polynesiensis populations from different Pacific islands for a ZIKV strain which circulated in this region during the 2013–2017 outbreak. Methodology/principal findings Field Ae. aegypti (three populations) and Ae. polynesiensis (two populations) from the Pacific region were collected for this study. Female mosquitoes were orally exposed to ZIKV (107 TCID50/mL) isolated in the region in 2014. At 6, 9, 14 and 21 days post-infection, mosquito bodies (thorax and abdomen), heads and saliva were analyzed to measure infection, dissemination, transmission rates and transmission efficiency, respectively. According to our results, ZIKV infection rates were heterogeneous between the Ae. aegypti populations, but the dissemination rates were moderate and more homogenous between these populations. For Ae. polynesiensis, infection rates were less heterogeneous between the two populations tested. The transmission rate and efficiency results revealed a low vector competence for ZIKV of the different Aedes vector populations under study. Conclusion/significance Our results indicated a low ZIKV transmission by Ae. aegypti and Ae. polynesiensis tested from the Pacific region. These results were unexpected and suggest the importance of other factors especially the vector density, the mosquito lifespan or the large immunologically naive fraction of the population that may have contributed to the rapid spread of the ZIKV in the Pacific region during the 2013–2017 outbreak.

Using paired serology and surveillance data to quantify dengue transmission and control during a large outbreak in Fiji

Abstract: Dengue is a major health burden, but it can be challenging to examine transmission dynamics and evaluate control measures because outbreaks depend on multiple factors, including human population structure, prior immunity and climate We combined population-representative paired sera collected before and after the major 2013/14 dengue-3 outbreak in Fiji with surveillance data to determine how such factors influence dengue virus transmission and control in island settings Our results suggested the 10-19 year-old age group had the highest risk of acquiring infection, but we did not find strong evidence that other demographic or environmental risk factors were linked to seroconversion Mathematical modelling showed that temperature-driven variation in transmission and herd immunity could not fully explain observed dynamics However, there was evidence of an additional reduction in transmission coinciding with a vector clean-up campaign, which may have contributed to the decline in cases and prevented transmission continuing into the following season

Worldwide survey reveals lower susceptibility of African Aedes aegypti mosquitoes to diverse strains of Zika virus

Abstract: Zika virus (ZIKV) is a flavivirus mainly transmitted to humans through the bite of infected Aedes aegypti mosquitoes. First isolated in Uganda in 1947, ZIKV was shown to circulate in enzootic sylvatic cycles in Africa and Asia for at least half a century before the first reported human epidemic occurred in 2007 on the Pacific island of Yap, Micronesia. Subsequently, larger ZIKV outbreaks were recorded in French Polynesia and other South Pacific islands during 2013-2014. In 2015, ZIKV reached Brazil from where it rapidly spread across the Americas and the Caribbean, causing hundreds of thousands of human cases. The factors that have fueled the explosiveness and magnitude of ZIKV emergence in the Pacific and the Americas are poorly understood. Reciprocally, the lack of major human epidemics of ZIKV in regions with seemingly favorable conditions, such as Africa or Asia, remains largely unexplained. To evaluate the potential contribution of vector population diversity to ZIKV epidemiological patterns, we established dose-response curves for eight field-derived Ae. aegypti populations representing the global range of the species, following experimental exposure to six low-passage ZIKV strains spanning the current viral genetic diversity. Our results reveal that African Ae. aegypti are significantly less susceptible than non-African Ae. aegypti across all ZIKV strains tested. We suggest that low susceptibility of vector populations may have contributed to prevent large-scale human transmission of ZIKV in Africa.

Ross River virus antibody prevalence in the Fiji Islands, 2013-2015

Abstract: A unique outbreak of Ross River virus (RRV) infection was reported in Fiji in 1979. In 2013, 29 RRV seroprevalence among residents was 46.5%. Of those born after 1982, 37.4% had anti-RRV 30 antibodies. Between 2013-2015, 10.9% of residents had seroconverted to RRV suggesting 31 ongoing endemic circulation of RRV in Fiji.

Insect-Borne Viruses and Host Skin Interface

Abstract: Arboviruses are viruses that are transmitted by arthropods. They play an increasing threat to man by their pathogenicity, genetic diversity, transmission by arthropod vectors that increase their geographic range through global climate change and modern transportation, and their adaptability to these vectors. A poorly addressed issue is the infection event occurring in the human skin. We therefore review arbovirus diversity and life cycle and focus on the experimental data that address the mechanisms of skin-residing cell infection of different arboviruses in different biological model systems. Taken together, although the studies present limitations, the data point toward the importance of skin-residing immune cells in general and of antigen-presenting cells in particular. However, clear hierarchy of the importance of the skin cells for infection is more complex due to the presence of salivary products, the type of skin, the arthropod vectors, and the virus itself. Further work is greatly needed to clarify skin infection events before proposing topical therapeutic measures.