Wild terrestrial rainforest mammals as potential reservoirs for flaviviruses (yellow fever, dengue 2 and St Louis encephalitis viruses) in French Guiana

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.

A systematic review of the microbial community in taiassuids: a One Health approach

Collared and white-lipped peccaries are sympatric and are distributed in most of South America and in the humid tropical forests of Mexico and Central America. Historically, these species have been used as a source of protein by traditional and/or indigenous human communities, but currently they have been used for legal consumption in different countries. Thus, there has been greater interaction between these wild species and domestic animals and humans, enabling microbial interactions between different niches. The present study presents a systematic review of the literature on the microbial community of collared peccaries and white-lipped peccaries distributed throughout the world, focusing on experimental studies related to the detection of microorganisms as well as the prevalence of the animal species and its characterization of the studied population, in situ or ex situ. Seventy-two studies were selected, mainly in South American countries, related to different species of microorganisms isolated or serologically detected (viruses, bacteria, fungi, and parasites), either as microbiota, pathogens or commensals, many of which are of zoonotic interest, such as Leptospira, Toxoplasma, Brucella, among others. Therefore, these wild mammals are characterized as sentinel agents of anthropic action and require the implementation of studies in relation to their contribution to the spread of microorganisms, being a potential source of amplification and transmission of pathogens.

Review on Main Arboviruses Circulating on French Guiana, An Ultra-Peripheric European Region in South America

French Guiana (FG), a French overseas territory in South America, is susceptible to tropical diseases, including arboviruses. The tropical climate supports the proliferation and establishment of vectors, making it difficult to control transmission. In the last ten years, FG has experienced large outbreaks of imported arboviruses such as Chikungunya and Zika, as well as endemic arboviruses such as dengue, Yellow fever, and Oropouche virus. Epidemiological surveillance is challenging due to the differing distributions and behaviors of vectors. This article aims to summarize the current knowledge of these arboviruses in FG and discuss the challenges of arbovirus emergence and reemergence. Effective control measures are hampered by the nonspecific clinical presentation of these diseases, as well as the Aedes aegypti mosquito's resistance to insecticides. Despite the high seroprevalence of certain viruses, the possibility of new epidemics cannot be ruled out. Therefore, active epidemiological surveillance is needed to identify potential outbreaks, and an adequate sentinel surveillance system and broad virological diagnostic panel are being developed in FG to improve disease management.

Arboviruses in Mammals in the Neotropics: A Systematic Review to Strengthen Epidemiological Monitoring Strategies and Conservation Medicine

Arthropod-borne viruses (arboviruses) are a diverse group of ribonucleic acid (RNA) viruses, with the exception of African swine fever virus, that are transmitted by hematophagous arthropods to a vertebrate host. They are the important cause of many diseases due to their ability to spread in different environments and their diversity of vectors. Currently, there is no information on the geographical distribution of the diseases because the routes of transmission and the mammals (wild or domestic) that act as potential hosts are poorly documented or unknown. We conducted a systematic review from 1967 to 2021 to identify the diversity of arboviruses, the areas, and taxonomic groups that have been monitored, the prevalence of positive records, and the associated risk factors. We identified forty-three arboviruses in nine mammalian orders distributed in eleven countries. In Brazil, the order primates harbor the highest number of arbovirus records. The three most recorded arboviruses were Venezuelan equine encephalitis, Saint Louis encephalitis and West Nile virus. Serum is the most used sample to obtain arbovirus records. Deforestation is identified as the main risk factor for arbovirus transmission between different species and environments (an odds ratio of 1.46 with a 95% confidence interval: 1.34-1.59). The results show an increase in the sampling effort over the years in the neotropical region. Despite the importance of arboviruses for public health, little is known about the interaction of arboviruses, their hosts, and vectors, as some countries and mammalian orders have not yet been monitored. Long-term and constant monitoring allows focusing research on the analysis of the interrelationships and characteristics of each component animal, human, and their environment to understand the dynamics of the diseases and guide epidemiological surveillance and vector control programs. The biodiversity of the Neotropics should be considered to support epidemiological monitoring strategies.

Absence of yellow fever virus circulation in wildlife rodents from Brazil

Yellow fever (YF), caused by the yellow fever virus (YFV), is an emerging viral zoonosis that affects humans and non-human primates (NHP). In South America, YF is naturally maintained through enzootic/sylvatic cycles involving NHPs and mosquitoes (Haemagogus and Sabethes). In this study, we retrospectively analyzed wildlife rodents to better understand their role in a potential alternative YF sylvatic cycle. The plaque reduction neutralization test was performed to detect anti-YFV antibodies, while qPCR targeting the NS5 region of flaviviruses and standard PCR targeting the CprM region were applied to detect YFV RNA in tissue and blood samples. YFV was not evidenced in any of the tested samples. These findings provide additional information regarding sylvatic YFV and emphasize the importance of YFV surveillance in wild animals as potential reservoirs/hosts given the well-established enzootic cycle in the studied areas, mainly in the Atlantic Forest.

Challenges in the control of neglected insect vector diseases of human importance in the Anglo-Caribbean

INTRODUCTION

Neglected tropical diseases (NTDs) in developing countries like the Caribbean, negatively affect multiple income-generating sectors, including the tourism industry upon which island states are highly dependent. Insect-transmitted NTDs include, but are not limited to, malaria, dengue and lymphatic filariasis. Control measures for these disease, are often ignored because of the associated cost. Many of the developing country members are thus retained in a financially crippling cycle, balancing the cost of prophylactic measures with that of controlling an outbreak.The purpose of the paper is to bring awareness to NTDs transmitted by insects of importance to humans, and to assess factors affecting such control, in the English-speaking Caribbean.

METHOD

Comprehensive literature review on reports pertaining to NTDs transmitted by insects in the Caribbean and Latin America was conducted. Data search was carried out on PubMed, and WHO and PAHO websites.

RESULTS AND CONCLUSION

Potential risk factors for NTDs transmitted by arthropods in the English-speaking Caribbean are summarised. The mosquito appears to be the main insect-vector of human importance within the region of concern. Arthropod-vectors of diseases of veterinary importance are also relevant because they affect the livelihood of farmers, in highly agriculture based economies. Other NTDs may also be in circulation gauged by the presence of antibodies in Caribbean individuals. However, routine diagnostic tests for specific diseases are expensive and tests may not be conducted when diseases are not prevalent in the population. It appears that only a few English-speaking Caribbean countries have examined secondary reservoirs of pathogens or assessed the effectivity of their insect control methods. As such, disease risk assessment appears incomplete. Although continuous control is financially demanding, an integrated and multisectoral approach might help to deflect the cost. Such interventions are now being promoted by health agencies within the region and various countries are creating and exploring the use of novel tools to be incorporated in their insect-vector control programmes.

Evolutionary analysis of the anti-viral STAT2 gene of primates and rodents: Signature of different stages of an arms race

STAT2 plays a strategic role in defending viral infection through the signaling cascade involving the immune system initiated after type I interferon release. Many flaviviruses target the inactivation or degradation of STAT2 as a strategy to impair this host's line of defense. Primates are natural reservoirs for a range of disease-causing flaviviruses (e.g., Zika, Dengue, and Yellow Fever virus), while rodents appear less susceptible. We analyzed the STAT2 coding sequence of 28 Rodentia species and 49 Primates species. Original data from 19 Platyrrhini species were sequenced for the SH2 domain of STAT2 and included in the analysis. STAT2 has many sites whose variation can be explained by positive selection, measurement by two methods (PALM indicated 12, MEME 61). Both evolutionary tests significantly marked sites 127, 731, 739, 766, and 780. SH2 is under evolutionary constraint but presents episodic positive selection events within Rodentia: in one of them, a moderately radical change (serine > arginine) at position 638 is found in Peromyscus species, and can be implicated in the difference in susceptibility to flaviviruses within Rodentia. Some other positively selected sites are functional such as 5, 95, 203, 251, 782, and 829. Sites 251 and 287 regulate the signaling mediated by the JAK-STAT2 pathway, while 782 and 829 create a stable tertiary structure of STAT2, facilitating its connection with transcriptional co-activators. Only three positively selected sites, 5, 95, and 203, are recognized members who act on the interface between STAT2 and flaviviruses NS5 protein. We suggested that due to the higher evolutionary rate, rodents are, at this moment, taking some advantage in the battle against infections for some well-known Flaviviridae, in particular when compared to primates. Our results point to dynamics that fit with a molecular evolutionary scenario shaped by a thought-provoking virus-host arms race.

Serosurvey of Nonhuman Primates in Costa Rica at the Human-Wildlife Interface Reveals High Exposure to Flaviviruses

Simple Summary

The presence of flavivirus-specific antibodies in neotropical non-human primates (NPs) (i.e., dengue virus) is well known. However, it is unclear if dengue virus or other flaviviruses could be maintained in sylvatic cycles. We detected the presence of antibodies against dengue virus (DENV-1, DENV-2), Saint Louis encephalitis virus (SLEV), West Nile virus (WNV), and several undetermined flaviviruses in NPs in Costa Rica. Our work suggests continuous exposure of NPs to several flaviviruses in Costa Rica. These findings open the question of whether bidirectional transmission between humans and non-human primates can occur due to human encroachment into NP habitats, the movement of NP into urban settings, or bridging vectors.

Abstract

Arthropod-borne viruses belonging to the flavivirus genus possess an enormous relevance in public health. Neotropical non-human primates (NPs) have been proposed to be susceptible to flavivirus infections due to their arboreal and diurnal habits, their genetic similarity to humans, and their relative closeness to humans. However, the only known flavivirus in the American continent maintained by sylvatic cycles involving NPs is yellow fever virus (YFV), and NPs’ role as potential hosts of other flaviviruses is still unknown. Here, we examined flavivirus exposure in 86 serum samples including 83.7% samples from free-range and 16.3% from captive NPs living in flavivirus-endemic regions of Costa Rica. Serum samples were opportunistically collected throughout Costa Rica in 2000–2015. We used a highly specific micro-plaque reduction neutralization test (micro-PRNT) to determine the presence of antibodies against YFV, dengue virus 1–4 (DENV), Zika virus, West Nile virus (WNV), and Saint Louis encephalitis virus (SLEV). We found evidence of seropositive NPs with homotypic reactivity to SLEV 11.6% (10/86), DENV 10.5% (9/86), and WNV 2.3% (2/86). Heterotypic reactivity was determined in 3.5% (3/86) of individuals against DENV, 1.2% (1/86) against SLEV, and 1.2% (1/86) against WNV. We found that 13.9% (12/86) of NPs were positive for an undetermined flavivirus species. No antibodies against DENV-3, DENV-4, YFV, or ZIKV were found. This work provides compelling serological evidence of flavivirus exposure in Costa Rican NPs, in particular to DENV, SLEV, and WNV. The range of years of sampling and the region from where positives were detected coincide with those in which peaks of DENV in human populations were registered, suggesting bidirectional exposure due to human–wildlife contact or bridging vectors. Our work suggests the continuous exposure of wildlife populations to various flaviviruses of public health importance and underscores the necessity of further surveillance of flaviviruses at the human–wildlife interface in Central America.

Animals as potential reservoirs for dengue transmission: A systematic review

Dengue is a rapidly spreading mosquito-borne flavivirus infection that is prevalent in tropical and sub-tropical regions. Humans are known to be the main reservoir host maintaining the epidemic cycles of dengue but it is unclear if dengue virus is also maintained in a similar enzootic cycle. The systematic review was conducted in accordance to Cochrane's PRISMA recommendations. A search was done on PubMed, EMBASE, Scopus and Cochrane Library. Key data on animal dengue positivity was extracted and classified according to animal type and diagnostic modes. Of the 3818 articles identified, 56 articles were used in this review. A total of 16,333 animals were tested, 1817 of which were positive for dengue virus by RT-PCR or serology. Dengue positivity was detected in bats (10.1%), non-human primates (27.3%), birds (11%), bovid (4.1%), dogs (1.6%), horses (5.1%), pigs (34.1%), rodents (3.5%), marsupials (13%) and other small animals (7.3%). While majority of dengue positivity via serology suggests potential enzootic transmission, but regular dengue virus spillback cannot be excluded. With the exception of bats, acute infection among animals is limited. Further investigation on animals is critically required to better understand their role as potential reservoir in dengue transmission.

Using Data Mining and Network Analysis to Infer Arboviral Dynamics: The Case of Mosquito-Borne Flaviviruses Reported in Mexico

Given the significant impact of mosquito-borne flaviviruses (MBFVs) on both human and animal health, predicting their dynamics and understanding their transmission cycle is of the utmost importance. Usually, predictions about the distribution of priority pathogens, such as Dengue, Yellow fever, West Nile Virus and St. Louis encephalitis, relate abiotic elements to simple biotic components, such as a single causal agent. Furthermore, focusing on single pathogens neglects the possibility of interactions and the existence of common elements in the transmission cycles of multiple pathogens. A necessary, but not sufficient, condition that a mosquito be a vector of a MBFV is that it co-occurs with hosts of the pathogen. We therefore use a recently developed modeling framework, based on co-occurrence data, to infer potential biotic interactions between those mosquito and mammal species which have previously been identified as vectors or confirmed positives of at least one of the considered MBFVs. We thus create models for predicting the relative importance of mosquito species as potential vectors for each pathogen, and also for all pathogens together, using the known vectors to validate the models. We infer that various mosquito species are likely to be significant vectors, even though they have not currently been identified as such, and are likely to harbor multiple pathogens, again validating the predictions with known results. Besides the above "niche-based" viewpoint we also consider an assemblage-based analysis, wherein we use a community-identification algorithm to identify those mosquito and/or mammal species that form assemblages by dint of their significant degree of co-occurrence. The most cohesive assemblage includes important primary vectors, such as A. aegypti, A. albopictus, C. quinquefasciatus, C. pipiens and mammals with abundant populations that are well-adapted to human environments, such as the white-tailed deer (Odocoileus virginianus), peccary (Tayassu pecari), opossum (Didelphis marsupialis) and bats (Artibeus lituratus and Sturnira lilium). Our results suggest that this assemblage has an important role in the transmission dynamics of this viral group viewed as a complex multi-pathogen-vector-host system. By including biotic risk factors our approach also modifies the geographical risk profiles of the spatial distribution of MBFVs in Mexico relative to a consideration of only abiotic niche variables.

Current Knowledge and Ecological and Human Impact Variables Involved in the Distribution of the Dengue Virus by Bats in the Americas

Dengue fever, caused by the dengue virus (DENV), is one of the most important reemerging viral diseases transmitted by arthropods worldwide. DENV is maintained in nature in two transmission cycles: urban and sylvatic. The latter has only been recorded in Africa and Asia and involves nonhuman primates as natural hosts, although it has been suggested that other mammals may play a secondary role as potential reservoir host, including bats. The objective of this article is to review the current state of knowledge about DENV-positive bats in the Americas and to determine what ecological and human impact variables could favor DENV infection in bats. We performed a search of published studies on natural and experimental DENV infection in bats. From 1952 to 2019, 14 studies have been carried out (71.4% in the last decade) examining DENV infection in bats in seven countries of the Americas. DENV infection was examined in 1884 bats of 63 species and DENV was detected in 19 of these species. Clench's model estimated that more than 75 species could be carriers of DENV; therefore, considering that at least 350 species of bats are distributed in the Americas, to detect 95% of the DENV-bearing species, it would be necessary to examine about 10,206 bats of ∼287 species that have not been analyzed until 2019. The species with the highest number of positive cases were Molossus sinaloae and Artibeus jamaicensis. Species, colony size, mean annual temperature, mean annual precipitation, human population size, and bat collection site (site inhabited by humans, vegetation cover, and caves) contributed to explain the variation in DENV detection in bats in the Americas. These results provide evidence on the exposure of bats to DENV in different geographic areas of the Americas and a bat sylvatic transmission cycle is very likely to be occurring, where bats may be either accidental hosts, dead-end hosts, or potential reservoir hosts for DENV.

Spatial epidemiology of yellow fever: Identification of determinants of the 2016-2018 epidemics and at-risk areas in Brazil

Optimise control strategies of infectious diseases, identify factors that favour the circulation of pathogens, and propose risk maps are crucial challenges for global health. Ecological niche modelling, once relying on an adequate framework and environmental descriptors can be a helpful tool for such purposes. Despite the existence of a vaccine, yellow fever (YF) is still a public health issue. Brazil faced massive sylvatic YF outbreaks from the end of 2016 up to mid-2018, but cases in human and non-human primates have been recorded until the beginning of 2020. Here we used both human and monkey confirmed YF cases from two epidemic periods (2016/2017 and 2017/2018) to describe the spatial distribution of the cases and explore how biotic and abiotic factors drive their occurrence. The distribution of YF cases largely overlaps for humans and monkeys, and a contraction of the spatial extent associated with a southward displacement is observed during the second period of the epidemics. More contributive variables to the spatiotemporal heterogeneity of cases were related to biotic factors (mammal richness), abiotic factors (temperature and precipitation), and some human-related variables (population density, human footprint, and human vaccination coverage). Both projections of the most favourable conditions showed similar trends with a contraction of the more at-risk areas. Once extrapolated at a large scale, the Amazon basin remains at lower risk, although surrounding forest regions and notably the North-West region, would face a higher risk. Spatial projections of infectious diseases often relied on climatic variables only; here for both models, we instead highlighted the importance of considering local biotic conditions, hosts vulnerability, social and epidemiological factors to run the spatial risk analysis correctly: all YF cases occurring later on, in 2019 and 2020, were observed in the predicted at-risk areas.

Encounter rate and behavior of Alouatta guariba clamitans in the Ilha Grande State Park, Rio de Janeiro state, Brazil

Alouatta guariba clamitans Cabrera, 1940 is an endemic species of the Atlantic Forest that occurs from south Bahia, Brazil, extending south to the province of Misiones, Argentina. In Rio de Janeiro state, the species was classified as threatened, indicating that attention is needed for the conservation of this taxon. Additionally, an outbreak of yellow fever spread throughout the southeastern states of Brazil from January 2017 until March 2018 seriously threatening Rio de Janeiro populations of the species. Herein, we aimed to provide the first estimates of A. g. clamitans encounter rate, density, and population size in the Ilha Grande State Park (PEIG), which is part of the Atlantic Forest biome of Brazil. Data were collected in two different periods, the first between December 2003 and May 2005, and the second from August 2009 to May 2010, and information on encounter rates and behavior was collected to better understand aspects of species' ecology. The estimated encounter rate in the first period through the distance sampling method was 0.04 ± 0.01 individuals per kilometer. Nine groups were recorded in the second period of the study, with 47 individuals along 3 km. Our estimates of encounter rate, density and population size were low and reinforces the need to initiate species monitoring and assess the impact that yellow fever outbreaks may have on PEIG populations. The results presented here can be a starting point to support future strategic actions for the species, to measure impacts and to the management of the species, and for a conservation program.

Sylvatic dengue virus type 4 in Aedes aegypti and Aedes albopictus mosquitoes in an urban setting in Peninsular Malaysia

Dengue fever is endemic in Malaysia, contributing to significant economic and health burden in the country. Aedes aegypti and Ae. albopictus are the main vectors of the dengue virus (DENV), which circulates in sylvatic and human transmission cycles and has been present in Malaysia for decades. The study investigated the presence and distribution of DENV in urban localities in the Klang Valley, Peninsular Malaysia. A total of 364 Ae. aegypti and 1,025 Ae. albopictus larvae, and 10 Ae. aegypti and 42 Ae. albopictus adult mosquitoes were screened for the presence of DENV. In total, 31 (2.2%) samples were positive, of which 2 Ae. albopictus larvae were co-infected with two serotypes, one with DENV-2 and DENV-3 and the other with DENV-3 and DENV-4. Phylogenetic analysis determined that the isolates belonged to DENV-1 genotype I (1 Ae. aegypti adult), DENV-2 (1 Ae. albopictus larva), DENV-3 genotype V (3 Ae. aegypti larvae and 10 Ae. albopictus larvae) and DENV-4 genotype IV (6 Ae. aegypti larvae and 12 Ae. albopictus larvae), a sylvatic strain of DENV-4 which was most closely related with sylvatic strains isolated from arboreal mosquitoes and sentinel monkeys in Peninsular Malaysia in the 1970s. All four DENV serotypes were co-circulating throughout the study period. The detection of a sylvatic strain of DENV-4 in Ae. aegypti and Ae. albopictus mosquitoes in urban areas in Peninsular Malaysia highlights the susceptibility of these vectors to infection with sylvatic DENV. The infectivity and vector competence of these urban mosquitoes to this strain of the virus needs further investigation, as well as the possibility of the emergence of sylvatic virus into the human transmission cycle.

Yellow Fever: Integrating Current Knowledge with Technological Innovations to Identify Strategies for Controlling a Re-Emerging Virus

Yellow fever virus (YFV) represents a re-emerging zoonotic pathogen, transmitted by mosquito vectors to humans from primate reservoirs. Sporadic outbreaks of YFV occur in endemic tropical regions, causing a viral hemorrhagic fever (VHF) associated with high mortality rates. Despite a highly effective vaccine, no antiviral treatments currently exist. Therefore, YFV represents a neglected tropical disease and is chronically understudied, with many aspects of YFV biology incompletely defined including host range, host–virus interactions and correlates of host immunity and pathogenicity. In this article, we review the current state of YFV research, focusing on the viral lifecycle, host responses to infection, species tropism and the success and associated limitations of the YFV-17D vaccine. In addition, we highlight the current lack of available treatments and use publicly available sequence and structural data to assess global patterns of YFV sequence diversity and identify potential drug targets. Finally, we discuss how technological advances, including real-time epidemiological monitoring of outbreaks using next-generation sequencing and CRISPR/Cas9 modification of vector species, could be utilized in future battles against this re-emerging pathogen which continues to cause devastating disease.

Sloths host Anhanga virus-related phleboviruses across large distances in time and space

Sloths are genetically and physiologically divergent mammals. Phleboviruses are major arthropod‐borne viruses (arboviruses) causing disease in humans and other animals globally. Sloths host arboviruses, but virus detections are scarce. A phlebovirus termed Anhanga virus (ANHV) was isolated from a Brazilian Linnaeus's two‐toed sloth (Choloepus didactylus) in 1962. Here, we investigated the presence of phleboviruses in sera sampled in 2014 from 74 Hoffmann's two‐toed (Choloepus hoffmanni, n = 65) and three‐toed (Bradypus variegatus, n = 9) sloths in Costa Rica by broadly reactive RT‐PCR. A clinically healthy adult Hoffmann's two‐toed sloth was infected with a phlebovirus. Viral load in this animal was high at 8.5 × 10⁷ RNA copies/ml. The full coding sequence of the virus was determined by deep sequencing. Phylogenetic analyses and sequence distance comparisons revealed that the new sloth virus, likely representing a new phlebovirus species, provisionally named Penshurt virus (PEHV), was most closely related to ANHV, with amino acid identities of 93.1%, 84.6%, 94.7% and 89.0% in the translated L, M, N and NSs genes, respectively. Significantly more non‐synonymous mutations relative to ANHV occurred in the M gene encoding the viral glycoproteins and in the NSs gene encoding a putative interferon antagonist compared to L and N genes. This was compatible with viral adaptation to different sloth species and with micro‐evolutionary processes associated with immune evasion during the genealogy of sloth‐associated phleboviruses. However, gene‐wide mean dN/dS ratios were low at 0.02–0.15 and no sites showed significant evidence for positive selection, pointing to comparable selection pressures within sloth‐associated viruses and genetically related phleboviruses infecting hosts other than sloths. The detection of a new phlebovirus closely‐related to ANHV, in sloths from Costa Rica fifty years after and more than 3,000 km away from the isolation of ANHV confirmed the host associations of ANHV‐related phleboviruses with the two extant species of two‐toed sloths.

Lack of Evidence of Sylvatic Transmission of Dengue Viruses in the Amazon Rainforest Near Iquitos, Peru

Dengue viruses (DENV) are currently responsible for more human morbidity and mortality than any other known arbovirus, and all four DENV are known to exist in sylvatic cycles that might allow these viruses to persist if the urban (Aedes aegypti) cycle could be controlled. To determine whether DENV were being maintained in a sylvatic cycle in a forested area about 14 km southwest of Iquitos, Peru, a city in which all 4 serotypes of DENV circulate, we placed 20 DENV seronegative Aotus monkeys in cages either in the canopy or near ground level for a total of 125.6 months. Despite capturing >66,000 mosquitoes in traps that collected some of the mosquitoes attracted to these monkeys, blood samples obtained once a month from each animal were tested and found to be negative by an enzyme-linked immunosorbent assay for IgM and IgG antibodies to dengue, yellow fever, Venezuelan equine encephalitis, Oropouche, and Mayaro viruses. Although all four DENV serotypes were endemic in nearby Iquitos, the findings of this study did not support a DENV sylvatic maintenance and transmission cycle in a selected area of the Amazon rainforest in northeastern Peru.

Infections tropicales graves dans les départements français d’Amérique, Antilles françaises et Guyane

Les Antilles-Guyane (AG) sont les départements français du continent américain, situés en zone intertropicale. La diversité des écosystèmes ainsi que le climat tropical à très forte pluviosité exposent à un vaste panel de pathologies infectieuses. Ces territoires sont de plus l’objet de mouvements importants de populations, voyageurs ou migrants, ce qui joue un rôle significatif dans le développement d’épidémies et/ou de pathologies émergentes. Ces pathologies infectieuses dites « tropicales » peuvent nécessiter une prise en charge en réanimation. Nous rapportons ici les principales données récentes concernant ces pathologies (hors infection liée au VIH) ainsi que les stratégies diagnostiques et thérapeutiques, à l’usage des réanimateurs amenés à exercer en zone tropicale AG ou recevant en métropole des patients issus de cette région.

The Importance of Coordinated Actions in Preventing the Spread of Yellow Fever to Human Populations: The Experience from the 2016-2017 Yellow Fever Outbreak in the Northeastern Region of São Paulo State

Yellow fever (YF) is a zoonotic arthropod-borne disease that is caused by the yellow fever virus (YFV) and characterized by a sylvatic and urban cycle. Its most severe presentation is manifested as a hemorrhagic disease, and it has been responsible for thousands of deaths in the last decades. This study describes the public health approaches taken to control the 2016-2017 YF outbreak in nonhuman primates (NHPs) that took place in the northeastern region of São Paulo state, Brazil. NHPs recovered from the field were necropsied, and YF diagnoses were made at the Laboratory of Molecular Virology, Ribeirão Preto Medical School and the Center of Pathology, Adolfo Lutz Institute of São Paulo. NHP samples were inoculated into Vero cells for YFV isolation. RNA extraction was performed directly from NHP tissues and tested by RT-qPCR. YFV-positive samples were confirmed by sequencing. Based on the rapid RT-qPCR results, surveillance actions were implemented in the entire region. Confirmatory histopathology and immunohistochemistry for YFV were also performed. Among nine NHPs, gross hepatic involvement was observed in six animals, five of which were YFV-RT-qPCR-positive. One YFV was isolated from the serum of an infant NHP. YFV RNA sequences diverged from the virus responsible for the last epizootic that occurred in São Paulo state, but it was similar to the current Brazilian epizootic. Public health actions included dissemination of information on YF transmission, investigation of the probable location of NHP infection, characterization of the environment, and subsequent creation of the blueprint from which prevention and control measures were implemented. The YFV sylvatic cycle occurred in the periurban areas of the northeastern region of São Paulo state, but no human cases were reported during this period, showing that integrated actions between human, animal, and environmental health professionals were critical to restrain the virus to the sylvatic cycle.

Monocyte-Derived Dendritic Cells as Model to Evaluate Species Tropism of Mosquito-Borne Flaviviruses

Several mosquito-borne Flaviviruses such as Japanese encephalitis virus (JEV), West Nile virus (WNV), Dengue Virus (DENV), and Zika virus (ZIKV) can cause severe clinical disease. Being zoonotic, Flaviviruses infect a wide variety of terrestrial vertebrates, which dependent of the virus-host interactions, can enhance ongoing epidemics and maintain the virus in the environment for prolonged periods. Targeted species can vary from amphibians, birds to various mammals, dependent on the virus. For many mosquito-borne flaviviruses the spectrum of targeted species is incompletely understood, in particular with respect to their contribution to the maintenance of virus in certain geographical regions. Furthermore, little is known about virus and host factors contributing to species tropism. The present study utilized human and porcine monocyte-derived dendritic cells (MoDC) as a cell culture model to better understand Flavivirus species tropism and innate immune responses. MoDC were selected based on their presence in the skin and their role as an early target cell for several Flaviviruses and their role as immune sentinels. While differences in viral infectivity and replication were minor when comparing porcine with human MoDC for some of the tested Flaviviruses, a particularly strong replication in human MoDC was found with USUV, while JEV appeared to have a stronger tropism for porcine MoDC. With respect to innate immune responses we found high induction of TNF and IFN-β in both human and porcine MoDC after infection with JEV, WNV, and USUV, but not with DENV, ZIKV, and Wesselsbron virus. Spondweni virus induced these cytokine responses only in porcine MoDC. Overall, innate immune responses correlated with early infectivity and cytokine production. In conclusion, we demonstrate Flavivirus-dependent differences in the interaction with MoDC. These may play a role in pathogenesis but appear to only partially reflect the expected species tropism.

Surveillance of Arboviruses in Primates and Sloths in the Atlantic Forest, Bahia, Brazil

From 2006 through 2014, we conducted seroepidemiological surveys on non-human primates and sloths to investigate the possible circulation of arboviruses in Bahia Atlantic Forest, Brazil. We collected a total of 196 samples from 103 Leontopithecus chrysomelas, 7 Sapajus xanthosternos, 22 Bradypus torquatus and 7 Bradypus variegatus. Serum samples were tested using neutralization test and hemagglutination inhibition test to detect total antibodies against 26 different arboviruses. The overall prevalence of arboviruses was 36.6% (51/139), with the genus Flavivirus having the highest prevalence (33.1%; 46/139), followed by Phlebovirus (5.0%; 7/139), Orthobunyavirus (4.3%; 6/139) and Alphavirus (0.7%; 1/139). Monotypic reactions suggest that the wild animals were exposed naturally to at least twelve arboviruses. Added results from the neutralization test, animals were exposed to thirteen arboviruses. Most of these viruses are maintained in transmission cycles independent of human hosts, although antibodies against dengue virus serotypes 1, 2 and 3 were found in this study. To our knowledge, this is the first study reporting exposure to arboviruses in L. chrysomelas, S. xanthosternos and B. torquatus. Our results also highlight that the Southern Bahia Atlantic Forest has a variety of vertebrate hosts and potential vectors, which may support the emergence or re-emergence of arboviruses, including those pathogenic to humans.

Survey of mosquito-borne flaviviruses in the Cuitzmala River Basin, Mexico: do they circulate in rodents and bats?

BACKGROUND

RNA viruses commonly infect bats and rodents, including mosquito-borne flaviviruses (MBFV) that affect human and animal health. Serological evidence suggests past interactions between these two mammalian orders with dengue viruses (DENV), West Nile virus (WNV), and yellow fever virus (YFV). Although in Mexico there are reports of these viruses in both host groups, we know little about their endemic cycles or persistence in time and space.

METHODS

Rodents and bats were captured at the Cuitzmala River Basin on the Pacific coast of Jalisco state, Mexico, where MBFV, such as DENV, have been reported in both humans and bats. Samples were taken during January, June, and October 2014, at locations adjacent to the river. Tissue samples were collected from both bats and rodents and serum samples from rodents only. Highly sensitive serological and molecular assays were used to search for current and past evidence of viral circulation.

RESULTS

One thousand nine hundred forty-eight individuals were captured belonging to 21 bat and 14 rodent species. Seven hundred sixty-nine liver and 764 spleen samples were analysed by means of a specific molecular protocol used to detect flaviviruses. Additionally, 708 serum samples from rodents were examined in order to demonstrate previous exposure to dengue virus serotype 2 (which circulates in the region). There were no positive results with any diagnostic test.

DISCUSSION

To our knowledge, this is the first survey of rodents and only the second survey of bats from the Pacific Coast of Mexico in a search for MBFV. We obtained negative results from all samples. We validated our laboratory tests with negative and positive controls. Our findings are consistent with other empirical and experimental studies in which these mammalian hosts may not replicate mosquito-borne flaviviruses or present low prevalence.

CONCLUSIONS

True-negative results are essential for the construction of distribution models and are necessary to identify potential areas at risk. Negative results should not be interpreted as the local absence of MBFV in the region. On the contrary, we need to establish a long-term surveillance programme to find MBFV presence in the mosquito trophic networks, identifying the potential role of rodents and bats in viral dynamics.

Successes and failures of sixty years of vector control in French Guiana: what is the next step?

Since the 1940s, French Guiana has implemented vector control to contain or eliminate malaria, yellow fever, and, recently, dengue, chikungunya, and Zika. Over time, strategies have evolved depending on the location, efficacy of the methods, development of insecticide resistance, and advances in vector control techniques. This review summarises the history of vector control in French Guiana by reporting the records found in the private archives of the Institute Pasteur in French Guiana and those accessible in libraries worldwide. This publication highlights successes and failures in vector control and identifies the constraints and expectations for vector control in this French overseas territory in the Americas.

First evidence of dengue infection in domestic dogs living in different ecological settings in Thailand

BACKGROUND

Dengue is a vector-borne disease transmitted by Aedes mosquitoes. It is considered an important public health problem in many countries worldwide. However, only a few studies have been conducted on primates and domestic animals that could potentially be a reservoir of dengue viruses. Since domestic dogs share both habitats and vectors with humans, this study aimed to investigate whether domestic dogs living in different ecological settings in dengue endemic areas in Thailand could be naturally infected with dengue viruses.

METHODOLOGY/PRINCIPAL FINDINGS

Serum samples were collected from domestic dogs in three different ecological settings of Thailand: urban dengue endemic areas of Nakhon Sawan Province; rubber plantation areas of Rayong Province; and Koh Chang, an island tourist spot of Trat Province. These samples were screened for dengue viral genome by using semi-nested RT-PCR. Positive samples were then inoculated in mosquito and dog cell lines for virus isolation. Supernatant collected from cell culture was tested for the presence of dengue viral genome by semi-nested RT-PCR, then double-strand DNA products were double-pass custom-sequenced. Partial nucleotide sequences were aligned with the sequences already recorded in GenBank, and a phylogenetic tree was constructed. In the urban setting, 632 domestic dog serum samples were screened for dengue virus genome by RT-PCR, and six samples (0.95%) tested positive for dengue virus. Four out of six dengue viruses from positive samples were successfully isolated. Dengue virus serotype 2 and serotype 3 were found to have circulated in domestic dog populations. One of 153 samples (0.65%) collected from the rubber plantation area showed a PCR-positive result, and dengue serotype 3 was successfully isolated. Partial gene phylogeny revealed that the isolated dengue viruses were closely related to those strains circulating in human populations. None of the 71 samples collected from the island tourist spot showed a positive result.

CONCLUSIONS/SIGNIFICANCE

We concluded that domestic dogs can be infected with dengue virus strains circulating in dengue endemic areas. The role of domestic dogs in dengue transmission needs to be further investigated, i.e., whether they are potential reservoirs or incidental hosts of dengue viruses.

Mosquito-borne and sexual transmission of Zika virus: Recent developments and future directions

Zika virus (ZIKV; Genus Flavivirus, Family Flaviviridae) has recently emerged in Asia and the Americas to cause large outbreaks of human disease. The outbreak has been characterized by high attack rates, birth defects in infants and severe neurological complications in adults. ZIKV is transmitted to humans by Aedes mosquitoes, but recent evidence implicates sexual transmission as playing an important role as well. This review highlights the transmission of ZIKV in humans, with a focus on both mosquito and sexually-transmitted routes and their outcomes. We also discuss critical directions for future research.

Neotropical bats that co-habit with humans function as dead-end hosts for dengue virus

Several studies have shown Dengue Virus (DENV) nucleic acids and/or antibodies present in Neotropical wildlife including bats, suggesting that some bat species may be susceptible to DENV infection. Here we aim to elucidate the role of house-roosting bats in the DENV transmission cycle. Bats were sampled in households located in high and low dengue incidence regions during rainy and dry seasons in Costa Rica. We captured 318 bats from 12 different species in 29 households. Necropsies were performed in 205 bats to analyze virus presence in heart, lung, spleen, liver, intestine, kidney, and brain tissue. Histopathology studies from all organs showed no significant findings of disease or infection. Sera were analyzed by PRNT₉₀ for a seroprevalence of 21.2% (51/241), and by PCR for 8.8% (28/318) positive bats for DENV RNA. From these 28 bats, 11 intestine samples were analyzed by RT-PCR. Two intestines were DENV RNA positive for the same dengue serotype detected in blood. Viral isolation from all positive organs or blood was unsuccessful. Additionally, viral load analyses in positive blood samples by qRT-PCR showed virus concentrations under the minimal dose required for mosquito infection. Simultaneously, 651 mosquitoes were collected using EVS-CO₂ traps and analyzed for DENV and feeding preferences (bat cytochrome b). Only three mosquitoes were found DENV positive and none was positive for bat cytochrome b. Our results suggest an accidental presence of DENV in bats probably caused from oral ingestion of infected mosquitoes. Phylogenetic analyses suggest also a spillover event from humans to bats. Therefore, we conclude that bats in these urban environments do not sustain DENV amplification, they do not have a role as reservoirs, but function as epidemiological dead end hosts for this virus.

Dengue is the most important human vector-borne disease. Several studies have shown DENV presence in mammalian wildlife such as bats, thus considering them putative reservoirs or hosts. We aimed to elucidate if bats that cohabit in houses in close proximity with humans may be involved in a dengue transmission cycle. We sampled bats in low and high dengue incidence areas during the dry (low mosquito abundance) and wet (high mosquito abundance) seasons. We analyzed blood and several organs. As previously reported, we found DENV nucleic acid and neutralizing antibodies in a small percentage of blood samples, but virus detection in all organs was negative. We were able to show that dengue found in all positive samples was in low concentration and thus virus isolation was unsuccessful. We found positive intestine samples which may suggest infection through DENV-positive mosquito ingestion. Furthermore, mosquitoes sampled in close vicinity of bats’ roosting place were not feeding on these mammals. Virus sequence analysis from bats and humans show a spillover effect from humans to bats. Taken together, our results indicate that bats do not sustain sufficient virus amplification in order to function as reservoirs and exclude them as players in the dengue virus transmission cycle.

Detection of the mosquito-borne flaviviruses, West Nile, Dengue, Saint Louis Encephalitis, Ilheus, Bussuquara, and Yellow Fever in free-ranging black howlers (Alouatta caraya) of Northeastern Argentina

Several medically important mosquito-borne flaviviruses have been detected in Argentina in recent years: Dengue (DENV), St. Louis encephalitis (SLEV), West Nile (WNV) and Yellow Fever (YFV) viruses. Evidence of Bussuquara virus (BSQV) and Ilheus virus (ILHV) activity were found, but they have not been associated with human disease. Non-human primates can act as important hosts in the natural cycle of flaviviruses and serological studies can lead to improved understanding of virus circulation dynamics and host susceptibility. From July-August 2010, we conducted serological and molecular surveys in free-ranging black howlers (Alouatta caraya) captured in northeastern Argentina. We used 90% plaque-reduction neutralization tests (PRNT90) to analyze 108 serum samples for antibodies to WNV, SLEV, YFV, DENV (serotypes 1and 3), ILHV, and BSQV. Virus genome detection was performed using generic reverse transcription (RT)-nested PCR to identify flaviviruses in 51 antibody-negative animals. Seventy animals had antibodies for one or more flaviviruses for a total antibody prevalence of 64.8% (70/108). Monotypic (13/70, 19%) and heterotypic (27/70, 39%) patterns were differentiated. Specific neutralizing antibodies against WNV, SLEV, DENV-1, DENV-3, ILHV, and BSQV were found. Unexpectedly, the highest flavivirus antibody prevalence detected was to WNV with 9 (8.33%) monotypic responses. All samples tested by (RT)-nested PCR were negative for viral genome. This is the first detection of WNV-specific antibodies in black howlers from Argentina and the first report in free-ranging non-human primates from Latin-American countries. Given that no animals had specific neutralizing antibodies to YFV, our results suggest that the study population remains susceptible to YFV. Monitoring of these agents should be strengthened to detect the establishment of sylvatic cycles of flaviviruses in America and evaluate risks to wildlife and human health.

Neotropical primary bat cell lines show restricted dengue virus replication

Dengue is the most widespread arboviral disease affecting humans. Bats are recognized carriers of emerging viral zoonoses and have been proposed as dengue reservoirs, since RNA/NS1 and/or antiviral antibodies have been detected. Yet, experimental inoculation of Artibeus bats failed to show virus replication. This conflicting results prevent drawing further conclusions of whether bats sustain dengue infection. To test bat cellular permissivity to dengue infection, we established primary bat embryonic cells from diverse organs and tissues of Artibeus jamaicensis, Molossus sinaloae, and Desmodus rotundus. We observed a limited serotype-, organ-, and bat species- specific dengue susceptibility. Only some Molossus-derived primary cells sustained poorly initial Dengue serotype-1 replication, though it was latter absent. To elucidate if Molossus bats may play a role in dengue replication, ecological or in vivo experiments must be performed. Taken together our results show that Dengue did not replicate efficiently in cell lines derived from Neotropical bat species.

Yellow fever impact on brown howler monkeys (Alouatta guariba clamitans) in Argentina: a metamodelling approach based on population viability analysis and epidemiological dynamics

In South America, yellow fever (YF) is an established infectious disease that has been identified outside of its traditional endemic areas, affecting human and nonhuman primate (NHP) populations. In the epidemics that occurred in Argentina between 2007-2009, several outbreaks affecting humans and howler monkeys (Alouatta spp) were reported, highlighting the importance of this disease in the context of conservation medicine and public health policies. Considering the lack of information about YF dynamics in New World NHP, our main goal was to apply modelling tools to better understand YF transmission dynamics among endangered brown howler monkey (Alouatta guariba clamitans) populations in northeastern Argentina. Two complementary modelling tools were used to evaluate brown howler population dynamics in the presence of the disease: Vortex, a stochastic demographic simulation model, and Outbreak, a stochastic disease epidemiology simulation. The baseline model of YF disease epidemiology predicted a very high probability of population decline over the next 100 years. We believe the modelling approach discussed here is a reasonable description of the disease and its effects on the howler monkey population and can be useful to support evidence-based decision-making to guide actions at a regional level.

Isolation of saint louis encephalitis virus from a horse with neurological disease in Brazil

St. Louis encephalitis virus (SLEV) is a causative agent of encephalitis in humans in the Western hemisphere. SLEV is a positive-sense RNA virus that belongs to the Flavivirus genus, which includes West Nile encephalitis virus, Japanese encephalitis virus, Dengue virus and other medically important viruses. Recently, we isolated a SLEV strain from the brain of a horse with neurological signs in the countryside of Minas Gerais, Brazil. The SLEV isolation was confirmed by reverse-transcription RT-PCR and sequencing of the E protein gene. Virus identity was also confirmed by indirect immunofluorescence using commercial antibodies against SLEV. To characterize this newly isolated strain in vivo, serial passages in newborn mice were performed and led to hemorrhagic manifestations associated with recruitment of inflammatory cells into the central nervous system of newborns. In summary this is the first isolation of SLEV from a horse with neurological signs in Brazil.

St. Louis encephalitis virus (SLEV), a member of the Flavivirus genus, which includes West Nile encephalitis virus, Japanese encephalitis virus, Dengue virus, and other medically important viruses, is a cause of encephalitis in humans and animals. SLEV is considered endemic in the Americas, and currently there is no vaccine or specific treatment available for controlling of preventing SLEV-induced encephalitis. In this study we describe the first isolation of SLEV from an adult male horse with neurologic disease, which was further characterized by molecular and serological methods. Phylogenetic analysis of a 903 base pairs amplified sequence from partial Envelope (E) gene region indicated that the isolate from the horse was within the cluster of the VB genotype. In addition, inoculation of the SLEV isolate intracranially in newborn mice resulted in circulatory and neurological changes. This is the first report of isolation of SLEV from a horse with neurological disease in Brazil.

Fever versus fever: the role of host and vector susceptibility and interspecific competition in shaping the current and future distributions of the sylvatic cycles of dengue virus and yellow fever virus

Two different species of flaviviruses, dengue virus (DENV) and yellow fever virus (YFV), that originated in sylvatic cycles maintained in non-human primates and forest-dwelling mosquitoes have emerged repeatedly into sustained human-to-human transmission by Aedes aegypti mosquitoes. Sylvatic cycles of both viruses remain active, and where the two viruses overlap in West Africa they utilize similar suites of monkeys and Aedes mosquitoes. These extensive similarities render the differences in the biogeography and epidemiology of the two viruses all the more striking. First, the sylvatic cycle of YFV originated in Africa and was introduced into the New World, probably as a result of the slave trade, but is absent in Asia; in contrast, sylvatic DENV likely originated in Asia and has spread to Africa but not to the New World. Second, while sylvatic YFV can emerge into extensive urban outbreaks in humans, these invariably die out, whereas four different types of DENV have established human transmission cycles that are ecologically and evolutionarily distinct from their sylvatic ancestors. Finally, transmission of YFV among humans has been documented only in Africa and the Americas, whereas DENV is transmitted among humans across most of the range of competent Aedes vectors, which in the last decade has included every continent save Antarctica. This review summarizes current understanding of sylvatic transmission cycles of YFV and DENV, considers possible explanations for their disjunct distributions, and speculates on the potential consequences of future establishment of a sylvatic cycle of DENV in the Americas.

Yellow Fever outbreak in Darfur, Sudan in October 2012; the initial outbreak investigation report

INTRODUCTION

Sudan is subject to repeated outbreaks, including Viral Hemorrhagic Fever (VHF), which is considered to be a very serious illness. Yellow Fever (YF) outbreaks in Sudan have been reported from the 1940s through 2005. In 2012, a new outbreak of YF occurred in the Darfur region.

OBJECTIVE

To identify the potential for an outbreak, to diagnose the disease and to be able to recognize its cause among the initial reported cases.

METHODOLOGY

>This is a descriptive and investigative field study that applies standard communicable disease outbreak investigation steps. The study involved clinical, serological, entomological and environmental surveys.

RESULTS

The field investigation confirmed the outbreak and identified its cause to be YF.

CONCLUSION

National surveillance systems should be strong enough to detect VHFs in a timely manner. Local health facilities should be prepared to promptly treat the initial cases because the case fatality ratios (CFRs) are usually very high among the index cases.

Experimental infection of Artibeus intermedius bats with serotype-2 dengue virus

Dengue fever is caused by a flavivirus that primarily infects humans and Aedes sp. mosquitoes. However, viral replication in wild animals other than non-human primates has been scarcely studied. In this report, the susceptibility of Artibeus intermedius frugivorous bat to serotype-2 dengue virus (DENV-2) infection was tested. Twenty-three bats were intraperitoneally inoculated with different viral loads of DENV-2 (New Guinea-C strain). Forty-three percent of the infected bats developed bruises on the chest or on the wings. Histological analyses showed structural alterations in the spleen and bleeding in liver and intestine, but the virus was not detected by RT-PCR in any of the analyzed tissues, and it was found in only one bat (kidney) by semi-nested RT-PCR. In sera, the viral RNA was detected by semi-nested RT-PCR in 39% of bats, but only 8% of bats seroconverted. Overall, these data indicate that DENV-2 replicates poorly in these bats, suggesting they are not suitable hosts to this virus.

Evolutionary and ecological factors underlying the tempo and distribution of yellow fever virus activity

Yellow fever virus (YFV) is historically one of the most important viruses to affect human populations. Despite the existence of highly effective vaccines for over 70 years, yellow fever remains a significant and re-emerging cause of morbidity and mortality in endemic and high-risk regions of South America and Africa. The virus may be maintained in sylvatic enzootic/epizootic, transitional and urban epidemic transmission cycles with geographic variation in terms of levels of genetic diversity, the nature of transmission cycles and patterns of outbreak activity. In this review we consider evolutionary and ecological factors underlying YFV emergence, maintenance and spread, geographic distribution and patterns of epizootic/epidemic activity.

Dengue--quo tu et quo vadis?

Dengue viruses (DENV) are by far the most important arboviral pathogens in the tropics around the world, putting at risk of infection nearly a third of the global human population. DENV are members of the genus Flavivirus in the Family Flaviviridae and comprise four antigenically distinct serotypes (DENV-1-4). Although they share almost identical epidemiological features, they are genetically distinct. Phylogenetic analyses have revealed valuable insights into the origins, epidemiology and the forces that shape DENV evolution in nature. In this review, we examine the current status of DENV evolution, including but not limited to rates of evolution, selection pressures, population sizes and evolutionary constraints, and we discuss how these factors influence transmission, pathogenesis and emergence.

Yellow fever virus maintenance in Trinidad and its dispersal throughout the Americas

Trinidad, like many other American regions, experiences repeated epizootics of yellow fever virus (YFV). However, it is unclear whether these result from in situ evolution (enzootic maintenance) or regular reintroduction of YFV from the South American mainland. To discriminate between these hypotheses, we carried out a Bayesian phylogeographic analysis of over 100 prM/E gene sequences sampled from 8 South American countries. These included newly sequenced isolates from the recent 2008-2009 Trinidad epizootic and isolates derived from mainland countries within the last decade. The results indicate that the most recent common ancestor of the 2008-2009 epizootic existed in Trinidad 4.2 years prior to 2009 (95% highest probability density [HPD], 0.5 to 9.0 years). Our data also suggest a Trinidad origin for the progenitor of the 1995 Trinidad epizootic and support in situ evolution of YFV between the 1979 and 1988-1989 Trinidad epizootics. Using the same phylogeographic approach, we also inferred the historical spread of YFV in the Americas. The results suggest a Brazilian origin for YFV in the Americas and an overall dispersal rate of 182 km/year (95% HPD, 52 to 462 km/year), with Brazil as the major source population for surrounding countries. There is also strong statistical support for epidemiological links between four Brazilian regions and other countries. In contrast, while there were well-supported epidemiological links within Peru, the only statistically supported external link was a relatively weak link with neighboring Bolivia. Lastly, we performed a complete analysis of the genome of a newly sequenced Trinidad 2009 isolate, the first complete genome for a genotype I YFV isolate.

Yellow fever virus exhibits slower evolutionary dynamics than dengue virus

Although yellow fever has historically been one of the most important viral infections of humans, relatively little is known about the evolutionary processes that shape its genetic diversity. Similarly, there is limited information on the molecular epidemiology of yellow fever virus (YFV) in Africa even though it most likely first emerged on this continent. Through an analysis of complete E gene sequences, including a newly acquired viral collection from Central and West Africa (Senegal, Cameroon, Central African Republic, Côte d'Ivoire, Mali, and Mauritania), we show that YFV exhibits markedly lower rates of evolutionary change than dengue virus, despite numerous biological similarities between these two viruses. From this observation, along with a lack of clock-like evolutionary behavior in YFV, we suggest that vertical transmission, itself characterized by lower replication rates, may play an important role in the evolution of YFV in its enzootic setting. Despite a reduced rate of nucleotide substitution, phylogenetic patterns and estimates of times to common ancestry in YFV still accord well with the dual histories of colonialism and the slave trade, with areas of sylvatic transmission (such as Kedougou, Senegal) acting as enzootic/epidemic foci.

RNA virus genomics: a world of possibilities

The increasing availability of complete genome sequences of RNA viruses has the potential to shed new light on fundamental aspects of their biology. Here, I use case studies of 3 RNA viruses to explore the impact of genomic sequence data, with particular emphasis on influenza A virus. Notably, the studies of RNA virus genomics undertaken to date largely focused on issues of evolution and epidemiology, and they have given these disciplines new impetus. However, genomic data have so far made fewer inroads into areas of more direct importance for disease, prevention, and control; thus, harnessing their full potential remains an important goal.

Dengue infection in neotropical forest mammals

In South America, dengue is the arbovirus-transmitted disease with the highest incidence. Unlike other arboviruses, wild mammals have no confirmed role in the cycle of dengue in the neotropics, although serological studies have suggested a possible secondary amplification cycle involving mammals other than nonhuman primates. In French Guiana, where all four serotypes (DENV-1, DENV-2, DENV-3, DENV-4) are present, the disease is endemic with outbreak events. To determine whether wild mammals can be infected by DENV, rodents, marsupials, and bats were captured over several periods, from 2001 to 2007, at two sites. The first location is a secondary forest surrounded by an urban area where dengue is endemic. The second location is a forest edge site where the disease has not yet emerged. A total of 10,000 trap-nights were performed and 616 mammals were captured. RNAs representing the four DENV serotypes were detected at both sites by reverse-transcriptase polymerase chain reaction in the livers and/or sera of 92 mammals belonging to 14 out of 32 species distributed among all the orders investigated: Rodentia (33 positive/146 tested), Marsupialia (40/318), and Chiroptera (19/152). Sequence analyses of a portion of the capsid and premembrane junction revealed that mammal strains of DENV-1, DENV-2, DENV-3, and DENV-4 had only 92.6%, 89%, 95%, and 95.8% identity, respectively, with strains circulating in the human population during the same periods. Regarding DENV-2, strains related (99% identity) to those responsible for an epidemic event in humans in French Guiana concurrent to the capture sessions were also evidenced, suggesting that wild mammals in edge habitats can be infected by circulating human strains. Our results demonstrate, for the first time, that neotropical wild mammals can be infected with dengue virus. The question of whether mammals maintain DENV in enzootic cycles and can play a role in its reemergence in human populations remains to be answered.

Pediculosis in Macaca sylvanus of Gibraltar

Pedicinus spp. parasitize several species of nonhuman primates. This is the first published report confirming the presence of Pedicinus albidus (Rudow) infestation in the free-ranging macaques (Macaca sylvanus) of Gibraltar. The diagnosis of pediculosis was based upon finding adult lice on host animals.

The global distribution of yellow fever and dengue

Yellow fever has been subjected to partial control for decades, but there are signs that case numbers are now increasing globally, with the risk of local epidemic outbreaks. Dengue case numbers have also increased dramatically during the past 40 years and different serotypes have invaded new geographical areas. Despite the temporal changes in these closely related diseases, and their enormous public health impact, few attempts have been made to collect a comprehensive dataset of their spatial and temporal distributions. For this review, records of the occurrence of both diseases during the 20th century have been collected together and are used to define their climatic limits using remotely sensed satellite data within a discriminant analytical model framework. The resulting risk maps for these two diseases identify their different environmental requirements, and throw some light on their potential for co-occurrence in Africa and South East Asia.