This might also explain why obtaining sequencing data related to WNV Portuguese infections has not been successful. To date, a single study has been published on the local phylogenetics of WNV, with sequencing solely obtained from mosquito pools Supplementary Table 3 Such sequences, based on a short segment of the NS5 gene, demonstrated a close genetic relationship with past WNV lineages circulating in the Mediterranean basin France, Morocco, and Italy , but fell short in providing definite conclusions on viral diversity, phylodynamics, and persistence in the country.
Such reports include evidence from avian species e. Accipiter gentilis, Ciconia ciconia, Strix aluco , equines, mosquitoes e. It is unknown whether this North-South dichotomy in observed WNV circulation stems from sampling bias or from disparate ecological conditions dictating different WNV epidemic activity.
Summary of data sources articles, national reports on various types of evidence for the circulation of WNV in Portugal. Positioning is only approximate, given that some reports refer to regions of different areas. For data sources referring to large areas e. Not all sources are mapped, e. The color scale on the right represents the different types of samples reported, and refers to both panels b and c.
Not all years between and had data sources. A detailed summary of data sources in Supplementary Table 1. On one hand, sampling bias could be due to large differences in regional biodiversity of host species e. On the other hand, disparate ecological conditions could be dictated by factors such as local differences in climate and landscape. To date, very few articles in the research literature have provided geo-temporal data on the population size and dynamics of mosquito species relevant for the transmission of WNV in Portugal Supplementary Table 2.
The methods of collection e. Summarizing the data revealed that both sampling coverage and the total number of yearly collections per county varied in time, both for adult Fig. We noticed that even in the presence of many project-related factors affecting sampling, Cx. Since Cx. Borders represent Portuguese counties, the level at which Cx. Counties for which there were zero counts are coloured in white.
Counties for which collections were not performed are in grey. The distribution of land types e. Therefore we used the distribution of different land types in Portugal see Land cover and land types for details to explore how they could contribute to the explanation of the North-South dichotomy in WNV circulation data.
We mapped the spatial distribution of land types Fig. The spatial distribution of different land types, which was quite stable over time, highlighted differences between the regions that were reminiscent of the North-South divide in existing WNV data.
The abundance of cropland in the south appeared linked with reports of WNV circulation, which conforms to mounting evidence of the positive link between cropland and the transmission activity of WNV both in humans and animals 49 , 50 , 51 , 52 , In all panels, colours for land types are shown on the right.
The North-South divide is the same as defined in the legend of Fig. Climate is a major driver of the population dynamics of mosquito and avian species participating in the zoonotic cycle of WNV We used a climate-driven suitability index termed index P to estimate the geo-temporal transmission potential of WNV in Portugal.
We aimed to understand whether the two types of climate could explain the North-South divide in existing WNV data, and to gain insights on the possible historical effects of long-term climate trends.
This index estimates the transmission potential of each adult female mosquito in the zoonotic reservoir, and can be interpreted as the risk of spillover to the human and equine populations see Transmission Suitability for details.
Typically, climate-driven suitability indices are validated by quantifying geo-temporal correlations between time series of the index and suspected or confirmed infections. However, this was not possible due to the absence of reported chains of transmission in Portugal. Nevertheless, the index was previously validated for WNV in Israel 54 , and for other mosquito-borne viruses elsewhere 13 , 55 , In this context, we proceeded to compare our estimated transmission potential with empiric mosquito data.
We thus first compared the only available time-series data related to WNV transmission in Portugal, which included the newly estimated index P and regional Cx. The map panel presents all districts, coloured by their location. The patterns in Fig. Seasons appeared to occur between the months of March and November of each year, often peaking in the summer and reaching minimum transmission potential values during the winter months.
When comparing the northern and southern districts for a longer time period —, Fig. However, compared to the northern districts, the southern districts presented wider seasonal waves, with transmission potential increasing earlier in the spring and remaining non-zero well into late autumn Fig. Yearly summary statistics per latitude-longitude coordinate revealed a North-South divide similar to the one presented by past evidence of WNV circulation in the country Fig.
This output showed that, in accordance with previously described geo-temporal patterns for other mosquito-borne viruses 55 and WNV 54 in different countries, natural climate variations strongly influence both inter- and intra-yearly variation in transmission potential.
When quantifying the number of months within a year for which the estimated transmission potential was not zero, we again found a clear division between the north and south Fig. Regions in the south and southwest typically spent nine or more months of the year with non-zero transmission potential, contrasting to regions in the north and northeast which spent only half or less of the year with non-zero transmission potential.
Both the higher yearly median and longer seasonal waves in the south compared to the north, could thus be seen to support the mentioned North-South divide in past evidence for WNV circulation in Portugal Fig. Boundaries in dark grey represent districts. We thus used the past 40 years of annual climate data per Portuguese county to explore long-time trends in climate variables and estimated WNV transmission potential, using linear quantile mixed models see Analysis of long-term climate and suitability trends for technical details.
We found that all four explored variables presented significant differences between the north and south regions of the country Fig. Such historical climate trends translated into an yearly increase in estimated transmission potential for both regions Fig. As described in Fig. To explore the possibility of periodicity beyond the 12 month cycles, we performed wavelet analysis on the north and south yearly median of transmission potential see Analysis of long-term suitability periodicity for details.
The analysis revealed longer periodic components in both regions, which were seen to change between and Fig. From onward, periodicity shifted to become strongly dominated not by one but two components at 2—3 and 4—5 years.
The presence of such quasi-periods indicates a Moran effect 57 , i. Finally, the significant shifts in the periodic components over the years do not support an historically stable influence of climate, but are rather suggestive that inter-year instability is an expected feature of WNV transmission potential in Portugal. Recently, several European countries in the Mediterranean basin have progressed from sporadically reporting WNV infections to reporting yearly epidemic activity affecting both humans and equines e.
To date, sufficient evidence has accumulated to support ongoing circulation of WNV in Portugal. However, despite Portugal sharing similar climate types and bird migration routes with nearby countries e. Without such reports, the perception of the public health importance of WNV in Portugal remains minimal.
Although several studies have focused on describing human, animal, and mosquito WNV infections in the country, its epidemiology remains largely uncharacterised and poorly understood.
In this study, we have generated a historical, comprehensive perspective of the virus in Portugal using a combination of existing data and climate-informed theoretical approaches. We collated existing data from the research literature, national databases, and recent serological samples in equines representative of the time period between and Recent data revealed that Cx. To consolidate and complement existing data, we explored the effects of local climate variation on theoretical estimations of WNV transmission potential over the years.
We estimated that, similarly to other countries in the northern hemisphere, WNV transmission seasons across the country tended to occur between March and November Spring, Autumn , often peaking in July Summer. The northern districts presented higher WNV transmission potential during the summer months, compatible with the expectation that WNV potential peaks at intermediate temperatures of 23—26 Celsius Hence, the generally warmer climate in the south may be detrimental for WNV transmission in the peak of the summer.
Additionally, we found that the inter- and intra-year median transmission potentials were substantially higher in the south when compared to the north.
This implies that the south presents longer seasons suitable for WNV transmission, including the spring and autumn months; while the suitable seasons in the north are mostly restricted to the summer months. The importance of longer seasons suitable for WNV transmission rests on prior data: Culex mosquitoes from North America and Europe have been observed to shift their feeding preferences by late summer and early autumn, coinciding with a decrease in abundance of particular avian species and increases in reported infections 61 , Together, these differences between the north and the south of Portugal support the existing North-South divide in the evidence of WNV circulation.
In light of the ongoing discussion of the effects of climate change on the long-term epidemiology of mosquito-borne viruses, we explored historical climate variations and the corresponding WNV transmission potential in Portugal.
Differences between the north and south of Portugal were clear and remained similar over the past 40 years. In general, we presented evidence that Portugal has slowly changed towards a warmer and dryer climate over this period.
Temperature remains a critical factor in mosquito-borne epidemiology, often positively affecting a large number of viral and entomological traits that favour transmission potential.
Key examples are the positive relationship of higher temperatures with a shorter viral extrinsic incubation period, longer adult mosquito life-span, and shorter aquatic mosquito development 19 , 63 , Following the aforementioned historical trends in climate, we also found a small but continuous increase in transmission potential over the years. Our analyses also suggest that recent changes in climate, since , appear to have introduced unstable inter-year variations in transmission potential, the practical consequences of which are difficult to assess.
Apart from climate, other ecological factors, such as the spatio-temporal distribution of land types, are known to affect the transmission potential of mosquito-borne viruses In Europe and North America, substantial positive associations have been found between human and animal WNV incidence and coverage of, or shorter distance to, cropland 49 , 50 , 51 , 52 , Associations between WNV incidence and natural types of land e.
Our results are consistent with these trends. We found that the south of Portugal is enriched with twice as much cropland compared to the north. Hence, it is possible that land type may also have contributed to the previously observed geographical distribution of WNV circulation in Portugal.
The data and modelling outputs presented include some limitations. For example, the geo-temporal patterns of transmission potential reflect solely the contribution of natural climate variation. Our estimations do not take into consideration other factors, such as the effects of land types and their proximity to human populations and animal farms, potential geo-temporal hotspots for inbound migratory avian species, mosquito and avian population sizes, biotype composition of the Cx.
We emphasize that this study has focused on a suitability index used previously for WNV in Israel that does not include such factors, but rather focuses on climate alone. Furthermore, we note that precipitation is not included in the estimation of the suitability index.
Many additional factors have been reported to be of potential interest for WNV epidemiology, and as such they can and should be the basis of future research, extending the methods and analyses presented in this study. Our theoretical results are solely intended to summarize the direct effect of climate on WNV and should be interpreted as such. The original resolution of the climate data has also restricted some of our outputs.
Namely, the resolution of our maps may have missed small-area regions of importance, and we were only able to estimate the duration of seasons non-zero transmission potential in the scale of months.
The collated empirical data of past WNV circulation may be another source of limitations. For instance, some evidence was impossible to map geographically, given deficiencies in reporting e.
It also remains unknown if the data includes a sampling bias towards the south of the country, which could partially explain the seemingly North-South divide in WNV circulation. This bias could arise from the reactive nature of surveillance initiatives responding to reports of symptomatic disease in sentinel species which may be distributed differently across the country, or alternatively, due to differences in WNV awareness among farmers, clinicians, and veterinarians. Countries implementing cross-sectoral and cross-disciplinary early warning systems based on a One Health surveillance approach vector, avian, equine, and human consistently reported positive impacts of such infrastructures Common areas for possible improvement included investment in and sustainability of mosquito surveillance, and improved information and media management.
In Portugal, mosquito surveillance remains an exception in an otherwise fragmented and insufficient WNV surveillance infrastructure. Key improvements would include sustainability of laboratory capacities and their timely responses, active One Health surveillance beyond the mosquito level, and investment in awareness and training across public health domains and the general public, in particular in the south of Portugal.
Our study provides a comprehensive, data-driven perspective of WNV in Portugal. It is still unclear whether WNV circulates endemically in any region of the country, but sufficient evidence exists to support ongoing seasonal circulation. Since data appeared unevenly geographically distributed across Portugal, we attempted to supplement them by describing distributions of mosquitoes and land types, as well as by estimating a theoretical WNV suitability index. The results support the geographical divide observed in molecular and serological data, and provide a first geo-temporal assessment of the contribution of local climate to the transmission potential of WNV in Portugal.
The south of Portugal may be more suitable for WNV transmission due to effects of climate and land type, but the possibility of the north supporting transmission in shorter periods of each year can not be rejected. Furthermore, climate change is gradually increasing suitability for WNV in Portugal. A shift from passive to active One Health surveillance will be necessary to manage future epidemics, which may result in public health emergencies, as reported recently in other European countries.
The query returned 43 hits as of March , from which 17 did not relate directly to the circulation of WNV or its vectors in the country. References within the studies found in our two searches were also scanned for potential studies related to WNV circulation in Portugal. The query returned 70 hits as of March , of which 62 did not relate to WNV genomic regions.
We provide the results of our literature review in the form of tables. All evidence related to the presence of WNV in Portugal across all studies found is summarized in Supplementary Table 1 also available in a permanent figshare repository Studies presenting time series of relevant mosquito species in Portugal are summarized in Supplementary Table 2.
Data included mosquito counts adult and immature stages for Cx. While a suitability index is an incomplete measure of the real transmission potential of a mosquito-borne virus, much work has been done to demonstrate the potential of an index to capture the geo-temporal dynamics of the number of reported mosquito-borne infections in host species 55 , 56 , Recently, the index was also successfully used to estimate the transmission potential of WNV in Israel dependent on local relative humidity and temperature variables In the current study, we use the same approach as applied to Israel, informed by the epidemiological priors applied in that study see Table in main text of 54 , which relate to Culex spp.
The choice of Culex spp. For each latitude-longitude location of the dataset, we used the MVSE R-package to estimate the index P 77 as described by Obolski et al.
The results are available as a comma-separated file in a permanent figshare repository Our data contained yearly median values of the mentioned variables for each Portuguese county. Our models contained a random intercept term for each region, a fixed effect dummy variable coding for north versus south, and a continuous variable representing the time unit year.
Detrending and wavelet analysis followed the workflow of Damineli et al. Between and the virology laboratory of INIAV performed molecular and serology testing in horses from several regions of the country, reacting to local suspected neuroinvasive disease.
Four of eight horses that were followed for clinical progression died or were euthanized. These results are summarized in Supplementary Table 1 , including the time and region of sampling. Land data were downloaded from the Copernicus platform at www. Land cover classification were aggregated into four classes: cropland vegetation classes 10, 11, 12, and 20 , natural vegetation classes 60, 70, 90, , , , , , and , mixed vegetation i.
Further information on research design is available in the Nature Research Reporting Summary linked to this article. Estimations of index P generated in this study are also made available on figshare This is because aspirin has been linked to Reye's syndrome, a rare but potentially life-threatening condition, in such children. Scientists are investigating interferon therapy — a type of immune cell therapy — as a treatment for encephalitis caused by West Nile virus. Some research shows that people who receive interferon recover better than those who don't receive the drug, but further study is needed.
If you have signs and symptoms of infection of the brain or spinal cord — high fever, severe headache, stiff neck, confusion or sudden muscle weakness — see your doctor right away or go to an urgent care center. Take a family member or friend along, if possible, to help you remember the information you're given. Mayo Clinic does not endorse companies or products.
Advertising revenue supports our not-for-profit mission. Check out these best-sellers and special offers on books and newsletters from Mayo Clinic Press. This content does not have an English version. This content does not have an Arabic version. Diagnosis Spinal tap lumbar puncture Open pop-up dialog box Close.
Updated October 9, World Health Organization. Published October 3, John Hopkins Medicine. Long-term neurological outcomes in West Nile virus—infected patients: An observational study. Am J Trop Med Hyg. Actively scan device characteristics for identification. Use precise geolocation data. Select personalised content. Create a personalised content profile. Measure ad performance. Select basic ads.
Create a personalised ads profile. Select personalised ads. Apply market research to generate audience insights. Measure content performance. Develop and improve products. List of Partners vendors. Table of Contents View All. Table of Contents. Viral Detection. Antibody Testing. Routine Lab Testing. When to Test. Next in West Nile Virus Guide. Testing for West Nile infection can be expensive and the results difficult to interpret.
Milder cases of West Nile virus infection can be indistinguishable from a seasonal cold. West Nile Virus Doctor Discussion Guide Get our printable guide for your next doctor's appointment to help you ask the right questions. Download PDF. Email the Guide Send to yourself or a loved one. Sign Up. How contagious is West Nile virus? When do symptoms of West Nile virus occur? What are the long-term effects of West Nile virus? Was this page helpful? Thanks for your feedback!
0コメント