A Snapshot Avian Surveillance Reveals West Nile Virus and Evidence of Wild Birds Participating in Toscana Virus Circulation

Susceptibility of diverse sand fly species to Toscana virus

Toscana virus (TOSV) is an emerging but neglected human pathogen currently circulating around the Mediterranean basin including North Africa. Human illness ranges from asymptomatic or mild flu-like syndromes to severe neurological diseases such as meningitis or meningoencephalitis. Despite its significant impact, understanding of TOSV transmission and epidemiology remains limited. Sand flies (Diptera: Phlebotominae), specifically Phlebotomus perniciosus and Phlebotomus perfiliewi, are believed to be the primary vectors of TOSV. However, the spread of TOSV to new geographical areas and its detection in other sand fly species suggest that additional species play a role in the circulation and transmission of this virus. This study investigated the vector competence of four sand fly species - P. tobbi, P. sergenti, P. papatasi, and Sergentomyia schwetzi - for two TOSV strains: 1500590 (TOSV A lineage) and MRS20104319501 (TOSV B lineage). Sand flies were orally challenged with TOSV via bloodmeals. None of the tested species showed susceptibility to the TOSV A strain. However, for TOSV B strain, P. tobbi demonstrated a high potential as a new vector, exhibiting high infection and dissemination rates. P. sergenti also showed some susceptibility to TOSV B, with the virus dissemination observed in all infected females. These finding suggests that P. tobbi and P. sergenti are new potential vectors for TOSV B. Given that P. tobbi and P. sergenti are the primary vectors of human leishmaniases in the Balkans, Turkey and Middle East, their susceptibility to TOSV could have significant epidemiological consequences. On the other hand, P. papatasi and S. schwetzi appeared refractory to TOSV B infection. Refractoriness of P. papatasi, a highly anthropophilic species distributed from the Mediterranean to the Middle East and India, suggests that this species does not contribute to TOSV circulation.

Toscana virus - an emerging Mediterranean arbovirus transmitted by sand flies

Toscana virus (TOSV) is an emerging arthropod-borne virus (arbovirus) of medical importance that is increasing its range across much of the Mediterranean Basin, Europe and the Middle East. Transmitted by Phlebotomus spp. sand flies, it is the most clinically relevant sand fly-borne phlebovirus. Initially isolated in the Tuscany region of Central Italy, it has now been detected in multiple countries that surround this geographical area. Infection of the vertebrate host can cause fever and neurological disease, following the dissemination of the virus to the brain. The prevalence is high in some regions, with a notable percentage of individuals showing seroconversion. TOSV can be a leading cause of acute meningitis and encephalitis (AME) during the summer months. In this comprehensive review, we will focus on several key topics. We discuss how TOSV has spread to establish outbreaks of infection in both humans and animals around the Mediterranean and the wider region. Clinical aspects of TOSV infection in humans are described, along with the best standards in diagnosis. Finally, we focus our discussion on the role of the sand fly vector, describing their biology, vector competency, implications for putative vertebrate reservoirs, the effect of the climate emergency on sand fly distribution and the putative role that sand fly-derived salivary factors may have on modulating host susceptibility to TOSV infection.

Toscana Virus in Wild-Caught Sand Flies in Portugal, Findings from the National Vector Surveillance Network, 2023

Phlebotomine sand flies play a crucial role in both human and veterinary medicine, acting as vectors for Leishmania parasites and most known phleboviruses. In Portugal, the REVIVE program, a comprehensive national surveillance network under the Ministry of Health, has included sand fly surveys since 2016. REVIVE aims to identify existing sand fly species in the country, determine which pathogens are circulating among them, and provide actionable insights for prevention and control measures when necessary. In this way, annually, from May to October, health technicians collect sand flies across mainland Portugal with CDC light traps. The collected sand flies are sent to the Centre for Vectors and Infectious Diseases Research for species identification and molecular screening of pathogens. On 21 September 2023, Toscana virus (TOSV), a well-known phlebovirus in the Mediterranean region due to its capacity to cause neurological disease, was detected in a pool of 30 sand flies collected in Algarve, the southernmost region of Portugal. A 668 bp partial sequence of the nucleoprotein gene shows similarity with TOSV strains from Spain. To our knowledge, this is the first detection of TOSV in its vector in this country, having previously only been reported in vertebrate hosts. These findings highlight the important role of ongoing surveillance efforts in monitoring and understanding the dynamics of sand fly-borne diseases in Portugal.

Population Genetics of Culex tritaeniorhynchus (Diptera: Culicidae) in Türkiye

PURPOSE

Mosquitoes are important vectors of pathogens that can affect humans and animals. Culex tritaeniorhynchus is an important vector of arboviruses such as Japanese encephalitis virus, West Nile virus among various human and animal communities. These diseases are of major public health concern and can have huge economic and health burdens in prevalent countries. Although populations of this important mosquito species have been detected in the Mediterranean and Aegean regions of Türkiye; little is known about its population structure. Our study is to examine the population genetics and genetic composition of Cx. tritaeniorhynchus mosquitoes collected from several localities using cytochrome oxidase subunit I (COI) and the NADH dehydrogenase subunit 5 genes (ND5). This is the first extensive study of Cx. tritaeniorhynchus in the mainland Türkiye with sampling spanning many of provinces.

METHODS

In this study, DNA extraction, amplification of mitochondrial COI and ND5 genes and population genetic analyses were performed on ten geographic populations of Culex tritaeniorhynchus in the Aegean and Mediterranean region of Türkiye.

RESULTS

Between 2019 and 2020, 96 samples were collected from 10 geographic populations in the Aegean and Mediterranean regions; they were molecularly analyzed and 139 sequences (50 sequence for COI and 89 sequence for ND5) were used to determine the population structure and genetic diversity. For ND5 gene region, the samples produced 24 haplotypes derived from 15 variable sites and for COI gene region, 43 haplotypes were derived from 17 variable sites. The haplotype for both gene regions was higher than nucleotide diversity. Haplotype phylogeny revealed two groups present in all populations. AMOVA test results show that the geographical populations were the same for all gene regions. Results suggest that Cx. tritaeniorhynchus is a native population in Türkiye, the species is progressing towards speciation and there is no genetic differentiation between provinces and regions.

CONCLUSION

This study provides useful information on the molecular identifcation and genetic diversity of Cx. tritaeniorhynchus; these results are important to improve mosquito control programs.

Do birds play a role in the transmission of Toscana virus? Initial isolation results from birds in northernmost Türkiye

AIMS

Recent research has prioritized emerging and re-emerging diseases that affect human and animal health, particularly to describe how these diseases enter countries and determine their transmission cycles. Given that migratory birds play a significant role in spreading infections, the present study analysed their migration paths and specimens to investigate Orthoflavivirus, Orthonairovirus, Alphavirus and Phlebovirus in birds in Samsun province, Türkiye.

METHODS AND RESULTS

For these viruses, 312 samples from 56 birds were analysed using RT-PCR and qRT-PCR. Toscana virus (TOSV) was identified in 14 birds (four mallards, five partridges, four quails and one pigeon), representing 25% of the birds sampled. Genotype B was reported in all 14 birds. After inoculating the positive tissues in cell cultures, TOSV was isolated from the organs of pigeons, mallards and partridges.

CONCLUSIONS

This is the first time TOSV has been isolated in cell culture from birds and indicates that they may play a role in spreading TOSV in Türkiye. The results also suggest that TOSV might be carried between countries by migratory birds.

West Nile virus seropositivity in Alanya, a coastal city in the Mediterranean region of Turkey

BACKGROUND

West Nile virus (WNV)-related illness is a global health problem. Understanding the seropositivity rates and identifying the risk factors related to WNV in various animal species including humans is crucial for the implementation of effective prevention strategies.

OBJECTIVES

Assess the rate of seropositivity and the risk factors associated with WNV seropositivity.

DESIGN

Descriptive, cross-sectional.

SETTING

Microbiology and virology departments in a veterinary college.

PATIENTS AND METHODS

In a sample of healthy human participants in Alanya, located close to regions where WNV activity has been detected, anti-WNV IgG antibody detection was performed using enzyme-linked immunosorbent assays. The positive results were confirmed by virus neutralization tests (VNTs). The sample was compared with a second group of age- and gender-matched healthy subjects selected from a previous cross-sectional study.

MAIN OUTCOME MEASURES

Determination of the seropositivity and risk factors that were associated with WNV in healthy humans.

SAMPLE SIZE

87 in current study; 356 in previous study.

RESULTS

The first group of 87, which had a high risk of encountering vector mosquitoes, had a positivity rate of 8% (7/87), whereas positivity in the second group was 4.5% (16/356; P=.181). In the entire sample, the anti-WNV IgG antibody was positive in 23 out of 443 (5.2%) samples by the ELISA test. Among these 23 samples, ten were confirmed as positive using VNTs. Therefore, the WNV IgG seropositivity was 2.3% (10/442). Confirmed IgG seropositivity rates were higher among male (3.8%) than female participants (0.9%; P=.054) and among adults aged ≥45 years (4%) than those aged 18-44 years (0.8%; P=.048).

CONCLUSION

This study highlights the presence of WNV infection in the research region. More comprehensive and multidisciplinary studies are required to increase our knowledge about this zoonotic infection including risk factors in line with the One Health approach.

LIMITATIONS

Small sample size.

Bidirectional tick transport by migratory birds of the African-Western Palearctic flyway over Turkish Thrace: observation of the current situation and future projection

This study was carried out at a vital stopover site of migrating birds in the Turkish Thrace, European part of Turkey, on the Mediterranean/Black Sea Flyway. Ticks were collected from the birds captured in the four migration periods, i.e., autumn 2020, spring 2021, autumn 2021, and spring 2022, and identified morphologically. Throughout the study, 10,651 birds from 77 species were examined, and 671 belonging to 34 species were found infested. The infestation prevalence in total birds and the mean number of ticks per infested bird were 6.3% and 3.8 (range: 1-142), respectively. A total of 2573 ticks were collected with the following species distribution and numbers: Ixodes spp. 70 larvae, I. frontalis 1829 larvae, 337 nymphs, and 30 adults, I. acuminatus 16 nymphs and 42 adults, I. ricinus 39 larvae, 141 nymphs, and one adult, Hyalomma spp. seven larvae and 60 nymphs, and Haemaphysalis sp. one larva. Prevalence, intensity, and species distribution of the ticks in birds varied depending on the month, season, year, and species-specific migration phenology of the birds. The results show that precise determination of the tick-borne risk associated with migratory birds for a particular region necessarily requires long-term and comprehensive studies and indicates that anthropogenic climate change and habitat degradation can significantly differentiate the risk by influencing the migration phenology in birds and by making new regions suitable for the establishment of different ticks.

Molecular investigation of Haemoproteus and Plasmodium species of some raptors in Hatay province: new CytB lineages for raptors of Accipitriformes in Turkey

Accipitriform raptors are significant indicators of biodiversity and environmental health. Currently, most of the studies on avian haemosporidian parasites are on passerine birds, and data on raptors is constricted, with similarities both around the world and in Turkey. This study aimed to investigate the presence of Haemoproteus and Plasmodium spp. in raptors by microscopy and nested PCR technique. The study material consisted of 47 accipitriform raptors (Buteo buteo: 14, Buteo rufinus: 7, Clanga pomarina: 8, Circaetus gallicus: 12, Milvus migrans: 6). The prevalence of haemosporidian infection was 12.8% (6/47, 1 from Buteo buteo, 4 from Clanga pomarina, 1 from Milvus migrans) microscopically and 14.9% (7/47) molecularly. One Circaetus gallicus, microscopically found to be negative, probably due to low parasitemia, was molecularly found to be positive. All PCR-positive amplicons were bidirectionally sequenced, and the identification of lineages of the isolates and phylogenetic analysis were performed using the MalAvi and GenBank databases. The study revealed H-MILANS02 lineage in Buteo buteo, H-MILANS02 and P-CIAE1 lineages in Clanga pomarina, P-GRW06 lineage in Circaetus gallicus, and P-RTSR1 lineage in Milvus migrans, respectively. While this study removes the uncertainty regarding the reporting of the H-MILANS02 lineage in Turkey, it is also the first report to reveal 3 different Plasmodium spp. CytB lineages in raptors. Moreover, the fact that the P-GRW06 lineage (Plasmodium elongatum) detected in passerine birds was detected in a raptor, Circaetus gallicus, draws attention to the need for further investigations on host-parasite interaction and gives clues about the host-shifting ability of this parasite.

Comprehensive Cross-Sectional Evaluation of Human Sandfly-Borne Phlebovirus Exposure in an Endemic Region

Sandfly-borne phleboviruses are endemic in countries around the Mediterranean Basin and pose a significant health threat for populations, with symptoms spanning from febrile diseases to central nervous system involvement. We carried out a comprehensive cross-sectional screening via microneutralization (MN) assays for a quantitative assessment of neutralizing antibodies (NAs) to seven phleboviruses representing three distinct serocomplexes, using samples previously screened via immunofluorescence assays (IFAs) in Turkey, an endemic region with various phleboviruses in circulation. We detected NAs to three phleboviruses: Toscana virus (TOSV), sandfly fever Naples virus (SFNV), and sandfly fever Sicilian virus (SFSV), while assays utilizing Adana virus, Punique virus, Massilia virus, and Zerdali virus remained negative. The most frequently observed virus exposure was due to TOSV, with a total prevalence of 22.6%, followed by SFNV (15.3%) and SFSV (12.1%). For each virus, IFA reactivity was significantly associated with NA detection, and further correlated with NA titers. TOSV and SFSV seroreactivities were co-detected, suggesting exposure to multiple pathogenic viruses presumably due to shared sandfly vectors. In 9.6% of the samples, multiple virus exposure was documented. In conclusion, our findings demonstrate widespread exposure to distinct pathogenic phleboviruses, for which diagnostic testing and serological screening efforts should be directed.

High rates of antibodies against Toscana and Sicilian phleboviruses in common quail Coturnix coturnix birds

Introduction

Birds are involved natural cycle of a number of vector-borne viruses in both rural and urban areas. Toscana (TOSV) and Sicilian (SFSV) phleboviruses are sandfly-borne viruses in the genus Phlebovirus that can cause diseases in human. However, there is limited information on the role of the birds in sandfly-borne phleboviruses natural cycle and reservoirs ofthese viruses remain unknown.

Methods

In this study, we analyzed Common Quail (Coturnix coturnix) sera from Spain to identify the seroprevalence of these two phleboviruses. We tested respectively, 106 and 110 quail serum against TOSV and SFSV from 2018, 2019, and 2021 from two locations in northern Spain with using virus neutralization test.

Results

We identified high neutralizing antibody rates for SFSV (45.45%) and TOSV (42.45%) with yearly fluctuation.

Discussion

This is the first identification of SFSV and TOSV neutralizing antibodies in wild birds. High seroprevalence rates of TOSV and SFSV in quail birds raises the question whether birds have a role as amplifying hosts in the natural cycle of phleboviruses.

Sandfly-Borne Phleboviruses in Portugal: Four and Still Counting

According to ICTV, there are currently 66 known phlebovirus species. More than 40 of these viruses were isolated or detected in phlebotomine sandflies and some of them are known pathogens. In Portugal, information about sandfly-borne phleboviruses is scarce and scattered sandfly-borne diseases are neglected and often not considered in differential diagnoses. The main objective of this work was to gather the existing information and to raise awareness about the circulating phleboviruses in this country. To date, Massilia and Alcube phleboviruses have been isolated from sandflies in southern Portugal. Human infections with Toscana and Sicilian phleboviruses have been reported, as well as seroprevalence in cats and dogs. More studies are needed in order to understand if the viruses isolated during the entomological surveys have an impact on human health and to fully understand the real importance of the already recognized pathogens in our country.

The initial detection of Toscana virus in phlebotomine sandflies from Turkey

Toscana virus (TOSV) is a prominent arthropod-borne viral agent of human central nervous system infections occurring in the Mediterranean region. The main transmission route to susceptible individuals involves sandflies as vectors. Despite several reports revealing widespread TOSV activity in Turkey, vectors remained unidentified. A sandfly field survey was carried out in five provinces in Central, Southeast and Mediterranean Anatolia in 2017 to identify TOSV and related sandfly-borne phleboviruses and Leishmania parasites, with evidence for circulation in the region. A total of 7136 sandfly specimens, collected via standard methods, were evaluated in 163 pools. TOSV was detected in 11 pools (6.7%), comprising Phlebotomus major sensu lato, Sergentomyia dentata and Phlebotomus papatasi species. TOSV partial L and S segment sequences were characterized, that phylogenetically clustered with local and global genotype A strains. An amino acid substitution outside the conserved motifs of the viral polymerase, also present in previous TOSV sequences in endemic regions, was observed. Leishmania tropica was detected in a single pool of Ph. sergentii (0.6%). This is the first report of TOSV in sandflies from Turkey, and this study further provides evidence for additional sandfly species with the potential to transmit TOSV.

Vector-borne viruses in Turkey: A systematic review and bibliography

Turkey serves as a natural hub for the dissemination of vector-borne viruses and provides many suitable habitats with diverse ecologies for introduction and establishment of new pathogens. This manuscript provides an updated systematic review and meta-analysis of the vector-borne viruses documented in Turkey. Following web-based identification, screening and eligibility evaluation, 291 published reports were reviewed. The publications were categorized and listed as a supplementary bibliography accompanying the manuscript. In brief, Crimean-Congo hemorrhagic fever virus (CCHFV) and West Nile virus (WNV) are currently documented as prominent tick and mosquito-borne viral pathogens in Turkey. CCHFV produces a significant number of infections annually, with severe outcome or death in a portion of cases. WNV gained attention following the clustering of cases in 2010. Exposure and infections with sandfly-borne phleboviruses, such as Toscana virus, are indigenous and widespread. Epidemiology, risk factors, symptomatic infections in susceptible hosts, vectors and reservoirs for these pathogens have been explored in detail. Detection of novel viruses in mosquitoes, sandflies and ticks from several regions is of particular interest, despite scarce information on their epidemiology and pathogenicity in vertebrates. Introduction and emergence of viruses transmitted by invasive Aedes mosquitoes constitute a threat, albeit only imported infections have so far been documented. Detection of Rift valley fever virus exposure is also of concern, due to its detrimental effects on livestock and spillover infections in humans. Vigilance to identify and diagnose probable cases as well as vector surveillance for established and potential pathogens is therefore, imperative.

Broader Geographical Distribution of Toscana Virus in the Mediterranean Region Suggests the Existence of Larger Varieties of Sand Fly Vectors

Toscana virus (TOSV) is endemic in the Mediterranean basin, where it is transmitted by sand flies. TOSV can infect humans and cause febrile illness as well as neuroinvasive infections affecting the central and peripheral nervous systems. Although TOSV is a significant human pathogen, it remains neglected and there are consequently many gaps of knowledge. Recent seroepidemiology studies and case reports showed that TOSV’s geographic distribution is much wider than was assumed a decade ago. The apparent extension of the TOSV circulation area raises the question of the sandfly species that are able to transmit the virus in natural conditions. Phlebotomus (Ph.)perniciosus and Ph. perfiliewi were historically identified as competent species. Recent results suggest that other species of sand flies could be competent for TOSV maintenance and transmission. Here we organize current knowledge in entomology, epidemiology, and virology supporting the possible existence of additional phlebotomine species such as Ph. longicuspis, Ph. sergenti, Ph. tobbi, Ph. neglectus, and Sergentomyia minuta in TOSV maintenance. We also highlight some of the knowledge gaps to be addressed in future studies.

Arboviral screening of invasive Aedes species in northeastern Turkey: West Nile virus circulation and detection of insect-only viruses

BACKGROUND

The recent reports of Aedes aegypti and Ae. albopictus populations in Turkey, in parallel with the territorial expansion identified in several surrounding countries, have raised concerns about the establishment and re-establishment of these invasive Aedes mosquitoes in Turkey. This cross-sectional study was performed to detect Aedes aegypti and Ae. albopictus in regions of recent incursions, and screen for viral pathogens known to be transmitted elsewhere by these species.

METHODOLOGY

Mosquitoes were collected at several locations in Artvin, Rize and Trabzon provinces of the Black Sea region during 2016-2017, identified morphologically, pooled and analyzed via generic or specific nucleic acid amplification assays. Viruses in positive pools were identified by product sequencing, cell culture inoculation and next generation sequencing (NGS) in selected specimens.

PRINCIPAL FINDINGS

The study group comprised 791 specimens. Aedes albopictus was the most abundant species in all locations (89.6%), followed by Ae. aegypti (7.8%) and Culex pipiens (2.5%). Mosquitoes were screened for viruses in 65 pools where fifteen (23.1%) were reactive. The infecting strains was identified as West Nile virus (WNV) in 5 pools (7.7%) with Ae. albopictus or Cx. pipiens mosquitoes. The obtained WNV sequences phylogenetically grouped with local and global lineage 1 clade 1a viruses. In 4 (6.2%) and 6 (9.2%) pools, respectively, cell fusing agent virus (CFAV) and Aedes flavivirus (AEFV) sequences were characterized. NGS provided a near-complete AEFV genome in a pool of Ae. albopictus. The strain is provisionally called "AEFV-Turkey", and functional analysis of the genome revealed several conserved motifs and regions associated with virus replication. Merida-like virus Turkey (MERDLVT), a recently-described novel rhabdovirus, was also co-detected in a Cx. pipiens pool also positive for WNV.

CONCLUSIONS/SIGNIFICANCE

Invasive Aedes mosquitoes are established in certain locations of northeastern Turkey. Herein we conclusively show the role of these species in WNV circulation in the region. Biosurveillance is imperative to monitor the spread of these species further into Asia Minor and to detect possible introduction of pathogens.

West Nile virus, Anopheles flavivirus, a novel flavivirus as well as Merida-like rhabdovirus Turkey in field-collected mosquitoes from Thrace and Anatolia

Mosquitoes are involved in the transmission and maintenance of several viral diseases with significant health impact. Biosurveillance efforts have also revealed insect-specific viruses, observed to cocirculate with pathogenic strains. This report describes the findings of flavivirus and rhabdovirus screening, performed in eastern Thrace and Aegean region of Anatolia during 2016, including and expanding on locations with previously-documented virus activity. A mosquito cohort of 1545 individuals comprising 14 species were collected and screened in 108 pools via generic and specific amplification and direct metagenomics by next generation sequencing. Seven mosquito pools (6.4%) were positive in the flavivirus screening. West Nile virus lineage 1 clade 1a sequences were characterized in a pool Culex pipiens sensu lato specimens, providing the initial virus detection in Aegean region following 2010 outbreak. In an Anopheles maculipennis sensu lato pool, sequences closely-related to Anopheles flaviviruses were obtained, with similarities to several African and Australian strains of this new insect-specific flavivirus clade. In pools comprising Uranotaenia unguiculata (n=3), Cx. pipiens s.l. (n=1) and Aedes caspius (n=1) mosquitoes, sequences of a novel flavivirus, distantly-related to Flavivirus AV2011, identified previously in Spain and Turkey, were characterized. Moreover, DNA forms of the novel flavivirus were detected in two Ur. unguiculata pools. These sequences were highly-similar to the sequences amplified from viral RNA, with undisrupted reading frames, suggest the occurrence of viral DNA forms in natural conditions within mosquito hosts. Rhabdovirus screening revealed sequences of a recently-described novel virus, named the Merida-like virus Turkey (MERDLVT) in 5 Cx. pipiens s.l. pools (4.6%). Partial L and N gene sequences of MERDLVT were well-conserved among strains, with evidence for geographical clustering in phylogenetic analyses. Metagenomics provided the near-full genomic sequence in a specimen, revealing an identical genome organization and limited divergence from the prototype MERDLVT isolate.