As climate change shifts the boundaries of disease risk across Europe, molecular diagnostics are stepping up as a core tool for surveillance and response. In a recent webinar hosted by the EU-funded PREPARE-TID consortium (Preparedness and Response Tools for Infectious Disease Outbreaks), researchers and clinicians gathered to discuss how vector-borne viral infections (VBVs), once considered exotic, are now emerging across Europe with increasing frequency.
The virtual event brought together a cross-section of expertise: virology, field epidemiology, molecular diagnostics, environmental health, and public health policy. Speakers from Italy, Germany, Serbia, and Turkey presented data and tools developed in direct response to outbreaks of Dengue virus (DENV), West Nile virus (WNV), Chikungunya virus (CHIKV), Yellow Fever virus (YFV) and Crimean-Congo Hemorrhagic Fever virus (CCHFV).
While the specific pathogens vary, one message was consistent: timely, field-adapted molecular diagnostics are now essential.
Expanding Boundaries: A New Geography of Risk
Prof. Luisa Barzon (University of Padova) opened the session with a comprehensive overview of vector-borne viral infections in Europe. Drawing on surveillance data and outbreak investigations across multiple Italian regions, including Veneto, Lazio, and Emilia-Romagna, she described how a combination of climate change, ecological shifts, and human mobility is making Europe increasingly vulnerable to tropical and subtropical viruses.
- In 2023, Italy recorded over 200 locally acquired dengue cases, and 480 imported cases, marking a sharp rise from the 2020 outbreak.
- Over the past 15 years, more than 1,200 West Nile Virus (WNV) cases have been documented, with notable spikes in 2018 and 2022.
- In 2022, WNV infections were detected in 11 EU countries, with more than 1,100 confirmed cases and 92 deaths reported by the ECDC.
- Aedes albopictus, the primary vector for dengue and chikungunya in Europe, has colonized most of southern and central regions. Aedes aegypti is now being reported in southern France and parts of the Iberian Peninsula.
- Surveillance efforts in Italy have identified seasonal spikes in mosquito abundance linked to urban heat islands and precipitation patterns, emphasizing the role of microclimatic shifts.
- The expansion of suitable habitats for vector populations is now occurring as far north as southern Germany and the Czech Republic, based on 2024 entomological surveys.
These shifts are creating new transmission zones and redefining what constitutes a "high-risk" region in Europe. National surveillance efforts are now coupled with real-time satellite and meteorological data to predict vector proliferation hotspots before they occur.
The Diagnostic Challenge: Early Detection in Low-Viremia Phases
Prof. Barzon detailed the diagnostic hurdles that persist in detecting arboviral infections, particularly during their early, low-viremia phase.
“Vector-borne viruses challenge conventional diagnostic workflows. The combination of nonspecific symptoms and low viral titers often leaves cases undiagnosed until it's too late.”
Highlighted challenges:
- Low viremia can lead to false negatives in RT-PCR.
- Serological assays (IgM/IgG ELISAs) are limited by cross-reactivity among flaviviruses.
- NS1 antigen detection is inconsistent, especially in WNV.
- Virus-specific neutralization assays, though accurate, are too slow for real-time response.
Emerging solutions:
- Urine-based PCR diagnostics can extend the detection window up to 14–21 days post-symptom onset.
- For neuroinvasive WNV, ~70% of cases test PCR-positive in blood or urine within 7 days.
- Dried blood spot (DBS) and saliva-based detection methods are being piloted as low-resource alternatives.
- Integrated use of metagenomic sequencing, particularly for febrile patients of unknown origin, is enabling faster identification of novel or unexpected pathogens.
- Point-of-care nucleic acid testing (POC-NAT) platforms are being trialed in rural and peripheral hospitals to decentralize diagnostics.
- Pre-analytical factors, such as sample type, storage temperature, and time to processing, are being evaluated systematically to optimize real-world diagnostic performance.
These improvements are reshaping diagnostic timelines and informing clinical decision-making, especially in settings where access to centralized laboratories is limited.
Genomic Surveillance and Molecular Tracing
Prof. Barzon emphasized the growing role of genomic epidemiology in characterizing outbreak dynamics and informing public health responses.
- Italy’s 2020 Dengue outbreak was linked to an imported DENV-1 strain from Indonesia.
- Recent WNV lineage 1 cases in Italy were genetically tied to strains from West Africa and Western Europe.
- In 2023, whole-genome sequencing confirmed co-circulation of Lineages 1 and 2 of WNV in northeastern Italy, highlighting the complexity of regional viral ecology.
- Cross-border sequencing initiatives, coordinated under the EU’s HERA program, are harmonizing protocols across national institutes to enable better outbreak tracking.
This level of tracing was made possible through Oxford Nanopore sequencing, integrated into mobile laboratories as part of the PREPARE-TID initiative. These tools are supporting not only diagnostics but also metagenomic pathogen discovery.
In addition, phylogenetic analyses are now being used to understand transmission chains within local communities, helping trace not only where the virus came from but also how it spreads between individuals and across regions.
One Health in Action: Coordinated Surveillance Frameworks
Italy’s national strategy is rooted in a coordinated One Health approach that combines entomological, veterinary, and clinical surveillance.
Core components:
- Mosquito testing and vector control initiatives
- Serosurveys in avian and equine populations
- NAT screening in blood and organ donors
- Cross-sector task forces for rapid outbreak containment
- Entomological risk assessments mapped against urban and agricultural land use
- Public engagement campaigns in high-risk areas to improve mosquito prevention behaviors
Between 2017 and 2022, the Italian One Health framework contributed to the early detection of over 85% of WNV human infections through entomological and veterinary signals. Similar frameworks are now being considered in Spain, Greece, and the Balkans, where Aedes species and WNV circulation are increasing.
Barzon noted that data integration remains a challenge, as systems across Europe use varying metadata standards and sampling protocols. Efforts are underway to unify platforms, guided by the European Centre for Disease Prevention and Control (ECDC) and WHO’s Regional Office for Europe.
> Continue to Part II