Crimean-Congo Hemorrhagic Fever Virus Genome in Tick from Migratory Birds, Italy

The actual contribution of migratory birds in spreading West Nile (WNV) and Usutu virus (USUV) across Europe and from Africa to old countries is still controversial. In this study, we reported the results of molecular and serological surveys on migrating birds sampled during peaks of spring and autumn migration at 11 Italian sites located along important flyways, from 2012 to 2014. A total of 1335 specimens made of individual or pooled sera, and organs from 275 dead birds were tested for WNV and USUV RNA by real time PCR (RT-PCR). Furthermore, sera were tested by serum neutralization assay for detecting WNV and USUV neutralizing antibodies. Molecular tests detected WNV lineage 2 RNA in a pool made of three Song Thrush (Turdus philomelos) sera sampled in autumn, and lineage 1 in kidneys of six trans-Saharan birds sampled in spring. Neutralizing antibodies against WNV and USUV were found in 5.80% (n = 72; 17 bird species) and 0.32% (n = 4; 4 bird species) of the tested sera, respectively. Our results do not exclude the role of migratory birds as potential spreaders of WNV and USUV from Africa and Central Europe to Mediterranean areas and highlight the importance of a more extensive active surveillance of zoonotic viruses.

The annual movements of migratory birds can contribute to the spread of African ticks and tick-borne pathogens of potential public health concern across Europe. The aim of the study was to investigate their role in the possible introduction of African ticks and tick-borne pathogens into European countries during spring migration. A total of 2344 ticks were collected during three spring seasons from 1079 birds captured on three Italian stop-over islands during their northbound migration. Once identified, each tick was tested by RT-PCR for the presence of Crimean-Congo hemorrhagic fever (CCHFV), West Nile (WNV), and Usutu (USUV) viruses. Moreover, carcasses of birds found dead were collected and tested for the possible presence of WNV and USUV. Results confirmed a higher contribution of trans-Saharan migrants compared to intra-Palearctic ones and the prevalence of African tick species in the sample. CCHFV was detected for the second time in Italy in a Hyalomma rufipes, and WNV was found in two ticks of the same genus, all carried by trans-Saharan birds. WNV lineage 1 was also found in the organs of a Garden warbler. These results confirm the role of migratory birds in carrying African ticks, as well as viruses of zoonotic importance, from Africa into Europe.

In 2024, Italy reported its first five cases of Oropouche fever in travelers returning from Cuba and Brazil. The Oropouche virus (OROV), an emerging Orthobunyavirus of the Peribunyaviridae family, is a zoonotic arbovirus responsible for febrile illnesses in humans, often misdiagnosed owing to its clinical similarity to those caused by dengue and Zika virus infections. Originally endemic to the Amazon region and first detected in Trinidad and Tobago in 1955, OROV has since spread throughout South and Central America. Recent outbreaks in Brazil and Cuba have been linked to the newly identified genotype V. Although Culicoides paraensis midges are recognized as the primary vector in the urban transmission cycle, their presence in Cuba was documented only after the outbreak. This late detection, coupled with a possibly low population density of this species, has raised concerns that other, more abundant arthropod species may have played a role in transmitting OROV to humans on the island. While some mosquito species have been implicated as potential OROV secondary vectors, their role remains uncertain. This study evaluates the vector competence of Italian populations of Aedes albopictus and Culex pipiens for the newly circulating OROV strain, which was introduced into the country by infected travelers. Experimental infections were conducted under biosafety level 3 conditions, exposing adult female mosquitoes to an infectious blood meal containing OROV. Viral presence was assessed using a real-time RT-PCR in mosquito bodies, legs + wings, saliva, and the first gonotrophic progeny (F1). Results indicated that, while both species successfully ingested infectious virus particles, Cx. pipiens exhibited no signs of infection, dissemination, or transmission at any time point. In Ae. albopictus, viral RNA was detected in two body samples but not in saliva or disseminated tissues, confirming an absence of transmission capability. In addition, no evidence of transmission to F1 generation was detected in either species. These findings are consistent with previous research on American mosquito populations, indicating that barriers to OROV transmission likely occur at the midgut level. Despite the apparent lack of vector competence in Italian Ae. albopictus and Cx. pipiens, the ongoing geographic expansion of OROV highlights the need for continued surveillance, particularly as the 2025 vector activity season approaches in Europe. The increasing circulation of the virus, along with its potential for adaptive evolution, highlights the importance of further research into the virus–vector interactions that could enable OROV to establish itself in new ecological niches. Graphical abstract