Experimental study of the susceptibility of a European Aedes albopictus strain to dengue virus under a simulated Mediterranean temperature regime

Dengue virus (DENV) has re-emerged in Europe driven by the geographic expansion of the mosquito species Aedes albopictus and Aedes aegypti (Diptera: Culicidae) and the introduction of the virus by viraemic travellers. In the present study, the vector competence (VC) of Ae. albopictus collected in Catalonia (northeast Spain) was evaluated for two different DENV strains, DENV-1 and DENV-2, the serotypes responsible for all outbreaks of dengue that have occurred in Europe. Mosquitoes were reared under environmental conditions mimicking the mean temperature and humidity recorded in July on the Mediterranean coast of Catalonia. Mosquitoes were fed on an artificial infectious bloodmeal and, at 14 days post-exposure, infection, disseminated infection and transmission rates (IR, DIR, TR) and transmission efficiency (TE) were determined by testing the virus in the body, legs and saliva. The tested Ae. albopictus strain was found to be susceptible to both DENV-1 and DENV-2 and to be able to transmit DENV-1. This is the first time that the VC of Ae. albopictus for DENV has been tested in Europe in this specific context (i.e. mimicking the Mediterranean temperature and humidity recorded in Catalonia in July). This study confirms the potential of Ae. albopictus to start autochthonous DENV transmission cycles in the Mediterranean basin.

Revealing potential bridge vectors for BTV and SBV: a study on Culicoides blood feeding preferences in natural ecosystems in Spain

Several species of Culicoides (Diptera: Ceratopogonidae) are vectors of pathogens, such as the bluetongue (BTV) and Schmallenberg (SBV) viruses, which cause important diseases in domestic and wild ruminants. As wild ruminants can contribute to overwintering and epizootics of both diseases, knowledge of the host-feeding behaviour of Culicoides in natural ecosystems is important to better understand their epidemiology. Blood-engorged Culicoides females trapped in natural areas inhabited by different wild ruminant species were genetically analysed to identify host species. The origin of bloodmeals was identified in 114 females of 14 species of Culicoides. A total of 104 (91.1%) Culicoides fed on mammals and 10 (8.9%) on birds. The most abundant host identified was red deer (66.7%), followed by humans (13%) and fallow deer (6.1%). Eleven of the 14 species of Culicoides fed exclusively on mammalian hosts. Among them, five are mammalophilic species considered to be important BTV and/or SBV vectors. The results of the present study confirm that Culicoides imicola, Culicoides obsoletus, Culicoides scoticus, Culicoides pulicaris and Culicoides punctatus fed on wild ruminants, and therefore support the hypothesis that these species can act as bridge vectors by facilitating the circulation of pathogens between wild and domestic ruminant communities.

Schmallenberg virus detection in Culicoides biting midges in Spain: First laboratory evidence for highly efficient infection of Culicoides of the Obsoletus complex and Culicoides imicola

Since Schmallenberg disease was discovered in 2011, the disease rapidly spread across Europe. Culicoides biting midges have been implicated as putative Schmallenberg vectors in Europe. The detection of Schmallenberg virus (SBV) in field collected Culicoides was evaluated through retrospective (2011-2012) collections and captures performed in 2013. This study represents the first detection of SBV in field collected Culicoides in Spain. Infectious midges were detected at the foothills of Pyrenees, Aramunt, in the summer 2012. All the specimens infected with Schmallenberg were of the species Culicoides obsoletus s.s. confirming its putative vector status in Spain. Experimental infection on field collected Culicoides provided evidence of atypical high efficiency for SBV vector infection and transmission potential in local populations of Culicoides imicola and in Culicoides of the Obsoletus complex. However, captured individuals of C. imicola were more susceptible to SBV infection than C. obsoletus s.l. (p < .001), with an infection ratio of 0.94 and 0.63, respectively. In contrast, a Culicoides nubeculosus colony appeared to be refractory to SBV infection.

Rift Valley fever virus and European mosquitoes: vector competence of Culex pipiens and Stegomyia albopicta (= Aedes albopictus)

Rift Valley fever (RVF) is a mosquito-borne disease caused by the Rift Valley fever virus (RVFV). Rift Valley fever affects a large number of species, including human, and has severe impact on public health and the economy, especially in African countries. The present study examined the vector competence of three different European mosquito species, Culex pipiens (Linnaeus, 1758) form molestus (Diptera: Culicidae), Culex pipiens hybrid form and Stegomyia albopicta (= Aedes albopictus) (Skuse, 1894) (Diptera: Culicidae). Mosquitoes were artificially fed with blood containing RVFV. Infection, disseminated infection and transmission efficiency were evaluated. This is the first study to assess the transmission efficiency of European mosquito species using a virulent RVFV strain. The virus disseminated in Cx. pipiens hybrid form and in S. albopicta. Moreover, infectious viral particles were isolated from saliva of both species, showing their RVFV transmission capacity. The presence of competent Cx. pipiens and S. albopicta in Spain indicates that an autochthonous outbreak of RVF may occur if the virus is introduced. These findings provide information that will help health authorities to set up efficient entomological surveillance and RVFV vector control programmes.

Morphology and DNA barcoding reveal three species in one: description of Culicoides cryptipulicaris sp. nov. and Culicoides quasipulicaris sp. nov. in the subgenus Culicoides

Species of the genus Culicoides (Diptera: Ceratopogonidae) are well known for their importance in the field of medical and veterinary entomology. Culicoides spp. transmit a wide variety of pathogens, primarily viruses that affect animals and humans. In Europe, the most economically important disease transmitted by Culicoides is bluetongue (BT). Culicoides spp. have been recently involved as primary vectors for Schmallenberg disease. The taxonomy within the subgenus Culicoides has been historically difficult and reorganizations have been proposed regularly. The subgenus Culicoides includes species that are considered to be potential vectors for BT. High morphological intraspecific variability has been attributed to these species. This highlights the apparent presence of previously undetected cryptic species diversity in the subgenus. In the present study, a detailed morphological and molecular study of specimens belonging to Culicoides pulicaris s.l. and specimens resembling a cross between C. pulicaris and Culicoides punctatus revealed the presence of two new species: Culicoides cryptipulicaris and Culicoides quasipulicaris. Females of C. quasipulicaris and males of both species were morphologically distinguished from C. pulicaris (Linnaeus, 1758), whereas females of C. cryptipulicaris were identified using molecular techniques exclusively.

Culex pipiens and Stegomyia albopicta (= Aedes albopictus) populations as vectors for lineage 1 and 2 West Nile virus in Europe

The emerging disease West Nile fever is caused by West Nile virus (WNV), one of the most widespread arboviruses. This study represents the first test of the vectorial competence of European Culex pipiens Linnaeus 1758 and Stegomyia albopicta (= Aedes albopictus) (both: Diptera: Culicidae) populations for lineage 1 and 2 WNV isolated in Europe. Culex pipiens and S. albopicta populations were susceptible to WNV infection, had disseminated infection, and were capable of transmitting both WNV lineages. This is the first WNV competence assay to maintain mosquito specimens under environmental conditions mimicking the field (day/night) conditions associated with the period of maximum expected WNV activity. The importance of environmental conditions is discussed and the issue of how previous experiments conducted in fixed high temperatures may have overestimated WNV vector competence results with respect to natural environmental conditions is analysed. The information presented should be useful to policymakers and public health authorities for establishing effective WNV surveillance and vector control programmes. This would improve preparedness to prevent future outbreaks.