Transplacental transmission of the Italian Bluetongue virus serotype 2 in sheep

In order to study the capability of a Bluetongue virus serotype 2 (BTV‑2) field isolate to cross the placental barrier, 2 groups of 5 pregnant ewes were infected with a field BTV‑2 Italian strain (Group A) or with the same strain passaged once in Culicoides cells (Kc) (Group B). Following infection, EDTA‑blood and serum samples were collected weekly and tested for the presence of BTV RNA/infectious virus and anti‑BTV‑2 antibodies, respectively. At lambing, precolostral EDTA‑blood and serum samples were collected from lambs and tested as before. The lambs were then sampled as scheduled for the dams. All sheep seroconverted on day 12 post‑infection (pi) and remained seropositive throughout the sampling period (day 68 pi). BTV was isolated from day 7 pi to day 14 pi in animals of Group A and from day 5 pi to day 12 pi in animals of Group B. None of the 14 lambs born had pre‑colostral antibodies. Three lambs born from two ewes of Group B were viraemic at birth and in one lamb infectious virus was isolated from blood up to 11 days of age. This study proved for the first time that a single passage of BTV‑2 field strain in Kc cells is able to give to BTV the ability to cross the placenta barrier and infect foetal tissues

Intravenous Infection of Small Ruminants Suggests a Goat-Restricted Host Tropism and Weak Humoral Immune Response for an Atypical Bluetongue Virus Isolate

Bluetongue virus (BTV) is the etiologic agent of bluetongue (BT), a viral WOAH-listed disease affecting wild and domestic ruminants, primarily sheep. The outermost capsid protein VP2, encoded by S2, is the virion’s most variable protein, and the ability of reference sera to neutralize an isolate has so far dictated the differentiation of 24 classical BTV serotypes. Since 2008, additional novel BTV serotypes, often referred to as “atypical” BTVs, have been documented and, currently, the full list includes 36 putative serotypes. In March 2015, a novel atypical BTV strain was detected in the blood of asymptomatic goats in Sardinia (Italy) and named BTV-X ITL2015. The strain re-emerged in the same region in 2021 (BTV-X ITL2021). In this study, we investigated the pathogenicity and kinetics of infection of BTV-X ITL2021 following subcutaneous and intravenous infection of small ruminants. We demonstrated that, in our experimental settings, BTV-X ITL2021 induced a long-lasting viraemia only when administered by the intravenous route in goats, though the animals remained healthy and, apparently, did not develop a neutralizing immune response. Sheep were shown to be refractory to the infection by either route. Our findings suggest a restricted host tropism of BTV-X and point out goats as reservoirs for this virus in the field

West Nile Virus in Italy: An Update of the Viral Strains Circulating in the Late 2022 Epidemic Season

West Nile virus (WNV) (Flaviviridae, Flavivirus) infection is a mosquito-borne zoonosis able of causing disease and death in humans and animals. Over the past decade, WNV infections have been a significant public health concern in Europe, and Italy has been among the most affected countries since 2008. The 2022 vector season has been characterized by an intense and early circulation of WNV. This report describes cases of co-circulation of WNV L1 and of WNV L2 occurring at the end of the 2022 vector season in Sicily and Tuscany, regions where no strains had ever been sequenced. The phylogenetic analysis of the detected strains confirmed the peculiar WNV scenario that has characterized the Italian West Nile disease (WND) epidemic since its appearance. The circulation observed in Tuscany was in fact a consequence of the spread of endemic strains to new areas while the Sicilian episodes were linked to new introductions of WNV L1 and L2 strains likely from other European countries

Vector Competence of Italian Populations of Culicoides for Some Bluetongue Virus Strains Responsible for Recent Northern African and European Outbreaks

The distribution of Bluetongue virus (BTV) in Europe can be represented by two distinct and interconnected epidemiological systems (episystems), each characterized by different ecological characteristics and vector species. This study investigated the vector competence of Italian populations of Culicoides imicola and Culicoides obsoletus/scoticus to some representative BTV strains after artificial oral infection. The BTV strains were selected according to their ability to spread to one or both episystems and included BTV-4 ITA, responsible of the recent Italian and French BTV-4 outbreaks; the BTV-2 strain which caused the first BTV incursion in Italy, Corsica, and Balearic Islands; BTV-4 MOR, responsible for the epidemic in Morocco; and BTV-8, the strain which spread through Europe between 2006 and 2008. Blood-soaked cotton pledgets and Hemotek membrane feeder using Parafilm® membrane were used to artificially feed midges. For each population/strain, recovery rates (positive/tested heads) were evaluated using serogroup- and serotype-specific RT-PCR. The trial demonstrated that, except for the Abruzzo population of C. obsoletus/C. scoticus, which was refractory to BTV-4 MOR infection, all the investigated Culicoides populations are susceptible to the selected BTV strains and that, if prompt vaccination programs and restriction measures had not been implemented, BTV-2 and BTV-4 MOR could have spread all over Europe