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.

Reemergence of an atypical bluetongue virus strain in goats, Sardinia, Italy.

Bluetongue virus (BTV) is the etiologic agent of bluetongue, a WOAH (founded as Office International des Épizooties, OIE)-notifiable economically important disease of ruminants. BTV is transmitted by Culicoides biting midges and 24 different "classical" serotypes have been reported to date. In recent years, several putative novel BTV serotypes, often referred to as "atypical" BTVs, have been documented. These are characterized by unusual biological characteristics, most notably avirulence and vector-independent transmission. Here, we describe the recurrence of such an atypical virus strain BTV-X ITL2021 detected in goats six years after its first discovery in Sardinia, Italy. Combined serological and genome analysis results clearly suggest that the two strains belong to the same BTV serotype. However, unlike the 2015 strain, BTV-X ITL2021 was successfully isolated in BSR cell-culture allowing further serological characterization. Lastly, seropositivity for BTV-X ITL2021 was detected by virus-neutralization in approximately 74% of animals tested, suggesting that this atypical BTV serotype has been circulating undetected in asymptomatic animals for years.

An Early Block in the Replication of the Atypical Bluetongue Virus Serotype 26 in Culicoides Cells Is Determined by Its Capsid Proteins.

Arboviruses such as bluetongue virus (BTV) replicate in arthropod vectors involved in their transmission between susceptible vertebrate-hosts. The "classical" BTV strains infect and replicate effectively in cells of their insect-vectors (Culicoides biting-midges), as well as in those of their mammalian-hosts (ruminants). However, in the last decade, some "atypical" BTV strains, belonging to additional serotypes (e.g., BTV-26), have been found to replicate efficiently only in mammalian cells, while their replication is severely restricted in Culicoides cells. Importantly, there is evidence that these atypical BTV are transmitted by direct-contact between their mammalian hosts. Here, the viral determinants and mechanisms restricting viral replication in Culicoides were investigated using a classical BTV-1, an "atypical" BTV-26 and a BTV-1/BTV-26 reassortant virus, derived by reverse genetics. Viruses containing the capsid of BTV-26 showed a reduced ability to attach to Culicoides cells, blocking early steps of the replication cycle, while attachment and replication in mammalian cells was not restricted. The replication of BTV-26 was also severely reduced in other arthropod cells, derived from mosquitoes or ticks. The data presented identifies mechanisms and potential barriers to infection and transmission by the newly emerged "atypical" BTV strains in Culicoides.

Shift in serotype distribution of Shigella species in China, 2003-2013.

We identified 2912 Shigella isolates from diarrhoeal patients in China during 2003-2013. The most common species was Shigella flexneri (55.3%), followed by Shigella sonnei (44.1%); however, S. sonnei is becoming increasingly prevalent. Among the S. flexneri isolates, serotypes 2a and X variant (-:7,8, E1037) were the two most prevalent serotypes, and serologically atypical isolates were also commonly identified. Overall, S. sonnei, S. flexneri 2a and S. flexneri X variant (-:7,8, E1037) accounted for 76.1% of all Shigella isolates, and their prevalence increased from 54.0% during 2003-2004 to 84.1% during 2011-2013. A change was observed in the serotype distribution of Shigella in China during this period, and we propose an ideal strategy to inform the development of a broadly effective Shigella vaccine candidate.