Japanese encephalitis virus (JEV) is a mosquito-borne zoonotic flavivirus and a major cause of human viral encephalitis in Asia. We provide an overview of the knowledge on vector competence, vector capacity, and immunity of mosquitoes in relation to JEV. JEV has so far been detected in more than 30 mosquito species. This does not necessarily mean that these species contribute to JEV transmission under field conditions. Therefore, vector capacity, which considers vector competence, as well as environmental, behavioral, cellular, and biochemical variables, needs to be taken into account. Currently, 17 species can be considered as confirmed vectors for JEV and 10 other species as potential vectors. Culex tritaeniorhynchus and Culex annulirostris are considered primary JEV vectors in endemic regions. Culex pipiens and Aedes japonicus could be considered as potentially important vectors in the case of JEV introduction in new regions. Vector competence is determined by various factors, including vector immunity. The available knowledge on physical and physiological barriers, molecular pathways, antimicrobial peptides, and microbiome is discussed in detail. This review highlights that much remains to be studied about vector immunity against JEV in order to identify novel strategies to reduce JEV transmission by mosquitoes.

Lumpy skin disease virus (LSDV) is a vector-transmitted capripox virus that causes disease in cattle. Stomoxys calcitrans flies are considered to be important vectors as they are able to transmit viruses from cattle with the typical LSDV skin nodules to naive cattle. No conclusive data are, however, available concerning the role of subclinically or preclinically infected cattle in virus transmission. Therefore, an in vivo transmission study with 13 donors, experimentally inoculated with LSDV, and 13 naïve acceptor bulls was performed whereby S. calcitrans flies were fed on either subclinical- or preclinical-infected donor animals. Transmission of LSDV from subclinical donors showing proof of productive virus replication but without formation of skin nodules was demonstrated in two out of five acceptor animals, while no transmission was seen from preclinical donors that developed nodules after Stomoxys calcitrans flies had fed. Interestingly, one of the acceptor animals which became infected developed a subclinical form of the disease. Our results show that subclinical animals can contribute to virus transmission. Therefore, stamping out only clinically diseased LSDV-infected cattle could be insufficient to completely halt the spread and control of the disease.

Lumpy Skin Disease virus is a poxvirus from the genus Capripox that mainly affects bovines and it causes severe economic losses to livestock holders. The Lumpy Skin Disease virus is currently dispersing in Asia, but little is known about detailed phylogenetic relations between the strains and genome evolution. We reconstructed a whole-genome-sequence (WGS)-based phylogeny and compared it with single-gene-based phylogenies. To study population and spatiotemporal patterns in greater detail, we reconstructed networks. We determined that there are strains from multiple clades within the previously defined cluster 1.2 that correspond with recorded outbreaks across Eurasia and South Asia (Indian subcontinent), while strains from cluster 2.5 spread in Southeast Asia. We concluded that using only a single gene (cheap, fast and easy to routinely use) for sequencing lacks phylogenetic and spatiotemporal resolution and we recommend to create at least one WGS whenever possible. We also found that there are three gene regions, highly variable, across the genome of LSDV. These gene regions are located in the 5′ and 3′ flanking regions of the LSDV genome and they encode genes that are involved in immune evasion strategies of the virus. These may provide a starting point to further investigate the evolution of the virus.

African swine fever (ASF) is one of the most important diseases in Suidae due to its significant health and socioeconomic consequences and represents a major threat to the European pig industry, especially in the absence of any available treatment or vaccine. In fact, with its high mortality rate and the subsequent trade restrictions imposed on affected countries, ASF can dramatically disrupt the pig industry in afflicted countries. In September 2018, ASF was unexpectedly identified in wild boars from southern Belgium in the province of Luxembourg, not far from the Franco-Belgian border. The French authorities rapidly commissioned an expert opinion on the risk of ASF introduction and dissemination into metropolitan France. In Europe, the main transmission routes of the virus comprise direct contact between infected and susceptible animals and indirect transmission through contaminated material or feed. However, the seasonality of the disease in some pig farms in Baltic countries, including outbreaks in farms with high biosecurity levels, have led to questions on the possible involvement of arthropods in the transmission of the virus. This review explores the current body of knowledge on the most common arthropod families present in metropolitan France. We examine their potential role in spreading ASF—by active biological or mechanical transmission or by passive transport or ingestion—in relation to their bio-ecological properties. It also highlights the existence of significant gaps in our knowledge on vector ecology in domestic and wild boar environments and in vector competence for ASFV transmission. Filling these gaps is essential to further understanding ASF transmission in order to thus implement appropriate management measures.

Small ruminant lentiviruses (SRLV) are a group of highly divergent viruses responsible for global and fatal infections in sheep and goats. Since the current phylogenetic classification of these viruses was proposed in 2004, it nowadays consists out of 5 genotypes and 28 subtypes. In support of our national SRLV control program, we performed the genetic characterization of SRLV strains circulating in the Belgian sheep and goat population. Fourteen sheep and 9 goat strains were sequenced in the gag-pol and pol regions using the method described by Shah. Most SRLV strains from sheep and goats belonged to prototype A1 and B1 subtypes, respectively. We, however, also found indications for cross-species transmission of SRLV strains between sheep and goats and vice versa, and identified a new subtype designated as B5. An in-depth analysis of the current SRLV phylogeny revealed that many subtypes have been defined over the years based on limited sequence information. To keep phylogeny as a useful tool, we advocate to apply more rigorous sequencing standards to ensure the correct classification of current and new emerging strains. The genetic characterization of Belgian SRLV strains will help in the development of appropriate diagnostic tools to assist the national control program.

Countries rely on good diagnostic tests and appropriate testing schemes to fight against economically important small ruminant lentivirus (SRLV) infections. We undertook an extensive comparative analysis of seven commercially available serological tests and one in-house real-time PCR (qPCR) detecting genotype A and B strains using a large panel of representative Belgian field samples and samples from experimentally infected sheep and goats. ELISAs generally performed well and detected seroconversion within three weeks post experimental infection. Two enzyme-linked immunosorbent assays (ELISAs) (Elitest and IDscreen^® kits) showed the highest sensitivities (>96%) and specificities (>95%) in both species, and their combined use allowed to correctly identify the infection status of all animals. Individual agar gel immunodiffusion (AGIDs) kits lacked sensitivity, but interestingly, the combined use of both kits had a sensitivity and specificity of 100%. qPCRs detected SRLV infection before seroconversion at two weeks post infection and showed a specificity of 100%. Sensitivity however remained suboptimal at 85%. These results allow to propose a faster and cheaper diagnostic testing strategy for Belgium by combining a first ELISA screening, followed by confirmation of positive samples in AGID and/or a second ELISA. Since genotypes A and B strains are predominant in many countries, these results are interesting for other countries implementing SRLV control programs.