Polymerase Fidelity Contributes to Foot-and-Mouth Disease Virus Pathogenicity and Transmissibility In Vivo

Epidemiological Dynamics of Foot-and-Mouth Disease in the Horn of Africa: The Role of Virus Diversity and Animal Movement

The Horn of Africa is a large area of arid and semi-arid land, holding about 10% of the global and 40% of the entire African livestock population. The region's livestock production system is mainly extensive and pastoralist. It faces countless problems, such as a shortage of pastures and watering points, poor access to veterinary services, and multiple endemic diseases like foot-and-mouth disease (FMD). Foot-and-mouth disease is one of the most economically important livestock diseases worldwide and is endemic in most developing countries. Within Africa, five of the seven serotypes of the FMD virus (FMDV) are described, but serotype C is not circulating anymore, a burden unseen anywhere in the world. The enormous genetic diversity of FMDV is favored by an error-prone RNA-dependent RNA polymerase, intra-typic and inter-typic recombination, as well as the quasi-species nature of the virus. This paper describes the epidemiological dynamics of foot-and-mouth disease in the Horn of Africa with regard to the serotypes and topotypes distribution of FMDV, the livestock production systems practiced, animal movement, the role of wildlife, and the epidemiological complexity of FMD. Within this review, outbreak investigation data and serological studies confirm the endemicity of the disease in the Horn of Africa. Multiple topotypes of FMDV are described in the literature as circulating in the region, with further evolution of virus diversity predicted. A large susceptible livestock population and the presence of wild ungulates are described as complicating the epidemiology of the disease. Further, the husbandry practices and legal and illegal trading of livestock and their products, coupled with poor biosecurity practices, are also reported to impact the spread of FMDV within and between countries in the region. The porosity of borders for pastoralist herders fuels the unregulated transboundary livestock trade. There are no systematic control strategies in the region except for sporadic vaccination with locally produced vaccines, while literature indicates that effective control measures should also consider virus diversity, livestock movements/biosecurity, transboundary trade, and the reduction of contact with wild, susceptible ungulates.

Complete genome and pathogenesis of a novel recombinant Senecavirus A isolate in P.R. China

Senecavirus A (SVA), formerly called Seneca Valley virus (SVV) was first isolated from the USA in 2002. This study isolated an SVA strain from a pig herd in Shandong Province, PR China and designated it SVA-CH-SDGT-2017. The full-length genome, excluding the poly(A) tails of the SVA isolates, was 7280 nucleotides long, with the genomic organization resembling and sharing high nucleotide identities of 90.7-96.9 % with other previously reported SVA isolates. To investigate the pathogenicity of the SVA isolates, experimental infections of pigs were performed. The SVA strains successfully infected the pigs, as evidenced by the presence of virus shedding and robust serum neutralizing antibody responses. In addition, the contact-exposed experiment showed that the virus shedding of the contact-exposed pigs was approximately a 100-fold reduced compared to that of the inoculated group, indicating that the virus is capable of transmission to pigs. Our findings provide useful data for studying the pathogenesis and transmission of SVA in pigs.

Genetic diversity through social heterosis can increase virulence in RNA viral infections and cancer progression

In viral infections and cancer tumours, negative health outcomes often correlate with increasing genetic diversity. Possible evolutionary processes for such relationships include mutant lineages escaping host control or diversity, per se, creating too many immune system targets. Another possibility is social heterosis where mutations and replicative errors create clonal lineages varying in intrinsic capability for successful dispersal; improved environmental buffering; resource extraction or effective defence against immune systems. Rather than these capabilities existing in one genome, social heterosis proposes complementary synergies occur across lineages in close proximity. Diverse groups overcome host defences as interacting 'social genomes' with group genetic tool kits exceeding limited individual plasticity. To assess the possibility of social heterosis in viral infections and cancer progression, we conducted extensive literature searches for examples consistent with general and specific predictions from the social heterosis hypothesis. Numerous studies found supportive patterns in cancers across multiple tissues and in several families of RNA viruses. In viruses, social heterosis mechanisms probably result from long coevolutionary histories of competition between pathogen and host. Conversely, in cancers, social heterosis is a by-product of recent mutations. Investigating how social genomes arise and function in viral quasi-species swarms and cancer tumours may lead to new therapeutic approaches.

Genomic characteristics and pathogenicity of a new recombinant strain of porcine reproductive and respiratory syndrome virus

Recombination is an important phenomenon that accelerates evolution and enriches the genetic diversity of porcine reproductive and respiratory syndrome virus (PRRSV). Recombinant PRRSV isolates sometimes have different genetic backgrounds. In this study, we report a recombinant PRRSV (SD-YL1712) isolated from a pig farm. The genome of SD-YL1712 is 15,014 nucleotides in length, and its nucleotide and amino acid sequence conservation is higher than that of PRRSV strain JXA1 except within the NSP2 region. The NSP2 region of SDYL1712 shares the highest nucleotide (85.9%) and amino acid (84.1%) sequence identity with PRRSV strain NADC30. SD-YL1712 was found to contain a characteristic 131-amino-acid deletion in the NSP2 region. Two recombination breakpoints were detected at nt 2134 and nt 3958 within the NSP2 region, which revealed that SD-YL1712 originated from a recombination event between NADC30-like and HP-PRRSV-derived MLV-like strains. Interestingly, SD-YL1712 had an additional deletion at position 586, similar to that found in strain TJnh1501. Moreover, the pathogenicity of strain SD-YL1712 was found to be similar to that of HP-PRRSV JXA1, which was higher than that of the CH1a strain. Further analysis indicated that SD-YL1712 might be a transitional intermediate in the evolution of TJbd1401 to TJnh1501.