Comparative analysis, distribution, and characterization of microsatellites in Orf virus genome

Insights into genome plasticity and gene regulation in Orientia tsutsugamushi through genome-wide mining of microsatellite markers

Microsatellite markers are being used for molecular identification and characterization as well as estimation of evolution patterns due to their highly polymorphic nature. The repeats hold 40% of the entire genome of Orientia tsutsugamushi (OT), but not yet been characterized. Thus, we investigated the genome-wide presence of microsatellites within nine complete genomes of OT and analyzed their distribution pattern, composition, and complexity. The in-silico study revealed that the genome of OT enriched with microsatellites having a total of 126,187 SSRs and 10,374 cSSRs throughout the genome, of which 70% and 30% are represented within the coding and non-coding regions, respectively. The relative density (RD) and relative abundance (RA) of SSRs were 42-44.43/kb and 6.25-6.59/kb, while for cSSRs this value ranged from 7.06 to 8.1/kb and 0.50 to 0.55/kb, respectively. However, RA and RD were weakly correlated with genome size and incidence of microsatellites. The mononucleotide repeats (54.55%) were prevalent over di- (33.22%), tri- (11.88%), tetra- (0.27%), penta- (0.02%), hexanucleotide (0.04%) repeats, with poly (A/T) richness over poly (G/C). The motif composition of cSSRs revealed that maximum cSSRs were made up of two microsatellites having unique duplication patterns such as AT-x-AT and CG-x-CG. To our knowledge, this is the first study of microsatellites in the OT genome, where characterization of such variations in repeat sequences would be important in deciphering the origin, rate of mutation, and role of repeat sequences in the genome. More numbers of microsatellites represented within the coding region provide an insight into the genome plasticity that may interfere with gene regulation to mitigate host-pathogen interaction and evolution of the species.

Comparative analysis of nine Tilletia indica genomes for the development of novel microsatellite markers for genetic diversity and population structure analysis

Karnal bunt (KB; Tilletia indica) is the prime quarantine concern for quality wheat production throughout the world. The most effective approach to dealing with this biotic stress is to breed KB-resistant wheat varieties, which warrants a better understanding of T. indica genome architecture. In India, the North Western Plain Zone is the prime hot spot for KB disease, but only limited efforts have been made to decipher T. indica diversity at the genomic level. Microsatellites offer a powerful and robust typing system for the characterization and genetic diversity assessment of plant pathogens. At present, inadequate information is available with respect to the development of genome-derived markers for revealing genetic variability in T. indica populations. In current research, nine complete genome sequences of T. indica (PSWKBGH_1, PSWKBGH_2, PSWKBGD_1_3, RAKB_UP_1, TiK_1, Tik, DAOMC236408, DAOMC236414, and DAOMC236416) that exist in the public domain were explored to know the dynamic distribution of microsatellites. Comparative genome analysis revealed a high level of relative abundance and relative density of microsatellites in the PSWKBGH_1 genome in contrast to other genomes. No significant correlation between microsatellite distribution for GC content and genome size was established. All the genomes showed the dominance of tri-nucleotide motifs, followed by mono-, di-, tetra-, hexa-, and penta-nucleotide motifs. Out of 50 tested markers, 36 showed successful amplification in T. indica isolates and produced 52 different alleles. A PCR assay along with analysis of the polymorphic information content (PIC) revealed 10 markers as neutral and polymorphic loci (PIC 0.37). The identified polymorphic SSR loci grouped a geographically distinct T. indica population of 50 isolates representing seven Indian regions (Jammu, Himachal Pradesh, Punjab, Haryana, Uttarakhand, Uttar Pradesh, and Rajasthan) into four distinct clusters. The results of the analysis of molecular variance identified 94% genetic variation within the population and 6% among the population. Structure analysis also confirmed the existence of four genetically diverse groups containing admixtures of T. indica isolates across populations. In nutshell, the current study was successful in identifying novel, neutral and polymorphic microsatellite markers that will be valuable in offering deep insight into the evolutionary relationship and dynamics of the T. indica population for devising effective KB management strategies in wheat.

Recent advances in diagnostic approaches for orf virus

Orf virus (ORFV), the prototype species of the Parapoxvirus genus, is an important zoonotic virus, causing great economic losses in livestock production. At present, there are no effective drugs for orf treatment. Therefore, it is crucial to develop accurate and rapid diagnostic approaches for ORFV. Over decades, various diagnostic methods have been established, including conventional methods such as virus isolation and electron microscopy; serological methods such as virus neutralization test (VNT), immunohistochemistry (IHC) assay, immunofluorescence assay (IFA), and enzyme-linked immunosorbent assay (ELISA); and molecular methods such as polymerase chain reaction (PCR), real-time PCR, loop-mediated isothermal amplification (LAMP), recombinase polymerase amplification (RPA), and recombinase-aided amplification (RAA) assay. This review provides an overview of currently available diagnostic approaches for ORFV and discusses their advantages and limitations and future perspectives, which would be significantly helpful for ORFV early diagnosis and surveillance to prevent outbreak of orf. KEY POINTS: • Orf virus emerged and reemerged in past years • Rapid and efficient diagnostic approaches are needed and critical for ORFV detection • Novel and sensitive diagnostic methods are required for ORFV detection.

Genome-Wide Analysis and Molecular Characterization of Orf Virus Strain UPM/HSN-20 Isolated From Goat in Malaysia

Contagious ecthyma commonly known as Orf is a globally important, highly contagious zoonotic, transboundary disease that affects domestic and wild ruminants. The disease is of great economic significance causing an immense impact on animal health, welfare, productivity, and trade. Detailed analysis of the viral genome is crucial to further elucidate the molecular mechanism of Orf virus (ORFV) pathogenesis. In the present study, a confluent monolayer of lamb testicle cells was infected with the processed scab sample obtained from an infected goat. The presence of the virus was confirmed using polymerase chain reaction and electron microscopy, while its genome was sequenced using next-generation sequencing technology. The genome sequence of Malaysian ORFV strain UPM/HSN-20 was found to contain 132,124 bp with a G + C content of 63.7%. The homology analysis indicates that UPM/HSN-20 has a high level of identity 97.3–99.0% with the other reference ORFV strain. Phylogenetic analysis revealed that ORFV strain UPM/HSN-20 is genetically more closely related to ORFV strain XY and NP from China. The availability of the genome-wide analysis of ORFV UPM/HSN-20 strain from Malaysia will serve as a good platform for further understanding of genetic diversity, ORFV infection, and strategic development for control measures.

A Review on Human Orf: A Neglected Viral Zoonosis

Orf virus (ORFV) is the etiologic agent of Orf or ecthyma contagiosum in humans but primarily affects different domestic and wild animals. The disease mostly affects sheep, goats and other small wild ruminants and spreads to humans through direct contact with infected animals or by way of contaminated fomites worldwide. ORFV is taxonomically classified as a member of the genus Parapoxvirus. It is known to have tolerance to inactivation in a drier environment, and it has been recovered from crusts after several months to years. Among immunocompetent people, the lesions usually resolve by its natural course within a maximum of 8 weeks. In immunosuppressed patients, however, it needs the use of various approaches including antiviral, immune modifier or minor surgical excisions. The virus through its association with divergent host ranges helps to develop a mechanism to evade the immune system. The relative emergence of Orf, diagnosed on clinical ground among human cases, in unusual frequencies in southwest Ethiopia between October 2019 and May 2020, was the driver to write this review. The objective was to increase health care providers' diagnostic curiosity and to bring the attentiveness of public health advisors for prevention, control and the development of schemes for surveillance of Orf zoonosis in a similar setting like Ethiopia.