Recent advances in diagnostic approaches for orf virus

Screening and characterization of a novel linear B-cell epitope on orf virus F1L protein

Background

Orf, also known as contagious ecthyma (CE), is an acute, contagious zoonotic disease caused by the orf virus (ORFV). The F1L protein is a major immunodominant protein on the surface of ORFV and can induce the production of neutralizing antibodies.

Methods

The prokaryotic expression system was used to produce the recombinant F1L protein of ORFV, which was subsequently purified and used to immunize mice. Positive hybridoma clones were screened using an indirect enzyme-linked immunosorbent assay (ELISA). The reactivity and specificity of the monoclonal antibody (mAb) were verified through Western blot and indirect immunofluorescence (IFA). The linear antigenic epitope specific to the mAb was identified through Western blot, using truncated F1L proteins expressed in eukaryotic cells. A multiple sequence alignment of the ORFV reference strains was performed to evaluate the degree of conservation of the identified epitope.

Results

After three rounds of subcloning, a mAb named Ba-F1L was produced. Ba-F1L was found to react with both the exogenously expressed F1L protein and the native F1L protein from ORFV-infected cells, as confirmed by Western blot and IFA. The mAb recognized the core epitope 103CKSTCPKEM111, which is highly conserved among various ORFV strains, as shown by homologous sequence alignment.

Conclusion

The mAb produced in the present study can be used as a diagnostic reagent for detecting ORFV and as a basic tool for exploring the mechanisms of orf pathogenesis. In addition, the identified linear epitope may be valuable for the development of epitope-based vaccines.

Diagnosis of bovine viral diarrhea virus: an overview of currently available methods

Bovine viral diarrhea virus (BVDV) is the causative agent of bovine viral diarrhea (BVD), which results in significant economic losses in the global cattle industry. Fortunately, various diagnostic methods available for BVDV have been established. They include etiological methods, such as virus isolation (VI); serological methods, such as enzyme-linked immunosorbent assay (ELISA), immunofluorescence assay (IFA), and immunohistochemistry (IHC); molecular methods, such as reverse transcription-polymerase chain reaction (RT-PCR), real-time PCR, digital droplet PCR (ddPCR), loop-mediated isothermal amplification (LAMP), recombinase polymerase amplification (RPA), and CRISPR-Cas system; and biosensors. This review summarizes the current diagnostic methods for BVDV, discussing their advantages and disadvantages, and proposes future perspectives for the diagnosis of BVDV, with the intention of providing valuable guidance for effective diagnosis and control of BVD disease.

Development of a real-time recombinase-aided amplification assay for rapid and sensitive detection of Edwardsiella piscicida

Edwardsiella piscicida, a significant intracellular pathogen, is widely distributed in aquatic environments and causes systemic infection in various species. Therefore, it's essential to develop a rapid, uncomplicated and sensitive method for detection of E. piscicida in order to control the transmission of this pathogen effectively. The recombinase-aided amplification (RAA) assay is a newly developed, rapid detection method that has been utilized for various pathogens. In the present study, a real-time RAA (RT-RAA) assay, targeting the conserved positions of the EvpP gene, was successfully established for the detection of E. piscicida. This assay can be performed in a one-step single tube reaction at a temperature of 39°C within 20 min. The RT-RAA assay exhibited a sensitivity of 42 copies per reaction at a 95% probability, which was comparable to the sensitivity of real-time quantitative PCR (qPCR) assay. The specificity assay confirmed that the RT-RAA assay specifically targeted E. piscicida without any cross-reactivity with other important marine bacterial pathogens. Moreover, when clinical specimens were utilized, a perfect agreement of 100% was achieved between the RT-RAA and qPCR assays, resulting a kappa value of 1. These findings indicated that the established RT-RAA assay provided a viable alternative for the rapid, sensitive, and specific detection of E. piscicida.

Finger nodules with a papulovesicular hands and feet eruption: a complicated human Orf virus infection

BACKGROUND

Orf virus (ORFV) is the pathogen responsible for Orf, a zoonotic viral infection that can be spread to humans from sheep and goats. Here, we present a case of human Orf complicated by an immune-related reaction, to raise awareness of this under-recognized disease avoiding unnecessary investigations and overtreatment.

CASE REPORT

A 51-year-old woman with no previous medical history presented with a one-week history of three asymptomatic swelling nodules with a grey necrotic center and red outer halo on her index finger. At physical examination there was also a pruritic papulovesicular eruption on her hands and feet. She reported a recent contact with a goat which had a similar nodular lesion in its mouth. A biopsy of the lesions was performed and a diagnosis of Orf complicated by widespread erythema multiforme was made based on the clinical and histopathological features. The lesions spontaneously resolved within the next 2 weeks.

CONCLUSIONS

Orf is not very prevalent in our region, so we performed a biopsy of the lesion to guide us toward a diagnosis. However, we should remember that the diagnosis of ecthyma relies on clinical evaluation and epidemiological criteria.

Development and performance of recombinase-aided amplification (RAA) assay for detecting Schistosoma haematobium DNA in urine samples

Rapid diagnosis of urogenital schistosomiasis caused by Schistosoma haematobium requires an accurate and timely assay, especially for low-intensity S. haematobium infection cases and in non-endemic areas. The mitochondrial cytochrome c oxidase 1 (cox1) gene fragment of S. haematobium was selected as detection target as this short fragment, which can be rapidly sequenced and yet possess good diagnostic resolution. A pair of primers and a fluorescent probe were designed according to the principle of recombinase-aided amplification (RAA), which was subsequently optimized and applied as an S. haematobium-specific RAA assay. Its diagnostic performance was validated for sensitivity and specificity in comparison to microscopy-based egg counting after urine filtration. The RAA assay could detect as little as 10 copies/μL of S. haematobium recombinant plasmid, and no cross-reactions were observed with S. mansoni, S. japonicum, Ancylostoma duodenale, Clonorchis sinensis, Echinococcus granulosus, or Ascaris lumbricoides. This test can be conducted at 39 °C and the whole RAA reaction can be completed within 20 min. The validation of the RAA assay showed that it had 100 % consistency with urine-egg microscopy, as it does not require an elaborate reading tool, is simple to use, and should be useful for field diagnostics and point-of-care applications.

Advances in the application of recombinase-aided amplification combined with CRISPR-Cas technology in quick detection of pathogenic microbes

The rapid diagnosis of pathogenic infections plays a vital role in disease prevention, control, and public health safety. Recombinase-aided amplification (RAA) is an innovative isothermal nucleic acid amplification technology capable of fast DNA or RNA amplification at low temperatures. RAA offers advantages such as simplicity, speed, precision, energy efficiency, and convenient operation. This technology relies on four essential components: recombinase, single-stranded DNA-binding protein (SSB), DNA polymerase, and deoxyribonucleoside triphosphates, which collectively replace the laborious thermal cycling process of traditional polymerase chain reaction (PCR). In recent years, the CRISPR-Cas (clustered regularly interspaced short palindromic repeats-associated proteins) system, a groundbreaking genome engineering tool, has garnered widespread attention across biotechnology, agriculture, and medicine. Increasingly, researchers have integrated the recombinase polymerase amplification system (or RAA system) with CRISPR technology, enabling more convenient and intuitive determination of detection results. This integration has significantly expanded the application of RAA in pathogen detection. The step-by-step operation of these two systems has been successfully employed for molecular diagnosis of pathogenic microbes, while the single-tube one-step method holds promise for efficient pathogen detection. This paper provides a comprehensive review of RAA combined with CRISPR-Cas and its applications in pathogen detection, aiming to serve as a valuable reference for further research in related fields.

Human Orf with Immune-Mediated Reactions: A Systematic Review

Background: Orf is a highly contagious zoonosis caused by Orf virus (ORFV), which is endemic in sheep and goats worldwide. Human Orf is usually a self-limiting disease, but potential complications, including immune-mediated reactions, may occur. Methods: We included all articles regarding Orf-associated immunological complications published in peer-reviewed medical journals. We conducted a literature search of the United States National Library of Medicine, PubMed, MEDLINE, PubMed Central, PMC, and the Cochrane Controlled Trials. Results: A total of 16 articles and 44 patients were included, prevalently Caucasian (22, 95.7%) and female (22, 57.9%). The prevailing immunological reaction was erythema multiforme (26, 59.1%), followed by bullous pemphigoid (7, 15.9%). In most cases, the diagnosis was made on the basis of clinical and epidemiological history (29, 65.9%), while a biopsy of secondary lesions was performed in 15 patients (34.1%). A total of 12 (27.3%) patients received a local or systemic treatment for primary lesions. Surgical removal of primary lesion was described in two cases (4.5%). Orf-immune-mediated reactions were treated in 22 cases (50.0%), mostly with topical corticosteroids (12, 70.6%). Clinical improvement was reported for all cases. Conclusions: Orf-related immune reactions can have a varied clinical presentation, and it is important for clinicians to be aware of this in order to make a prompt diagnosis. The main highlight of our work is the presentation of complicated Orf from an infectious diseases specialist's point of view. A better understanding of the disease and its complications is essential to achieve the correct management of cases.