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Abdelaziz R, Abd El-Hamid MI, El-Wafaei N, Ghaly MF, Askora A, El-Didamony G, AboElmaaty SA, Ismail TA, Ibrahim D, Eissa SA. Phage-resistant Streptomyces abietis and its telomycin bioactive metabolite as a possible alternative to antibiotics. Microb Pathog 2024; 194:106822. [PMID: 39047802 DOI: 10.1016/j.micpath.2024.106822] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2024] [Revised: 07/19/2024] [Accepted: 07/21/2024] [Indexed: 07/27/2024]
Abstract
Multidrug-resistant pathogens are now thought to be the primary global causes of disease and death. Therefore, it is imperative to develop new effective bioactive compounds from microbial sources, such as Streptomyces species. Nevertheless, the pharmaceutical industry suffered financial losses and low-quality end products as a result of Streptomyces bacteriophage contamination. To reduce the likelihood of phage-induced issues in the medical industry, it is crucial to develop a method for finding phage-resistant strains. Hence, we aimed to isolate and characterize Streptomyces spp. and Streptomyces phages from various rhizospheric soil samples in Egypt and to investigate their antibacterial activities. Moreover, we targeted development of a Streptomyces phage-resistant strain to extract its active metabolites and further testing its antibacterial activity. Herein, the antibacterial activities of the isolated 58 Streptomyces isolates showed that 10 (17.2 %) Streptomyces isolates had antibacterial activities against the tested bacteria including Listeria monocytogenes, E. coli O157, Acinetobacter baumannii, methicillin resistant-vancomycin-intermediate Staphylococcus aureus (MRSA-VISA) and Micrococcus luteus. Three lytic bacteriophages (ϕPRSC1, ϕPRSC2, and ϕPRSC4) belonging to the families Siphoviridae and Podoviridae were obtained from the rhizospheric soil samples using the most potent S. abietis isolate as the host strain. The three isolated Streptomyces phages were thermostable, ultraviolet stable, infectious, and had a wide range of hosts against the 10 tested Streptomyces isolates with antibacterial activities. The DNA of the ϕPRSC1 and ϕPRSC4 phages were resistant to digestion by EcoRI and HindIII, but the DNA of ϕPRSC2 was resistant to digestion by EcoRI and sensitive to digestion by HindIII. Of note, we developed a S. abietis strain resistant to the three isolated phages and its antibacterial activities were twice that of the wild strain. Finally, telomycin was recognized as an antibacterial metabolite extracted from phage-resistant S. abietis strain, which was potent against the tested Gram-positive bacteria including L. monocytogenes, MRSA-VISA, and M. luteus. Thus, our findings open new horizons for researching substitute antimicrobial medications for both existing and reemerging illnesses.
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Affiliation(s)
- Rewan Abdelaziz
- Department of Microbiology, Ain Shams University, Faculty of Science, 11566, Egypt.
| | - Marwa I Abd El-Hamid
- Department of Microbiology, Faculty of Veterinary Medicine, Zagazig University, 44511, Egypt.
| | - Nahed El-Wafaei
- Department of Agricultural Microbiology, Faculty of Agriculture, Zagazig University, 44511, Egypt.
| | - Mohamed F Ghaly
- Department of Botany and Microbiology, Zagazig University, Faculty of Science, Zagazig, 44519, Egypt.
| | - Ahmed Askora
- Department of Botany and Microbiology, Zagazig University, Faculty of Science, Zagazig, 44519, Egypt.
| | - Gamal El-Didamony
- Department of Botany and Microbiology, Zagazig University, Faculty of Science, Zagazig, 44519, Egypt.
| | - Sabah A AboElmaaty
- Department of Botany and Microbiology, Banha University, Faculty of Science, Banha, 44519, Egypt.
| | - Tamer A Ismail
- Department of Clinical Laboratory Sciences, Turabah University College, Taif University, Taif, 21944, Saudi Arabia.
| | - Doaa Ibrahim
- Department of Nutrition and Clinical Nutrition, Faculty of Veterinary Medicine, Zagazig University, Egypt.
| | - Samar A Eissa
- Department of Medical Microbiology and Immunology, Faculty of Medicine-Kafrelsheikh University, 31511, Egypt.
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Amoia CF, Hakizimana JN, Chengula AA, Munir M, Misinzo G, Weger-Lucarelli J. Genomic Diversity and Geographic Distribution of Newcastle Disease Virus Genotypes in Africa: Implications for Diagnosis, Vaccination, and Regional Collaboration. Viruses 2024; 16:795. [PMID: 38793675 PMCID: PMC11125703 DOI: 10.3390/v16050795] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2024] [Revised: 05/10/2024] [Accepted: 05/14/2024] [Indexed: 05/26/2024] Open
Abstract
The emergence of new virulent genotypes and the continued genetic drift of Newcastle disease virus (NDV) implies that distinct genotypes of NDV are simultaneously evolving in different geographic locations across the globe, including throughout Africa, where NDV is an important veterinary pathogen. Expanding the genomic diversity of NDV increases the possibility of diagnostic and vaccine failures. In this review, we systematically analyzed the genetic diversity of NDV genotypes in Africa using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Information published between 1999 and 2022 were used to obtain the genetic background of different genotypes of NDV and their geographic distributions in Africa. The following genotypes were reported in Africa: I, II, III, IV, V, VI, VII, VIII, XI, XIII, XIV, XVII, XVIII, XX, and XXI. A new putative genotype has been detected in the Democratic Republic of the Congo. However, of 54 African countries, only 26 countries regularly report information on NDV outbreaks, suggesting that this number may be vastly underestimated. With eight different genotypes, Nigeria is the country with the greatest genotypic diversity of NDV among African countries. Genotype VII is the most prevalent group of NDV in Africa, which was reported in 15 countries. A phylogeographic analysis of NDV sequences revealed transboundary transmission of the virus in Eastern Africa, Western and Central Africa, and in Southern Africa. A regional and continental collaboration is recommended for improved NDV risk management in Africa.
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Affiliation(s)
- Charlie F. Amoia
- Department of Veterinary Microbiology, Parasitology and Biotechnology, Sokoine University of Agriculture, P.O. Box 3019, Morogoro 67125, Tanzania;
- SACIDS Africa Centre of Excellence for Infectious Diseases, SACIDS Foundation for One Health, Sokoine University of Agriculture, P.O. Box 3297, Morogoro 67125, Tanzania
| | - Jean N. Hakizimana
- OR Tambo Africa Research Chair for Viral Epidemics, SACIDS Foundation for One Health, Sokoine University of Agriculture, P.O. Box 3297, Morogoro 67125, Tanzania;
| | - Augustino A. Chengula
- Department of Veterinary Microbiology, Parasitology and Biotechnology, Sokoine University of Agriculture, P.O. Box 3019, Morogoro 67125, Tanzania;
| | - Muhammad Munir
- Division of Biomedical and Life Sciences, Faculty of Health and Medicine, Lancaster University, Lancaster LA1 4YG, UK;
| | - Gerald Misinzo
- Department of Veterinary Microbiology, Parasitology and Biotechnology, Sokoine University of Agriculture, P.O. Box 3019, Morogoro 67125, Tanzania;
- SACIDS Africa Centre of Excellence for Infectious Diseases, SACIDS Foundation for One Health, Sokoine University of Agriculture, P.O. Box 3297, Morogoro 67125, Tanzania
- OR Tambo Africa Research Chair for Viral Epidemics, SACIDS Foundation for One Health, Sokoine University of Agriculture, P.O. Box 3297, Morogoro 67125, Tanzania;
| | - James Weger-Lucarelli
- Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA 24060, USA
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Abdelaziz R, Tartor YH, Barakat AB, El-Didamony G, Gado MM, Zaki MSA, Eid RA, El-Samadony HA. Alpha-sitosterol: a new antiviral agent produced by Streptomyces misakiensis and its potential activity against Newcastle disease virus. BMC Vet Res 2024; 20:76. [PMID: 38413949 PMCID: PMC10898069 DOI: 10.1186/s12917-023-03875-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2023] [Accepted: 12/29/2023] [Indexed: 02/29/2024] Open
Abstract
BACKGROUND Newcastle Disease Virus (NDV) causes severe economic losses in the poultry industry worldwide. Hence, this study aimed to discover a novel bioactive antiviral agent for controlling NDV. Streptomyces misakiensis was isolated from Egyptian soil and its secondary metabolites were identified using infrared spectroscopy (IR), gas chromatography-mass spectrometry (GC-MS), and nuclear magnetic resonance (NMR) spectroscopy. The inhibitory activity of bioactive metabolite against NDV were examined. Three experimental groups of 10-day-old specific pathogen-free embryonated chicken eggs (SPF-ECEs), including the bioactive metabolite control group, NDV control positive group, and α-sitosterol and NDV mixture-treated group were inoculated. RESULTS α-sitosterol (Ethyl-6-methylheptan-2-yl]-10,13-dimethyl-dodecahydro-1H-cyclopenta[a]phenanthren-3-ol), a secondary metabolite of S. misakiensis, completely inhibited hemagglutination (HA) activity of the NDV strain. The HA activity of the NDV strain was 8 log2 and 9 log2 for 0.5 and 0.75% RBCs, respectively. The NDV HA activity for the two concentrations of RBCs was significantly (P < 0.0001) inhibited after α-sitosterol treatment. There was a significant (P < 0.0001) decrease in the log 2 of HA activity, with values of - 0.500 (75%, chicken RBCs) before inoculation in SPF-ECEs and - 1.161 (50%, RBCs) and - 1.403 (75%, RBCs) following SPF-ECE inoculation. Compared to ECEs inoculated with NDV alone, the α-sitosterol-treated group showed improvement in histological lesion ratings for chorioallantoic membranes (CAM) and hepatic tissues. The CAM of the α-sitosterol- inoculated SPF-ECEs was preserved. The epithelial and stromal layers were noticeably thicker with extensive hemorrhages, clogged vasculatures, and certain inflammatory cells in the stroma layer in the NDV group. However, mild edema and inflammatory cell infiltration were observed in the CAM of the treated group. ECEs inoculated with α-sitosterol alone showed normal histology of the hepatic acini, central veins, and portal triads. Severe degenerative alterations, including steatosis, clogged sinusoids, and central veins, were observed in ECEs inoculated with NDV. Mild hepatic degenerative alterations, with perivascular round cell infiltration, were observed in the treated group. CONCLUSION To the best of our knowledge, this is the first study to highlight that the potentially bioactive secondary metabolite, α-sitosterol, belonging to the terpene family, has the potential to be a biological weapon against virulent NDV. It could be used for the development of innovative antiviral drugs to control NDV after further clinical investigation.
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Affiliation(s)
- Rewan Abdelaziz
- Department of Microbiology, Faculty of Science, Ain Shams University, Cairo, 11566, Egypt.
| | - Yasmine H Tartor
- Department of Microbiology, Faculty of Veterinary Medicine, Zagazig University, Zagazig, 44511, Egypt.
| | - Ahmed B Barakat
- Department of Microbiology, Faculty of Science, Ain Shams University, Cairo, 11566, Egypt
| | - Gamal El-Didamony
- Department of Botany and Microbiology, Faculty of Science, Zagazig University, Zagazig, 44519, Egypt
| | - Marwa M Gado
- Department of Microbiology, Faculty of Science, Ain Shams University, Cairo, 11566, Egypt
| | - Mohamed Samir A Zaki
- Anatomy Department, College of Medicine, King Khalid University, P.O. Box 62529, Abha, Saudi Arabia
| | - Refaat A Eid
- Department of Pathology, College of Medicine, King Khalid University, Abha, 12573, Saudi Arabia
| | - Hanaa A El-Samadony
- Department of Poultry, Animal Health Research Institute, Dokki, Agriculture Research Center, Giza, 44511, Egypt
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Abdelaziz R, Tartor YH, Barakat AB, El-Didamony G, El-Samadony HA, Amer SA, Gado MM. Streptomyces coeruleorubidus as a potential biocontrol agent for Newcastle disease virus. BMC Vet Res 2022; 18:241. [PMID: 35751117 PMCID: PMC9229119 DOI: 10.1186/s12917-022-03349-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Accepted: 06/10/2022] [Indexed: 11/10/2022] Open
Abstract
Background Newcastle disease virus (NDV) is a severe disease that affects domestic and wild birds. Controlled antibiotics derived from probiotics have been examined as prospective solutions for preserving seroconversion in NDV-vaccinated fowl. In this study, the secondary metabolite “telomycin” was extracted from Streptomyces coeruleorubidus (S. coeruleorubidus) isolated from Egypt's cultivated soil. The structure of telomycin was determined by the elucidation of spectroscopic analysis, including nuclear magnetic resonance (NMR) and mass spectrometry (MS) spectra, and comparison with the literature. The antiviral activity of the secondary metabolite was tested by checking its effect on NDV hemagglutination activity (HA). Moreover, HA of NDV was tested after inoculation of NDV (control) and a combination of telomycin and NDV in 10- days- specific pathogen-free embryonated chicken eggs (SPF-ECE) daily candling. Histopathological examination was performed for chorioallantoic membranes and liver of SPF-ECE. Results S. coeruleorubidus secondary metabolite “telomycin” showed complete hemagglutination inhibition (HI) activity of NDV strain (MN635617) with log106 infectivity titers (EID50/mL). The HA of NDV strain was 8 log2 and 9 log2 with 0.5% and 0.75% of chicken RBCs, respectively. Preserved structures of chorioallantoic-membranes (CAM) with dilated capillary networks were observed in the treated group inoculated with telomycin and NDV. Histological changes in SPF-ECE liver were examined after inoculation in ova to further characterize the telomycin effect. Telomycin and NDV mixture inoculated group showed preserved cytoarchitecture of hepatocytes with the presence of perivascular foci of lymphocytes. The group that was inoculated with telomycin alone showed normal histology of hepatic acini, central veins, and portal triads. Conclusion S. coeruleorubidus telomycin is a promising bioactive agent that might be a biological weapon against a deadly chicken NDV that costs farmers a lot of money. Supplementary Information The online version contains supplementary material available at 10.1186/s12917-022-03349-7.
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Affiliation(s)
- Rewan Abdelaziz
- Department of Microbiology, Faculty of Science, Ain Shams University, Cairo, 11566, Egypt
| | - Yasmine H Tartor
- Department of Microbiology, Faculty of Veterinary Medicine, Zagazig University, Zagazig, 44511, Egypt
| | - Ahmed B Barakat
- Department of Microbiology, Faculty of Science, Ain Shams University, Cairo, 11566, Egypt
| | - Gamal El-Didamony
- Department of Botany and Microbiology, Faculty of Science, Zagazig University, Zagazig, 44519, Egypt
| | - Hanaa A El-Samadony
- Department of Poultry, Dokki, Agriculture Research Center, Animal Health Research Institute, Giza, 44511, Egypt
| | - Shimaa A Amer
- Department of Nutrition & Clinical Nutrition, Faculty of Veterinary Medicine, Zagazig University, Zagazig, 44511, Egypt.
| | - Marwa M Gado
- Department of Microbiology, Faculty of Science, Ain Shams University, Cairo, 11566, Egypt
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Chegrynets AI, Saliy ОО, Sobko IA, Krasinko VO. Immunological evaluation of inactivated Newcastle disease vaccine depending on adjuvant composition. REGULATORY MECHANISMS IN BIOSYSTEMS 2021. [DOI: 10.15421/022167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Newcastle disease is a global problem that is being recorded in most countries and also a serious obstacle to exchange of genetic material of poultry in various countries of the world. Control of the Newcastle disease comprises correct injection of efficacious vaccines so as to decrease or eliminate the clinical disease. Our goal was to perform comparative studies of the vaccines against Newcastle disease of water in oil type, the adjuvant being mineral oil mixed with emulsifiers (Span-80 and Tween-80) and ready-to-use adjuvant system (Montanide ISA 70), and study the impact of composition of adjuvant constituent on physical-chemical and immunogenic properties of inactivated vaccines. To reproduce virus-containing material and carried out titration of the viruses, we used chicken embryos free of pathogenic microflora. Aqueous phase for the preparation of emulsion-based vaccines of water in oil type consisted of antigen to Newcastle disease of La-Sota strain, manufactured by Biotestlab Ltd, and phosphate-saline buffer. To evaluate the effectiveness of the vaccine and induce immune response, we used 1-day old pathogen-free chickens, which were obtained from chicken embryos free of pathogenic microflora. As the positive control in the experiment, we used commercial vaccine. One-day chickens were divided into 3 groups (I, II, III) comprising 12 individuals each and one group (IV) consisting of 8 individuals as the control group with individual numeration. Chickens in groups I, II and III were divided into two subgroups (n = 8 and n = 4) to determine immunogenic efficiency and safety of the vaccine. Immunization was carried out through single subcutaneous injections in the region of the neck. To study immunogenic efficiency, the chickens were immunized with the dose of 0.1 mL (1 dose), and 0.2 mL (2 doses) to determine safety. After the immunization of 1-day old pathogen-free chickens with 0.1 mL dose, the obtained level of antibodies in the serum of vaccinated chickens on days 14, 21, 28, 35 and 42 after the vaccination indicated the ability of provoking the immune response to Newcastle disease at high level and safety of the vaccination for chickens. All the recipes of the examined series of the vaccines and the commercial vaccine produced appropriate level of viscosity according to the criterion equaling ≤ 200 mm2/s at Р <0.05, promoting fluidity of the vaccine and providing easier passage through the needle during the application. Both of the studied vaccines may be used in poultry farming for prophylaxis of Newcastle disease among chickens.
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Karamendin K, Kydyrmanov A. Cormorants as a Potentially Important Reservoir and Carrier of Newcastle Disease Virus on the Asian Continent. Front Vet Sci 2021; 8:648091. [PMID: 34195243 PMCID: PMC8236515 DOI: 10.3389/fvets.2021.648091] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2020] [Accepted: 05/21/2021] [Indexed: 11/13/2022] Open
Abstract
Despite numerous disease prevention measures and control programs, Newcastle disease (ND) remains one of the most significant infections in poultry worldwide, especially in developing countries. It is known that wild birds, mainly of the Anseriformes order, are the main carrier of lentogenic (non-pathogenic) variants of Newcastle disease virus (NDV) in nature. But the question of the reservoir of velogenic (highly pathogenic) NDV in nature still remains open. In the 1970s, 1990s, and 2000s in North America during epizootics among cormorants, velogenic NDV strains were isolated. It was later concluded that cormorants play an important role in the maintenance and circulation of NDV in North America. New data have been obtained on the circulation of velogenic NDV strains in wild birds in Central Asia: VIIb and XIII genotype strains were isolated from cormorants for the first time in Kazakhstan. Interestingly, outbreaks of NDV registered in poultry in Central and Southern Asia were phylogenetically close to the viruses from cormorants that support the idea that cormorants can serve as the potential reservoir of velogenic NDV in developing countries of Asia. The seasonal migrations of cormorants may contribute to the distribution of the virus throughout Asia but more evidence must be obtained to confirm this hypothesis. There is increasing evidence of the introduction of NDV into the poultry farms from wild nature worldwide. This article continues the discussion on the likelihood of cormorants to serve as a reservoir and carrier of NDV on the Asian continent.
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Affiliation(s)
- Kobey Karamendin
- Laboratory of Viral Ecology, Scientific and Production Center of Microbiology and Virology, Almaty, Kazakhstan.,Kazakh National Agrarian University, Almaty, Kazakhstan
| | - Aidyn Kydyrmanov
- Laboratory of Viral Ecology, Scientific and Production Center of Microbiology and Virology, Almaty, Kazakhstan.,Kazakh National Agrarian University, Almaty, Kazakhstan
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Hidaka C, Soda K, Nomura F, Kashiwabara Y, Ito H, Ito T. The chicken-derived velogenic Newcastle disease virus can acquire high pathogenicity in domestic ducks via serial passaging. Avian Pathol 2021; 50:1-12. [PMID: 33576245 DOI: 10.1080/03079457.2021.1889461] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Accepted: 02/08/2021] [Indexed: 10/22/2022]
Abstract
Velogenic Newcastle disease virus (NDV) strains, which show high mortality in chickens, generally do not cause severe disease in waterfowl such as ducks. To elucidate the difference in the pathogenic mechanisms of NDV between chickens and ducks, a chicken-derived velogenic strain (9a5b) was passaged in domestic ducks five times in their air sacs, followed by 20 times in their brains. Eventually, 9a5b acquired higher intracerebral and intranasal pathogenicity in ducks. The intracerebral pathogenicity index (ICPI) value increased from 1.10 to 1.88. All one-week-old ducks intranasally inoculated with the passaged virus (d5a20b) died by 5 days post-inoculation, whereas 70% of the ducks inoculated with parental 9a5b survived for 8 days. The d5a20b strain replicated in broader systemic tissues in ducks compared with the 9a5b strain. The velogenic profile of 9a5b in chickens was maintained after passaging in ducks. The d5a20b suppressed IFN-β gene expression in duck embryo fibroblasts and replicated more rapidly than 9a5b. A total of 11 amino acid substitutions were found in the P, V, M, F, HN, and L proteins of d5a20b. These results suggest that chicken-derived velogenic NDVs have the potential to become virulent in both chickens and ducks during circulation in domesticated waterfowl populations. RESEARCH HIGHLIGHTSChicken-derived NDV acquired high pathogenicity in ducks with serial passaging.The passaged NDV showed intracerebral and intranasal pathogenicity in ducks.The passaged NDV efficiently replicated in systemic tissues in ducks.Of 11 amino acid substitutions some or all are likely involved in pathogenicity.
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Affiliation(s)
- Chiharu Hidaka
- Department of Joint Veterinary Medicine, Faculty of Agriculture, Tottori University, Tottori, Japan
- The United Graduate School of Veterinary Science, Yamaguchi University, Yamaguchi, Japan
| | - Kosuke Soda
- Department of Joint Veterinary Medicine, Faculty of Agriculture, Tottori University, Tottori, Japan
- The United Graduate School of Veterinary Science, Yamaguchi University, Yamaguchi, Japan
- Avian Zoonosis Research Center, Faculty of Agriculture, Tottori University, Tottori, Japan
| | - Fumie Nomura
- Department of Joint Veterinary Medicine, Faculty of Agriculture, Tottori University, Tottori, Japan
| | - Yukie Kashiwabara
- Department of Joint Veterinary Medicine, Faculty of Agriculture, Tottori University, Tottori, Japan
| | - Hiroshi Ito
- Department of Joint Veterinary Medicine, Faculty of Agriculture, Tottori University, Tottori, Japan
- The United Graduate School of Veterinary Science, Yamaguchi University, Yamaguchi, Japan
- Avian Zoonosis Research Center, Faculty of Agriculture, Tottori University, Tottori, Japan
| | - Toshihiro Ito
- Department of Joint Veterinary Medicine, Faculty of Agriculture, Tottori University, Tottori, Japan
- The United Graduate School of Veterinary Science, Yamaguchi University, Yamaguchi, Japan
- Avian Zoonosis Research Center, Faculty of Agriculture, Tottori University, Tottori, Japan
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