Study of the emergent properties and paths of spreading of PEDV was carried out in a model experiment on newborn non-immune piglets obtained from a PED virus-free pig-breeding enterprise. The piglets were kept in separate specialized containers, with a volume of 1.0 m3, with access only through the opening at the top of the containers. The experimental group of the animals was infected with PEDV isolate extracted on one of the pig farms from the central region of Ukraine. Infection was carried out orally in a dose of 1–10 genome equivalents of virions. The control piglets, which were situated in the same room as the infected animals, were not deliberately infected. The study of biological material from piglets was carried out using the methods of bacteriology, histology and RT-PCR. To confirm the capability of PEDV to spread through house flies, specimens of Musca domestica vicina Mcq. were caught in the building where the experiment was carried out. The washings from the surface of their bodies were collected with sterile saline. Individually, 28 specimens of flies were selected. They were divided into two parts and the amount of virus in the homogenate of the fly bodies in these groups was determined with an interval between measurements of 72 hours. Study of PEDV in the washings and in flies body homogenates were carried out using RT-PCR. It is established that the field strain PEDV, belonging to the North American grouping II of the second group of the PED virus strains, is an emergent highly pathogenic agent for non-immune newborn piglets. In the model of piglets’ infection it is established that the tested PEDV strain has a high virulence for newborn piglets, DCL is 1–10 virions and the incubation period is 18–26 hours. PED is acute with lethality to 100% within 68–72 hours after infection. According to the results of RT-PCR in washing from the surface of the bodies of flies, it is established that one of the ways piglets are infected and the environment contaminated with the PED virus is the spread of the pathogen by the flies M. domestica vicina Mcq. This leads to the induction of the emergent form of PED in piglets. The presence of PEDV in the homogenate from bodies of M. domestica caught in the focus of infection and the absence of virus reproduction in their body confirms the role of the house fly in the mechanical spread of PEDV in the external environment.
The spread of PEDV of pigs continues in various countries and regions of the world. PED was first registered in several areas of Ukraine in 2014. At present, there is a limited number of publications on the characteristics of the spread of the virus infection in Ukraine. Moreover, obtained research data do not clarify the epizootic situation as a whole. Having regard to the state of pig farm industry and permanent growth of losses caused with PEDV infection, the study of PED in Ukraine is relevant and important. Therefore, the goal of the work was to clarify the epizootic situation of PED in various areas of Ukraine. We studied the epizootic state of PED with a typical course in pig farms and the made a primary assessment of the relation of genetic groups between identified pathogens from distinct regions of the country where the highest intensity of the epizootic process was determined. The work was carried out in the Biosafety Center (Ukraine). To determine the epizootic situation of PED during 2016–2017 we collected samples of the blood serum and biological materials from pigs from 105 agricultural enterprises that are located in 85 administrative regions of Ukraine. In total we tested 543 serum samples and 591 samples of pathological tissues. The detection of PEDV was performed by PCR-RT. Serological diagnostics were tested with ELISA. Sequence analysis was performed according to Sanger. The results of sequences were analyzed in the FinchTV / Chromas program. The analysis of the epizootic features of PED in different areas of Ukraine for 2016–2017 established that PEDV is the main causative agent of the infection. An infection circulates among sensitive animals in pig farms and induces PED, which is difficult to control and weakly managed as a particularly dangerous emergent infectious disease of pigs. In 2016, 6.5% of administrative districts located in 12 of the 25 regions of Ukraine were included in the study, and in 2017, 10.8% of administrative districts located in the 14 regions of the 25 regions of the country were investigated. In general, during 2016 and 2017 1134 samples of blood serum and animal tissue were collected from 105 agricultural enterprises from 17.3% of the administrative regions of Ukraine. The obtained results showed that in 2016 PED was registered in 7 administrative districts from 4 regions of Ukraine, and in 2017 the infection was registered in 2 regions. The results of RNA sequence analysis of the PED virus identified the characteristics of the PEDV genes which reflect a high degree of homology with the Chinese strain BJ-2011-1. The analysis of the obtained results revealled the relation of PEDV circulating in Ukraine to the strains identified in the USA. Moreover, the samples of PEDV from Ukrainian pig farms have the sequences that belong to the North American clade II from the group of 2 strains of the PED virus. However, the PEDV observed in Ukraine is different from them by at least one nucleotide replacement of the gene which codes a protein of the S domain. Based on the obtained results, it can be assumed that in Ukraine the PED virus could have spread from East Asia.
The development of an epizootic situation for emergent infections is characterized by the emergence of the pathogen beyond the borders of countries and even continents. In some developed countries, the epizootic situation of PED is complex and tense. The emergence of the disease is facilitated by various factors: insufficient level of biosecurity and biosafety of farms, lack of information on the spread of infection, mechanisms of transmission of the pathogen, lack of effective means of specific prevention, etc. Changing the form of the epizootic process and the emergence of PED outbreaks in new territories have caused economic consequences for pork producers in the USA, China, South Korea, Thailand, Vietnam and others. The purpose of our work was to identify the historical aspects and epizootic situation about the PED. Scientific publications were used to analyze epizootic data. In studying the epizootic situation of PED in Ukraine, the results of laboratory studies of the Research Center for Biosafety and Environmental Control of the Agroindustrial Complex of the Dnipro State Agrarian and Economic University during 2015–2018 were used. The first is from the time of the description of the disease until 2010. During this period, there was a gradual spread of PED to European and Asian countries. Epizootic outbreaks of the disease were rare and isolated, and in certain territories were enzootic. The second – from 2010 and to the present. As a result of the genome mutation, the PED virus has acquired high virulence and emergent properties. There was a transcontinental introduction of the pathogen and rapid expansion of the nosoareal of the disease. The epizootic process of PED is characterized by epizootic and panzootic forms of manifestation. Despite preventive and well-being anti-epizootic measures, the epizootic situation regarding PED in Ukraine is consistently unfavorable: Zaporizhzhia, Cherkasy, Dnipropetrovsk and Kharkiv regions were identified as the most unfavorable in relation to the PED.
Porcine epidemic diarrhea virus (PEDV) has been circulating in Ukraine since 2014 and induces an especially dangerous viral infection with a lethal diarrheal syndrome in newborn piglets, with the primary occurrence of a foci of infection. The number of infected and lethality among diseased pigs 1-5 days of age can reach 100%, which together with the forced anti-epizootic measures brings significant economic losses. PED can spread to all pigs, but the emergent qualities of infectious pathology shows on newborn piglets. Effective and biosafety means of specific antiviral prophylaxis, cardinally stopping epizootic process is not registered, and etiopathogenetic therapy is not developed, therefore PED is a difficultly controlled emergent infection. With done up to three times a year over time appear stationary foci of infection, where the evolutionary changes in relationships occur quickly enough in the host-parasite system, since pigs are prolific and maturing animals and generational change. This leads to a significant variability in interpopulation relationships and the induction of biodiversity in the molecular mechanisms
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