Endemic course of epidemic diarrhea of pigs in the stabilized focus of infection

Abstract

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 initial appearance at the focus of infection. The number of infected cases and lethality among diseased piglets of 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 quality of infectious pathology appears in newborn piglets. No effective and biologically safe means of specific antiviral prophylaxis, which substantially halts the epizootic process is registered, and etiopathogenetic therapy is not developed, therefore PED is an emergent infection which is difficult to control. Over time there appear stationary foci of infection, where evolutionary changes in relationships in the host-parasite system take place fairly rapidly, since pigs are prolific and fast maturing animals able to replace each generation up to three times each year. This leads to a significant variability in interpopulation relationships and the induction of biodiversity in the molecular mechanisms of adaptation and processing of the viral genome. Clinically, genetic modifications of local variants of PEDV populations are manifested in the form of changes in epizootic peculiarities in the course of infectious pathology in different age groups of animals. Modifications of PEDV may be accompanied by a slight weakening of the intensity of the infectious process, a decrease in mortality and a decrease in the severity of the pathogenesis of diarrheal syndrome. At the same time, the age range of severe abdominal lesions expands from newborn piglets to fattening animals of older age groups of 28, 32, 70 days. Using a set of measures to combat the PED, including ``reverse feeding{''} recycled infected biomaterial from convalescent pigs, eradication of the pathogen from the environment of the host macroorganisms through a total disinfection regime and strict compliance with veterinary and sanitary rules of animal husbandry provide temporary positive results, but in theory this approach is incorrect, since contamination of animals leads to the dispersal of the virus and the formation of endemic foci of infection. The persistence of the virus in convalescent organisms is not fixed, the external inanimate environment can only be a mechanical factor in transmission of the pathogen preserving the viability of PEDV over time. Stabilization of the epizootic foci of infection is possible due to three factors: a) dissemination of the virus in ``reverse feeding{''}; b) preservation of the virus in the external environment as a result of poor-quality disinfection; c) occurrence of a non-immune element among the convalescent young gilts, who as a result of juvenile insufficiency of the immune system have a low titer accumulation of colostral antibodies to the virus received in the biomaterial through reverse feeding. Due to the lack of ``lactogenic immunity{''}, neonatal pigs as biological indicators for the presence of PEDV in the environment begin reproducing the virus in the enterocytes and develop a typical diarrheal syndrome PED.