Uticaj kolostralnih antitela na stepen imunosti prasadi vakcinisanih protiv klasične kuge svinja / Influence of colostral antibodes on immunity of piglets vaccinated against classical swine fiver

The aim of the research was to establish possible interference of colostral immunity with the production of own antibodies in piglets originating from vaccinated sows, after immunization with attenuated and subunit vaccine, as well as to examine whether post-vaccination immune response prevents the development of the disease, virus shedding and spread of the Classical Swine Fever (CSF). The experimental research included 60 piglets aged 45 days (18 non-vaccinated piglets originating from non-vaccinated sows and 42 non-vaccinated piglets originating from sows immunized with China (C)-strain of CSF virus). Experimental research was conducted in two phases: the first phase encompassed a trial with the attenuated (Cstrain) vaccine, whilst the second phase was focused on the application of a subunit vaccine. To determine presence of colostral antibodies in the serum of piglets, blood sampling was performed in 100 piglets aged 43 days. Based on serological examination (ELISA test), three experimental groups consisting of seven animals each were formed: Positive Group (confirmed presence o V 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26 and 28 post infection (dpi) to detect the presence of specific antibodies against CSF and viraemia (ELISA test and RT-PCR). The control of CSF virus shedding by vaccinated, artificially infected piglets was performed by RT-PCR analysis of oropharyngeal and rectal swabs (0, 2, 4, 6, 8 and 10 dpi). After death or sacrificing the animals, autopsy was performed along with the patho-morphological examination and organ- and tissue sampling to the purpose of determining the presence and distribution of CSF virus (ELISA and RT-PCR). Control of colostral antibodies in the blood sera from piglets at age 43 days, originating from sows immunized with C-strain of CSF virus, revealed their presence in 44% of investigated piglets, whereas negative or suspect finding was obtained in more then a half of the animals. In piglets vaccinated with C-strain of CSF virus, colostral antibodies suppressed the immune response to vaccine antigen. It was established that higher levels of colostral antibodies at vaccination are associated with more potent inhibition of active immunity development, i.e. lower level of synthesis of own antibodies after artificial infection. In the group of piglets vaccinated with C-strain of CSF virus, following artificial infection with virulent viral strain, shedding and contact infection in seronegative i.e. unvaccinated animals in cohabitation was detected. Application of subunit vaccine (the first dose at age 45 and second dose at age 73 days) in piglets originating from sows vaccinated with C-strain resulted in good active immune response in a view of synthesis of specific antibodies. In the group of piglets vaccinated with subunit vaccine following artificial infection virus shedding (carrier status) was confirmed but without contact infection in unvaccinated animals in cohabitation. Applying antigen ELISA test and RT-PCR analysis, in piglets vaccinated with attenuated and subunit vaccine, after artificial infection replication and excretion of virus was detected, without distinct clinical symptoms of CSF (latent infection). In the group of piglets vaccinated with subunit vaccine, by the control of oropharyngeal and rectal swabs the genome of CSF virus was detected (RT-PCR), and environmental contamination and horizontal transmission of the virus infection in the field conditions, however cannot be excluded. Applying of existing vaccination programs with the C-strain virus subclinically infected animals (carriers) may be present in the population and contribute to the spread VI of CSF. The results indicate that subunit vaccine may have potential application in the control of CSF in regions where the disease is enzootic. The obtained results strongly indicate that besides the immunoprophylactic measures, serological control is of paramount importance in conditions of enzootic infection, as it enables better insight in the immune status of the herd (colostral immunity) and better assessment of the effectiveness of vaccination against CSF.