Short communicationDetection of classical swine fever vaccine virus in blood and tissue samples of pigs vaccinated either with a conventional C-strain vaccine or a modified live marker vaccine
Introduction
Classical swine fever (CSF) is an often fatal viral disease affecting pigs and wild boar. The infection causes major economic losses, especially in countries with an industrialised pig production system. In case of an outbreak, a non-vaccination policy based on the strategy of stamping-out infected herds and controlling the movement of pigs and pig products has been followed so far in the European Union (Anon., 2001). However, several epidemics which occurred in Europe during the last decade have pointed out that eradication according to the present legislation may be very costly and ethically unacceptable, particularly in areas with a high pig density (Pittler et al., 1995, Van Temsche, 1995, Horst et al., 1999). Therefore, under certain conditions, emergency vaccination combined with control measures might be a future option for disease eradication and control (Anon., 2003). The EU has even established a Community stock of 1 million doses of live attenuated C-strain vaccine as well as an E2 subunit marker vaccine bank, showing the preparedness to use vaccines in case of emergency (Anon., 2003).
At present, two subunit vaccines based on the E2-glycoprotein of the classical swine fever virus (CSFV) and several conventional live attenuated vaccines are available (Hulst et al., 1993, Luetticken et al., 1998). However, both vaccine types have disadvantages which hamper eradication and control strategies. The conventional live attenuated vaccines do not allow a serological distinction between vaccinated animals and pigs reconvalescent from natural infection. Although these vaccines are very efficient, the differentiating infected from vaccinated animals strategy (DIVA) cannot be followed. The subunit vaccines permit discrimination from field-infection, but their immunogenic properties are rather poor. For a protective immune response, two vaccine applications are needed which in case of emergency vaccination (e.g., ring vaccination) might not be realizable (Depner et al., 2001, Uttenthal et al., 2001).
Reimann et al. (2004) described a modified live attenuated marker vaccine based on a bovine viral diarrhoea virus (BVDV) expressing the E2-protein of the CSFV strain Alfort187 (CP7_E2alf). This prototype vaccine combines the advantages of both above mentioned vaccine types. In first experiments with immunized domestic pigs and wild boar, it could be shown that the animals were completely protected against lethal CSFV challenge infection. Furthermore, using a commercial Erns-blocking-enzyme-linked immunossorbent assay (ELISA), vaccinated pigs could be discriminated from infected animals (Reimann et al., 2004). However, there are still open questions regarding diagnosis, immunogenicity and safety. This short communication describes the outcome of two experiments designed to further evaluate and compare the modified live prototype vaccine CP7_E2alf with the conventional C-strain vaccine. Emphasis was put on the detection of virus, antigen and genome in blood and tissue samples of pigs during the first 42 days after vaccination.
Section snippets
Experiment 1
Sixteen weaner pigs free of pestivirus antibodies were divided into two groups of eight pigs each (CP7_E2alf group and C-strain group). They were housed under identical conditions in two different units and were monitored for clinical signs, body temperatures and leukocyte counts throughout the experiment. At a weight of about 12 kg and an age of 2 months, the pigs received a single intramuscular vaccination. The first group was immunized with 2 ml [>102 50% protective doses (PD50) corresponding
Results and discussion
Prior to the application of emergency vaccination as an additional tool for control and eradication of CSF, comprehensive data concerning the vaccines and diagnostic tests to be applied are required. Especially for the development of novel CSF vaccines, vaccine safety and identification of vaccinated animals are of central importance. Application of live CSF vaccines presupposes substantial investigations on safety aspects, such as vaccine virus replication in the host and possible transmission
Acknowledgements
The studies were financially supported by the European Union “CSFV and Wild Boar” (SSPE-CT-2003-501599). We thank Ulrike Polenz for excellent technical assistance.
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2014, Virus ResearchCitation Excerpt :The C-strain vaccinated pigs show a slight decrease in IgM+ lymphocytes and CD4+ lymphocytes, and a moderate increase in monocytes, which is significantly different from those of non-vaccinated pigs (Lee et al., 1999). The C-strain is able to replicate in lymphoid organs, mainly in the tonsils, between 6 and 42 days post-vaccination (dpv) (Koenig et al., 2007). Completed protection in C-strain vaccinated pigs is launched as early as 5 dpv and lasts for 6–18 months (Franzoni et al., 2013; Graham et al., 2012a; Suradhat et al., 2007; van Oirschot, 2003).