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TDK conference 2008

Evolutionary studies of porcine circovirus genomes in the Central European region
Tombácz Kata - year 4
Department of Microbiology and Infectious Diseases
Supervisors: Attila Cságola, Tamás Tuboly


Porcine circovirus type 2 (PCV2) infections of swine herds worldwide are among those of the highest economic impact. PCV2 can be responsible for a variety of clinical conditions that are usually referred to as PCV2 associated diseases (PCVADs). The first known such disease, postweaning multisystemic wasting syndrome (PMWS), was initially described in Canada, in 1991. The PCV2 presence in North America, the eastern part of Asia and West Europe had already become enzootic, while the infection is still spreading towards the east from the western part of Europe. The clinical picture is changing accordingly; the porcine respiratory disease complex (PRDC) is becoming a more common PCVAD in the west, while PMWS is still dominating the east (including Hungary).

Porcine circovirus is an icosahedral, non-enveloped, single-stranded DNA virus, type one (PCV1) is non-pathogenic, whereas the strains of the pathogenic PCV2 type are responsible for all of the known PCVADs. PCV2 can also be divided into two groups: one of them (PCV2B) has a genome size of 1767 nucleotides (nt), while the other (PCV2A) is 1768 nt long. During the worldwide spread of PCV2 the temporal distribution of these groups is also changing. The viruses identified in the regions hit initially by the infection were of the PCV2A group, but new infections especially after the year 2003 are mostly due to PCV2B viruses. Significant genetic differences can be detected among viruses in epizootic areas, providing a background for the current study, where the epidemiological situation was analysed by comparing viral DNA sequences gathered between 1999 and 2007 in Hungary, Central and Eastern Europe, and based on the available literature, also worldwide, focusing on the status of the year 2007. DNA was isolated from the samples collected by our laboratory and an international team, amplified, sequenced and compared with PCV2 genomes from the GenBank database.

The first Central European sequences available in the GenBank were of Austrian and Hungarian origin from 2003 and were mainly of genotype PCV2A. Our study (comparing genotypes from the Czech Republic, Croatia, Hungary, Poland, Romania and Slovakia) indicated that by 2007 this situation has changed and PCV2B is present today in most swine herds of the region. This seems a worldwide tendency, the shorter genotype is spreading faster than the longer one and the genetic variability of PCV2 is decreasing. This suggests that although the adaptation of PCV to the swine species is slowing, it has not been finished yet.

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