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We aimed to estimate the proportion of the population infected with SARS-CoV-2 in the first year of the pandemic. The study population consisted of outpatient adults with mild or no COVID-19 symptoms, and was divided into subpopulations with different levels of exposures. Of the subpopulation without known previous COVID-19 contacts 4143, of the subpopulation with known COVID-19 contacts 594 persons were investigated. IgG- and IgA-seroprevalence and RT-PCR positivity were determined in context with COVID-19 symptoms. We hope to have contributed to the understanding of the significance of the asymptomatic and mild infections in the long persistence of the pandemic.

In recent years, the number of cases of disease caused by canine parvovirus 2 (CPV-2) in vaccinated dogs has increased. The aim of the present study was to identify CPV-2 strains present in Hungary. Forty-two out of 50 faecal specimens examined were positive, and 25 VP2 sequences were determined and analysed. Based on the current classification, the Hungarian viruses belong to New CPV-2a type, except two viruses that are recombinants of vaccine viruses and CPV-2a strains. The Tyr324Ile alteration was detected for the first time in Europe, and a "Hungarian-specific" substitution (Ala516Thr) was also identified in this study. The immunologically important parts of the currently spreading canine parvoviruses were examined and found to differ greatly from the vaccine strains that are widely used in Hungary.

Transmissible gastroenteritis (TGE) is a coronavirus-induced disease of pigs, characterised by diarrhoea and vomiting. The incidence of the disease had been decreasing since the late 1980s when deletion mutant variants (porcine respiratory coronavirus, PRCoV) of the virus emerged, repressing TGE gradually. Although disease manifestations are infrequent, the virus is still present in pig herds, causing sporadic outbreaks in a milder form. Identification and characterisation of the spike genes from TGEV and PRCoV, detected in such outbreaks, were performed in Hungary. Analysis of the amplified partial gene sequences showed that TGEV was present in herds with TGE clinical signs together with PRCoV. The sequences, apart from the deletions in PRCoV, were identical and at least two types of PRCoV spike proteins could be identified based on the length of the deleted sequence.

Recently a new group of circoviruses have been detected in tissues of Barbel fish and European catfish in Hungary. In our study circovirus genomes were screened in eight additional fish species for the detection and characterization of circoviruses. Two species of these bore circoviral sequences based on conventional PCR assay targeting the replication-associated protein coding gene fragments. Interestingly, the methods successfully used before failed to amplify other parts of the circular viral genome, suggesting the presence of partial, integrated genetic elements in the genome of the host. The successfully sequenced fragments of the Indian rohu (Labeo rohita) encoded mutations which may cause frameshifts or termination in the coding region described previously in other vertebrates. Phylogenetic analyses presumed that integration of the viral genetic elements might have progressed concurrently or following the diversification of cyprinid fish. Further studies on the nature of whole circovirus genomes and integrated elements may help to understand their potential role and evolution in different fish species.

Circular single-stranded DNA viral genomes had been identified worldwide in different species and in environmental samples. Among them, viruses belonging to the genus Circovirus of the family Circoviridae are present in birds and pigs, and recently, they were detected in barbels. The present study reports the identification of a new circovirus in fish. PCR amplification and sequencing were used to identify the novel circular DNA virus in European catfish (Silurus glanis). Full genome characterization and phylogenetic analysis showed that the virus belonged to the family Circoviridae and that it was distantly related to the previously described barbel circovirus.

Circoviruses are present worldwide in birds and pigs but their occurrence in fish has not yet been reported. Recently, increased mortality was observed in barbel fry (Barbus barbus) in Hungary. This paper reports the detection of previously unknown circular viral DNA genomes in barbels by the use of a circovirus-specific wide-range nested PCR. The analysis of two complete genomes (Barbel circovirus, BaCV1 and BaCV2) indicated that they belonged into a new genetic group within the family Circoviridae, distinct from known circoviruses and circovirus-like genomes. Their genome size was 1957 bases and contained two major ORFs similar to the capsid and replication-associated protein genes of circoviruses. A connection between the presence of the virus and clinical manifestations of the infection could not be proved.

Porcine circoviruses (PCV) are widespread in domestic pigs worldwide and there is growing information about the presence of PCV in other suid species. Based on serological studies with sera of wild boars, it was established that PCV1 was present in these animals and antibodies specific to PCV2 were also detected in wild boars living in captivity or in sylvatic areas, both with or without clinical signs of PMWS. Studies including PCV2 genome or antigen detection confirmed the previous findings. This is the first report about the presence of PCV in Transylvanian wild boar populations. Four hundred and sixty-nine samples were collected and grouped according to geographic origin, tested for the presence of PCV DNA using a real-time quantitative polymerase chain reaction assay, and 13.52% of the animals proved to be positive for one or in three cases both of the PCV genotypes. PCV2 was detected in all of the PCV-positive samples.

Porcine circoviruses (PCV) are present worldwide, infecting domestic pigs and wild boars alike. Studies under laboratory conditions indicated that PCV can be taken up by mice and the virus can replicate in these animals. The possible role of rodents in maintaining and transmitting PCV2 infection in the field has not been investigated yet. The present study reports the detection of PCV2, the pathogenic form of the virus, in mice and rats. A number of rodents, such as mice, rats and voles, were collected at PCV2-infected farms and also outside pig herds and tested for the presence of the virus by polymerase chain reaction (PCR). The results indicated that PCV2 can be present both in mice and rats (65.0% and 23.8% positivity, respectively) on the infected premises, but those rodents that were collected outside pig farms remained negative for PCV2.

To elucidate the spatiotemporal phylodynamics, dispersion and evolutionary processes underlying the emergence of novel porcine parvovirus 2 (PPV2), PPV3 and PPV4 species, we analysed all available complete capsid genes, together with ours, obtained in Europe. Bayesian phylogeography indicates that Romania (PPV2 and PPV4) and Croatia (PPV3) are the most likely ancestral areas from which PPVs have subsequently spread to other European countries and regions. The timescale of our reconstruction supported a relatively recent history of the currently circulating novel PPV species (1920s to 1980s) in the domestic or sylvatic host. While PPV2 strains exhibited a large genetic exchange characterized by significant recombination and gene flow between distinct regions and hosts, PPV3 and PPV4 showed a diversification reflected by the accumulation of geographically structured polymorphisms. The RNA-like evolutionary rates detected inter- and intrahost recombination and the positive selection sites provided evidence that the PPV2–4 capsid gene plays a prominent role in host adaptation.

Porcine parvovirus (PPV) is widespread among swine and is responsible for reproductive failure of susceptible sows, characterized by embryonic and fetal death. Studies showed that PPV in domestic pig is genetically diverse and some strains differ from the ones used for vaccination. Organ samples from wild boars and domestic pigs were collected in Transylvania (Romania) and tested for the presence of PPV by polymerase chain reaction. Positive samples were grouped and 14 from the wild boar and 1 from the domestic pig PPVs were selected for VP1/VP2 sequence analysis and comparison with available GenBank data. The molecular clock analysis revealed that PPV has a relatively recent evolutionary history, originated approximately 120 years ago and the main divergence occurred in the last 20–60 years. Phylogenetic and residue substitution analysis showed that the viruses could be divided into 6 distinct clusters and that wild boar PPVs were partially different and independent from domestic pig PPVs. PPVs of wild boars proved to be more diverse than viruses of domestic pigs. The presence of the highly virulent 27a-like PPV strains in wild boars was also detected.

A number of newly identified porcine parvoviruses had been described during the last decade, but the presence and prevalence of these viruses are unknown in Hungary and only partly known for Europe. The present study was conducted to detect and measure the prevalence of these viruses, namely porcine parvovirus (PPV) 2, PPV3, PPV4, porcine bocavirus (PBoV) 1, PBoV2, PBo-likeV and the 6V and 7V parvoviruses. The prevalence of PPV1 and porcine circovirus type 2 (PCV2) was also investigated. Faecal samples, blood serum samples, organ tissues, foetuses and semen were collected from different swine herds in Hungary and tested by polymerase chain reaction methods specific for the different viruses. The results indicated that all of the examined parvoviruses were present in Hungary, hence in Europe. The prevalence was 18.1% for PCV2, 0.5 % for PPV1, 6.4% for PPV2, 9.7% for PPV3, 6.4% for PPV4, 1.5% for PBo-likeV, 4.8% for PBoV1 and PBoV2 and 1.8% for 6V and 7V. Based on the analysis of partial PPV4 and PBo-likeV sequences, these viruses showed a high degree of sequence conservation, whereas PPV3 and the majority of PPV2, PBoV1, PBoV2, 6V and 7V sequences showed higher variability. Possible sites of recombination were also identified between PBoV1 and PBoV2 genomes.

Novel porcine parvoviruses showing the genetic characteristics of bocaviruses have recently been identified. The first such porcine bocavirus (PoBoV1), described as boca-like virus (PBo-likeV), was discovered in PMWS affected pigs in Sweden. Later, several other bocaviruses with divergent genomes were reported under various names in domestic pigs. This is the first report of the presence of bocaviruses in European wild boars. 842 wild boar samples originating from the Western region of Romania (Transylvania) were collected during the 2006/2007 and the 2010/2011 hunting seasons and tested for the presence of PoBoV1 by polymerase chain reaction and sequencing. The results showed 12.94% (109/842) overall positivity, with an increasing prevalence from the 2006/2007 (9.14%, 43/470) to the 2010/2011 (17.74%, 66/372) season (P < 0.01). Differences between the prevalence of the virus in 6–12-month-old-animal (77.06%, 84/109) and 12–36-month-old-animal (22.94%, 25/109) (P < 0.01) indicated that the infection occurred mainly in younger pigs. Comparative sequence analysis of partial VP1/2 genes from wild boars and those available in the GenBank showed only minor differences, indicating that PoBoV1 circulating within the wild boar populations and domestic pigs from different geographic regions were highly similar.

The aim of this study was to obtain prevalence estimates about the most important enteropathogenic bacteria: Lawsonia intracellularis, Brachyspira hyodysenteriae, Brachyspira pilosicoli, Salmonella enterica and Clostridium perfringens A and C in Hungarian farrow-to-finish pig herds. A total of 31 herds were selected, from where six pooled faecal samples, each containing three individual rectal faecal samples were collected from fattening pigs of 5–6 months of age. All 186 samples were examined by polymerase chain reaction (PCR) for the presence of the pathogens mentioned above. Lawsonia intracellularis was found in 29 herds (93.55%) and in 108 samples (58.06%); B. hyodysenteriae in 14 herds (45.16%) and in 23 samples (12.37%); B. pilosicoli in 19 herds (61.29%) and in 53 samples (28.49%); S. enterica in 17 herds (54.83%) and in 40 samples (21.50%). We detected the presence of C. perfringens A in 19 herds (61.29%) and in 46 samples (24.73%), while C. perfringens C was found in 8 herds (25.81%) and in 11 samples (5.91%). All examined herds were infected with one or more of these agents. Herds with diarrhoea in the mid-to late finishing phase had almost 10 times higher prevalence of B. hyodysenteriae than herds without such a history.