Molecular characterization of type 1 porcine reproductive and respiratory syndrome viruses (PRRSV) isolated in the Netherlands from 2014 to 2016.

Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of a devastating pig disease present all over the world. The remarkable genetic variation of PRRSV, makes epidemiological and molecular analysis of circulating viruses highly important to review current diagnostic tools and vaccine efficacy. Monitoring PRRS viruses supports modern herd management by explaining the source of found viruses, either internally or externally from the herd. No epidemiological or molecular study has been published on circulating PRRS-viruses in the Netherlands, since the early nineties. Therefore, the objective of this study is to investigate circulating PRRS-viruses in the Netherlands in 2014, 2015 and 2016 on a molecular level by sequencing ORF2, ORF3, ORF4, ORF5, ORF6 and ORF7. The results demonstrate that the 74 PRRSV strains belong to PRRSV-1, but the diversity among strains is high, based on nucleotide identity, individual ORF length and phylogenetic trees of individual ORFs. Furthermore, the data presented here show that the phylogenetic topology of some viruses is ORF dependent and suggests recombination. The identity of the strain of interest might be misinterpreted and wrong conclusions may be drawn in a diagnostic and epidemiological perspective, when only ORF5 is analyzed, as performed in many routine sequencing procedures.

The prevalence of PCV2 viremia in newborn piglets on four endemically infected Dutch sow farms is very low.

Porcine circovirus type 2 (PCV2) systemic disease is currently considered one of the most relevant infectious diseases in swine industry worldwide from an economical point of view. Although piglets generally become diseased between 8 and 16 weeks of age, they can be infected much earlier, even already in utero. However, data on the prevalence of PCV2 infection in newborn piglets are very variable (lower than 40 up to 82%) and most of the studies have been performed in US. In European pig farms, using group-housing systems for gestating sows, a different herd PCV2 infection and immunological status may be expected and was recently reported in Germany. If that is the current scenario in most European farms, strategies to prevent horizontal transmission become essential for the control of the infection. The aim of our study was to determine the PCV2 prevalence in newborn piglets on 4 endemically infected farms in the Netherlands under European conditions. Eleven sows and 8 piglets per litter from 4 farms selected by their assumed PCV2 endemic infection status were sampled. Plasma from piglets was analysed with a PCV2 qPCR and serum from the sows was analysed with a commercial circovirus IgG ELSIA, circovirus IgM ELISA and PCV2 qPCR. In none of the samples from the piglets PCV2 was detected by the qPCR. None of the samples from the sows tested positive in the qPCR and circovirus IgM ELISA. The true- and apparent prevalence of IgG at herd and sow level were 0.75 and 0.81 and, 0.30 and 0.32, respectively, and no statistically significant association with sow parity was observed. These results reveal a very low prevalence of PCV2 in newborn piglets on endemically infected farms in The Netherlands, opening the opportunity of re-evaluation of the control measures applied in these farms.

Economic analysis of outbreaks of porcine reproductive and respiratory syndrome virus in nine sow herds.

The economic losses due to porcine reproductive and respiratory syndrome virus (PRRSv) outbreaks are reported in the literature to be substantially high, but recent figures are not available. The aim of this study was to quantify the economic effects of epidemic PRRSv outbreaks in Dutch sow herds. Nine sow herds were selected based on a confirmed PRRSv outbreak within those populations. The economic impact during the first 18 weeks after the outbreak was estimated by comparing the overall costs between pre- and postoutbreak periods, using different factors (production data, medication, diagnostics, labour, etc.). An outbreak of PRRSv resulted in a reduced number of sold pigs per sow of 1.7. The economic loss varied between €59 and €379 for one sow per 18-week period outbreak. The mean loss per sow per outbreak was €126. The costs after the outbreak varied significantly from €3 to 160 per sow, due to the different methods used by farmers to tackle PRRSv outbreaks. The calculated costs in this study correlate with the costs of the initial outbreak in The Netherlands of 98 per sow.

Detection of PRRSV circulation in herds without clinical signs of PRRS: comparison of five age groups to assess the preferred age group and sample size.

A cross-sectional study was conducted to find the most effective diagnostic approach to detect circulation of porcine reproductive and respiratory syndrome virus (PRRSV). The study was performed in 10 Dutch swine herds, with sows and fattening pigs or breeding stock. Herds did not experience clinical signs of PRRS during the last 6 months before sampling, but a PRRSV infection was confirmed at most 2 years before sampling. Blood samples were collected from 5 age groups: sows during early and late gestation, weaners at 9 weeks of age, fatteners or breeding stock at 16 and 22 weeks of age. For each category, 20 serum samples were examined; in total 100 serum samples per herd. Samples were analysed for PRRSV antibodies with ELISA (n=1002), and rt-PCR when ELISA S/P-ratios were above 1.5 (n=307) or below 0.4 (n=187; random selection from each age group). A logistic regression analysis was used to obtain factors associated with the probability of virus detection in a pig (PCR positive test result). Herd, ELISA-result, and age group were included as explanatory variables. Variables remained in the model when statistically significant. ELISA results showed that none of the herds could be considered to be free of PRRSV infection. Mean PRRSV seroprevalence in unvaccinated animals varied between 18% and 82%, and mean PRRS-virus prevalence varied between 0% and 41%. In only one of the 10 herds, no PRRS-virus could be detected. The odds of finding PRRS-virus in blood samples were 8.6 (95% CI, 5.3-13.9) in pigs of 9 weeks of age and 4.6 (95% CI, 3.0-7.0) in pigs of 16 weeks of age, compared with fatteners of 22 weeks of age. This result indicates that 9- to 16-week-old pigs are the preferred age group to detect PRRS-virus, in herds without clinical signs of PRRS. We concluded that PRRS-virus circulation could be detected in 8 out of 9 of the study-herds, with a relatively low number of blood samples. Testing 12 blood samples in both rt-PCR and ELISA, with 6 samples in pigs 9 weeks of age and 6 samples in pigs 16 weeks of age, will lead to a cost-efficient first evaluation of the PRRSV infection-status in herds without clinical signs of PRRS.

[Multiresistant Brachyspira hyodysenteriae in a Dutch sow herd]. / Multiresistentie bij Brachyspira hyodysenteriae-isolaten op een varkensvermeerderingsbedrijf in Nederland.

This case study describes the isolation ofa multiresistant strain ofBrachyspira hyodysenteriae in April 2007 in a Dutch sow herd with recurrent diarrhoea. Examination of faecal samples taken from 7-month-old breeding gilts with diarrhoea revealed the presence of resistance against tiamulin, lincomycin, tylosin, doxycycline, and tylvalosin (the active substance in Aivlosin) in four of five samples. Tiamulin resistance has not been reported in The Netherlands before. The repeated use of tiamulin on the affected farm was assumed to be the main cause of the development of resistance to the drug. The farmer was advised to adopt a medication strategy and to implement management practices that would prevent an ongoing cycle of infection on the farm. It is important that the Dutch swine industry appreciates that tiamulin-resistant strains of B. hyodysenteriae may be found on other farms as well. The appropriate and prudent use of antibiotics is essential in order to prevent the development of resistance against the last option left to cure B. hyodysenteriae infections: valnemulin.

Aujeszky's disease virus eradication campaign successfully heading for last stage in The Netherlands.

The Aujeszky's disease virus (ADV) eradication campaign in The Netherlands is based on compulsory vaccination and certification of ADV-free herds and consists of three stages: reduction of transmission of ADV, tracing and elimination of remaining sources of ADV, and, in the last stage prohibition of vaccination. This paper summarizes the progress made in the first two stages of the eradication. Between 1994-1999, ADV seroprevalence decreased sharply in all four regions in The Netherlands, both in the sow and the finishing pig population. In the sow population, the mean ADV prevalence in the northern, eastern and western regions decreased to less than 0.5% in the first quarter of 1998, and to approximately 1% in the southern region. For the finishing pig population, the mean ADV prevalence decreased to less than 0.6% in all four regions in the first quarter of 1998. The proportion of sow herds that were certified ADV-free increased steadily from approximately 40% in the last quarter of 1996 to 96% in the first quarter of 1999. The proportion of finishing pig herds that were certified ADV-free showed the same spectacular increase as in the sow population: from approximately 14% in the last quarter of 1996 to 90% in the first quarter of 1999. It is anticipated that the last stage of the ADV eradication campaign, stopping vaccination, will be achieved very soon. Monitoring wild boars for ADV between 1994 and 1999 indicated that ADV is uncommon within the wild boar population. Therefore, it seems that ADV infection in the wild boar population is not an important reservoir in The Netherlands.