Subpolar North Atlantic western boundary density anomalies and the Meridional Overturning Circulation.

Changes in the Atlantic Meridional Overturning Circulation, which have the potential to drive societally-important climate impacts, have traditionally been linked to the strength of deep water formation in the subpolar North Atlantic. Yet there is neither clear observational evidence nor agreement among models about how changes in deep water formation influence overturning. Here, we use data from a trans-basin mooring array (OSNAP-Overturning in the Subpolar North Atlantic Program) to show that winter convection during 2014-2018 in the interior basin had minimal impact on density changes in the deep western boundary currents in the subpolar basins. Contrary to previous modeling studies, we find no discernable relationship between western boundary changes and subpolar overturning variability over the observational time scales. Our results require a reconsideration of the notion of deep western boundary changes representing overturning characteristics, with implications for constraining the source of overturning variability within and downstream of the subpolar region.

A sea change in our view of overturning in the subpolar North Atlantic.

To provide an observational basis for the Intergovernmental Panel on Climate Change projections of a slowing Atlantic meridional overturning circulation (MOC) in the 21st century, the Overturning in the Subpolar North Atlantic Program (OSNAP) observing system was launched in the summer of 2014. The first 21-month record reveals a highly variable overturning circulation responsible for the majority of the heat and freshwater transport across the OSNAP line. In a departure from the prevailing view that changes in deep water formation in the Labrador Sea dominate MOC variability, these results suggest that the conversion of warm, salty, shallow Atlantic waters into colder, fresher, deep waters that move southward in the Irminger and Iceland basins is largely responsible for overturning and its variability in the subpolar basin.

[Risk factors for clinical signs of PMWS and PDNS in pigs in The Netherlands: a case-control study]. / Bedrijfsrisicofactoren voor varkens met klinische verschijnselen van PMWS of PDNS in Nederland : een case-control onderzoek.

Potential risk factors for clinical signs of post-weaning multisystemic wasting syndrome (PMWS) and porcine dermatitis and nephropathy syndrome (PDNS) in pigs in the Netherlands were investigated in a matched case-control study using a questionnaire (personal interview). Eighty-two pig farmers were questioned about management, hygiene, husbandry systems, disease history, and preventive health care. In this study, 30 pig herds with (cases) and 30 pig herds without (controls) characteristic clinical signs of PMWS were compared. For PDNS, 11 pig herds with (cases) and II pig herds without (controls) characteristic clinical signs of PDNS were compared. Univariate analysis (P < 0.10) showed that the following occurred relatively more often in the PMWS case herds than in the control herds: 1) clinical signs of PDNS, porcine reproductive and respiratory syndrome (PRRS), porcine parvovirus (PPV) infections, meningitis, coccidiosis, and pre-weaning diarrhoea observed by the farmer; 2) vaccination against PRRS and mycoplasma; 3) non-optimal climatic conditions in the nursery rooms, a large variation in weaning age, a high occurrence of cross-fostering of piglets, a large number of sows with lactation problems, poor colostrum intake by piglets; and 4) (historical) use of breeding stock (including semen for artificial insemination) of Anglo-Saxon origin. In the final multivariate statistical model, one variable remained significantly associated with PMWS case herds, namely, the presence of clinical signs of PRRS (and/or the associated use of vaccination against PRRS). It should be noted that in almost all cases animals were vaccinated against PRRS because of clinical signs of PRRS that appeared a few months after the first occurrence of clinical signs of PMWS. This excludes PRRS vaccination as a primary factor in causing PMWS. Analysis of the PDNS case-control data showed comparable results with those of the PMWS study. In the final statistical model, the presence of clinical signs of PRRS (and/or the associated use of vaccination against PRRS) was significantly associated with PDNS case herds.

The presence of co-infections in pigs with clinical signs of PMWS in The Netherlands: a case-control study.

In this study, 60 pigs with clinical signs of post-weaning multisystemic wasting syndrome (PMWS) from 20 different pig herds and 180 control pigs (without clinical signs of PMWS) were examined to get more insights into the frequencies of porcine circovirus 2 infections and the presence of co-infections in pigs with and without clinical signs of PMWS in the Netherlands. Porcine circovirus type 2 was detected in 100% of the pigs with clinical signs of PMWS by virus isolation and/or PCR and in 50% of the pigs from PMWS-free herds. There was an association between the levels of infectious PCV2 and/or PCV2 DNA load and the severity of clinical signs as described for PMWS. A high variation in PCV2 antibody titres was found in the clinically affected pigs, and 27% of these pigs did not mount PCV2 antibody titres higher than 1:200. A concurrent infection of PCV2 and porcine reproductive and respiratory syndrome virus (PRRSV) was found in at least 83% of the pigs with clinical signs of PMWS and in 35% of the pigs from PMWS-free herds. Co-infections of European- and American-type PRRSV were detected only in PMWS herds and in one control herd with a history of PMWS clinical signs.

Excessive porcine circovirus type 2 antibody titres may trigger the development of porcine dermatitis and nephropathy syndrome: a case-control study.

In a case-control study, the role of porcine circovirus 2 (PCV2) and putative co-factors in the development of porcine dermatitis and nephropathy syndrome (PDNS) were investigated. Pigs with and without PDNS were examined for macroscopic lesions and histopathology. In addition, organs and tissues were collected at necropsy and examined for the presence of fibrinous deposits (immune complexes), CD8+ cells, and for the presence of bacterial and viral infections. Results from PDNS cases were compared with those of three control groups comprising pigs without clinical signs of PDNS and selected from; (1) the same compartment as PDNS cases, (2) another compartment but in the same PDNS herd, and (3) a control herd without any history of PDNS or post-weaning multisystemic wasting syndrome. Macroscopic and histopathological lesions found in PDNS cases were comparable to those previously documented for PDNS e.g. skin lesions and renal lesions representing glomerulonephritis associated with fibrinous deposits and to a lesser extent with interstitial nephritis. PCV2 was detected by PCR in 100% of the PDNS cases, mainly in lymph nodes and tonsils, and in 63% of the control pigs from PDNS free herds. Virus isolation did not reveal infectious PCV2 in all cases. In PDNS affected pigs the PCV2 serum antibody titres were consistently extremely high and the mean PCV2 antibody titre in PDNS pigs was significantly higher than the mean PCV2 antibody titres in pigs from all 3 control groups. Immunohistochemical investigation of kidneys from PDNS affected pigs revealed an increased accumulation of IgG1 + IgG2 and IgM, the complement factors C1q and C3, but also an increase of CD8+ cells. The amounts of IgA and the complement factor C5 in kidneys of PDNS pigs were only slightly increased as compared to control pigs. This study demonstrates that PCV2 infections can result in extremely high PCV2 antibody titres and that PCV2 is a candidate as primary agent in the development of PDNS. The causative physiological basis for PDNS may be the excessive levels of PCV2 antibodies.

Isolation and characterization of porcine circovirus type 2 from pigs showing signs of post-weaning multisystemic wasting syndrome in The Netherlands.

Pigs with wasting syndrome were examined for macroscopic and histopathological lesions, and for porcine circovirus (PCV). Histopathological lesions were comparable to those previously documented for post-weaning multisystemic wasting syndrome (PMWS). In addition, in seven out of ten examined PMWS-affected pigs focal-to-slight mononuclear meningitis and focal cerebral mononuclear infiltrates (4 out of 10) were observed. A virus was isolated from organs and sera from pigs showing wasting syndrome. An immunoperoxidase monolayer assay and an indirect immunofluorescence assay were performed on the infected PK-15 and Dulac cell cultures, respectively, and both assays indicated the presence of PCV type 2 (PCV2). The nested-polymerase chain reaction (nPCR) technique, based on the use of PCV2 specific oligonucleotides, revealed specific amplified products of 481 bp. Nucleotide sequence analysis of the entire genome of the Dutch PCV isolate 24657 NL showed a homology with known nucleotide sequences of porcine PCV type 1 (PCV1) and PCV2 isolates of 77.1% and >96%, respectively. This is the first report of the isolation and characterization of PCV2 in PMWS-affected pigs in the Netherlands.

A specific and sensitive PCR assay suitable for large-scale detection of toxigenic Pasteurella multocida in nasal and tonsillar swabs specimens of pigs.

A polymerase chain reaction (PCR) assay for the detection of toxigenic Pasteurella multocida in nasal and tonsillar swab specimens collected from pigs was developed. Target DNA was isolated with guanidine thiocyanate and diatomite, and 2 primer sets derived from sequences in the gene that encodes the dermonecrotic toxin of P. multocida were used simultaneously. The method was adapted to microtiter plate format allowing large-scale use of the PCR assay. To identify false-negative test results caused by failure of amplification, a positive control template was constructed that was spiked to each DNA sample. The PCR assay was evaluated with clinical samples and compared with 2 routinely used methods for detection of toxigenic P. multocida: isolation from a selective agar and direct detection of the toxin in extracts of primary cultures by an enzyme-linked immunosorbent assay (ELISA). The sensitivity of the PCR assay was tested with 346 nasal and tonsillar swabs specimens collected from pigs of 9 herds known to be infected with toxigenic P. multocida. Toxigenic P. multocida was isolated from 22 specimens, only 28 specimens tested positive in ELISA, but 40 tested positive in the PCR assay; thus the PCR assay is the most sensitive of the 3 methods. The specificity of the PCR assay was tested with 372 swab specimens collected from pigs of 6 herds certificated to be free from toxigenic P. multocida. Toxigenic P. multocida was not isolated from any of these specimens, all tested negative in ELISA, and 370 tested negative in PCR. The 2 positive specimens came from 2 pigs of 1 litter and tested only weakly positive in the PCR assay. From these results, it was concluded that the PCR assay is not only highly sensitive but also highly specific.

[Testing area Wehl: study of risks of contacts in behalf of foot-and-mouth disease]. / Proefgebied Wehl: onderzoek naar risico's van contacten ten behoeve van mond- en klauw-zeerbestrijding.

A study on contacts between livestock holdings was conducted in a geographically defined area of 4 by 6 km in the Netherlands. The farmers were asked to record all contact on and off farm during a period of 2 weeks. The number of contacts in the 2 week period was high, on average 91.8 contacts per farm. The risk of spreading foot-and-mouth disease on or off the farm was greater for cattle farms than for swine farms. Relatively more people had contact with the animals while visiting cattle farms, thereby causing the higher risk. Most contacts occurred over short distances. Almost 50% of the contacts were within the research area. This finding confirms the importance of restricted areas around farms with foot-and-mouth disease infections.

Estimating sample sizes for a two-stage sampling survey of seroprevalence of pseudorabies virus (PRV)-infected swine at a regional level in The Netherlands.

In the European Union, vaccination campaigns against Pseudorabies virus (PRV) in swine have been started to eradicate PRV. Specific sampling designs are needed to monitor PRV seroprevalence at a regional level. This paper demonstrates how sampling theory can be applied to design a disease seroprevalence survey, using PRV as an example. In the spring of 1994, the four regions in the Netherlands covered by the regional Animal Health Services were monitored with respect to PRV seroprevalence. Per region, blood samples from approximately 1400 herds, with two animals per herd, were collected. The sampling design accounted for stratification by fattening pig and sow population within each region. The regional PRV seroprevalence of swine in the Southern region was the highest (24.9%), closely followed by the PRV seroprevalence of swine in the Eastern region (20.5%). These regions have the highest density of swine in the Netherlands. The PRV seroprevalence in the Western and Central region (11.7%) was about half of the seroprevalence in the Southern and Eastern regions; the lowest regional PRV seroprevalence was observed in the Northern region (3.5%). The Northern part also has the lowest pig density. The PRV seroprevalence was approximately two times higher in sows than in fattening pigs.

PRRS: effect on herd performance after initial infection and risk analysis.

In early 1991, the Dutch pig industry was struck by Porcine Reproductive and Respiratory Syndrome (PRRS). Data from 91 breeding and/or farrow to finish herds that were positive for PRRS were used to investigate the impact of PRRS on productivity and to evaluate the relationship between PRRS and farm and management factors. The farms involved used the CBK management information system. Results show that herd performance was severely affected by PRRS over a period of 4-6 months. A rough economic evaluation, using a fixed price for piglets, indicated that the economic loss on the 91 farms averaged Hfl. 215,- (= 65 pounds) per sow per year due to a decreased number of piglets raised per sow per litter, a prolonged farrowing interval and a higher replacement rate of sows. The analysis of possible risk factors did not reveal major factors that could be helpful in reducing the negative effect of PRRS on Piglets Reared per Sow per Year and on the Economic Index of farms experiencing an outbreak of PRRS.

Intranasal administration of Pasteurella multocida toxin in a challenge-exposure model used to induce subclinical signs of atrophic rhinitis in pigs.

A challenge-exposure model was developed for dose-dependent induction of subclinical (moderate) atrophic rhinitis (AR) in conventionally raised Dutch Landrace and Large White pigs, about 4 weeks old. Under favorable climatic and housing conditions, pigs were intranasally challenge-exposed with Pasteurella multocida-derived toxin (Pm-T) 3 days after pretreatment by inoculation with 1% acetic acid. Pigs were challenge-exposed with 1 of the following Pm-T doses: 0 (control), 5, 13, 20, or 40 micrograms of Pm-T/ml of phosphate-buffered saline solution (PBSS), 0.5 ml/nostril/d on 3 consecutive days. Five weeks after challenge exposure, subclinical (moderate) AR status was defined as intermediate conchal atrophy (grade 2 for ventral conchae on a 0 to 4 scale and grade 1 or 2 for dorsal conchae on a 0 to 3 scale, respectively) and perceptible difference in change in brachygnathia superior (cBS) between control and challenge-exposed pigs between the beginning and end of the study. All Pm-T-exposed pigs had nasal damage that was dose-dependent. The higher Pm-T doses resulted in higher ventral conchae atrophy and dorsal conchae atrophy scores. The cBS increased with applied Pm-T dose, resulting in significant (P < 0.05) differences between controls (3.88 mm) and the 13-, 20-, and 40-micrograms Pm-T-treated groups (7.77, 6.58, and 7.98 mm, respectively). In response to the applied dose, weight gain per week for Pm-T-exposed pigs was lower than that of controls after week 3 (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

[Atrophic rhinitis A.D. 1991]. / Atrofische rhinitis A.D. 1991.

In the Netherlands the Central Veterinary Institute (CVI) and the Animal Health Services carried out investigations on aetiology, pathogenesis, therapy and prevention of Atrophic Rhinitis (AR) since 1970. Since the discovery of AR toxin in AR pathogenic P. multocida in SPF piglets, quicker and cheaper tests were developed e.g. the mouse test and guinea pig skin test. Today ELISA-tests with poly- and monoclonals are also available. The CVI carried out DNA probes and is developing a PCR-test. Tests to detect a natural infection were difficult to develop. The SN test by Bechmann, the skin test by Schimmelpfenning and the ELISA test by Foged give some perspectives. From investigations with B. bronchiseptica in piglets, it appears that the role of this germ is overestimated in the development of AR. On 16-week-old pigs an infection with AR toxigenic P. multocida caused conchae atrophy and septum deviation within 4 weeks. This fact has to be taken into account concerning the preventive medications in piglets. Only high maternal antibody titres against the AR toxin are able to protect the piglets for a sufficiently long period. Conchae atrophy and brachygnathia superior are indicators for suspicion of AR but do not prove the diagnosis of AR. By means of selective agars the isolation of P. multocida from nose, tonsils and lungs could be improved. The incubation period of clinical AR may last longer than two years. The AR pathogenic P. multocida is predominantly transmitted by pigs, incidentally also by rabbits, cattle, sheep, goat, poultry, dogs and cats. Humans can get infected and diseased. The AR pathogenic P. multocida has to be classified as a zoonosis. By way of stamping out and air filtering the transmission can be prevented. Vaccination cannot avoid an infection with the AR pathogenic P. multocida. The Animal Health Services developed a program to certify breeding herds 'free of AR pathogenic P. multocida'.

[Serological study of the presence of Actinobacillus pleuropneumoniae antibodies serotype 2 and 9 on pig-breeding farms in the provinces of North Brabant and Overijssel (The Netherlands)]. / Serologisch onderzoek naar het voorkomen van antilichamen tegen Actinobacillus pleuropneumoniae-serotype 2 en 9 op varkensfokbedrijven in de provincies Noord-Brabant en Overijssel (Nederland).

Serological studies for the presence of CFT antibodies to Actinobacillus pleuropneumoniae, both to serotype 2 and serotype 9, were done in twenty-five sows on each of thirty pig-breeding farms in the provinces of North Brabant and Overijssel. Antibodies to serotype 2 and/or serotype 9 were detected in one or several sows on forty-two out of sixty farms. Similar findings were recorded on eighteen and twenty-four farms respectively in the provinces of Overijssel and North Brabant; the number of herds showing positive reactions to serotype 2 was sixteen and twenty-three in these provinces respectively, that showing positive reactions to serotype 9 being six and five respectively. An average proportion of nineteen per cent of the samples taken on the farms having serologically positive animals was positive for serotype 2, and twelve per cent for serotype 9. Only one of the twenty-five animals on twelve farms was found to be positive; serotype 2 was present in ten cases and serotype 9 in two cases. A marked effect of the size of the herds on the serological status of the farms was not observed in the present studies. This was also true of the purchasing policy; there was no difference between farms which had no longer purchased any breeding pigs for an average period of seventeen years and for one year respectively. Clinical symptoms of an infection due to Actinobacillus pleuropneumoniae were only reported as occurring on two farms having serologically positive animals.

Atypical Pasteurella strains producing a toxin similar to the dermonecrotic toxin of Pasteurella multocida subspecies multocida.

This paper is the first report of the production of a dermonecrotic toxin by pasteurella strains that do not belong to the species Pasteurella multocida subspecies multocida. Four strains, isolated from cattle with atrophic rhinitis, were characterised phenotypically. The strains were related to pasteurellaceae, but their taxonomic position remained unclear. The strains produced a toxin that caused a haemorrhagic dermonecrosis in guinea pigs and was lethal to mice. Both effects were neutralised by an antiserum against the purified dermonecrotic toxin of P multocida subspecies multocida. Western blot analysis of culture filtrates of the bovine strains revealed a protein, with the same molecular weight as dermonecrotic toxin, which reacted with both polyclonal and monoclonal antibodies against the toxin. In an immunodiffusion test, anti-dermonecrotic toxin serum did not discriminate between the toxin of the bovine strains and the toxin of P multocida subspecies multocida. It is concluded that these atypical pasteurella strains produce a toxin that is closely related to the dermonecrotic toxin of P multocida subspecies multocida.

Prevention of atrophic rhinitis in piglets by means of intranasal administration of a live non-AR-pathogenic Bordetella bronchiseptica vaccine.

The effect of intranasal vaccination of piglets with live non-AR-pathogenic Bordetella bronchiseptica (BB-) against Atrophic Rhinitis (AR) was investigated in a preliminary investigation and in a field trial. In the preliminary investigation 2-day-old SPF piglets (n = 13) were vaccinated. Three weeks after vaccination, challenges were carried out by means of a spray with an AR-pathogenic B (BB+) or an AR-pathogenic Pasteurella multocida (PM+) broth-culture. Four weeks later the piglets were necropsied and examined for atrophy of the ventral conchae (AVC). In contrast with the non-vaccinated SPF piglets, the vaccinated piglets showed a strong and significant reduction of AVC, after both BB+ and PM+ challenge. In the field trial three groups were formed by drawing lots: ten litters (82 piglets) were vaccinated; ten litters (92 piglets) formed the control group and 11 litters (104 piglets) were treated with a placebo. The litters were spread over two units. In unit 1 AR and PM+ were demonstrated incidentally, in unit 2, however, persistently. BB+ was isolated equally frequently in both units. Clinical and bacteriological examinations were done in piglets of 3, 6 and 8 weeks of age. Necropsy examinations was carried out in 41 piglets of 8 weeks of age, chosen randomly by drawing lots. In spite of a second vaccination at the age of 3 weeks, BB- was not well established; this was possibly caused by maternal BB antibodies. In the control and placebo groups PM+ was isolated earlier and more frequently than BB+. It appeared that AVC was correlated more strongly with PM+ than with BB+ infection in the field trial. The percentage of piglets with Brachygnathia superior (BS) at the age of 8 weeks indicated the AR situation in the herd. Although a significant reduction of AVC was determined in unit 2, it was not sufficient to indicate that this method of intranasal vaccination is useful in the prevention of AR in practice.

A field evaluation of Nobi-Vac atrophic rhinitis vaccine.

A field trial was carried out with Nobi-Vac AR vaccine in 11 swine breeding herds. One herd suffered from severe B. bronchiseptica (BB+) rhinitis in piglets, while no clinical Atrophic Rhinitis (AR) was observed. Ten herds were described as AR problem herds, because clinical AR was observed for at least 1 year in spite of the fact that medication of sows and piglets was carried out and adequate housing and management systems were available in most herds. BB+ was isolated in 9 of these 10 farms and the AR pathogenic P. multocida (PM+) in all these farms. The trial started when piglets were born of sows which had been vaccinated 3 times. All piglets between 7 and 10 weeks old were examined clinically for AR. Nasal swabs from 20 pigs on each farm were screened bacteriologically for BB+ and PM+ every other month. A severe reoccurrence of AR was found in 2 of the 10 AR problem farms. In these 2 herds the 'all in-all out' system was not applied in farrowing and weaning houses. In the 8 other AR problem herds the percentage of pigs with AR decreased significantly below the average level of 1% per year. The percentage of pigs infected with BB+ and PM+ also decreased significantly. PM+ was significantly related to the percentage of clinical AR piglets. Seasonal effects contributed to a minor extent to the percentage of AR piglets. After 2.5 years of this trial PM+ could not be isolated during the last 12 months in six of the remaining AR problems herds. The conclusion is that Nobi-Vac AR vaccination of the sow gave protection against clinical AR in piglets on those farms (80%) which provided adequate housing and management systems.