Search

The Irminger Current (IC) brings relatively warm and saline waters northward in the North Atlantic subpolar gyre, contributing to the upper limb of the Atlantic Meridional Overturning Circulation. The IC is a two‐core current with surface‐intensified velocities. The eastern core, closest to the Reykjanes Ridge, is warmer and more saline than the western core. To investigate the source waters of the two IC cores, using a 1/10° ocean model, we track Lagrangian particles released in the IC at OSNAP East (∼59.5°N) in the upper 1,000 m backward in time for one model year. Over a 1‐year time scale, nearly all particles are sourced from nearby regions of the Irminger Sea and Iceland Basin. Those seeded in the western IC core mostly originate from the Irminger Sea (83%), while those in its eastern core mostly originate from the Iceland Basin (69%). Iceland Basin water feeding the IC predominantly crosses the Reykjanes Ridge near 57°N and 59°N. Generally, particles from the Irminger Sea are colder and fresher than particles from the Iceland Basin. The fraction of waters from the Iceland Basin and the Irminger Sea varies from month to month. So, to explain monthly variations of the two IC cores at the OSNAP East line, changes in hydrographic properties in both basins as well as their contributions must be considered. Based on this model study, we interpret the Irminger Sea circulation as a basin‐wide recirculation with an increasing contribution of Iceland Basin waters toward the ridge which is subject to monthly variations. Plain Language Summary: The Irminger Current (IC) brings warm and saline waters northward along the western side of the Mid Atlantic Ridge. The IC is a two‐core current where the eastern core is warmer and more saline than the western core. Here, we investigate the sources of the IC with a focus on the different water mass properties of the two cores to understand the observed transport variability of the IC. We release virtual particles in the IC in an ocean model simulation with a 1/10° resolution and track their paths backward in time for 1 year. We find that the western core has its main source in the Irminger Sea with colder and fresher properties while the eastern core is mostly fed by warmer and more saline waters from the Iceland Basin. The mix of waters from the Iceland Basin and the Irminger Sea varies from month to month. So, to explain monthly variations of the two IC cores at the OSNAP East line, this model suggests that changes in hydrographic properties in both basins as well as their contributions must be considered. Key Points: Both Irminger Current (IC) cores at 59.5°N are fed by the Irminger Sea and Iceland Basin, with more Irminger water in the western coreIceland Basin water feeding the IC at that latitude predominantly crosses the Reykjanes Ridge near 57°N and 59°NThe ratio of waters from the two basins varies on a monthly time scale which may lead to hydrographic and transport variability in the IC [ABSTRACT FROM AUTHOR]

The lower limb of the Atlantic meridional overturning circulation (AMOC) is the equatorward flow of dense waters formed through the cooling and freshening of the poleward‐flowing upper limb. In the subpolar North Atlantic (SPNA), upper limb variability is primarily set by the North Atlantic Current, whereas lower limb variability is less well understood. Using observations from a SPNA mooring array, we show that variability of the AMOC's lower limb is connected to poleward flow in the interior Irminger Sea. We identify this poleward flow as the northward branch of the Irminger Gyre (IG), accounting for 55% of the AMOC's lower limb variability. Over 2014–2018, wind stress curl fluctuations over the Labrador and Irminger Seas drive this IG and AMOC variability. On longer (>annual) timescales, however, an increasing trend in the thickness of intermediate water, from 2014 to 2020, within the Irminger Sea coincides with a decreasing trend in IG strength. Plain Language Summary: In the subpolar North Atlantic, warm salty waters get transported northwards by the upper branch of the meridional overturning circulation. As they travel northwards, they transform: cooling, densifying, and sinking. The cooler deeper waters then get transported back southwards toward the equator in the lower branch of the overturning circulation. The transformation and transport of these waters plays a critical role in our climate system. However, the lower branch of the overturning circulation and the mechanisms controlling how it changes are still not well understood. Observations from a fixed array of moorings between Greenland and Scotland are used here to identify the interior (away from land boundaries) Irminger Sea as a region important for the overturning's lower branch. Specifically, we find that a closed system of currents in the western Irminger Sea, known as the Irminger Gyre, plays an important role in the overturning's variability. Gyre strength is then linked to the recirculation of newly transformed waters that get exported as part of the overturning's lower branch. Finally, we investigate the impact of the atmosphere on Irminger Sea circulation and find that fluctuations of the winds are important drivers of change in this gyre and the overturning. Key Points: The interior Irminger Sea, where the poleward limb of the Irminger Gyre (IG) dominates, is a hotspot for the overturning's lower limb variabilityA trend in IG transport is linked to deep intermediate water masses found in the Irminger SeaWind stress curl over the Labrador and Irminger Seas drives IG and Atlantic meridional overturning circulation variability [ABSTRACT FROM AUTHOR]

The Irminger Current (IC), flowing northeastward along the western flank of the Reykjanes Ridge, is an important component in the overturning of the North Atlantic subpolar gyre. A 2‐year (2014–2016) time series from moored observations shows that the IC consists of two highly variable current cores. A subsampling experiment, using an ocean reanalysis, showed that this current's variability is adequately captured by the array. The two current cores contribute nearly equally to the mean volume transport. The total 2‐year mean transport was found to be 10.6 Sv with a standard deviation of daily (monthly) values of 9.2 Sv (4.4 Sv) and a standard error of 1.4 Sv. Mean heat and freshwater transport were 0.21 PW and −22.5 mSv, respectively (Sref = 34.92). The volume transport is strongest in spring, and the average over the first year (8.6 Sv) was lower than that of the second year (12.4 Sv), coinciding with an increase in the density gradient over the array in the second year. The variability of the total transport is dominated by variations in the western core, while the warmer, saltier eastern core contributes more to the heat and (negative) freshwater transport. During the two observed winters, which were marked by exceptional deep convection in the central Irminger Sea, mixed layer deepening down to 400 m depth and outcropping of the 27.7 kg m3 isopycnal were observed within the IC.Plain Language Summary: The Irminger Current flows northeastward along the Reykjanes Ridge in the Irminger Sea. It transports warm saline water originating from the North Atlantic Current in the upper layers and deep waters coming from the overflows on the Iceland‐Scotland Ridge. This paper describes the first year‐round moored observations of velocity, temperature, and salinity of this current system. These new observations show that the Irminger Current consists of two cores that contribute equally to the mean transport. The core closer to the top of the ridge is more stable and transports warmer, more saline water, while the core closer to the center of the Irminger Basin is more variable in location and transport. During the observed winters, strong atmospheric cooling created deep mixed layers down to 400 m at the mooring locations. This observed cooling and densification of the upper ocean waters indicate that this current system is an important contributor to the overturning in the Northeastern Atlantic.Key Points: First year‐round observations of the two‐core Irminger Current over the Reykjanes Ridge show a mean transport of 10.6 ± 1.4 Sv (st error)IC transports are highly variable with a std of 9.2 Sv (daily values) and 4.4 Sv (monthly values); the western core is the most variableMixing to densities near 27.7 kg m−3 occurred over the array in both winters (deepest in the west), contributing to the overturning [ABSTRACT FROM AUTHOR]

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.

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.

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.

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 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.

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.

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.

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.

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)

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'.

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.

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.

The piglets of two multiplier herds (M and B) showing clinically apparent atrophic rhinitis (AR) were treated by the nasal-spray method. A solution of oxytetracycline hydrochloride (OTC, 50 mg/ml.) was used as a spray fluid. The course of the disease in the herds was followed by studying the development of foreshortening of the upper jaws in the heads. Brachygnathia superior (BS), from the eighth to tenth week of life. Efforts were made to gain an impression of the effects of treatment on the frequency with which Bordetella bronchiseptica and Pasteurella multocida were isolated by bacteriological examination of the nose. Treatment by the nasal-spray method up to an age of approximately five weeks, of seven weeks were treated at least once weekly. The proportion of animals in which the disease was clinically apparent decreased from 25 per cent to 0 per cent in herd M and from 41 per cent to 0 per cent in herd B. Treatment by the nasal-spray method up to an age approximately five weeks, in which feed medicated with OTC was also given up to the age of eight to ten weeks also had a satisfactory effect. The frequency with which Bordetella bronchiseptica and Pasteurella multocida were isolated, was reduced by treatment, elimination of these agents was not.

Two hundred eight-week-old piglets from 20 pig-breeding farms, on which the clinical findings did not provide any justification for suspecting the presence of atrophic rhinitis (AR), were examined for this disease. Clinical parameters were brachygnathia superior (BS) and snout-distorsion (KD). Piglets with BS (n = 48) were observed on 13 farms and with KD on 8 farms. Morbid anatomical parameters were deviation of the nasal septum (SD) and atrophy of the ventral conchae (AVC). SD was observed in 76 piglets from 17 farms. Piglets with AVC gradation greater than or equal to 1 were recorded on 20 farms and with grade greater than or equal to 3 on 12 farms. The average gradation of AVC over all farms was 1.3 varying from 0.2 to 2.9. Bacteriological studies were done in the piglets for Bordetella bronchiseptica (BB) and AR pathogen Pasteurella multocida (PM+). The score of AVC showed a significant increase on farms on which infections with PM+ and BB was present. It is indicated that pig-herds with an average AVC gradation smaller than 0.7 do have a chance of less than 10% to be infected with PM+. BB was isolated from 52 piglets, from the nose in 49 cases and from the trachea in 27 cases respectively. PM was isolated from 67 piglets. Examination by equine blood agar showed that 15 piglets were positive for PM in the nose, 32 animals being found to be positive for PM by examination using mice. When mice were used in studies of the tonsils, 59 were found to be positive for PM. Of 45 piglets infected with type D, 16 were found te be PM+ following the guinea-pig skin test, the results being regarded as doubtful in two cases. Epidemiological studies for BB and PM+ on 117 breeding-farms in the Province of Overijssel showed that 92% of these farms were infected with BB and 28% with PM+. To be able to qualify breeding-farms as 'not being suspected of AR' concentrated clinical, pathological and bacteriological studies are required.