Persistent spatial clusters of plasmacytosis among Danish mink farms

Aleutian disease (Plasmacytosis) is caused by the Aleutian mink disease virus (AMDV), an autonomous parvovirus and affects many mustelid species, including the American mink (Neovisonvison). In Denmark, an eradication program reduced the prevalence of test-positive farms from 100% in 1976 to 15% in 1996. Nevertheless, the disease persists in the Vendsyssel district of Northern Jutland, despite the eradication efforts. In this study, we used spatial epidemiological analysis to test for spatial autocorrelation of the distribution of farms positive for the disease. We investigated 2375 farms in Denmark (342 of which were located in the Vendsyssel district), during the period 2000-2008. For the purpose of our study, a farm was considered positive when, on any test conducted in a year, at least three animals were tested positive. To detect spatial clusters, we performed a retrospective analysis with spatial scan statistics. We performed one analysis for each of the nine years (2000-2008). A separate analysis was conducted with only the farms in Vendsyssel included. The spatial cluster analysis revealed a significant cluster throughout the time period studied in Northern Jutland. The only exception was 2002 when an outbreak was detected in the southern part of Jutland, and not in the north. The farm-level prevalence of the disease in Denmark was highest in this year, suggesting that the outbreak in the south could have masked the persistent signal from the north; the northern cluster was still significant when analysing only the Vendsyssel populations. These results confirm that Northern Jutland continues to have a significantly higher number of cases than expected if the disease was randomly distributed.     

Molecular epidemiology of Aleutian mink disease virus in Finland

Aleutian mink disease virus (AMDV) is a parvovirus that causes an immune complex-mediated disease in minks. To gain a more detailed view of the molecular epidemiology of mink AMDV in Finland, we phylogenetically analysed 14 new Finnish strains from 5 farms and all 40 strains with corresponding sequences available in GenBank. A part of the major non-structural (NS1) protein gene was amplified and analysed phylogenetically. A rooted nucleotide tree was constructed using the maximum parsimony method. The strains described in this study showed 86-100% nucleotide identity and were nearly identical on each farm. The ratio of synonymous to non-synonymous substitutions was approximately 2.7, indicating a mild purifying selection. Phylogenetic analysis confirmed that AMDV strains form three groups (I-III), all of which contained Finnish strains. The tree inferred that the three lineages of AMDV have been introduced to Finland independently. The analysis suggested that AMDV strains do not cluster into genotypes based on geographical origin, year of isolation or pathogenicity. Based on these data, the molecular clock is not applicable to AMDV, and within this gene area no recombination was detected.     

Monitoring chronic infection with a field strain of Aleutian mink disease virus

Aleutian mink disease virus (AMDV) readily spread within farmed mink and causes chronic infections with significant impacts for welfare and economy. In the present study a currently circulating Danish AMDV strain was used to induce chronic experimental infection of farmed mink.PCR was used to detect viral DNA in full blood, organs, faeces and oro-nasal swabs weekly for the first 8 weeks and then biweekly for another 16 weeks after AMDV challenge inoculation of wild type mink. The mink (n = 29) was infected and seroconverted 2–3 weeks after AMDV inoculation and AMDV antibodies persisted during the maximum experimental period of 24 weeks. Viraemia and faecal excretion of viral DNA was detected in the mink (n = 29) at various and intermittent time intervals. Excretion of viral DNA in oro-nasal swabs was detected for 1–8 weeks in 21 mink. This highlights the risk of transmitting AMDV between infected farms.PCR was successfully used to detect viral DNA in organs 8, 16 and 24 weeks after AMDV inoculation with only minor differences between these weeks which is of diagnostic interest.This AMDV challenge model was also used to mimic natural infection of susceptible sapphire mink. Four of 6 sapphire mink were infected indirectly via the AMDV inoculated wild type mink whereas the other 2 sapphire mink remained uninfected.     

A survey of Aleutian mink disease virus infection of feral American mink in Nova Scotia

Spleen samples from 14 mink that were trapped in 4 counties of Nova Scotia were tested for the presence of the Aleutian mink disease virus (AMDV) by polymerase chain reaction. Viral DNA was not detected in samples from Kings County (n = 2), but was detected in all the mink sampled from Colchester (n = 2) and Halifax (n = 6) counties, and 3 of 4 mink from Yarmouth County. The high level of AMDV-infected mink in Colchester and Halifax counties may pose a serious threat to the captive mink and wild animal populations. Because treatment of infected free-ranging mink is not an option, AMDV control strategies for the captive mink should be primarily focused on bio-security to protect clean ranches.     

Comparison of Pseudomonas aeruginosa isolates from mink by serotyping and pulsed-field gel electrophoresis

Isolates of Pseudomonas aeruginosa from clinical infections in mink were subjected to serotyping and pulsed-field gel electrophoresis (PFGE) using SpeI. A total of 212 isolates of P. aeruginosa from the year 1998 to 2001 were included in this study: 168 isolates from mink obtained from 74 farm outbreaks of haemorrhagic pneumonia. Isolates from mink were separated into 34 distinct clones by PFGE subtyping. All isolates from mink infected during the same farm outbreak were identical, except in one case where two different strains were isolated from mink obtained from the same farm outbreak. P. aeruginosa of specific PFGE types were found to cause clusters of outbreaks on several farms within a few weeks of each other. However, PFGE types of strains causing clusters of farm outbreaks changed from year to year. These results suggest that some outbreaks of haemorrhagic pneumonia are caused by pathogenic strains of P. aeruginosa spread between farms and animals either mechanically, or through feed or water from a common source, rather than by random nosocomial infections with strains from the farm environment.     

Mortality in farmed mink: systematic collection versus arbitrary submissions for diagnostic investigation

The distribution of diagnoses of mortality in mink submitted to the Danish Veterinary Laboratory (DVL) for diagnostic investigation in the calendar year 1997 was compared with the diagnoses of mortality in all dead mink collected at 4 selected farms (project farms) during the same period. A total of 1,015 submitted mink and 1,149 mink from the 4 project farms were subjected to post mortem investigation. The average size (breeding stock) of the project farms was larger than Danish farms on average. However, the distribution of colour types of the mink was comparable. The seasonal distribution of the material from project farms and that of the submissions were approximately the same. Differences in the distribution of diagnoses as well as recovered microorganisms were found, however, mainly related to the proportion of gastro-intestinal disorders and E. coli respectively. These proportions were negatively correlated. Overall the results showed that extrapolating diagnostic results of laboratory submissions to the population of farmed mink may be problematic, and more reliable methods for disease surveillance must be considered.     

Aleutian mink disease virus in furbearing mammals in Nova Scotia,Canada

Background

Aleutian mink disease virus (AMDV) is widespread among ranched and free-ranging American mink in Canada, but there is no information on its prevalence in other wild animal species. This paper describes the prevalence of AMDV of 12 furbearing species in Nova Scotia (NS), Canada.

Methods

Samples were collected from carcasses of 462 wild animals of 12 furbearing species, trapped in 10 NS counties between November 2009 and February 2011. Viral DNA was tested by PCR using two primer pairs, and anti-viral antibodies were tested by counterimmunoelectrophoresis (CIEP) on spleen homogenates.

Results

Positive PCR or CIEP samples were detected in 56 of 60 (93.3%) American mink, 43 of 61 (70.5%) short-tailed weasels, 2 of 8 (25.0%) striped skunks, 2 of 11 (18.2%) North American river otters, 9 of 85 (10.6%) raccoons, and 2 of 20 (10.0%) bobcats. Samples from six fishers, 24 coyotes, 25 red foxes, 58 beavers, 45 red-squirrels and 59 muskrats were negative. Antibodies to AMDV were detected by CIEP in 16 of 56 (28.6%) mink and one of the 8 skunks (12.5%). Thirteen of the mink were positive for PCR and CIEP, but three mink and one skunk were CIEP positive and PCR negative. Positive CIEP or PCR animals were present in all nine counties from which mink or weasel samples were collected.

Conclusions

The presence of AMDV in so many species across the province has important epidemiological ramifications and could pose a serious health problem for the captive mink, as well as for susceptible wildlife. The mechanism of virus transmission between wildlife and captive mink and the effects of AMDV exposure on the viability of the susceptible species deserve further investigation.     

Evaluation of two enzyme-linked immunosorbent assays for serodiagnosis of Aleutian mink disease virus infection in mink

Background

Aleutian disease in mink is caused by infection with Aleutian mink disease virus (AMDV). In Sweden, the infection most commonly causes classical Aleutian disease in which the immune system fails to neutralize the virus and the infection becomes persistent. Diagnosis of AMDV infection is based on serological methods that detect virus-specific antibodies. Traditionally counterimmunoelectrophoresis (CIEP) has been the preferred method, but in order to enable automation interest has been paid to other antibody detecting systems. Recently, at least two different ELISA systems that detect antibodies to AMDV have been manufactured; one is based on an in vitro grown AMDV as antigen, and the other system is based on the AMDV capsid protein VP2 as antigen. The aim of this study was to evaluate the two ELISA systems for detection of antibodies to AMDV using CIEP as the gold standard.

Results

When employing the mean optical density of the samples from CIEP negative mink plus three standard deviations as cut-off value, the ELISA with the VP2 antigen had a sensitivity of 99.7% and a specificity of 98.3% compared to CIEP (n = 364). Analysis of samples with the AMDV-G antigen based ELISA employing an assay cut-off value based on the negative control samples, as suggested by the manufacturer, resulted in a sensitivity of 54.3% and a specificity of 93.2% with reference to CIEP as the gold standard (n = 359). When employing the mean optical density of the samples from CIEP negative mink plus three standard deviations as cut-off value, the AMDV-G ELISA had a sensitivity of 37.6% and a specificity of 98.3%.

Conclusions

The ELISA system based on VP2 antigen had high sensitivity and specificity, and was concluded to be an alternative to the CIEP as a diagnostic tool for AMDV antibodies. In contrast, the AMDV-G ELISA suffered from low sensitivity when compared to CIEP.     

An outbreak of excessive neonatal mortality in four Danish mink farms. II. Analytic epidemiological investigations

Data collected from an outbreak of excessive mortality of mink kits in 4 Danish mink farms in 1982 were analysed. The mortality of the mink kits was found to be highest for the kits from Aleutian Disease (AD)-positive females, and the Scanblack mink was found to be the most frequently affected mink type. Furthermore the mortality was found to depend on the farm of origin and to be highest for the lastest born kits. The age of the females and their location in sheds were found not to influence the mortality of the kits. However, the mortality for the Pastel mink decreased with increasing distance from the Scanblack mink. The possibility that the excess mortality of the kits might be due to an AD-virus infection is discussed.Key words: mink, neonatal mortality, mink kits, Aleutian Disease, analytic epidemiology     

丹麦水貂饲养业

通过对丹麦 3个大规模水貂饲养场、饲养加工厂、饲养设备加工厂、取皮设备加工厂的考察 ,初步了解和认识了丹麦水貂品种的特征特性 ,饲养管理和取皮加工的系统性 ,以及丹麦水貂养殖业的特点     

Influence of farm, feed-producer and season on incidence of gastrointestinal disorders in Danish farm mink

The distribution of gastrointestinal disorders in mink in Danish farms is presented based on data collected in a longitudinal design. The time at risk was from weaning in June until pelting in November. The occurrence of gastrointestinal disorders after weaning of the mink kits together with the distribution within farms was studied. The period of highest risk was in the months immediately after weaning (July and August). More than 17% of the farms recorded GI disorders among ≥10% of pairs of animals. A multilevel statistical analysis showed that besides the effect of time after weaning, a significant part of the variation in the incidence could be attributed to the farm and feed-producer. The potential for bias is discussed.     

水貂绿脓杆菌分离株的血清型分析和Eric-PCR指纹图谱多样性研究

为了掌握山东地区水貂出血性肺炎流行情况,从2012年山东省内多个养貂社区进行水貂出血性肺炎流行病学调查。从病貂中分离获得48株绿脓杆菌,分别测定了分离株的生化特性、血清型以及部分菌株对小鼠与水貂的半数致死量（LD50）,同时运用Eric-PCR方法对分离进行了进行分型。结果显示,48株分离菌株与标准菌株生化特性基本一致,血清型G型为36株,血清型Ⅰ型为7株,血清型C型为4株;48株分离株大多数对恩诺沙星最敏感;动物试验显示,48株分离株对小鼠与水貂均能致病,所选4株分离株对小鼠与水貂的LD50有差异,且水貂对所选菌株显著敏感于小鼠;分子分型分为13个基因型。结果表明,该地区水貂出血性肺炎病原呈现遗传多样性。本试验为水貂出血性肺炎的防治提供了理论依据。     

Staphylococcus spp., Streptococcus canis,and Arcanobacterium phocae of healthy Canadian farmed mink and mink with pododermatitis

Pododermatitis is a disease of concern for mink breeders in Canada and worldwide, as it causes discomfort and lowers the breeding rates on farms affected by the disease. Unfortunately, the etiology and pathogenesis of pododermatitis are still unknown. In this study, we compared Staphylococcus spp. and Streptococcus canis isolates from healthy mink with isolates from animals with pododermatitis on 2 farms in Ontario. Almost all hemolytic Staphylococcus spp. isolated were shown to be Staphylococcus delphini Group A by 16S ribosomal ribonucleic acid (rRNA) sequence analysis and polymerase chain reaction (PCR). Pulsed-field gel electrophoresis (PFGE) did not reveal any S. delphini or S. canis clonal lineages specifically associated with pododermatitis, which suggests that these bacteria do not act as primary pathogens, but does not dismiss their potential roles as opportunistic pathogens. While S. delphini and S. canis were the most prevalent bacterial pathogens in mink pododermatitis, they were also present in samples from healthy mink. Arcanobacterium phocae is occasionally isolated from pododermatitis cases, but is difficult to recover with conventional culture methods due to its slow growth. A quantitative real-time PCR was developed for the detection of A. phocae and was tested on 138 samples of footpad tissues from 14 farms. The bacterium was detected only in pododermatitis-endemic farms in Canada and was at higher concentrations in tissues from infected footpads than in healthy tissues. This finding suggests that A. phocae is involved in the pathogenesis of pododermatitis.     

水貂阿留申病毒诱导猫肾细胞(CrFK)凋亡

为研究水貂阿留申病毒(AMDV)在体外诱导猫肾细胞(CrFK)凋亡情况,用AMDV-G株感染CrFK细胞,采用CCK-8法检测CrFK细胞感染后的细胞存活率,用AO/EB染色法检测CrFK细胞核的形态变化,用Annexin V-FITC/PI双染流式细胞术检测细胞凋亡率,并通过分光光度计法检测细胞凋亡执行分子Caspase-3活性。结果显示,AMDV-G株感染可导致CrFK细胞增殖率下降,产生明显的形态学凋亡特征;流式细胞术检测结果显示,AMDV-G株感染可引起CrFK细胞凋亡并随着感染时间的延长凋亡率增加,同时Caspase-3活性显著升高。上述结果表明,AMDV-G株在体外能够诱导CrFK细胞凋亡,为进一步研究AMDV致病机理奠定基础。     

Prevalence of the Aleutian mink disease virus infection in Nova Scotia, Canada

Despite many years of testing mink for serum antibodies against the Aleutian mink disease virus (AMDV) by counterimmunoelectrophoresis (CIEP) and elimination of reactors, this virus has remained the number one disease threat for the mink industry in Nova Scotia (NS). The objective of this study was to analyze CIEP test results to determine the success of the AMDV-control strategy in NS. A total of 2,964,920 CIEP test results from 82 ranches, spanning an eight-year period between 1998 and 2005, were analyzed. This survey included approximately 60% of the active ranchers in the province. The number of ranchers that tested their animals was 42 in 1998, gradually increased to 58 in 2003 and then showed some decline. The overall proportion of CIEP-positive mink was 3.34%, and varied between 5.22% in 1999 and 1.35% in 2005. The proportion of infected ranches ranged between 23.8% in 1998 and 70.7% in 2003. The overall trend was for a smaller proportion of infected animals but a larger proportion of infected ranches during this time period. Of the 82 ranches, 24 (29.3%) had negative CIEP in all tests, 15 (18.3%) had CIEP positive animals in every year tested, and 43 (52.4%) had positive and negative results in different years, indicating that AMDV infection was widespread in NS. There were 23 infected ranches with 8years of uninterrupted testing. These ranchers performed 75.8% of the total samples tested (2,246,711), implying that they have diligently been trying to eradicate the virus. Infection persisted on three of these ranches for the entire 8year period, and only two of the ranches remained CIEP negative for longer than four years. The average percentage of CIEP-positive mink on these ranches was 2.2, which was lower than 6.35% for the 33 infected ranches with occasional testing, and 73.6% and 82.4% for two ranches that had never used the CIEP test, showing that persistent test-and-removal strategy has been effective in reducing the prevalence of infected animals but has failed to eradicate the virus from most of the infected ranches.     

A survey of the causes of mortality in adult mink, with emphasis on the lactation period

A study of the pattern and relative frequency of diseases in adult female mink during the lactation period was undertaken. All adult females that died between parturition (April/May) and July 1, 1990, from 48 farms in southern Ontario were selected for study, and the cause of death was determined by gross necropsy. In addition, the cause of death was determined by gross necropsy for all adults and weaned kits that died on one farm between April 1988 and March 1989.

The mortality rate among farms in the 1990 study, for adult females during the lactation period, ranged from 0.2% to 10.1%, with a median of 1.9%. Nursing disease (56%) was the most common diagnosis, followed by mastitis (11%), metritis (8%), and dystocia (7%). Escherichia coli and Staphylococcus spp. were the most frequent isolates from the cases of mastitis. In the 1988/1989 study, the mortality rate was highest from May to July, with a large increase in June as a result of nursing disease.

     

Serogroups and antimicrobial susceptibility among Escherichia coli isolated from farmed mink (Mustela vison Schreiber) in Denmark

Escherichia coli is commonly found in outbreaks of diarrhoea in mink during the production season although its role as a primary causal organism remains unclear. The present study was undertaken to determine the serogroups and antimicrobial susceptibility of E. coli isolates from healthy and diarrhoeic mink. Rectal swabs were taken from healthy and diseased animals, on six different farms, once at the onset of disease and again approximately 2 weeks later. The swabs were subjected to bacteriological investigation; a total of 210 E. coli were isolated, 98 from healthy animals and 112 from diseased. All isolates were serotyped and MICs were determined for nine antimicrobial compounds. Non-haemolytic isolates numbered 147, whereas 63 were haemolytic. Both haemolytic and non-haemolytic isolates were isolated from both healthy and diseased animals.A wide range of serogroups was detected, the most frequent being O2 (11.0%), O78 (11.0%), O153 (7.1%), O25 (5.7%), O6 (4.8%), and O15 (4.8%), but diarrhoea was not associated with specific serogroups. All isolates were sensitive to enrofloxacin, neomycin, gentamicin and colistin. In contrast, considerable variations in susceptibility were found among the six mink farms, for tetracycline (0-46.4%, average 21.9), ampicillin (2.9-50.0%, average 23.3), spectinomycin (8.0-35.7%, average 21.9), sulfamethoxazole (8.6-57.7%, average 30.0) and trimethoprim (0-35.7%, average 9.5). Resistance to tetracycline was statistically more prevalent among haemolytic than among non-haemolytic strains.In conclusion, serogrouping and haemolysin testing failed to identify any association with diarrhoeal disease and antimicrobial resistance was highly variable between different mink farms.     

Genetic and phenotypic parameters for Aleutian disease tests and their correlations with pelt quality,reproductive performance,packed-cell volume,and harvest length in mink

Aleutian disease (AD), caused by the Aleutian mink disease virus (AMDV), is a major health concern that results in global economic losses to the mink industry. The unsatisfactory outcome of the culling strategy, immunoprophylaxis, and medical treatment in controlling AD have urged mink farmers to select AD resilient mink based on several detection tests, including enzyme-linked immunosorbent assay (ELISA), counterimmunoelectrophoresis (CIEP), and iodine agglutination test (IAT). However, the genetic analysis of these AD tests and their correlations with pelt quality, reproductive performance, packed-cell volume (PCV), and harvest length (HL) have not been investigated. In this study, data on 5,824 mink were used to estimate the genetic and phenotypic parameters of four AD tests, including two systems of ELISA, CIEP, and IAT, and their genetic and phenotypic correlations with two pelt quality, five female reproductive performance, PCV, and HL traits. Significances (P < 0.05) of fixed effects (sex, year, dam age, and color type), covariates (age at harvest and blood sampling), and random effects (additive genetic, permanent environmental, and maternal effects) were determined under univariate models using ASReml 4.1 software. The genetic and phenotypic parameters for all traits were estimated under bivariate models using ASReml 4.1 software. Estimated heritabilities (±SE) were 0.39 ± 0.06, 0.61 ± 0.07, 0.11 ± 0.07, and 0.26 ± 0.05 for AMDV antigen-based ELISA (ELISA-G), AMDV capsid protein-based ELISA, CIEP, and IAT, respectively. The ELISA-G also showed a moderate repeatability (0.58 ± 0.04) and had significant negative genetic correlations (±SE) with reproductive performance traits (from −0.41 ± 0.16 to −0.49 ± 0.12), PCV (−0.53 ± 0.09), and HL (−0.45 ± 0.16). These results indicated that ELISA-G had the potential to be applied as an indicator trait for genetic selection of AD resilient mink in AD endemic ranches and therefore help mink farmers to reduce the adverse effects caused by AD.     

Toxoplasma gondii infection in Polish farmed mink

The aim of this study was to determine the seroprevalence of Toxoplasma gondii antibodies in Polish farmed mink according to way of feeding as well as to confirm the role of toxoplasmosis in reproductive losses in mink farms. The serological examinations were carried out on 961 mink randomly selected from 12 Polish farms. Blood sera were examined for the presence of T. gondii antibodies with the use of the latex agglutination test. The examinations for the presence of T. gondii in organ tissues were performed on five neonatal mink kits with the use of immunofluorescence method. In total 133 (13.9%) out of 961 examined mink had T. gondii antibodies. In large farms the seropositivity was lower (2.9%), than in small farms (26.33%) (P < 0.001). Significant difference was found in seroprevalence according to way of feeding. In farms feeding fish, percentage of seropositivity was lower (2.2%), than in farms based on non-frozen slaughter offal (43.4%). Titres of T. gondii antibodies were usually lower than 120 IU/ml. Using the immunofluorescence method, T. gondii was detected in impression smears from liver and brain of two neonatal mink kits derived from one seropositive female.     

Verrucous endocarditis associated with Streptococcus bovis in mink (Mustela vison)

Between 1998 and 2001, mortalities due to verrucous endocarditis were experienced at several mink farms. Gram-positive cocci were isolated from the endocardium of all the animals examined but not always from other internal organs. Almost all the isolates were identified as Streptococcus bovis and only a few isolates belonged to other Streptococcus species. Typing by pulsed-field gel electrophoresis of a selection of isolates revealed several patterns and several different clones. Attempts to reproduce disease by the injection of cultures of a field isolate into healthy mink failed.