Paratuberculosis in Iceland: epidemiology and control measures, past and present

Paratuberculosis as well as the slow virus infections maedi/visna and jaagsiekte came to Iceland in 1933 when 20 sheep of the Karakul breed were imported from Halle, Germany. At least five of these sheep were subclinical carriers of paratuberculosis. Within 16 years paratuberculosis together with the other Karakul diseases (maedi/visna and jaagsiekte) almost ruined sheep farming, the main agricultural industry in Iceland. The first clinical case of paratuberculosis in sheep was confirmed in 1938, and in cattle in 1944. The first cattle cases of paratuberculosis appeared on farms where the disease had been prevalent in sheep for years. The virulence in cattle appeared to be considerably lower than in sheep. Extensive measures were used to control the spread of paratuberculosis in sheep. Hundreds of kilometres of fences were put up and used together with natural geographic borders to restrict the movement of sheep from infected areas. Serological and other immunological tests were also used to detect and dispose of infected individuals. These measures proved inadequate and the disease could not be eradicated. Culling and restocking of uninfected sheep in endemic areas eradicated maedi/visna and jaagsiekte but not paratuberculosis. Experiments showed that vaccination against paratuberculosis could reduce mortality in sheep by 94%. Vaccination of sheep in endemic areas has been compulsory in Iceland since 1966 and as a result losses have been reduced considerably. Today, serology is used to detect and control infection in cattle herds. Furthermore, serology is used to control vaccination of sheep and screen for infection in non-endemic areas. The complement fixation (CF) test for paratuberculosis has been used until now, but recently we have started comparing the CF test with the CSL absorbed ELISA test.     

Survival and quality of halibut larvae (Hippoglossus hippoglossus L.) in intensive farming: Possible impact of the intestinal bacterial community

The high mortality commonly observed during the early life stages of intensively reared halibut (Hippoglossus hippoglossus L) is believed to be caused by e.g. opportunistic bacteria. However, the impact of particular bacterial species is poorly defined and still remains disputable. The study describes the bacterial diversity in the gastrointestinal tract of halibut larvae in a large number of incubators at a commercial production site. The overall success of larvae was found to be highly variable and analysis of the gut microbiota revealed high variation of the cultivable part as well as the bacterial community of surface sterilised larvae analysed by denaturing gradient gel electrophoresis (DGGE) of PCR amplified 16s rDNA products. Analysis of the bacterial community of unfed yolk sac larvae revealed higher diversity than previously reported, with Marinomonas, Marinobacter, Aeromonas and Shewanella dominating the community structure. There are indications that Marinomonas is found only in the overall most successful first feeding larvae of the period where the Vibrio group dominated the bacterial community together with Shewanella. Vibrio wodanis was identified as a part of the bacterial community of feeding larvae that yielded the poorest overall success of the period. α-Proteobacteria, not previously reported in halibut, were also found as a part of the bacterial community of first feeding larvae. The diverse bacterial community was only partly reflected in the cultivable part which, however, may reflect the dominating bacterial groups of the highly heterogeneous bacterial community of larvae in the production system as a whole. The bacterial community of the Artemia was found to be highly variable in different samples collected through the period. Only a small part of the different groups observed in the bacterial community of surface sterilised larvae was reflected in the cultivable part which was dominated by highly variable groups in different samples of Artemia. Also, the numbers of cultivable bacteria were found to positively correlate with jaw deformation of unfed yolk sac larvae as well as incomplete metamorphosis of feeding larvae.     

Virulence properties of Moritella viscosa extracellular products

Moritella viscosa is the causative agent of winter ulcer disease of marine fish. Knowledge of its pathogenicity is limited and there are no reports comparing the virulence properties of a collection of bacterial isolates. The in vivo and in vitro virulence of the extracellular products (ECP) of 22 M. viscosa isolates was screened. Two non-virulent Canadian isolates and a Norwegian isolate with reduced virulence produced non-lethal ECP. Correlation was obtained between cytotoxin and haemolysin production of M. viscosa. Isolates from salmon produced ECP with lower cytotoxic and haemolytic activities than ECP of isolates originating from other hosts. Correlation was not found between lethality of ECPs in salmon and cytotoxic or haemolytic activities. All isolates secreted esterases and a metallopeptidase (MvP1), degraded starch and produced siderophores. Variable levels of ECP protein concentration, different enzymatic activities and siderophore production could not explain differences in virulence. The results show that virulent M. viscosa isolates secrete a lethal toxic factor of unknown nature and that cytotoxin production may reflect host adaptation. Cell-culture models may not be optimal for determining the virulence of M. viscosa, as no association between cytotoxicity and bacterial virulence was obtained. Non-virulent strains may be useful in future research on M. viscosa virulence, as construction of mutants has not been successful.     

木豆杂种优势利用研究进展

自1974年发现木豆雄性不育株以来,国际上不断对木豆核雄性不育(GMS)和核质互作雄性不育(CGMS)基因及其种质资源进行研究和挖掘,最终实现了木豆杂种优势的成功利用。本文系统总结了过去30多年来,国际上木豆杂种优势机理、表现及授粉方式等基础研究,GMS、CGMS不育系及其配套制种体系研究,杂种优势强度研究,以及木豆杂交种生产技术研究进展。提出了木豆杂种优势利用的具体研究方向和展望。     

Yersiniosis in Atlantic cod,Gadus morhua (L.), characterization of the infective strain and host reactions

A disease outbreak in farmed Atlantic cod caused by Yersinia ruckeri is reported. Mortality started following vaccination of cod reared in two tanks (A and B). The accumulated mortality reached 1.9% in A and 4.8% in B in the following 30 days when treatment with oxytetracycline was applied. Biochemical and molecular analysis of Y. ruckeri isolates from the cod and other fish species from fresh and marine waters in Iceland revealed a high salinity‐tolerant subgroup of Y. ruckeri serotype O1. Infected fish showed clinical signs comparable with those of Y. ruckeri ‐infected salmonids, with the exception of granuloma formations in infected cod tissues, which is a known response of cod to bacterial infections. Immunohistological examination showed Y. ruckeri antigens in the core of granulomas and the involvement of immune parameters that indicates a strong association between complement and lysozyme killing of bacteria. Experimental infection of cod with a cod isolate induced disease, and the calculated LD₅₀ was 1.7 × 10⁴ CFU per fish. The results suggest that yersiniosis can be spread between populations of freshwater and marine fish. Treatment of infected cod with antibiotic did not eliminate the infection, which can be explained by the immune response of cod producing prolonged granulomatous infection.     

Construction of Aeromonas salmonicida subsp. achromogenes AsaP1‐toxoid strains and study of their ability to induce immunity in Arctic char,Salvelinus alpinus L.

The metalloendopeptidase AsaP1 is one of the major extracellular virulence factors of A. salmonicida subsp. achromogenes, expressed as a 37‐kDa pre‐pro‐peptide and processed to a 19‐kDa active peptide. The aim of this study was to construct mutant strains secreting an AsaP1‐toxoid instead of AsaP1‐wt, to study virulence of these strains and to test the potency of the AsaP1‐toxoid bacterin and the recombinant AsaP1‐toxoids to induce protective immunity in Arctic char. Two A. salmonicida mutants were constructed that secrete either AsaP1_E294A or AsaP1_Y309F. The secreted AsaP1_Y309F‐toxoid had weak caseinolytic activity and was processed to the 19‐kDa peptide, whereas the AsaP1_E294A‐toxoid was found as a 37‐kDa pre‐pro‐peptide suggesting that AsaP1 is auto‐catalytically processed. The LD₅₀ of the AsaP1_Y309F‐toxoid mutant in Arctic char was significantly higher than that of the corresponding wt strain, and LD₅₀ of the AsaP1_E294A‐toxoid mutant was comparable with that of an AsaP1‐deficient strain. Bacterin based on AsaP1_Y309F‐toxoid mutant provided significant protection, comparable with that induced by a commercial polyvalent furunculosis vaccine. Detoxification of AsaP1 is very hard, expensive and time consuming. Therefore, an AsaP1‐toxoid‐secreting mutant is more suitable than the respective wt strain for production of fish bacterins aimed to protect against atypical furunculosis.     

Listeria monocytogenes in horses in Iceland

Twenty isolates of Listeria monocytogenes associated with five confirmed and four suspected incidents of listeriosis in horses in Iceland were characterised by serotyping, pulsed-field gel electrophoresis and ribotyping. Semiquantitative estimates of the numbers of L monocytogenes were made on faeces from horses with clinical signs of listeriosis and on grass silage fed to them. Large numbers of L monocytogenes were often found in the faeces of horses with severe signs of disease. The 20 isolates could be divided into six genotypes, each incident involving only one genotype. One serovar 1/2a genotype was associated with three confirmed incidents of listeriosis in 1991, 1993 and 1997. In one incident, the same genotype was isolated from the organs of a horse with listeriosis and from the spoiled grass silage fed to it.     

Identification of Polymorphisms in the Osteopontin Gene and Their Associations with Certain Semen Production Traits of Water Buffaloes in the Brazilian Amazon

The osteopontin gene may influence the fertility of water buffaloes because it is a protein present in sperm. The aim of this work was to identify polymorphisms in this gene and associate them with fertility parameters of animals kept under extensive grazing. A total of 306 male buffaloes older than 18 months, from two farms, one in the state of Amapá and the other in the state of Pará, Brazil were used in the study. Seven SNPs were identified in the regions studied. The polymorphisms were in gene positions 1478, 1513 and 1611 in the region 5′upstrem and positions 6690, 6737, 6925 and 6952 in the region amplified in intron 5. The SNPs were associated with the traits, namely scrotal circumference, scrotal volume, sperm motility, sperm concentration and sperm pathology. There were significant SNPs (p < 0.05) for all the traits. The SNP 6690 was significant for scrotal circumference, sperm concentration, sperm motility and sperm pathology and the SNP 6737 for scrotal volume. The genotype AA of SNP 6690 presented the highest averages for scrotal circumference, sperm concentration and motility and the lowest total number of sperm pathologies. For the scrotal volume trait, the animals with the largest volume were correlated with the presence of the genotype GG of SNP 6737. These results indicate a significance of the osteopontin gene as it seems to exert a substantial influence on the semen production traits of male buffaloes.