Risk factors for outbreaks of infectious salmon anemia in farmed Atlantic salmon, Salmo salar

Infectious salmon anemia (ISA) is a viral disease occurring in farmed Atlantic salmon (Salmo salar) that is characterized by lethargy, anorexia, anemia and death. To control the disease in New Brunswick, Canada, 7.5 million fish from outbreak cages have been destroyed since 1997. Despite changes made by farmers, 2002 was the worst year ever for ISA losses in the region.

We evaluated the associations between potential risk factors and ISA outbreaks in the Atlantic-salmon sites in New Brunswick. This was a multilevel study in which the site-level design was a retrospective cohort study while the cage-level design was a modified case-cohort study. The questionnaire was divided into site-level questions, cage-level questions and hatchery information.

The important factors identified by this study can be categorized as environmental, farmer controlled or industry controlled according to the capacity to change or eliminate them. Environmental risk factors such as increasing the depth of the net (if nets were ≤9 m, odds ratio (OR) = 3.34) and decreasing the depth of water underneath the net (if depth of water underneath the net >3 m, OR = 3.34) are for the most part dictated by site location. Wild pollock (Pollachius virens) in the cage reflects the number of wild pollock that live in the site location. If there were ≥1000 pollock in the cage, the odds of disease in the cage increased 4.43-fold. Risk factors that are under farm control include increasing the number of times that the salmon are treated for sea lice (OR = 3.31 if lice treatments are ≤2 times), transferring small smolts into seawater (OR = 2.40 if smolts weighed >99 g) and improving on the adaptation of smolts to seawater to reduce post-transfer mortalities (OR = 4.52 if there was at least one cage with post-transfer mortalities >5%). The industry-controlled factors need to be addressed by the industry as a whole. Organizing boat travel to minimize the time and frequency of boats travelling to or by sites currently is being reviewed. This will be extremely important because the OR = 9.43 if processing boats travel within 1 km of the site and the OR = 4.03 if the site has dry feed delivered by the feed company. Because the hazard ratio increased stepwise from 1 if the nearest neighbor with ISA was ≥5 km up to 5.5 if the nearest site with ISA was within 0.5 km, increasing the distance between sites might be necessary for effective control.     

The persistence of infectious pancreatic necrosis virus in Atlantic salmon

Atlantic salmon leucocytes from Infectious Pancreatic Necrosis Virus (IPNV) carriers showed a suppressed response to phytohemagglutinin stimulation compared with uninfected controls. A significant degree of inhibition of DNA synthesis was observed using 3H-thymidine incorporation. IPNV was isolated from 41% of the stimulated leucocyte cultures supernatants, while only 6% of the unstimulated cultures were found to be positive.     

Enhanced platelet reactivity in cats experimentally infected with feline infectious peritonitis virus

Platelet function was evaluated in six specific-pathogen-free cats prior to and following intraperitoneal inoculation with feline infectious peritonitis virus (FIPV). By 4 days post-inoculation, platelet samples from five of six cats responded with irreversible platelet aggregation to threshold concentrations of adenosine diphosphate (ADP). This was accompanied by enhanced platelet 14C-serotonin release (greater than 10%) in two cats. Compared to one of six baseline samples, five of five post-inoculation samples exhibited microaggregate formation in response to 20 microM epinephrine. Enhanced platelet 14C-serotonin release did not accompany these responses. Enhanced platelet responses to ADP and epinephrine were also observed on day 11 post-inoculation and day 16 (when one cat died) or 21 (the end of the study). Platelet 14C-serotonin release in response to 20 microM epinephrine increased markedly in three of five cats on day 21. Enhanced collagen-induced platelet responses were not demonstrated. Although the mechanism for the enhanced platelet responses observed on day 4 was unknown, a direct effect on the virus on platelets, mononuclear inflammatory cells, and endothelial cells must be considered.     

Immunohistochemical identification of infectious pancreatic necrosis virus in paraffin-embedded tissues of Atlantic salmon (Salmo salar)

Infectious pancreatic necrosis virus serotype Sp was identified by immunohistochemistry in formaldehyde-fixed and paraffin-embedded tissue of Atlantic salmon (Salmo salar). The immunoreaction was present in degenerating and necrotic cells in exocrine pancreatic cells. Cross reactions were observed with rabbit antisera against serotypes Sp, Ab, and VR-299 in neutralization tests and western blotting. Immunohistochemically, only Sp antiserum produced positive immunostaining to Sp antigens, whereas antisera to serotypes Ab and VR-299 were negative.     

Nephropathogenesis of chickens experimentally infected with various strains of infectious bronchitis virus

Four-day-old specific-pathogen-free chickens were inoculated by eyedrop with four different strains (Gray, JMK, CV56b, and Wolgemuth) of infectious bronchitis virus (IBV). Birds were monitored clinically and euthanatized at 1, 4, 7, and 14 days postinfection and tissues were collected for virus isolation, histopathologic examination, in situ hybridization (ISH), and immunohistochemistry (IHC). Clinical disease was severe in chickens infected with Wolgemuth, but no overt disease was observed with the other strains. Virus was isolated from the kidneys of chickens infected with the Gray-, CV56b-, and Wolgemuth-strains of IBV. Histologically, interstitial nephritis was evident in chickens infected with these same 3 strains. However, viral nucleic acid and antigen were detected only with Wolgemuth-infected kidneys by ISH and IHC. These results indicate that the pathological changes in kidneys from chickens infected with Gray and CV56b may not have resulted from the cytolytic action of the virus.     

Hepatic lesions in young rabbits experimentally infected with rabbit haemorrhagic disease virus

Twenty young rabbits (eleven 2-week-old and nine 4-week-old) were experimentally infected with rabbit haemorrhagic disease virus (RHDV) to clarify susceptibility. They were killed chronologically up to 96 hours post-inoculation (PI) and examined for lesions. All inoculated rabbits were clinically normal, but grossly minute white or grey spots were detected throughout the liver. Histologically, the lesions consisted of aggregates of lymphocytes, macrophages and heterophils, with or without acidophilic bodies and necrotic hepatocytes. Immunohistochemically, RHDV antigens were found in the degenerated hepatocytes and in macrophages. The cellular aggregates were considered to be a reaction to necrotic hepatocytes infected with RHDV. It was concluded that some hepatocytes are susceptible to RHDV in young rabbits.     

感染马传染性贫血病毒的巨噬细胞差异表达蛋白质组分析

为研究马传染性贫血病毒(EIAV)感染其主要靶细胞马巨噬细胞(eMDM)后与细胞蛋白的相互作用,本研究采用EIAV强毒株EIAVDLV34感染48 h后的马外周血单核细胞分化的eMDM,并以未感染eMDM为对照,提取细胞的蛋白质样品,进行双向凝胶电泳(2-DE)分离,并分析凝胶中差异蛋白点。结果共检测出19个表达差异的蛋白点(ratio1.4,p0.05),其中感染组相对于对照组有7个蛋白质上调表达,12个蛋白质呈现下调表达。将差异蛋白进行串联质谱分析进行鉴定,并通过生物信息学方法对这19个差异表达蛋白进行了蛋白互作用分析。此外,对其中5个比较重要蛋白的mRNA水平进行了荧光定量PCR分析,其表达变化与2-DE结果一致。本研究为进一步分析EIAV与其宿主细胞eMDM的相互作用提供了参考。     

Isolation of avian infectious bronchitis virus from experimentally infected chickens.

Virus was recovered from the faeces of chickens infected at three or four weeks of age for more than 20 weeks after infection with commercial vaccines or with the T strain of avian infectious bronchitis virus (IBV). Virus was not recovered from the trachea, liver, spleen, bursa or kidneys of T strain infected birds longer than 29 days after infection at which point IBV was recovered from the bursa of a single infected bird. In a subsequent experiment IBV was recovered from the caecal lymph nodes and faeces of one of five birds 14 weeks after infection with a commercial vaccine but no virus was isolated from the trachea, kidneys, duodenum, bursa, ovaries or testes of any of the five birds at this time.     

Characterization of Chinook head salmon embryo phenotypes of infectious salmon anemia virus by real-time RT-PCR

We have previously described the development of a one-tube SYBR Green real-time RT-PCR assay for the detection and quantitation of infectious salmon anemia virus (ISAV) in various biological samples. The twofold aim of the present study was to verify that the optimized SYBR Green real-time RT-PCR conditions could detect ISAV isolates of different geographic origins, and to analyze the growth patterns of the selected ISAV isolates in the Chinook head salmon embryo (CHSE)-214 cells by this assay to better characterize their CHSE-phenotypes. A total of 24 ISAV isolates were used in this study. The results indicated that the SYBR Green real-time RT-PCR could detect ISAV of different geographic origins or laboratory sources. The capacity of ISAV isolates to cause cytopathic effects (CPE) in the CHSE-214 cell line, viral titration of the infected CHSE-cell harvests, and analysis of viral RNA levels in CHSE-214 cells at post-infection day zero, 7 and 14 by SYBR Green real-time RT-PCR confirmed the existence of three CHSE-phenotypes of ISAV: replicating cytopathic, replicating non-cytopathic, and non-replicating non-cytopathic. The identification of these three CHSE-phenotypes of ISAV has important implications from diagnostic and biological points of view.     

Tissue distribution of virus replication in cats experimentally infected with distinct feline calicivirus isolates.

Four specific pathogen-free (SPF) cats were each inoculated with one of two genetically and antigenically well characterized feline caliciviruses originally isolated from cats with acute respiratory disease (FCV-KS100/2), or with chronic stomatitis (FCV-KS20). Two cats of each group were euthanized at day 10 post infection and two cats at day 28. No clear differences between the clinical disease induced by the two isolates could be observed, and no apparent differences in the tissue spectrum were seen between day 10 and 28. No persistent virus shedding was observed over the 4-week period of this experiment.     

鸡传染性支气管炎人工感染模型的中药保护作用

传染性支气管炎(IB)是由传染性支气管炎病毒(IBV)引起的急性、高度接触性呼吸道传染病,其特征是咳嗽、打喷嚏和气管哕音、呼吸困难.该病可引起鸡的增重、饲料报酬以及生产性能降低,当继发或并发感染支原体或大肠杆菌等时可使鸡群死亡率增加,是严重危害世界养禽业的重大传染病之一.由于IBV毒株具有高度易变异和多血清型的特点,给该病的免疫和防治带来了很大困难,因此,研制有效的防治药物具有重要意义.     

马传染性贫血病毒弱毒疫苗S2基因在体内变异分析

为研究马传染性贫血病毒(EIAV)驴白细胞弱毒疫苗EIAVDLV121的S2基因在马体内的变异规律,本研究选用4匹成年马,其中2匹(#1、#2)接种EIAVDLV121,另外2匹作为对照.免疫后监测马体温、血小板含量以及病毒载量结果显示,免疫马未出现马传染性贫血体征.通过RT-PCR方法检测病毒S2基因在感染马体内不同时期的基因序列,结果显示,免疫马体内EIAVDLV121 S2蛋白的突变主要发生在氨基酸第17位、22位、39位、41位、51位和55位.另外,#1马免疫后70 d以及#2马免疫后第14 d和第28 d检测疫苗毒S2蛋白序列与EIAVDLV121亲缘关系较近,而#1马免疫后第42 d、第112 d和第140 d的疫苗毒S2蛋白序列与EIAVDLV121的致病性亲本强毒株EIAVDN40亲缘关系最近.本研究结果有助于对EIAV及EIAV疫苗株在马体内感染进程的研究.