A framework for understanding the potential for emerging diseases in aquaculture

Numerous diseases have emerged as serious economic or ecological problems in aquaculture species. The combination of factors behind the emergence of each disease is unique, but various common factors are apparent. We combine risk-analysis methods and virulence theory with historical examples (mainly from salmonid production) to identify key disease-emergence risk factors. Diseases have emerged through pathogen exchange with wild populations, evolution from non-pathogenic micro-organisms and anthropogenic transfer of stocks. Aquacultural practices frequently result in high population densities and other stresses (such as intercurrent disease) which increase the risk of infection establishment and spread. As aquaculture expands and new species are farmed, diseases will continue to emerge and affect both wild and farmed fish adversely. The rate and extent of emergence can be reduced by the application of biosecurity programmes designed to mitigate the risk factors for disease emergence.     

Advances in the molecular understanding of canine retinal diseases

Retinal dystrophies are a common cause of blindness in purebred dogs. Progressive retinal atrophy, the canine equivalent of retinitis pigmentosa in humans, is the most common dystrophy. Molecular studies have led to the identification of the genetic defect underlying some forms of progressive retinal atrophy and the mapping of the chromosomal location of others. Additionally, the gene mutation that causes a severe retinal dystrophy in the briard, which is the equivalent of Leber congenital amaurosis in humans, has been identified. These advances have led to the development of DNA-based diagnostic tests for some retinal dystrophies, thus facilitating their eradication. The study of these dystrophies in dogs has also provided useful information about the equivalent diseases in humans. Recently, gene therapy has been used to restore vision to dogs with a retinal dystrophy due to a mutation in the RPE65 gene. Such studies are important in the quest to develop therapies for similar conditions in humans.     

The molecular diagnosis of porcine viral diseases: a review

The worldwide occurrence and re-occurrence of transboundary diseases like foot-and-mouth disease or classical swine fever indicates that there is a high need for the development of powerful, robust and high-capacity new diagnostic methods, which are able to detect the causative agents before they could spread to large populations and cause tremendous losses. This article reports the experiences of a research group on the development of molecular methods for the improved diagnosis of a range of porcine viral diseases, including diseases on List A of the Office International des Epizooties (OIE). Nucleic acid hybridisation and various polymerase chain reaction (PCR) assays have been applied for routine diagnosis of a large range of viral diseases. During the last one-and-a-half decade more than 40 nested PCR assays have been developed to detect a variety of DNA and RNA viruses. False positive and negative results are avoided by the use of special tools, practices and internal controls of amplification (mimics). Recently, real-time PCR methods (TaqMan, molecular beacons, Primer-Probe Energy Transfer system) have been developed for the diagnosis of a wide range of diseases, such as foot-and-mouth disease, swine vesicular disease and vesicular stomatitis. Multiplex PCR packages have been developed for the simultaneous detection of eight important viruses of swine. By introducing nucleic acid extraction and pipetting robotics, together with the multi-channel real-time PCR machines, the diagnostic procedures have become rapid, robust and automated. In order to standardise the real-time PCR assays, the rules of OIE are considered. By following the five steps of OIE standardisation and validation, the new diagnostic procedures are nationally and internationally standardised and harmonised. The rapid, powerful and internationally standardised molecular diagnosis contributes to the reduction of losses caused by the transboundary viral diseases in swine populations.     

Equine viral arteritis — epidemiology and control

The epizootic of equine viral arteritis (EVA) in the Thoroughbred population in central Kentucky in 1984 aroused concern for a disease whose previous sporadic occurrences had gone largely unnoticed.The threat of spread of EVA through the internal movement of horses led to the imposition of considerable restrictions by other major bloodstock-raising countries on the importation of horses of all breeds from the US. Though in no way disputing the importance of spread of the EVA infection at racetracks, sales and equestrian events, etc., it has become evident that the long-term carrier stallion probably plays a major epidemiologic role in perpetuating the virus from year to year. In contrast to the stallion, the carrier state has not yet been confirmed in the mare, nor has there been any evidence of a congenitally acquired carrier state in foals.     

Use of molecular fingerprinting to assist the understanding of the epidemiology of Salmonella contamination within broiler production

1. We analysed Salmonella isolates by conventional sero- and phage-typing, as well as by molecular techniques within the broiler production chain in two integrated companies. The most prevalent serovars were selected for genetic fingerprinting. 2. Isolates were first screened by plasmid profiling; subsequently, the most common plasmid types within the prevalent zoonotic serovars (enteritidis and typhimurium) and S. agama were further characterised by PstI-SphI ribotyping, and XbaI pulsed field gel electrophoresis (PFGE). 3. Salmonella binza, S. kedougou, and S. 4,12:d:- were endemic in the feed mills over long periods of time, and a variety of plasmid types for each of the serovars were found in the premises. 4. A similar situation was found with S. binza and S. senftenberg within the hatchery in company B. The Salmonella serovars which were resident in those locations were also the ones most widely distributed throughout the broiler flocks. 5. Plasmid profiling was useful to subdivide clusters of isolates within serovars, but for each serovar a high percentage (36 to 79%) of the isolates tested fall within a prevalent plasmid type. 6. A more detailed genetic analysis of the isolates by a multiple typing approach allowed for further strain differentiation, and allowed some epidemiological conclusions to be drawn.     

Observations on the epidemiology and control of viral respiratory disease in cats

The factors which influence the epidemiology of feline upper respiratory disease are defined and their properties considered. The interplay of these factors in determining the pattern of disease outbreaks is explained and, in the light of these interrelationships, logical methods of control are described. Zusammenfassung. Die Faktoren, welche die Epidemiologie der Erkrankungen der oberen Atemwege der Katze beeinflussen, werden definiert und ihre Eigenschaften betrachtct. Das Zusamrnenwirken dieser Faktoren bei der Bestimmung des Verlaufs des Krankheitsausbruchs wird erklärt, und im Licht dieser Wechselbeziehungen werden logische Methoden der Kontrolle dieser Zustände beschrieben. Résumé. Définition et discussion des facteurs qui influencent l'épidémiologie des infections du tractus respiratoire supétrieur du chat. Les interactions de ces facteurs déterminent le mode d'éclosion de l'épidémie et à la lumière de ces données on propose des mesures logiques de lutte contre ces affections.     

水禽的主要病毒性疾病及其防控方法

尽管鸡和火鸡是兽医临床实践中见到的主要家禽种类,但鸭和鹅等水禽偶尔也会遇到。水禽的一个重要特征是它们的生活环境通常会涉及到人造或天然的水体。这提高了野生和家养的水禽混合生活的概率,最终促进了疾病的传播。此外,环境条件也有可能影响家养水禽疾病的临床表现。许多疾病能够影响各种水禽。本文所介绍的传染性疾病是家养水禽中最常见的病毒性疾病。病毒性疾病似乎将是今后引起水禽发病的重要因素。我们需要对这些疾病的来源给予较大的关注。     

Major viral diseases of waterfowl and their control

1鸭肝炎病毒鸭肝炎 (Duck Virus Hepatitis,DH)是一种具有高度致命性、传染性的疾病,能在1～28日龄的幼龄雏鸭中迅速传播.迄今,已有三种不同的病毒被认为与此病有关,分别是鸭肝炎病毒(DHV)1型、2型和3型.自从1949年长岛首次报道DHV-1感染以来,世界各地都已有感染的报告,并且对所有养鸭场都具最重要的经济意义,因为在感染未得到控制时,会引起较高的死亡率.     

卫星会聚焦疫苗来控制猪病毒性疾病

最近,在韩国济州岛召开的国际猪病大会上,Komipharm国际公司主办了一个卫星会议。1 PRRSV疫苗的开发美国的X.J.Meng教授提交了一篇报告,其内容是关于最新的PRRSV疫苗和控制措施。     

Characteristics in the epidemiology of bovine viral diarrhea virus (BVDV) of relevance to control

An understanding of the driving forces of BVDV transmission can be gained by considering the reproductive rate, between individuals and between herds. The former determines the prospects for eliminating the infection from herds, and the latter is the key to persistence at the population level. In this paper, the relation between these two characteristics, their underlying parameters and measures and priorities for BVDV control are discussed. A general model for BVDV control is outlined, with bio-security, virus elimination and monitoring as three necessary consecutive elements, and with immunization as an optional step. A distinction is made between systematic and non-systematic approaches to BVDV control (where the former refers to a monitored and goal-oriented reduction in the incidence and prevalence of BVDV infection and the latter to where measures are implemented on a herd-to-herd decision basis and without systematic monitoring in place). Predictors of progress for systematic control approaches in general are discussed in terms of the abilities: to prevent new infections, to rapidly detect new cases of infection, to take action in infected herds and to gain acceptance by stakeholders. We conclude that an understanding not only of the biology, but also of the social factors - human behavior, the motives that makes stakeholders follow advice and the cultural differences in this respect - are important factors in forming recommendations on alternative strategies for BVDV control.     

The role of mathematical modelling in understanding the epidemiology and control of sheep transmissible spongiform encephalopathies: a review

To deal with the incompleteness of observations and disentangle the complexities of transmission much use has been made of mathematical modelling when investigating the epidemiology of sheep transmissible spongiform encephalopathies (TSE) and, in particular, scrapie. Importantly, these modelling approaches allow the incidence of clinical disease to be related to the underlying prevalence of infection, thereby overcoming one of the major difficulties when studying these diseases. Models have been used to investigate the epidemiology of scrapie within individual flocks and at a regional level; to assess the efficacy of different control strategies, especially selective breeding programmes based on prion protein (PrP) genotype; to interpret the results of scrapie surveillance; and to inform the design of surveillance programmes. Furthermore, mathematical modelling has played an important role when assessing the risk to human health posed by the possible presence of bovine spongiform encephalopathy in sheep. Here, we review the various approaches that have been taken when developing and analysing mathematical models for the epidemiology and control of sheep TSE and assess their impact on our understanding of these diseases. We also identify areas that require further work, discuss future challenges and identify data gaps.     

The epidemiology of viral infections in dogs and cats

Understanding the epidemiology of an infectious disease is a prerequisite to be being able to suggest the most appropriate methods for prevention and control of the disease. This article reviews some important epidemiologic concepts.     

The role of epidemiology in the prevention, diagnosis, and control of infectious diseases of fish

Epidemiologic methods are essential to understanding infectious diseases in aquaculture. Unfortunately, many of these methods are poorly understood or not utilized by fish-health scientists and aquaculturists — often because of the lack of contact with epidemiologists who are willing to investigate fish diseases. In this paper, we describe direct interactions between epidemiologists and fish-health specialists that have resulted in an improved understanding of the causes and management of infectious diseases in aquaculture. We focus on risk-factor studies, risk analysis and infectious-disease modeling, evaluation of diagnostic tests and experimental studies. We also describe characteristics of confined fish populations that make them ideal for developing and testing epidemiologic models and the theoretical and practical challenges of designing and conducting epidemiologic studies in fish farms. Throughout our presentation, emphasis is given to characteristics, opportunities and problems associated mainly with conducting epidemiologic studies to intensive aquaculture systems. We conclude that the development of increased cooperation among epidemiologists, fish-health scientists and aquaculturists will be mutually beneficial and, therefore, efforts for such collaboration should be initiated from all parties involved.     

The epidemiology of infectious diseases of livestock

From the time of the first modern studies of infectious diseases, by Koch, Pasteur, Theiler and their colleagues, it has been clear that laboratory investigation must be complemented by epidemiologic investigation. The measurement of all aspects of the natural history of a disease in naturally affected populations is necessary if we are to rationally design control regimens. Building upon a historic perspective, this paper presents a view of the present status of epidemiology as it pertains to animal disease control, and presents a view of the merits of expanding the use of this science in future animal disease control programs, internationally, in developed and developing countries. The basis for this view lies in adaptation of principles employed in human infectious disease epidemiology, and principles which guide the organization of international disease control agencies.     

牛常见病毒性疾病及其防控方法

<正>牛病毒性疾病是牛养殖业中的常见病,由病毒引起的病毒性疾病具有传播速度快、流行范围广、传播途径多和发病率高等特点,可给牛养殖业带来较大的危害。为此,应明确牛病毒性疾病的发病原因和临床症状,并进行科学诊断,为之后的防控提供依据。