Volume : 3
Localisation : PUBLICATION OIE
The clinical signs in fish with the diseases listed in the OIE International Aquatic Animal Health Code (referred to hereafter as the Code) are not pathognomonic. Moreover, these infections may occur as subclinical infections of asymptomatic pathogen carriers.
The only dependable approach for diagnosis of fish diseases therefore lies in the specific identification of the pathogens using laboratory methods. These methods, which are suitable for the diagnosis of isolated cases of disease as part of national aquatic animal health surveillance/control programmes, form the main contents of this the Diagnostic Manual of Aquatic Animal Diseases (referred to hereafter as the Manual).
Such health surveillance programmes aim to determine, from the results provided by standardised laboratory procedures performed with samples collected according to defined rules, the health status of aquatic animal stocks from a particular production site and even a geographical zone or entire country. The satisfactory implementation of such aquatic animal health surveillance/control programmes, requires the existence of both adequate legislation and resources in each country interested in aquatic animal health.
The diagnostic methods presented in this Manual are all direct diagnostic methods. Due to the insufficient development of serological methodology, the detection of antibodies to pathogens in fish has not thus far been accepted as a routine diagnostic method for assessing the health status of fish populations. However, the validation of some serological techniques for diagnosis of certain infections could arise in the near future, rendering the use of serology more widely acceptable for diagnostic purposes. At present, the only diagnostic methods that are accepted in those countries where aquatic animal health control programmes are implemented, are based either on isolation of the pathogen followed by its specific identification, or on the demonstration of pathogen-specific antigens using an immunological detection method. General information on diagnostic techniques for fish diseases is given in Chapter I.1.
Molluscan and crustacean diseases differ in some ways from fish diseases. For example, diagnostic methods must be direct because these animals do not produce antibodies to pathogens. General information on diagnostic techniques for mollusc diseases is given in Chapter I.2. and for crustacean diseases in Chapter I.3.
As detailed in Parts 2, 3 and 4 of the Code, the list of notifiable diseases of aquatic animals includes only major diseases of proven aetiology and limited geographical range. The OIE Fish Diseases Commission, therefore, recommended the creation of a list entitled 'Other significant diseases'. The diseases on this list include:
* those that are serious, but that have a broad geographical distribution;
* those causing significant mortality, that are transmissible and of limited geographical range, but for which the aetiological agent has not yet been identified, or for which standard diagnostic methods are not yet available;
* those with the potential for causing large losses, but which are too new for the geographical range to be defined or for the essential epizoological elements to be understood.
It is expected that the diseases on this list will either be elevated to notifiable status or dropped from the list as new information is obtained.
The Manual includes descriptions of diagnostic methods for these 'Other significant diseases' as well as for the notifiable diseases.