National biosecurity approaches, plans and programmes in response to diseases in farmed aquatic animals: evolution, effectiveness and the way forward.

The rapid increase in aquaculture production and trade, and increased attention to the negative effects of disease, are becoming stimuli for developing national biosecurity strategies for farmed fisheries, for which the World Organisation for Animal Health (OIE) Aquatic Animal Health Code and Manual of Diagnostic Tests for Aquatic Animals serve as an excellent framework. Using examples from a few countries and selected diseases, this paper provides a general overview of the development of approaches to implementing biosecurity strategies, including those emerging in the national legislation and regulations of some countries, and those being initiated by industries themselves. The determination of disease status in different epidemiological units (from a farm to a nation), appropriate approaches for preventing the introduction of disease and developing contingencies for disease control and eradication are also discussed. Important to the effectiveness of such strategies are provision of financial, personnel and other resources to implement them, including incentives such as indemnification or compensation in eradication programmes, and practical linkage to regulatory or government policy initiatives.

A new system for monitoring health status in Norwegian aquaculture.

In Norway there is an official system (ANISTAT) for reporting notifiable diseases to the Norwegian Food Safety Authority, which is mainly done by veterinarians and laboratories. Another separate official system (HAVBRUKSDATA) is also in place, for reporting production data from fish farms, such as the number of fish put into the sea, and their weight, density, feed consumption and mortality. The reported data are aggregated monthly with information from companies' private databases related to each production site and each production unit. There also are official procedures in place for the registration of drugs used in aquaculture, based on veterinary prescriptions. However there is no electronic system for active reporting diseases influencing production and/or welfare. It is our aim to establish a more advanced official system for monitoring the health situation in Norwegian fish farms (MFISK) by linking relevant production data from the various private databases to an official disease database. The output of the new system will be improved statistics on diseases in the Norwegian fish farming industry, with diseases sorted by their impact on production and welfare. This will enable us to identify diseases that, over time, cause such losses that they should be dealt with by the authorities, or by the farmers themselves. It will also have an early warning function regarding new/emerging diseases or disease trends. This system quantifies losses due to health problems and, in the long run, will be a useful tool for strengthening fish health. The system aims to combine data from various sources: the veterinary and fisheries authorities in Norway, farmers, veterinarians and laboratories. To be sustainable, it will need the active and constructive cooperation of all these stakeholders.

Nephrotoxicity of Narthecium ossifragum in cattle in Norway.

During the summer of 1992 renal failure was diagnosed in 232 grazing cattle in 85 herds on the west coast of Norway. The salient clinical signs were depression, anorexia and melaena or fresh blood in the faeces; diarrhoea was also commonly observed. The serum concentrations of creatinine, urea, magnesium and phosphorus, and the activities of glutamate dehydrogenase, aspartate aminotransferase and creatine kinase were above normal and the serum calcium concentration was below normal. Post mortem examinations consistently revealed renal tubular necrosis. In some cases there was liver necrosis and also erosions at the base of the tongue, in the oesophagus and in the jejunum and colon. The toxicity was probably caused by the plant Narthecium ossifragum (bog asphodel).

Relationships between teat characteristics and udder health. A field survey.

A field survey in 13 Norwegian dairy herds showed a marked increase in teat size and degree of teat canal eversion during a period of six months while most of the cows were still in the same lactation period. There was a statistically significant relationship between the following variables: teat location (front/rear) and teat length, teat shape and teat size, teat end shape and mastitis prevalence, teat end shape and canal eversion, severe teat canal eversion and mastitis prevalence, teat canal eversion and rough/cracked teat canal, teat canal eversion and teat end oedema, teat end oedema and mastitis prevalence. Many young cows had a normal teat orifice or mild teat canal eversions, but also a greater proportion of young cows had distinct or severe teat canal eversions compared with older cows.

Effect of teatcup liner design on teat characteristics and udder health.

A 6-month field experiment was carried out to test effects of liner design on teats and udder health. 13 herds with 138 cows participated. The liners tested had mouthpiece and barrel diameters of 24/24 mm (A) and 20/21 mm (B), both were Alfa Laval products. Teat length and diameter measured on unstimulated teats between milkings, were significantly affected by the liner used. Liner A gave 2.6 mm longer and 1.4 mm wider teats than liner B at the end of the experiment. The choice of liner had no effect on the severity of teat canal eversions. CMT-score increased over the period, but no difference between liners was observed when data for all cows were included. For first lactating cows there was a different response in the liner groups, with lowest CMT-scores at the end of the experiment for the narrowest liner (B). Laboratory diagnoses of quarter milk samples revealed no effect of liner when all cows were included. The first calvers, however, had significant lower mastitis prevalence rate in the liner B group at the end of the experiment. A tendency towards lower new infection rate, and fewer clinical mastitis cases was also observed for the narrowest liner (B).

Isolation of Bacillus subtilis in connection with bovine mastitis.

Bacillus subtilis has only seldom been associated with pathological conditions in mammals. As the organism is considered to be ubiquitous in the environment, care has to be taken not to put too much emphasis on the pathogenicity of the organism, even in cases where it is isolated in pure culture. Bacillus subtilis was isolated from 17 cases of bovine mastitis in which it was considered to be the etiological factor.

Disease in 27 Norwegian dairy goat farms.

A combination of field registrations and laboratory examinations was used to describe the distribution, morbidity and mortality of disease among dairy goats in the western part of Norway.

Effect of a shielded liner on new mastitis infection.

Results from a field trial involving 23 Norwegian dairy herds support the theory that deflector shields inserted into the teatcup liner can reduce the risk of intramammary infection. However, the effectiveness of this measure is questionable in cows already infected and in problem herds.