Summary There is strong evidence to suggest that climate change has, and will continue to affect the occurrence, distribution and prevalence of livestock diseases in Great Britain (GB). This paper reviews how climate change could affect livestock diseases in GB. Factors influenced by climate change and that could affect livestock diseases include the molecular biology of the pathogen itself; vectors (if any); farming practice and land use; zoological and environmental factors; and the establishment of new microenvironments and microclimates. The interaction of these factors is an important consideration in forecasting how livestock diseases may be affected. Risk assessments should focus on looking for combinations of factors that may be directly affected by climate change, or that may be indirectly affected through changes in human activity, such as land use (e.g. deforestation), transport and movement of animals, intensity of livestock farming and habitat change. A risk assessment framework is proposed, based on modules that accommodate these factors. This framework could be used to screen for the emergence of unexpected disease events.

During 1993 outbreaks of diarrhoea in adult dairy cows in three geographically unrelated herds were found to be caused by bovine viral diarrhoea virus (BVDV). The affected animals showed signs of acute watery diarrhoea, agalactia and pyrexia (39.4 to 42 degrees C). Ulceration of the buccal mucosa, a mucoid nasal discharge and stiffness were inconsistent signs. The disease spread rapidly in each case. The diagnosis was confirmed by the isolation of non-cytopathic BVDV from blood and tissues and by the demonstration of significantly rising titres to BVDV by an ELISA. The highest morbidity recorded was 40 per cent with one herd experiencing a 10 per cent mortality. There was no increased incidence of abortion in any of the herds, either at the time of or subsequent to the outbreaks of diarrhoea. In one herd the purchase of a persistently viraemic heifer 14 days before the outbreak was thought to be the source of infection, but in the other two herds the source was not established.

A total of 253 submissions from adult cattle 'found dead' in England and Wales were referred to the Veterinary Laboratories Agency in 2004. Carcases accounted for 54 per cent of the submissions and were of more diagnostic value than other types of sample. Whether the animals were beef or dairy, their distance from the laboratory and the number of deaths in the incident affected the likelihood of samples being submitted. The probability of reaching a diagnosis was influenced by the type of sample, the level of testing and the interval from sampling to receipt in the laboratory. Systemic disease was the most frequent cause of death in both dairy and beef cattle with hypomagnesaemia being the most frequent diagnosis (52 per cent) in beef cattle. In dairy cattle, 34 per cent of the diagnoses were for sporadic events, including haemorrhage and torsions of the digestive and reproductive tracts.

The analysis of laboratory data can provide information about the health of livestock populations; in Great Britain the Veterinary Investigation Diagnosis Analysis (VIDA) system has provided such data since 1975. However VIDA covers only known diagnoses, with limited epidemiological characterisation. The unexpected outbreak of bse showed that it was necessary to improve surveillance to detect new diseases, and a necessary update of the VIDA database for the millennium date change provided the opportunity. The information required to enhance the value of laboratory data was identified, a new form and database, 'FarmFile', were designed to record it, and they began to be used in 1999. The detection of new diseases depends on making comparisons with the expected or 'usual' levels of unexplained disease. The data are analysed quarterly to assess any changes in the levels of unexplained disease in different species, categorised in terms of clinical sign or body system, by comparison with previous years. No new diseases have been detected either through FarmFile or more traditional means since the new analyses started in earnest in 2004, but they have indicated that an unexplained event was not a new disease of concern, and developments continue to improve the system's sensitivity and specificity.

The monitoring and surveillance of animal diseases is becoming increasingly important to policy-makers in Great Britain particularly given recent incursions of avian influenza and the emergence of bovine spongiform encephalopathy. To meet this surveillance objective, data from British livestock is collected and analysed retrospectively on an ongoing basis. However, these data can also be analysed prospectively within an early detection system which raises alerts to significant increases in disease reporting soon after they occur in the field. The feasibility of such an approach has been examined previously for Salmonella. This paper applied the approach to a further subset of surveillance data to alert those monitoring disease to increases in potentially new and emerging diseases. Thus far, the analysis, conducted on a quarterly basis, has proved a useful additional tool in enhanced surveillance by raising alerts to significant increases in several syndromes in both sheep and cattle.