R. M. Christley

Recent network evolution increases the potential for large epidemics in the British cattle population

Following the foot and mouth disease epidemic in Great Britain (GB) in 2001, livestock movement bans were replaced with mandatory periods of standstill for livestock moving between premises. It was anticipated that these movement restrictions would limit each individuals contact networks, the extent of livestock movements and thus the spread of future disease outbreaks. However, the effect of behaviour changes on the global network in adapting to these restrictions is currently unknown. Here, we take a novel approach using GB cattle movement data to construct week-by-week contact networks between animal holdings (AH) to explore the evolution of the network since this policy was introduced, the first time network theory has been used for this purpose. We show that the number of AH moving cattle as part of the giant strong component (GSC), representing the region of maximal connectivity, has been increasing linearly over time. This is of epidemiological significance as the size of the GSC indicates the number of holdings potentially exposed to disease, thus giving a lower bound of maximum epidemic size. Therefore, despite restriction of cattle movements, emergent behaviour in this self-organizing system has potentially increased the size of infectious disease epidemics within the cattle industry.

A case‐control study of respiratory disease in Thoroughbred racehorses in Sydney, Australia

In order to investigate the role of infectious agents in the aetiology of lower respiratory tract disease in Thoroughbred racehorses, a matched case-control study was conducted. Cases were identified by the presence of coughing, and were compared to a control population matched on time of sample collection and location within the same training establishment. Tracheal wash samples were collected from 100 cases and 148 controls. Case horses were more likely than controls to have endoscopic and cytological evidence of airway inflammation. There was no significant association between serological evidence of infection by commonly implicated respiratory viruses and coughing. Similarly, mycoplasma were rarely isolated and were not associated with disease. In contrast, there was a strong association between isolation of greater than a total of 10(3) colony-forming units/ml of tracheal wash and coughing. Individual bacterial species associated with disease included Streptococcus zooepidemicus, Streptococcus pneumoniae, Streptococcus suis, Streptococcus sanguis, Pasteurella spp and Bordetella bronchiseptica. This study provides evidence of the role of bacterial infection in the aetiology of lower respiratory tract inflammation in racehorses. However, in 58% of cases, few or no bacteria were isolated. Hence, at the time of identification of disease, there was no evidence of viral, bacterial or mycoplasmal infection in the majority of coughing horses. The aetiology of the signs observed in these horses requires further investigation.

Factors related to the risk of neonatal mortality, birth-weight and serum immunoglobulin concentration in lambs in the UK.

Neonatal-lamb mortality represents an economic loss and welfare concern. Two factors often associated with the risk of mortality are birth-weight and serum immunoglobulin concentration. We used data from two studies to investigate risk factors for mortality between 2 and 14 days of age and factors affecting birth-weight and serum immunoglobulin concentration at 48h of age. Dataset 1 included 1339 lambs born on eight farms during the 1995 spring lambing season; dataset 2 included 3172 lambs on seven farms during the 1991 spring lambing season. To account for some of the potential clustering within the data, multilevel models were used. Most (>75%) of the variation in the risk of mortality was at the lamb level. In dataset 1, factors significantly associated with increased odds of lamb mortality included low birth-weight and low serum immunoglobulin concentration. In dataset 2, significant risk factors for mortality included low birth-weight, ewe body-condition score, being born late in the season (relative to other lambs on the farm) and being born in multiple litters. There was a significant interaction between the effects of litter size and birth-weight. (Serum immunoglobulin concentration was not available for dataset 2.) More than half of the variation in birth-weight was at the ewe level, 27% at the lamb level, and 18% at the farm level (dataset 1). Single birth and being male were associated with increased birth-weight in both datasets. In dataset 2 only, increasing ewe condition score and birth early in the study period were also associated with increased birth-weight. Fifty-six percent of the variation in immunoglobulin concentration was at the lamb level, 36% at the ewe level and only 7% at the farm level. Factors associated with reduced serum immunoglobulin concentration included early or late birth in the lambing season, being born later than 14 days after the first lamb born on the farm, multiple-birth litters and maternal mastitis.

A survey of horse owners in Great Britain regarding horses in their care. Part 1: Horse demographic characteristics and management.

REASONS FOR PERFORMING STUDY Information is scarce as to how horses are kept and managed in the general horse population of Great Britain. OBJECTIVES To characterise the demographics of horses in Great Britain and assess their care (with particular reference to the respiratory system). METHODS Horse owners were surveyed using a self-administered postal questionnaire. These owners were selected randomly, following geographical stratification, using 2-stage cluster sampling of veterinary practices and their clients. RESULTS The overall response proportion to the survey was 68.2%. An investigation of nonresponse bias detected minimal differences between responders and nonresponders. A summary of the demographic characteristics, feeding and management of horses in a sample of the general population of Great Britain is presented. CONCLUSIONS AND POTENTIAL RELEVANCE Horses are kept under a great variety of conditions with some potentially exposed to high concentrations of organic dusts associated with stabling. This information is relevant to their health and welfare.

Factors associated with dog ownership and contact with dogs in a UK community

BackgroundDogs are popular pets in many countries. Identifying differences between those who own dogs or have contact with dogs, and those who do not, is useful to those interested in the human-animal bond, human health and for provision of veterinary services. This census-based, epidemiological study aimed to investigate factors associated with dog ownership and contact with dogs, in a semi-rural community of 1278 households in Cheshire, UK.ResultsTwenty-four percent of households were identified as dog-owning and 52% owned a pet of some type. Multivariable logistic regression suggested that households were more likely to own a dog if they had more occupants (five or more); if they had an adult female household member; or if they owned a horse. The age structure of the households was also associated with dog ownership, with households containing older children (between six and 19 years of age) and young adults (between 20 and 29 years of age), more likely to own dogs. We also found that dog owning households were more likely to be multi-dog households than single-dog if they also owned a cat or a bird, or if the household contained a person of 20–29 years old. Dog owners reported increased contact with dogs, other than their own, compared to those that did not own dogs and this contact appeared to be mainly through walking.ConclusionSome household types are more likely to own a dog than others. This study supports the suggestion that dogs are more common in families who have older children (6–19 years), as has been generally observed in other countries. Dog owners are also more likely to have contact with dogs other than their own, compared with those not owning a dog.

Dog-human and dog-dog interactions of 260 dog-owning households in a community in Cheshire.

This study investigated the nature and frequency of the contacts that occur between dogs, and between dogs and people, by means of a questionnaire survey of 260 dog-owning households in a community in Cheshire, uk. The contacts were highly variable and were affected by the size, sex and age of the dog, individual dog behaviours, human behaviours and human preferences in the management of the dog. A number of situations were identified that may be important in relation to zoonoses, including sleeping areas, playing behaviours, greeting behaviours, food sources, walking, disposal of faeces, veterinary preventive treatment and general hygiene.

Power and error: Increased risk of false positive results in underpowered studies

It is well recognised that low statistical power increases the probability of type II error, that is it reduces the probability of detecting a difference between groups, where a difference exists. Paradoxically, low statistical power also increases the likelihood that a statistically significant finding is actually falsely positive (for a given p-value). Hence, ethical concerns regarding studies with low statistical power should include the increased risk of type I error in such studies reporting statistically significant effects. This paper illustrates the effect of low statistical power by comparing hypothesis testing with diagnostic test evaluation using concepts familiar to clinicians, such as positive and negative predicative values. We also note that, where there is a high probability that the null hypothesis is true, statistically significant findings are even more likely to be falsely positive.

Epidemiological consequences of an incursion of highly pathogenic H5N1 avian influenza into the British poultry flock

Highly pathogenic avian influenza and in particular the H5N1 strain has resulted in the culling of millions of birds and continues to pose a threat to poultry industries worldwide. The recent outbreak of H5N1 in the UK highlights the need for detailed assessment of the consequences of an incursion and of the efficacy of control strategies. Here, we present results from a model of H5N1 propagation within the British poultry industry. We find that although the majority of randomly seeded incursions do not spread beyond the initial infected premises, there is significant potential for widespread infection. The efficacy of the European Union strategy for disease control is evaluated and our simulations emphasize the pivotal role of duck farms in spreading H5N1.

Direct and indirect contacts between cattle farms in north-west England

Little is known regarding the types and frequencies of contact that exist between farms and which of these may act as pathogen transmission routes; however it is likely that farms demonstrate considerable heterogeneity in such contacts. In this cross-sectional study, we explored the direct and indirect contact types and frequencies that exist between cattle farms within a region, focusing on potential routes of pathogen transmission. The owners/managers of 56 farms located in a 10 km by 10 km study area in north-west England were administered an interview-based questionnaire between June and September 2005. Information was obtained relating to contact types and frequencies, including those involving animal movements, equipment sharing between farms and any contractors or companies visiting the farms. The data was explored using hierarchical cluster analysis and network analysis. There was considerable variation between farms arising from different contact types. Some networks exhibited great connectivity, incorporating approximately 90% of the farms interviewed in a single component, whilst other networks were more fragmented, with multiple small components (sets of connected farms not linked with other farms). A range of factors influencing contact between farms were identified. For example, contiguous farms were more likely to be linked via other contacts, such as sharing of equipment and direct farm-to-farm animal movements (p<0.001 and p=0.02, respectively). The frequency of contacts was also investigated; it is likely that the amount of contact a farm receives from a company or contractor and whether or not biosecurity is performed after contact would impact on disease transmission potential. We found considerable heterogeneity in contact frequency and that many company and contractor personnel undertook little biosecurity. These findings lead to greater understanding of inter-farm contact and may aid development of appropriate biosecurity practices and control procedures, and inform mathematical modelling of infectious diseases.

A randomized triple blind trial to assess the effect of an anthelmintic programme for working equids in Morocco

BackgroundGastro-intestinal parasitism has been identified as a significant cause of disease in working equids in many countries. This randomized triple-blind trial was designed to assess the impact of an anthelmintic treatment programme (using oral ivermectin and fenbendazole) comparing treated and placebo control populations of working donkeys, mules and horses in field conditions in Morocco. In particular, we assessed animal body weight and condition score, together with a questionnaire-based owner evaluation of number of subjective animal health parameters. Faecal worm egg count was also measured.Results239 animals completed the full study, 130 in the treatment group and 109 in the control group. Although the average animal weight increased during the study, this change was not significantly different between the two groups. Animals in the treatment group had a significantly lower strongyle worm egg count and increased in body condition score compared to animals in the control group at each examination during the study period. Owners of animals in the treatment group reported improvement in health and work ability and a beneficial effect on pruritus during the early period of the study. These differences in owner perception between treatment groups had disappeared in the latter stages of the study.ConclusionThis study demonstrated that a routine anthelmintic treatment programme of three treatments annually can have a significant effect on faecal worm egg count. There may be beneficial consequences for the animal health and productivity. Further research on other populations of working equids in different environments would facilitate the objective planning of effective parasite control strategies for specific situations and provide better understanding of the likely clinical benefits of such programmes.