Theoretical value of pre-trade testing for Salmonella in Swedish cattle herds

The Swedish Salmonella control programme includes mandatory action if Salmonella is detected in a herd. The aim of this study was to assess the relative value of different strategies for pre-movement testing of cattle. Three fictitious herds were included: dairy, beef and specialised calf-fattening. The yearly risks of introducing Salmonella with and without individual serological or bulk milk testing were assessed as well as the effects of sourcing animals from low-prevalence areas or reducing the number of source herds. The initial risk was highest for the calf-fattening herd and lowest for the beef herd. For the beef and dairy herds, the yearly risk of Salmonella introduction was reduced by about 75% with individual testing. Sourcing animals from low-prevalence areas reduced the risk by >99%. For the calf-fattening herd, the yearly risk was reduced by almost 50% by individual testing or sourcing animals from a maximum of five herds. The method was useful for illustrating effects of risk mitigation when introducing animals into a herd. Sourcing animals from low-risk areas (or herds) is more effective than single testing of individual animals or bulk milk. A comprehensive approach to reduce the risk of introducing Salmonella from source herds is justified.

Molecular insights into farm animal and zoonotic Salmonella infections

Salmonella enterica is a facultative intracellular pathogen of worldwide importance. Infections may present in a variety of ways, from asymptomatic colonization to inflammatory diarrhoea or typhoid fever depending on serovar- and host-specific factors. Human diarrhoeal infections are frequently acquired via the food chain and farm environment by virtue of the ability of selected non-typhoidal serovars to colonize the intestines of food-producing animals and contaminate the avian reproductive tract and egg. Colonization of reservoir hosts often occurs in the absence of clinical symptoms; however, some S. enterica serovars threaten animal health owing to their ability to cause acute enteritis or translocate from the intestines to other organs causing fever, septicaemia and abortion. Despite the availability of complete genome sequences of isolates representing several serovars, the molecular mechanisms underlying Salmonella colonization, pathogenesis and transmission in reservoir hosts remain ill-defined. Here we review current knowledge of the bacterial factors influencing colonization of food-producing animals by Salmonella and the basis of host range, differential virulence and zoonotic potential.

Towards incorporating spatial risk analysis for Salmonella sero-positivity into the Danish swine surveillance programme

An increased incidence of pork-related human salmonellosis in Denmark led to the development of a national control programme for Salmonella in Danish swine herds in 1993. The aim of the programme has been met and now the issue of cost-effectiveness is receiving greater attention. An appropriate way to address this is to bring a risk-based focus to the programme. We describe a practical approach to risk-based surveillance through spatial risk assessment using serological and questionnaire data from 2280 herds in 1995. A mixed effects logistic regression model was fitted and both first- and second-order spatial properties of the random effects were investigated. We identified wet-feeding (OR: 0.64; 95% CI: 0.54-0.75) and SPF health status (OR: 0.65; 95% CI: 0.52-0.81) as protective factors for Salmonella sero-positivity. Purchasing feed (OR: 1.81; 95% CI: 1.61-2.04) was a risk factor. The west of the study area generally, and the north of Jutland in particular, experienced the greatest disease risk after controlling for the covariates. There was some evidence for spatial dependency between farms at distances of 6 km (95% CI: 2-35 km) on the Jutland peninsula. We conclude that when farm location details are analysed in conjunction with routinely recorded surveillance information (such as that collected by the Danish swine Salmonella control programme) and targeted industry surveys (such as those conducted by slaughterhouse co-operatives), our knowledge of the behaviour of disease in animal populations is enhanced and this provides a more informed framework for designing efficient, risk-based surveillance strategies.

A cost-benefit analysis of Salmonella-control strategies in Danish pork production

In Denmark, it was agreed to lower the Salmonella prevalence in pork to 1.2% before the end of 2006. The current control did not seem to be sufficient to attain this goal. Therefore, four alternatives to the existing Danish control strategy for Salmonella in pork were compared in a cost-benefit analysis: (1) hot-water decontamination of all pigs at slaughter, (2) sanitary slaughter of pigs from herds with high levels of Salmonella, (3) use of home-mixed feed in herds with slaughter pigs and (4) use of acidified feed for slaughter pigs. The data originated from official statistics, published papers as well as expert opinion. The partial cost-benefit analysis was restricted to slaughterhouses affiliated with the Danish Meat Association and Danish human cases ascribable to pork from these slaughterhouses. Only hot-water decontamination was socio-economically profitable. Hot-water decontamination had a net present value over 15 years of 3.5 million euros. For sanitary slaughter the net present value was - 43.6 million euros, for home-mixed feed it was - 262.3 million euros and for acidified feed it was - 79.9 million euros. For all alternatives the costs were born solely by the pig sector, whereas primarily the consumers and public authorities received the benefits. The conclusions were robust in sensitivity analyses.

[The importance of different pig diseases in the Netherlands]

As part of the project 'Clean pigs', IPG Institute for Pig Genetics BV made an inventory of the impact of different diseases on the Dutch pig industry. An expert panel assessed the importance of the different diseases with regard to public health, farm economy, the pig sector and export sales. The possibilities for the diagnosis of the different pathogens were listed and the goal for the next years, was set. Diseases were classified into three categories, according to their importance for the Dutch pig industry (Table 2). The diseases that can be eradicated are Salmonella (only specific strains), Pasteurella multocida DNT + PAR), Actinobacillus pleuropneumoniae, Haematopinus suis (lice) and Sarcoptes scabei (var. suis) (mange). National introduction of list A en most list B diseases of the OIE classification must be prevented.

Some aspects of the epidemiology and control of Salmonella typhimurium infection in outwintered suckler cows

Two outbreaks of Salmonella typhimurium infections affected outwintered, spring-calving suckler cows in late pregnancy. The infections spread rapidly both within and between groups of stock on the affected farms, with morbidity in the infected groups varying from 14.5 per cent to over 60 per cent, and mortality in adult cattle varying from 0 to 14.3 per cent. Prophylactic measures included the use of antibiotics and killed vaccines against Escherichia coli, Salmonella dublin, S typhimurium, and Pasteurella multocida. In one outbreak, use was also made of a polyvalent serovaccine and hyperimmune serum against E coli, S typhimurium, and S dublin. In both outbreaks no new cases were reported in the affected groups after the administration of the second dose of vaccine, and there was no resurgence of disease on the affected farms within 18 months of the primary outbreaks.

The economic impact of poultry-borne salmonellosis: how much should be spent on prophylaxis?

Foodborne salmonellosis constitutes a major health problem in many countries. Moreover, the costs associated with salmonellosis could be considerable. There are thus strong arguments for preventive efforts. Ambitious, often government-sponsored, programmes aimed at preventing and controlling salmonellosis in for instance, poultry production represent one alternative to lower salmonellosis-related illness and economic costs. On the other hand, such comprehensive programmes are rather resource-demanding. From the economic point of view the key problem is to find the optimal level for prophylactic measures. The purpose of this study is to compare two different approaches to preventing poultry-borne salmonellosis among humans. We identify and compare the economic costs of illness due to poultry-borne salmonellosis and the costs of salmonella control in England and Wales and Sweden, respectively. An alternative option is then introduced: the concept of competitive exclusion (CE). Our results show that the cost of illness constitutes the major part of the total cost in England and Wales, whereas in Sweden, the control cost amounts to 95% of the total cost. By using the CE concept, the cost of illness due to poultry-borne salmonellosis in England and Wales could be reduced by at least GB pound 12.6 million. These advantages apply to individuals, producers, and to society, and we thus conclude that the CE concept is a very cost-effective way of using scarce resources.

[Payment of the "Niedersachsen epizootic cash" for animal loss by salmonellosis with regard to the structure of cattle farms]

An evaluation of data from the "Niedersächsische Tierseuchenkasse" with reference to various forms of cattle husbandry shows the crucial influence quality of farm management resp. age structure of the stock are having upon the frequency of animal diseases at least as far as the salmonellosis of cattle is concerned. The assessment takes into account the earlier repeatedly identified relationship between occurrence of animal diseases and stock size. The obligations of the "Niedersächsische Tierseuchenkasse" per contributory animal due to losses in fattening calves farms are about three times as high as in "conventional" cattle farms keeping stock of all ages. The "Niedersächsische Tierseuchenkasse" has therefore developed a special premium class for this specific type of farming with a generally higher premium level. Further measures aiming to improve the current situation of cattle salmonellosis are being discussed.

The impact of zoonotic diseases transmitted by pets on human health and the economy

In the context of all causes of human morbidity and mortality, or even within the context of all infectious diseases affecting the public health, pet-associated zoonotic infections are of moderate importance. The data documented in Table 1, however, indicate that they do exact significant human health and economic costs. If complete data were available for all of the infections shown in Table 1, the costs would be considerably higher. Moreover, most of these diseases are preventable through educating the public, particularly pet owners, of the zoonotic potential of these diseases, so that they may take precautions to minimize the risks leading to infection. These measures include appropriate health care of pets to eliminate infectious agents, reducing the number of uncontrolled, ownerless pets as well as unwanted or poorly supervised pets, preventing pets from soiling public places with their feces, excluding animals from areas where children play, enforcing leash laws, and promoting responsible pet ownership. Veterinarians, physicians, and public health agencies can aid in these efforts; ultimately, however, the responsibility lies with the pet owner.

Is salmonellosis still a serious problem in veterinary practice?

Salmonella infections of food animals are of concern to both the food industry and to the public health authorities. Salmonellosis is one of the major zoonotic diseases and its impact on veterinary practice may be judged by a number of criteria. Some of these are examined to determine the extent of the problem.