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Effective epidemic control can't be had for nothing

14/2001, 24.04.2001

Strict controls of the global animal trade are the only way of preventing the risks of infection

Are infectious diseases in our animals on the advance and to what extent is there a risk for consumers? Many people in Germany are asking this question given the headlines about BSE, bovine tuberculosis and foot-and-mouth disease. Thanks to concerted control measures major epizootics of relevance to man could be eradicated or dramatically reduced in the past. They include bovine, sheep, goat and porcine tuberculosis, bovine and porcine brucellosis and contagious bovine, sheep and goat pleuropneumonia. These and other infectious diseases and pathogens can (re)enter Germany at any time through the animal trade and animal transports (over long distances and through regions with a different incidence of pathogens), through food and other products of animal origin but also through humans themselves. Even if no worrying trends for the consumer can be identified from the current data, BgVV is still advising against relaxing epidemic control on the basis of the successes achieved. Infection risks can only be contained by strict health controls of all animals in the animal trade. They can never by completely ruled out. The necessary tests are both staff intensive and costly but without this outlay the health protection of consumers cannot be guaranteed.

Diseases which can be transmitted through direct contact or from foods of animal origin to humans are called zoonoses. They include a number of diseases that can be transmitted through bacteria and viruses as well as, for instance, bovine spongiform encephalopathy (BSE). Foot and mouth disease is not a zoonosis in the narrower sense of the word. It does, however, rank amongst the most infectious epizootics although it is of scarcely any relevance for human health. The case of tuberculosis demonstrates just how important consistent and ongoing epidemic control is. Bovine tuberculosis is caused by Mycobacterium (M) bovis. This epizootic occurs all over the world. The pathogen can be transmitted through insufficiently heated, contaminated milk but also directly to humans and trigger classical tuberculosis. In 1950 10 to 30% of all cases of tuberculosis in humans in Germany and Europe were still infections with M. bovis. Thanks to the consistent state control of bovine tuberculosis and the strict pasteurisation of milk, infections with M. bovis have largely lost their importance for man. Since 1997 Germany has been considered to be "free" from bovine tuberculosis, i.e. isolated cases of tuberculosis only occur in less than 0.01% of all stocks.

As a consequence of the decline in cases of tuberculosis, proven epidemic control and epizootic diagnostic measures have been markedly reduced since the mid-1990s. For instance, intracutaneous sampling is no longer undertaken of cattle stocks. This skin test not only provided indications of infections with M. bovis but (when using avian tuberculin) also of M. avium, the pathogen of avian tuberculosis. This was expected to lead to savings of around DM 10 million. BgVV pointed out that the downside to these savings was the acceptance of a step back in consumer protection and the reduction in diagnostic monitoring was pointless against the backdrop of the worldwide animal trade. Since then, infections with M. avium have taken on new health relevance around the world. To the fore are infections of HIV infected persons often leading to death. An increase in infections with M. avium has also been recorded for non-HIV infected persons. The risk potential lies above all in the resistance of the pathogens to conventional medicines. Another mycobacterium, the pathogen of bovine paratuberculosis, M. avium ssp. is also being discussed in connection with its involvement in the occurrence and development of Crohn's disease, a severe chronic intestinal infection in man.

Another worrying development in respect of epidemic hygiene is confirmed in the zoonosis reports published every year by BgVV. According to them, there is a general drop in diagnostic laboratory pathogen differentiations. However, the value of their predictive power depends on the number undertaken. What makes the situation even more complicated is that a change in eating habits goes hand in hand with the increased risk of the transmission of zoonoses. In particular the trend towards the consumption of untreated, raw food is to be viewed critically from the angle of epizootic hygiene. Raw milk and non-heated meat products or meat products contaminated again after heating can be the ideal breeding ground for a series of pathogens.

A number of reference and consultant laboratories have been set up in Germany for the control and surveillance of the major zoonoses and epizootic pathogens. Some of them are attached to BgVV. They elaborate and assess new diagnostic laboratory methods and lay the foundations for understanding infection sources and chains by developing molecular biological characterisation processes. A free overview of the German reference and consultant laboratories can be obtained by writing to the BgVV Press and Public Relations Office. The annual zoonosis reports can be found on the Institute website on www.bgvv.de.

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