Paratuberculosis (Johne’s Disease)

Dear Colleagues,

Johne’s disease is a chronic granulomatous enteritis of ruminants and camelids caused by the bacterium Mycobacterium avium subsp. paratuberculosis (Map). In cattle, the disease typically causes intractable diarrhea and severe wasting in mature animals. The increased awareness of Johne’s disease in the dairy community has also been fostered by reports of the negative impact of Johne’s disease on milk production and the overall economic health of dairies. The disease is also an important issue in meat cattle since in the final and terminal aspects of the disease, animals become emaciated with fluid diarrhea and develop “bottle jaw”, and the carcass may not pass meat inspection for human consumption. From this perspective, paratuberculosis is not a dairies-only problem. There have also been discussions in Europe of disease control programs on a state-by-state or even national level. To establish program effectiveness, baseline prevalence data are needed (especially for different geographic areas and management schemes). Surveys for Map are difficult to accomplish because of the chronic nature of the infection and the lack of good testing methods for animals in the preclinical stages. The route of transmission is largely fecal–oral, with a very large number of organisms being shed in the feces by clinically affected animals. Lower bacterial counts are shed by infected animals without clinical signs of the disease. It has long been recognized that the most susceptible animals are young calves and that it becomes increasingly difficult to infect cattle as they mature. The reason for this resistance in older animals is not known, but this feature of the disease has been used as the cornerstone of JD control programs in dairy herds for many years. So-called “management control programs”, “herd management practices”, “risk management plans”, and “guidelines for the control” or the “manual for the control” focus on strategies that limit the exposure of calves to Map by avoiding both contact with adult cattle and their feces and, in more recent years, also by adopting aggressive culling practices. Cow-calf producers seek to improve the future health and productivity of their breeding herd by selectively culling animals which are diseased, producing suboptimally and raising poor-growing offspring. The culling policies of producers reflect, if only quantitatively, expectations of future herd and individual animal health and performance. For JD, the biological basis of these expectations is influenced by the recurrence rate of disease conditions, such as diarrhea, the production, and the probability of survival for another season. Research into cow-calf culling decision is centered on modeling optimal herd culling policies. Unfortunately, the recommendations set in these programs are generally complex, and it is therefore difficult to determine which recommendations are key elements for JD control and which have limited importance in this respect. Moreover, most, if not all, of the published guidelines for the control of JD are based on within-herd prevalence data and do not take into account that valid prophylaxis measures are not effective until thoroughly applied to all farms in a given area. On the other hand, true prevalence (TP) data extended to expected countrywide/areawide cow level or countrywide/areawide herd level can be deceiving because of several critical issues intrinsic to the tests or to the sampling scheme. These include discrepancies between comparison from the same country or area, sampling schemes used in study design not suitable for inference in the target population, discrepancies between TPs calculated by authors, and most likely test accuracy estimates.

For these reasons and in an attempt to shed some light especially, but not limited to the selection of the most promising control measures along with diagnosis tests, we have decided to publish a special issue on Johne's disease and are inviting researchers to contribute. We believe that this special issue can become a reference collection of documents to improve the knowledge of this disease and help a wide audience of readers, including professionals, veterinarians, farmers and students get up-to-date information and suggestions at hands.

Prof. Dr. Beniamino T. Cenci-Goga
Dr. Luca Grispoldi
Guest Editors

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• Johne’s disease
• paratuberculosis
• cattle
• ruminants
• Mycobacterium
• shedder
• diarrhea