Bovine Tuberculosis in Swedish Farmed Deer: Detection and Control of the Disease

Bovine tuberculosis (BTB) was introduced into Swedish farmed deer herds in 1987. Epidemiological investigations showed that 10 deer herds had become infected (July 1994) and a common source of infection, a consignment of 168 imported farmed fallow deer, was identified (I). As trace-back of all imported and in-contact deer was not possible, a control program, based on tuberculin testing, was implemented in July 1994. As Sweden has been free from BTB since 1958, few practicing veterinarians had experience in tuberculin testing. In this test, result relies on the skill, experience and conscientiousness of the testing veterinarian. Deficiencies in performing the test may adversely affect the test results and thereby compromise a control program. Quality indicators may identify possible deficiencies in testing procedures. For that purpose, reference values for measured skin fold thickness (prior to injection of the tuberculin) were established (II) suggested to be used mainly by less experienced veterinarians to identify unexpected measurements. Furthermore, the within-veterinarian variation of the measured skin fold thickness was estimated by fitting general linear models to data (skin fold measurements) (III). The mean square error was used as an estimator of the within-veterinarian variation. Using this method, four (6%) veterinarians were considered to have unexpectedly large variation in measurements. In certain large extensive deer farms, where mustering of all animals was difficult, meat inspection was suggested as an alternative to tuberculin testing. The efficiency of such a control was estimated in paper IV and V. A Reed Frost model was fitted to data from seven BTB-infected deer herds and the spread of infection was estimated (< 0.6 effective contacts per deer and year) (IV). These results were used to model the efficiency of meat inspection in an average extensive Swedish deer herd. Given a 20% annual slaughter and meat inspection, the model predicted that BTB would be either detected or eliminated in most herds (90%) 15 years after introduction of one infected deer. In 2003, an alternative control for BTB in extensive Swedish deer herds, based on the results of paper V, was implemented.

ANIMAL POPULATION ECOLOGY AND CONTROL FUNDAMENTALS

Expensive, extensive and apparently lethal control measures have been applied against many species of pest vertebrates and invertebrates for decades. In spite of this, few pests have been annihilated, and in many cases the stated goals have become progressively more modest, so that now we speak of saving foliage or a crop, rather than extermination. It is of interest to examine the reasons why animals are so difficult to exterminate, because this matter, of course, has implications for the type of control policy we pursue in the future. Also, it has implications for the problem of evaluating comparatively various resource management strategies. There are many biological mechanisms which could, in principle, enhance the performance of an animal population after control measures have been applied against it. These are of four main types: genetic, physiological, populationa1, and environmental. We are all familiar with the fact that in applying a control measure, we are, from the pest's point of view, applying intense selection pressure in favor of those individuals that may be preadapted to withstand the type of control being used. The well-known book by Brown (1958) documents, for invertebrates, a tremendous number of such cases. Presumably, vertebrates can show the same responses. Not quite so familiar is the evidence that sub-lethal doses of a lethal chemical may have a physiologically stimulating effect on population performance of the few individuals that happen to survive (Kuenen, 1958). With further research, we may find that this phenomenon occurs throughout the animal kingdom. Still less widely recognized is the fact that pest control elicits a populational homeostatic mechanism, as well as genetic and physiological homeostatic mechanisms. Many ecologists, such as Odum and Allee (1950, Slobodkin (1955), Klomp (1962) and the present author (1961, 1963) have pointed out that the curve for generation survival, or the curve for trend index as a function of last generations density is of great importance in population dynamics.

SIGNIFICANCE AND CONTROL OF FUNGAL DISEASES RELATED TO BIRD ROOSTS

Certain fungi have been found frequently as saprophytes in areas containing large amounts of bird excreta. These fungi have the ability to survive, multiply, and cause disease once they have entered a host. Two of these are Crypto-coccus neoformans and Histoplasma capsulatum. Both may easily become airborne and be disseminated throughout an area by the prevailing winds. C. neo-formans is commonly isolated from the excreta of pigeon habitats, and in turn has been associated with clinical cases of cryptococcosis, while blackbird roosts, harboring H. capsulatum, have been responsible for several outbreaks of histoplasmosis. When either of these fungi have become established in nature, the sites may become foci for infection and epidemics may occur if the sites are disturbed. This has led to investigation of these organisms with respect to: 1) the frequency of isolation of H. capsulatum from the soil beneath blackbird roosts in a histoplasmosis endemic area; 2) the infectivity of undisturbed roosts positive for H. capsulatum; and 3) the effectiveness of chemical decontamination of areas containing C. neoformans or H. capsulatum.

BLACKBIRD DAMAGE AND CONTROL--AN INFORMAL SEMINAR

The object is to hash over a few problems as we see them on this red-winged blackbird situation. I'm Mel Dyer, University of Guelph, Guelph, Ontario. Around the table are Tom Stockdale, Extension Wildlife Specialist, Ohio Cooperative Extension Service, Columbus; Maurice Giltz, Ohio Agriculture Research and Development Center, Wooster, Ohio; Joe Halusky, U.S. Fish and Wildlife Service, Columbus, Ohio; Daniel Stiles, U.S. Fish and Wildlife Service, Washington, D.C.; Paul Rodeheffer, U.S. Fish and Wildlife Service, Columbus, Ohio; Brian Hall, Blackbird Research Project, University of Guelph, Guelph, Ontario; George Cornwell, Virginia Polytechnic Insti¬tute, Blacksburg, Va.; Dick Warren, Peavey Grain Company, Minneapolis, Minn.; Bob Fringer, N.J. Department of Agriculture, Trenton, N.J.; Charles Stone, U.S. Fish and Wildlife Service, Columbus, Ohio; Larry Holcomb, Ohio Agricultural Research and Development Center, Wooster, Ohio; Doug Slack, Ohio Agricultural Research and Development Center, Wooster, Ohio; Charles Wagg, N.J. Department of Agriculture, Trenton, N.J.; Dick Smith, U.S. Fish and Wildlife Service, Columbus, Ohio; and Jim Caslick, U.S. Fish and Wildlife Service, Gainesville, Fla. As I see the situation, as a director of a red-winged blackbird research project, we have a problem which has been defined in human terms concerning a natural animal population.

THE ORGANISATION OF RABBIT CONTROL (Oryctolagus cuniculus) IN WESTERN AUSTRALIA

ABSTRACT: Under Western Australian legislation, landholders have an obligation to control rabbits on their properties; local authorities the responsibility to supervise their work whilst the Agriculture Protection Board has a Statewide supervisory and co-ordination role. Prior to 1950 (when the Agriculture Protection Board was formed) the central role was in the hands of a Government department which, through lack of staff and money was unable to provide adequate supervision, and rabbits were in plague proportions. Since 1950, the Board has actively engaged in a vigorous policy aimed at tighter control and supervision. To enable this, the Board has entered into a voluntary scheme with local authorities whereby the role of local supervision of landholders is passed to staff employed by the Board, but jointly financed by the local authority and the Board. A contract poisoning service is also pro¬vided by the Agriculture Protection Board to any landholder who is unable or unwilling, to meet his obligations in this area. Both services are subsidised. Two of the major reasons for the poor level of control existing before 1950, have thereby been minimised. Soon after its formation, the Board set up a research section which has devoted nearly all of its activities to applied research on control of the State's many vertebrate pest problems. In the rabbit control area, poisoning has received most attention. The "One-Shot" method of poisoning was developed after years of research. Fumigation is at present being closely studied as is the economics of complete eradication from some areas of the State. Greatest needs in the applied rabbit research field at present are: (1) a selective poison, or poisoning regime, which will not harm stock, and (2) a more complete understanding of the economics of control and eradication. The serious rabbit problem which existed in 1950 has been reduced to very small proportions, by organisational development using local research findings. These organisational developments have been implemented by circumvention rather than confrontation.