Outbreaks of Pneumocystis carinii pneumonia occurred in colonies of nulnu and scidlscid mice at four different institutions. The disease, which was characterized by chronic wasting and respiratory insufficiency, was more severe in older mice and in animals housed in cages with special protective tops. Histopathologic features included alveolar filling with the typical foamy honeycomb material and a mild, nonspecific host inflammatory response. Immunofluorescence and immunoblotting studies suggested the P. carinni isolate was of mouse rather than of rat or human origin, and the outbreaks could be related to each other by common vendor or source of breeding animals. Once P. carinii became established in a mouse colony, the organism tended to persist for long periods of time. The principal control measure was depopulation of the colony, although limited experience with the administration of trimethoprim-sulfamethoxazole was encouraging. Thus, outbreaks of pneumocystosis are a serious problem among colonies of immunodeficient mice, with important implications for the use of these animals in biomedical research. Data obtained by studying these outbreaks should enhance understanding of the pathogenesis of P. carinii pneumonia and be helpful in formulating improved methods of detection and control.
Environmental variables can have profound effects on the biological responses of research animals and the outcomes of experiments dependent on them. Some of these influences are both predictable and unpredictable in effect, many are challenging to standardize, and all are influenced by the planning and conduct of experiments and the design and operation of the vivarium. Others are not yet known. Within the immediate environment where the research animal resides, in the vivarium and in transit, the most notable of these factors are ambient temperature, relative humidity, gaseous pollutant by-products of animal metabolism and physiology, dust and particulates, barometric pressure, electromagnetic fields, and illumination. Ambient temperatures in the animal housing environment, in particular those experienced by rodents below the thermoneutral zone, may introduce degrees of stress and thermoregulatory compensative responses that may complicate or invalidate study measurements across a broad array of disciplines. Other factors may have more subtle and specific effects. It is incumbent on scientists designing and executing experiments and staff responsible for animal husbandry to be aware of, understand, measure, systematically record, control, and account for the impact of these factors on sensitive animal model systems to ensure the quality and reproducibility of scientific studies.
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