Damage control: a guide to dealing with an infectious break.

A change in the microbial status of laboratory animals can represent a disruptive event in the research process. The author suggests a sequence of events from the time a facility learns of a potential infectious "break," through investigation of its source, and its ultimate control.

Latent Pneumocystis carinii infection in commercial rat colonies: comparison of inductive immunosuppressants plus histopathology, PCR, and serology as detection methods.

Histopathologic evaluation combined with a period of immunosuppression has been the standard procedure for detection of Pneumocystis carinii in commercial rat colonies. Variation in induction regimens and in the sensitivity of detection methods may result in underreporting of the presence of P. carinii in breeding colonies or delay its detection. In the present study, methylprednisolone and cyclophosphamide were evaluated for the ability to induce P. carinii infection in rats from an enzootically infected commercial barrier colony. The presence of P. carinii was detected by histopathologic methods and by amplification of a targeted region of the P. carinii thymidylate synthase gene by PCR over the 8-week study period. Sera taken from rats prior to either induction regimen were evaluated for the presence of P. carinii-specific antibodies by the immunoblotting technique. Few significant differences in ability to induce organism burden or in histopathology were observed between the two immunosuppressive regimens. However, a dramatic loss of weight over the study period was observed in rats treated with methylprednisolone but not in rats treated with cyclophosphamide. Although histopathologic changes attributable to P. carinii did not appear before 2 weeks with either immunosuppressant, the presence of the organism in these animals was detected by immunoblotting and PCR. Cyst scores and the intensities of the histopathologic lesions increased during the study period, but the number of rats exhibiting evidence of P. carinii infection did not change after week 3. These results suggest that use of the PCR method on postmortem lung tissue of rats without prior induction regimens or identification of anti-P. carinii antibodies in antemortem serum samples is a sufficiently sensitive method for detection of the presence of a P. carinii carrier state in rodent breeding colonies.

Epizootic of group B Streptococcus agalactiae serotype V in DBA/2 mice.

Beta-hemolytic Streptococcus agalactiae serotype V was identified as the cause of an infection in laboratory mice. Principally, the organism induced fatal septicemia in DBA/2 breeding-age mice. The syndrome appeared to originate as an ascending pyelonephritis, which progressed to septicemia. Microscopic lesions were found in the heart, kidneys, spleen, and liver, and less commonly in the uterus, thoracic cavity, lymph nodes, and lungs. The epizootic was controlled by eradication of the breeding colonies, disinfection of the barrier, and autoclaving of all equipment. The new replacement colonies have remained free of the organism.

Detection of Pneumocystis carinii in rats by polymerase chain reaction: comparison of lung tissue and bronchoalveolar lavage specimens.

The purpose of this study was to determine and compare the efficiency of detection of Pneumocystis carinii in rats by polymerase chain reaction (PCR) of DNA extracted from two sampling locations: lung tissue and bronchoalveolar lavage. The study involved naturally infected F344 rats that were allotted to groups to intercollate the investigation of several variables, including nonimmunosuppressed rats, rats subjected to a timed induction sequence of 1 to 4 weeks of immunosuppression, and two immunosuppressants: a corticosteroid and cyclophosphamide. The PCR amplified a 357-base pair region contained within the gene encoding the large ribosomal RNA subunit of P. carinii mitochondrial DNA. The identity of the PCR product was confirmed by Southern blot analysis with an oligonucleotide probe. In a comparison of lung bronchoalveolar lavage specimens after immunosuppression, P. carinii was detected by PCR in 100% of lung tissue but in only 87.5% of the lavage specimens. Lung tissue of three animals was test-positive when the corresponding lavage specimen was negative by PCR analysis. The PCR detected P. carinii in both types of specimens from the same two of three nonimmunosuppressed rats. In all there was 88% agreement of PCR results between the two sampling techniques. The difference in diagnostic outcome for the two specimen types was not statistically significant (Fisher's exact test). It was concluded that both specimen types were adequate for PCR detection of P. carinii in rats.

Methylmethacrylate: tissue distribution and pulmonary damage in rats following acute inhalation.

Distribution in blood, brain and lungs, and histopathologic changes in brain and lungs of rats following inhalation exposure to methylmethacrylate monomer (MMA) are reported. On exposing groups of four male rats to air containing 100 ppm of MMA, the concentration of MMA in the tissues determined by headspace gas chromatography, was found to be 11.14 +/- 1.05 mg % in blood, 25.24 +/- 2.04 micrograms/g in brain, 20.60 +/- 1.01 micrograms/g in lungs; these did not change significantly with different exposure periods. Interalveolar congestion/hemorrhage, pulmonary vasodilation and edema were observed with rats exposed for 2,3 and 4 hours but not for 1 hour. No histopathologic changes were seen in the brain of any of the exposed rats.

Effect of propoxur-impregnated pesticide tape on mouse cholinesterase levels.

Mice housed in polycarbonate cages, either with or without fiberglass filter bonnets, were exposed to propoxur-impregnated tape for 2 hours, 24 hours, or 7 days. Both erythrocyte and serum cholinesterase levels were determined at each time point. Body weights were also measured. There was no change in body weight or serum cholinesterase level. Erythrocyte cholinesterase level showed significant decrease, related to increasing length of exposure.

Pancreatic carcinoma induced by N-methyl-N'-nitrosourea in aged mice.

We have studied the ability of N-methyl-N'-nitrosourea to induce pancreatic carcinoma within 5 months when single doses were administered to C57BL/6J male mice at 3, 12 and 24 months of age. Pancreatic tumors were not observed in the young and middle-aged animals, but 3/15 of the surviving aged mice showed gross evidence of carcinoma. Ultrastructural analysis revealed in each tumor the presence of two populations of undifferentiated cells, both cell types possibly being of acinar cell origin. The observation of pancreatic carcinoma only in aged animals treated with an environmental carcinogen may be a model paralleling the human condition, which also shows a strong age dependency.

Reaginic hypersensitivity in Otodectes cynotis infestation of cats and mode of mite feeding.

Otodectes cynotis infestations were induced in barrier-reared mite-free cats. By monitoring the infested cats, sequence of humoral and cellular immune reactions to the mites was determined. Delayed hypersensitivity was not demonstrated in vivo, using intradermal skin tests. Reaginic (immunoglobulin E) antibodies, as detected by 72-hour passive cutaneous anaphylaxic reactions, were the earliest form of immune expression. Precipitating antibodies developed later in the course of the experimental infestation. Hematologic indices, including eosinophil counts, were not affected by established infestations. Antibodies prepared against feline whole blood, lymph, epithelium, and RBC indicated that these regularly occurred in extracts prepared from whole mites. It was concluded, therefore, that the feeding mode of mites required that they ingest feline tissue fluids. This mode is the interface by which the host becomes exposed to, and immunized against, mite antigens.

Development of an 82.2 degrees C (180 degrees F) temperature indicatior system for monitoring equipment washing and sanitizing programs.

A survey performed at 12 institutions showed that while the temperatures in the water tanks of mechanical cage washers were monitored, these temperatures deviated from the temperatures obtained on the items actually being washed. Most surveyed facilities were not meeting the 82.2 degrees C (180 degrees F) standard in the washing chamber. A temperature indicator was developed which revealed whether 82.2 degrees C had been reached at the surface of the items being sanitized. The indicator was a sealed glass ampule which produced a visible color change when exposed to temperatures of 82.2 degress C or higher. The indicator was located on the items being washed. Due to the variability of water heating in washing machines, it was recommended that one indicator be used in each load of equipment being sanitized.

Evaluation of a disposable water system during shipment of laboratory rats and mice.

The efficacy of a newly developed system for providing water to boxed rodents during shipment was evaluated. The system, composed of a water filled disposable plastic pouch and a disposable automatic drinking valve, was measured against two products commonly used to provide moisture during transit, canned gelled rodent diet and potatoes. The evaluations were made under conditions of both long (72-88 hour) and short (26 hour) duration trips using regularly scheduled commercial common carriers. Differences in body weight of shipped animals compared to that of non-shipped controls of the same age, and differences in body weight between groups were measured. Under all conditions investigated, rats and mice provided with the transit water system lost significantly less weight during transit than those provided with either of the other two water sources. The equilibration period (the time required to recover body weight lost during shipment) was found to be influenced by both the type of water source and the duration of transit. Under all conditions investigated, animals provided with the transit water system recovered more rapidly and had shorter equilibration periods.

The parasitic ecology of the rodent mite, Myobia musculi. IV. Life cycle.

The life cycle of Myobia musculi was determined by daily examination (under anesthesia) of experimentally infested mice. It was found that the larval period lasted 10 days followed by a 5-day nymphal period. Adult forms were seen on the 16th day. Adults produced fertile eggs within 24 hours of their appearance and eggs hatched in 7 days. Thus, the life cycle was completed in 23 days. Application of this information for a successful treatment regimen was discussed. Any treatment which does not kill embryonated eggs must be repeated subsequent to hatching of the eggs but prior to oviposition of fertile eggs by newly hatched females.

The parasitic ecology of the rodent mite, Myobia musculi. III. Lesions in certain host strains.

Mice (C57BL/6N) from a commercial production colony with ulcerative skin lesions were shown to have low level infestations with Myobia musculi. Lesions were abolished by exposure to dichlorvos-impregnated plastic strips. Experimental reinfestation with M musculi resulted in prompt exacerbation of lesions in previously healed mice. Exacerbated lesions were again abolished by subsequent dichlorvos treatments. The histopathology of such lesions was shown to be similar to those in cats allergic to Otodectes cynotis; and a morphologic basis for an allergic interpretation of the myobic lesions in the C57BL/6 mice was described. Other evidence supporting an allergic interpretation included the heritability of susceptibility to such lesions in certain strains, the paucity of mites required for extensive lesions, the chronic duration of infestation required prior to lesion development, and the apparent anamnesis to experimental reinfestation. A large commercial hybrid production colony requiring C57BL/6 females had an incidence of ulcerative lesions (in females) of 20% and depressed reproductive indices. Two 48 hour treatments at an interval of 14 days utilizing dichlorvos-impregnated strips (1 square inch per cage) abolished lesions and elevated production indices for a period of 5 months.

The parasitic ecology of the rodent mite Myobia musculi. II. Genetic factors.

Mice of 4 strains, C57BL/6J, CD2F1(BALB/cCum female times DBA/2Cum male), BRVR/SrCr and BSVS/SrCr, were monospecifically infested with an equal number of Myobia musculi. A single skin field (7mm diam) in the dorsal midline slightly posterior to the eyes was used for periodic observation of mite populations. Mite counts were made by direct microscopic examination of the skin field at 10-da intervals. Data were obtained on mice thus infested and observed for 130 da. Between-strain comparisons differed significantly in the number of Myobia maintained in all cases except between BRVR and BSVS strains. Factors bearing on heritable differences in susceptibility were discussed.

Sialocele (ranula) simulating oral papillomatosis in a domestic (Oryctolagus) rabbit.

A sialocele originating in the duct of the sublingual salivary gland near its opening, close to the lingual frenulum, was observed as a naturally-occurring lesion in a laboratory rabbit. The lesion was assumed during necropsy dissection to be an oral papilloma. Microscopic examination of histologic sections revealed the lesion to have the characteristics of a sialocele (ranula).

Naturally occurring hypertrophic pyloric stenosis in the domestic rabbit.

Hypertrophic pyloric stenosis was observed to occur naturally in laboratory rabbits. Three cases in juvenile and adult rabbits and their antemortem histories were examined. The gross and microscopic pathology were studied. It was shown that not only the pylorus, but the stomach as a whole was increased in size both relatively and absolutely. The thickness of the pylorus was doubled, but its circumference was not increased, in hypertrophic stenosis. The chief histologic finding was hypertrophy of circular and longitudinal smooth muscles and their enveloping fascia. The myenteric plexi were essentially normal in appearance. The literature on a similar condition in man, dog, and cat was reviewed.

Fatal intussusception associated with intestinal coccidiosis (Eimeria perforans) in a rabbit.

Fatal intussusception was observed to be the proximate cause of death in a young (14 wk old) pet male New Zealand white rabbit. The intussusception was ileo-ileal, and this region was shown to be extensively parasitized by Eimeria perforans. It was concluded that the intussusception was consequent to hyperperistalsis induced by the coccidial infection of the intestines.