Disseminated histoplasmosis by Histoplasma capsulatum var. duboisii in a paediatric patient from the Chad Republic, Africa.

Histoplasmosis caused by Histoplasma capsulatum var. duboisii is an endemic mycosis of sub-Saharan Africa that usually affects the skin, subcutaneous tissue, lymph nodes and bones. We present a case of a 10-year-old immunocompetent girl with severe cutaneous and subcutaneous abscesses affecting the head and upper body. Microscopic examination showed polar budding yeasts and short mycelium compatible with H. capsulatum var. duboisii. Cultures were not possible but serology showed antibodies against both H. capsulatum var. duboisii and H. capsulatum var. capsulatum antigens. Presumptive diagnosis of histoplasmosis was done but treatment with itraconazole was inefficacious. After 15 days of treatment with Amphotericin B i/v, improvement was evident and, three months later, the patient was discharged with only residual lesions. Seven months later, no relapses were observed.

Twelve cases of tinea unguium in a pediatric clinic in 9 years.

Tinea of the nails is not an exclusively adult pathology. The pediatrician should include this entity in the differential diagnosis.

Seasonal distribution of Alternaria, Aspergillus, Cladosporium and Penicillium species isolated in homes of fungal allergic patients.

BACKGROUND: Allergy to airborne fungi can cause rhinitis and severe asthma, hence the exposure to spores inside home is an important factor of sensitization. The aim of this study was to determine the distribution and prevalence of species of Alternaria, Aspergillus, Cladosporium and Penicillium inside and outside of homes of patients allergic to fungi and to evaluate seasonal variations. METHODS: Air samples were collected in 22 selected homes of patients with allergy to fungi using a volumetric method of impacting plates with culture media. The isolated species were identified and statistical analysis of the presence of the four fungi was carried out. RESULTS: A total of 431 indoor and 150 outdoor exposed plates were cultured, leading to isolation of 11,843 colonies of fungi (range 0- 1 666 colony-forming units per cubic meter (CFUs/m(3)). 85.5% of total colonies belonged to the four genera considered. The highest presence of Aspergillus, Cladosporium and Penicillium in indoor environment was registered in autumn. Alternaria was more frequent in summer. In the outdoor environment, Penicillium was more abundant in winter and Aspergillus in summer (P= .002). The largest numbers of isolations were of Cladosporium and Penicillium during all four seasons, indoors as well as outdoors. Alternaria was present in all the homes studied both in summer and in autumn. The most prevalent species were: Alternaria alternata, Cladosporium herbarum, Cladosporium cladosporioides, Aspergillus niger and Penicillium chrysogenum. CONCLUSIONS: The quantitative analysis of the four taxa related with respiratory allergies demonstrated considerable seasonal variability. Statistical differences between the indoor and outdoor prevalence were detected only in Alternaria. In summer and autumn, the greater level of exposure to the four studied taxas occurred inside homes.

Celulitis y onicomicosis proximal de ambos ortejos mayores producida por Fusarium solani / Bilateral proximal cellulitis and onychomycosis in both big toes due to Fusarium solani

Se presenta un caso de celulitis del pliegue proximal de ambos dedos gordos de los pies (ortejos mayores), asociados a una onicomicosis proximal podal bilateral y un intertrigo del cuarto espacio interdigital producida por Fusarium solana. La infección se contrajo probablemente en un país tropical, ocasionando el desprendimiento de las uñas (onicomadesis). Siete meses más tarde se produjo una recidiva en la uña izquierda, que fue tratada con urea al 40% más bifonazol para eliminarla químicamente, instaurándose un tratamiento de ciclopirox-olamina en laca ungueal durante 12 meses. La curación fue total, y al o largo de 10 años de seguimiento no se han observado recidivas. El estudio de la sensibilidad in vitro demostró que dos de las cepas aisladas eran resistentes al itraconazol y al voriconazol(AU)

We report a case of proximal fold cellulitis in both big toes, associated with a bilateral proximal onychomycosis and an intertrigo of the fourth space due to Fusarium solani. The infection occurred in an immunocompetent man with diabetes mellitus type II. Apparently, the infection was acquired in a tropical country and once the patient was in Spain the infection progressed causing nail detachment (onychomadesis). Seven months later a relapse that affected the left toenail occurred. The patient was treated topically with chemical toenail avulsion contained 40% urea associated with bifonazole followed by ciclopirox-olamine nail lacquer for 12 months. Complete cure without relapse was observed after 10 years of follow-up. In vitro antifungal susceptibility study demonstrated that two of the recovered isolates were both resistant to itraconazole and voriconazole(AU)

¿Está infradiagnosticada la “tinea pedis”en pediatría? Estudio en una población escolar de Barcelona / Is tinea pedis underdiagnosed in children? Study in Barcelona school children

La tiña de los pies es menos frecuente en el niño que en el adulto y raramente aparece antes de los 4 años. Para identificar la prevalencia de este tipo de tiñas entre escolares se planificó un estudio en 39 escuelas del distrito que es área de referencia del Hospital del Mar de Barcelona. Se examinaron 2.613 escolares de edades comprendidas entre los 3 y 15 años. Se detectaron 72 casos con cultivo positivo a dermatófitos, 3 padecían conjuntamente afectación ungueal. La prevalencia era del 2,75% y aumentaba con la edad: un 0,86% entre los 3 y 5 años, un 2,08% entre los 10 y 12 años, y un 7,04% entre los 13 y 15 años. Los agentes fueron Trichophyton mentagrophytes (48,6%), J: rubrum (40,27%), Epidermophyton mophyton floccosum(6,94%y) J:t onsurans( 4,16%). De los 72 casos de dermatofitosis, sólo 49 tenían lesiones clínicas evidentes. Sólo 19 de los 49 con manifestacionesc línicas tenían conocimiento de sus lesiones, y 8 habían realizado tratamiento antifúngico de forma irregular unos meses antes. Posibles razones del bajo nivel diagnóstico podrían estar en: a) el bajo interés familiar por las lesiones, al no haber sido verbalizadas, y ser valoradas como triviales; b) la consideración de situación propia de la edad y asociada a la actividad deportiva; c) reducida sintomatología subjetiva; d) falta de práctica exploratoria sistemática de zonas interdigitales de los pies; e) la falta de un correcto diagnóstico diferencial; f) bajo interés de los adolescentes en acudir a visitas pediátricas; y g) autodiagnóstico y automedicación

Tinea pedís is less common in children than in adults and rarely appears before the age of tour years. A cross-sectional study was performed to determine the prevalence of this type of tinea in schoolc hildren in BarcelonaS, pain. A total of 2,613s choocl hildrenw ith the agesf rom 3 to 15, from 39 schools located in the municipal district in the vicinity of the hospital, were examinedto identity the presence of dermatophytogis of the feet. Seventy-two had positive cultures for tínea pedis and dermatophytes, while in three, the nail was involved as well. The overall prevalence was 2.75%, and increased with age, being 0.86% in 3 to 5-year-olds, 2.08% in 10 to 12-year-old and 7.04% in 13 to 15-year-old. The fungi found were Tríchophyton mentagrophytes (48.6%),T rubrum( 40.27%)Epidermophyton floccosum (6.94%) and T. tonsurans(4.16%).Of these 72 children, 49 had interdigital lesions, only 19 of them were aware of their presence and 8 had received antifungal therapy previously, although not consistently. Although the incidence of tinea pedís is low in children, we think that it is underdiagnose. Possible reasons for this could be the limited interest in the lesions on the part of parents, who consider them trivial and do not mention them during physical examinations; the consideration that the condition is characteristic of the age group and is associated with sports and the generalized use of athletic foot wear, the lack of proper foot hygiene after doing sports; the fact that there are few subjective symptoms; the failure on the part of the pediatrician to systematically and carefully examine the interdigital skin of the feet of healthy children; the lack of an accurate differential diagnosis; the reluctance of adolescents to visit the pediatrician; self-diagnosis and self-medication

Early diagnosis of candidiasis in non-neutropenic critically ill patients.

OBJECTIVE: To determine a method for the early diagnosis of candidiasis in non-neutropenic critically ill patients in order to reduce mortality. METHODS: A prospective study in non-neutropenic critically patients in whom Candida spp. were detected, was made in an intensive care unit (ICU) during an 8-year period from 3389 patients admitted. A diagnostic and therapeutic protocol was designed. Invasive candidiasis was defined according to dissemination and multifocality. RESULTS: Candida spp. were found in 145 cases (4.3%): 120 (83%) were considered as invasive candidiasis and 25 as colonisation (17%). The hospital mortality was 46% (67/145). A post-mortem study was carried out in 54% (36/67) of hospital deaths. Candida albicans was the most frequently isolated species (87%), followed by Candida glabrata (18%). There were 24 candidemias and three cases of endophtalmitis. Digestive and respiratory samples and non-C. albicans yeasts were risk factors for invasive candidiasis. The mortality rate was related statistically to invasive candidiasis and inversely to the appropriate antifungal treatment. CONCLUSIONS: Invasive candidiasis is related to digestive and respiratory samples and to the presence of non-C. albicans species. A simpler definition of invasive candidiasis in non-neutropenic critically ill patients will permit more rapid and accurate specific antifungal therapy.

[Lung aspergillosis. Role of the corticoids as associated risk factor in the patient with chronic bronchitis]. / Aspergilosis pulmonar. Papel de los corticoides como factor de riesgo asociado en el bronquítico crónico.

BASIS: Description of a situation of incidence increase of bronchial secretions with positive cultures for Aspergillus fumigatus, and analysis of the related risk factors in the invasive aspergillosis. METHODS: Between January 1999 and February 2000, a prospective study of the patients was conducted with culture of bronchial secretions and with positive result for A. fumigatus. VARIABLES STUDIED: age, sex, primary diagnosis, type of cultivated sample, clinical interpretation (colonization/infection), probable source (community/nosocomial), situation of the patient after discharge, and risk factors for opportunistic infection. The results were compared among the colonized and infected patients. RESULTS: Fifty-two patients showed positive cultures of bronchial secretions to A. fumigatus, 43 (82.6%) colonized and 9 (17.3%) infected. Cultivated sputum sample on 30 occasions (57.6%) and bronchial aspiration in 22 (42.3%). Median age: 70 years (31-84). Sex: 40 men (76.9%). Probable source of infection/colonization: nosocomial in 18 cases (34.6%), community in 3 (5.7%) and unknown in 31 (59.6%). Mortality: 15 patient colonized (34.8%) and 8 infected (88.8%). Risk factors with statistical significance for invasive infection by A. fumigatus: diagnosis of chronic bronchopathy (COPD) (p=0.007) and treatment with prednisone in dose higher than 60 mg/day (p=0.0005). CONCLUSIONS: The patients with positive culture of bronchial secretions to A. fumigatus with COPD and treatment with prednisone in dose higher than 60 mg/day should be considered with a greater risk for infection by this pathogen. A more restricted use and adequate of the corticoids in these patients, and an early diagnosis and treatment in light of the suspicion of infection by A. fumigatus in patients with COPD, it could imply a reduction of morbidity and mortality.

Aspergilosis pulmonar. Papel de los corticoides como factor de riesgo asociado en el bronquítico crónico / Lung aspergillosis. Role of the corticoids as associated risk factor in the patient with chronic bronchitis

Fundamentos. Descripción de una situación de aumento del número de cultivos de secreciones bronquiales positivos para Aspergillus fumigatus y análisis de los factores de riesgo asociados en la aspergilosis invasora. Métodos. Entre enero de 1999 y febrero de 2000 se efectuó un estudio prospectivo de los enfermos con cultivo de secreciones bronquiales positivo para A. fumigatus. Variables estudiadas: edad, sexo, diagnóstico principal, tipo de muestra cultivada, interpretación clínica (colonización/infección), probable adquisición (extrahospitalaria/ intrahospitalaria), situación al alta y factores de riesgo de infección oportunista. Se compararon los resultados entre los pacientes colonizados e infectados. Resultados. Se detectan 52 enfermos con cultivos de secreciones bronquiales positivos a A. fumigatus, 43 (82,6 por ciento) colonizados y 9 (17,3 por ciento) infectados. Muestras cultivadas de esputo en 30 ocasiones (57,6 por ciento) y broncoaspirado en 22 (42,3 por ciento). Edad media: 70 años (31-84). Sexo: 40 varones (76,9 por ciento). Probable adquisición: intrahospitalaria en 18 casos (34,6 por ciento), extrahospitalaria en tres (5,7 por ciento) y en 31 (59,6 por ciento) desconocida. Mortalidad: 15 pacientes colonizados (34,8 por ciento) y 8 infectados (88,8 por ciento). Factores de riesgo con significación estadística para presentar una infección por A. fumigatus: diagnóstico de broncopatía crónica (enfermedad pulmonar obstructiva crónica [EPOC]) (p= 0,007) y el tratamiento con prednisona en dosis superiores a 60 mg/día (p= 0,0005).Conclusiones. Los enfermos con cultivo de secreciones bronquiales positivas a A. fumigatus con EPOC y tratamiento con prednisona en dosis superiores a 60 mg/día deben considerarse con un riesgo mayor de sufrir una infección por este patógeno. Un uso más restringido y adecuado de los corticoides en estos pacientes, y un diagnóstico y tratamiento precoces ante la sospecha de infección por A. fumigatus en pacientes con EPOC, podría suponer una disminución de la morbimortalidad (AU)

Pathogenicity of Cryptococcus neoformans var. gattii in an immunocompetent mouse model.

The pathogenicity of two different genomic profiles of Cryptococcus neoformans var. gattii serotype B isolated from goats that died from cryptococcal pneumonia was assessed in an experimental model of immunocompetent mice. One strain of each randomly amplified polymorphic DNA (RAPD) profile (GR52 and GR56) and three reference C. neoformans isolates representing serotypes B, D and C were used. BALB/c male mice were inoculated by the intraperitoneal route with each strain. After 4 weeks of follow-up, the animals were sacrificed and autopsy specimens of testes, liver, spleen, kidney, lungs and brain were cultured and stained for histopathology. Although spontaneous mortality was only 2% (one animal), all mice except for those inoculated with serotype C showed positive cultures in almost one organ. The strain GR52 isolated from goat showed the highest rate of positive cultures (80%) followed by serotype D (77%). Serotype B reference strain and second goat strain GR56 were both isolated from 70% of samples. Serotype C was recovered in only 33% of organs, and never from brain or lung specimens. GR52 grew abundantly from all lung cultures, and yeast cells with large capsules were seen in histopathology inside the alveoli, peribronchial vessels and interalveolar spaces. They appeared to elicit no inflammatory response. We conclude that intraperitoneally inoculated C. neoformans var. gattii shows high virulence in this immunocompetent mouse model. Strain GR52 was highest in pathogenicity and had marked lung tropism. In contrast, the serotype C reference strain showed the lowest pathogenicity and seemed not to spread outside the abdominal viscera.

In vitro susceptibility of Cryptococcus neoformans serotypes to GM 237354 derivative of the sordarin class.

In vitro susceptibility to the sordarin derivative GM 237354 and amphotericin B were tested in a total of 190 Cryptococcus neoformans clinical isolates from different geographical areas of Spain and South American countries. Minimal inhibitory concentrations (MICs) were obtained using the NCCLS reference microbroth dilution method and analysed according the serotypes of Cr. neoformans. The MICs for amphotericin B were lower than 1.0 microg ml(-1) (MIC90% 0.5 microg ml(-1) , MIC50% 0.125 microg ml(-1)) but five isolates showed MICs of 2.0 microg ml(-1) to GM 237354 (MIC90% 1.0 microg ml(-1), MIC50% 0.5 microg ml(-1)). Cryptococcus neoformans var. gattii serotype B, was significantly less susceptible than A and AD serotypes (P = 0.047 and P = 0.022, respectively).

[In vitro antifungal susceptibility of dematiaceous filamentous fungi using the E-test]. / Sensibilidad in vitro de hongos dematiáceos a los antifúngicos utilizando E-test.

The usefulness of the E-test((R) )has been studied to determine the in vitro susceptibility of 52 isolates of 17 species to five antifungal drugs: amphotericin B, 5-flucytosine, ketoconazole, itraconazole and fluconazole. Minimal inhibitory concentrations were determined following the manufacturers' instructions, except in the preparation of the inoculum. In this case a spectrophotometric method was used to obtain 1-5 ' 10(6) CFU/ml. Two different culture media were included: casitone-agar and RPMI 1640 agar. Most isolates showed clear growth in both media after 96 h of incubation at 37 degrees C. The species showed low MIC concentrations to ketoconazole and itraconazole. Only 55.8% of isolates showed MICs

The utility of serology in diagnosing candidosis in non-neutropenic critically ill patients.

This study was carried out to evaluate the utility of serological tests in the diagnosis of candidal infections in non-neutropenic critically ill patients. A prospective study was carried out in a 10-bed general intensive care unit; all patients with at least one organic sample with Candida spp. were included. A therapeutic-diagnostic algorithm was designed, and patients were treated or not, according to a classification. Blood samples were taken, and serological tests included: antigenaemia detection using two different commercial latex kits (Cand-Tec and Pastorex) and antibody detection by indirect haemagglutination (IHA) and indirect germ tube immunofluorescence (IFA). A total of 56% of antibody tests (IHA 45% and IFA 64%) and 26% of antigen tests (Cand-Tec 36% and Pastorex 17%) were positive. The sensitivity and specificity of these tests with respect to systemic candidosis were 37% and 78%, respectively, for antibodies, and 0% and 90% for antigens. There was statistical significance for mortality and low levels of antibodies; Candida glabrata was detected by IFA and Candida tropicalis by Cand-Tec. Serological tests may help to define the prognosis of these patients and to support the detection of specific Candida species.

Sensibilidad in vitro de hongos dematiáceos a los antifúngicos utilizando E-test® / Antifungal susceptibility of dematiaceous filamentous fungi using the E-test®

Se ha determinado la concentración mínima inhibitoria (CMI) mediante E-test® en 52 aislamientos de hongos filamentosos dematiáceos pertenecientes a 17 especies. Se han utilizado los cinco antifúngicos sistémicos disponibles comercialmente: amfotericina B, 5-fluorocitosina, ketoconazol, fluconazol e itraconazol. Se ha utilizado el método recomendado por los fabricantes, con la excepción de la preparación del inóculo, que para que fuera más preciso se ha estandarizado por espectrofotometría hasta obtener 1 a 5x 106 UC/ml. Todas las cepas fueron sembradas simultáneamente en dos medios de cultivo: agar casitona y agar RPMI 1640. El crecimiento de casi todos los aislamientos fue evidente a partir de las 96 horas de incubación. El 55,8 por ciento de las cepas presentaron una CMI £2 mg/l para la amfotericina B y el 98 por ciento una CMI de 32 mg/l para la 5-fluorocitosina. Todas las especies mostraron valores bajos de CMI para el itraconazol y el ketoconazol, con una media geométrica de 0,19 y 0,26 mg/l, respectivamente. Excepto una cepa, con CMI de 8 mg/l, el resto presentaron valores ñ256 mg/l para el fluconazol. No se encontraron diferencias en los valores de las CMI para ambos medios de cultivo y la reproducibilidad fue del 100 por ciento; no obstante, la lectura de las CMI resultó más fácil con el agar casitona debido a un mejor contraste de la elipse de inhibición. Estos resultados ugieren que el itraconazol y el ketoconazol podrían ser los antifúngicos de primera elección en el tratamiento de las infecciones producidas por las especies evaluadas. Se considera que el E-test® es una prueba adecuada para determinar la sensibilidad in vitro a los antifúngicos en hongos filamentosos dematiáceos (AU)

Changes in androgenic steroid profile due to urine contamination by microorganisms: a prospective study in the context of doping control.

Urine contamination by microorganisms may affect the interpretation of urinalysis in different areas of clinical diagnosis. This is particularly relevant in doping control. A prospective study was designed to assess the effects of urine contamination by selected pathogens on the endogenous androgenic steroid profile. Pooled urine from a healthy male volunteer with standard steroid profile compared with reference values for the Caucasian population was sterilized by filtration and stored in sterile glass tubes. Aliquots were inoculated with known amounts of 15 different organisms (bacteria, fungi, and moulds) and incubated at 37 degrees C for 2 weeks. Different markers of urine contamination, such as pH, deconjugation of steroids, and metabolic by-products, were determined. Alkalization of urinary pH was not a reliable indicator of urine contamination as several organisms grew in this medium and no alteration of this parameter was found. In uncontaminated urine, less than 10% of steroid glucuronide conjugates were spontaneously hydrolyzed. Higher rates of hydrolysis for sulfate conjugates were found. An unconjugated fraction higher than 10% of the total amount of testosterone was a reliable indicator of urine contamination. However, microbial production of testosterone or epitestosterone was not detected. In contrast, a few organisms were able to synthesize 5alpha-androstanedione, 5beta-androstanedione, and androstenedione using endogenous steroids as substrates.

[Epidemiological study of cryptococcosis in Spain: first results]. / Estudio epidemiologico de la criptococosis en España: primeros resultados.

The study constitutes an approach to the knowledge of the epidemiology of cryptococosis in Spain. For detection of cases 167 Spanish hospitals were contacted. All cases included were accompanied by the correspondent isolate of Cryptococcus neoformans, together with clinical, demographic and mycological data. Results obtained from January 1998 to end of December 1999 are analysed and presented here. Fifty-six Spanish hospitals reported 58 cases of cryptococcosis; only 43 of them were adequately documented and accompanied by the clinical isolate. The results showed a higher incidence in males (88.4%) than in females (11.6%); being most frequently affected those between 30 and 40 years old (48.8%). The 84.6% (33) corresponded to new cases and 15.4% (6) to relapses of the disease. The HIV infection was the most frequent risk factor reported (86%) and, for 29.7% (11) of them, cryptococcosis was the AIDS defining disease. For the diagnosis, CSF analysis showed the best results (India ink; culture and antigen detection). All strains collected (100%) corresponded to C. neoformans variety neoformans. Serotypes distribution was 45.5% for serotype A and 22.7% for each of serotypes D and AD.

Successful treatment with liposomal amphotericin B of an intraabdomianl abscess due to Candida norvegensis associated with a Gore-Tex mesh infection.

There are few reports of severe infections caused by Candida norvegensis. We here describe a case of C. norvegensis-associated intraabdominal abscess and Gore-Tex mesh-associated infection, successfully treated with liposomal amphotericin B and removal of the mesh. This is, to our knowledge, the first report of C. norvegensis causing this type of infection.

In vitro susceptibility of Cryptococcus neoformans isolates to five antifungal drugs using a colorimetric system and the reference microbroth method.

Minimum inhibitory concentrations (MICs) of amphotericin B, 5-flucytosine, fluconazole, itraconazole and ketoconazole were determined against 42 clinical isolates of Cryptococcus neoformans var. neoformans using the Alamar YeastOne colorimetric method and the NCCLS reference microdilution method. No strains with resistance to amphotericin B, itraconazole or ketoconazole were detected with either method. Using the reference method, the MICs of fluconazole were >/= 64 mg/L, whereas using the colorimetric method all MICs were >/=16 mg/L. The MIC values of 5-flucytosine were also higher using the reference method (8-16 mg/L for 32% of isolates) compared with the colorimetric method. The percentage of agreement between the methods, using a difference of two dilutions, was 70.7% for itraconazole, 73.2% for amphotericin B, 80% for fluconazole, 88% for 5-flucytosine and 95% for ketoconazole. Overall, we conclude that for fluconazole and 5-flucytosine, in a low but not insignificant number of isolates, results with the two methods are discordant, some isolates being found sensitive with the colorimetric test, but resistant with the reference method.

Antifungal compounds: controversies, queries and conclusions.

A new session in this Congress was the development of a discussion panel regarding controversies and queries about the main topics of treatment and prophylaxis of severe systemic mycoses. Experts presenting each side of three controversial areas provided an interchange of ideas and clarified those areas where there remain substantial disagreements. Some common recommendations have been made, and some differences persist. The contents of this session are compiled in this paper. Due to the limitations of space, this paper presents the most relevant parts of each presentation. The large and up-to-date list of references should be useful to gain a better understanding of these subjects.

Natural pathogens of laboratory animals and their effects on research.

The natural fungal pathogens of laboratory animals such as rabbits and guinea pigs are mainly dermatophyte species, most commonly Trichophyton mentagrophytes and also, less frequently Microsporum gypseum and M. canis. However, the incidences of infection and clinical disease are low in well-managed animal facilities. Young or immunocompromised rabbits are thought to be most susceptible. Dermatophytes infect the epidermis and adnexal structures, including hair follicles and shafts, usually on or around the head, and cause pruritus, patchy alopecia, erythema and crusting. Histopathological changes in the underlying skin occur and these changes could confound histological studies involving the skin. Yeast infections usually due to Candida spp. have been reported occasionally in laboratory animals. In this paper, the role of rodents in the evaluation of topical antifungal agents, dermatophytosis and two species of Candida, which are natural pathogens of laboratory animals, are discussed in relation to their effects on research. Pneumocystis carinii, an inhabitant of the respiratory tract of laboratory mice and rats, is a pathogen only under conditions of induced or inherent immunodeficiency. Infected mice and rats are likely to develop severe pneumocystosis following immunosuppression and will be rendered unsuitable for most experimental purposes.