Question

A 5 year-old girl from a farm town in Ohio was admitted to the regional hospital for suspected tuberculosis. She possessed a chronic cough with productive sputum, and she complained of breathlessness, tiredness, and weight loss over the last several months. Multiple sputum specimens showed no acid-fast bacilli; her tuberculin skin test was negative. Abnormal hematologic findings were anemia, a low white blood cell count, and some monocytes containing intracellular yeasts with a narrow isthmus between mother an daughter cells. Blood specimens were drawn into a Dupont Isolator, processed, and placed on brain heart infusion agar with blood at room temperature. After 3 weeks, tan, fluffy colonies formed. Microscopically, the fungus produced only microconidia along the sides of they hyphae.

What disease do you suspect and why? Give two reasons

How would you confirm the identity of the isolate? Present two ways.

What was the probable mode of exposure to the etiologic agent?

An opportunistic fungus is morphologically similar to the characteristic structures of the causative organism. Name it and provide two ways it may be differentiated from the disease agent in this case study.

Answer 1

The 5-year-old girl likely has histoplasmosis based on hematological findings and culture results. Confirmation requires DNA sequencing or serological assays. Exposure likely occurred from inhaling spores in her farm environment, and the similar opportunistic fungus, P. jirovecii, can be differentiated by specific staining and serological tests.

Step-by-step explanation:

The disease suspected in the case of the 5-year-old girl from a farm town in Ohio is histoplasmosis. Histoplasmosis is a lung infection caused by inhaling the spores of the fungus Histoplasma capsulatum. The negative test for acid-fast bacilli and tuberculin skin test, along with the presence of monocytes containing intracellular yeasts with a narrow isthmus between mother and daughter cells, are indicative of a fungal rather than bacterial infection, typical of histoplasmosis. Two reasons for suspecting this disease are:

1. Abnormal hematological findings with monocytes showing intracellular yeasts.
2. Cultures showing tan, fluffy colonies with microconidia along the sides of hyphae, which is characteristic of Histoplasma capsulatum.

To confirm the identity of the isolate, one could:

1. Conduct DNA sequencing or PCR-based methods to verify the genetic material matches that of Histoplasma capsulatum.
2. Carry out antigen detection tests or serological assays for specific antibodies to Histoplasma.

The probable mode of exposure is inhalation of spores, often from soil contaminated with bird or bat droppings, which is common in a farm setting. The opportunistic fungus similar to Histoplasma capsulatum is Pneumocystis jirovecii, which could be differentiated by observing the cysts and trophic forms unique to Pneumocystis in stained respiratory fluid samples, and by other serological tests.