A student coming back from a year abroad in South Africa with the Peace Corps re

Question

A student coming back from a year abroad in South Africa with the Peace Corps reports night chills and sweats, loss of appetite and weight, and recurrent fever. A blood smear reveals no presence of parasites. As you are reviewing information with the student, he is interrupted by violent coughing and the sputum is streaked with blood. You send a sample of sputum to the pathology lab for staining and culture. The lab detected no unusual bacteria in the Gram stained sputum sample. An acid-fast stain reveals bright red bacilli. A culture on Löwenstein-Jensen medium confirms later your diagnosis. To guide you through the process of solving a case study, I have broken down the process of answering the main question “What is the disease?” into several short questions which will lead you to the answer:

1.What pathogens are stained using the acid fast stain because they do not stain well with the Gram stain?

2.What are prevalent infectious diseases in South Africa that cause the signs and symptoms reported by the student?

3.Which pathogen causes the infection described in the case study?

4.What is the specific use of a culture on Löwenstein-Jensen medium?

5.What other three common tests for the diagnosis of this disease are not mentioned here (don’t mention stains)?

Explanation / Answer

1. Pathogens containing mycolic acid in their cell wall are stained with acid fast stain and do not take the gram staining.

For ex. Mycobacterium.

2. The symptoms reported by student are of tuberculosis, which is is prevalent in south africa. According to literature South Africa is one of the country with highest level of TB.

3. various strains of Mycobacterium especially Mycobacterium tuberculosis is the causing agent.

4. Specific use of LJ media: It contains egg, malachite green and glycerol. (1) Egg is an enrichment material which stimulates the growth of tubercle bacilli, (2) Malachite green inhibits growth of organisms other than mycobacteria, (3) Glycerol promotes the growth of Mycobacterium tuberculosis but not Mycobacterium bovis.

5. Other tests for this disease are: PPD test: Skin test involves injecting a small amount of fluid (called tuberculin) into the skin in the lower part of the arm.A raised hard area or swelling, and if there is one will be measured.The TB skin test result depends on the size of the raised hard area or swelling. The larger the size of the affected area the greater the likelihood that the person has been infected with TB bacteria at some time in the past.

X ray imaging: White spots observed if infected with TB.

Blood tests: TB Interferon gamma release assays (IGRAs)- IGRAs are blood tests that measure a person’s immune response to the bacteria that cause TB.

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