Microbiology-Endemic Mycoses Flashcards
What determines what form dimorphic fungi will take?
The temperature. In colder temps they form molds and warmer they become a yeast.
What are you looking for that is characteristic of a specific organism when you culture a fungus in the lab?
Their spores
What does the mold look like in histoplasmosis?
Large and small conidia (spike-like projections) grown on cyclohexamide.
What does the yeast form of histoplasmosis look like?
Dot disease. Oval yeasts found inside macrophages. This is what you will see on tissue biopsy of a patient.
What form of histoplasmosis is most common in North America? Africa?
NA = capsulatum (thinner capsule). A = duboisii
2 years ago a high school was remodeling their courtyard. 350 people presented to their doctors with headache, fatigue, fever, cough, dyspnea and chills. What likely caused this outbreak?
Histoplasmosis is endemic in the midwest and especially in soil with high levels of nitrogen (bird droppings). Construction likely kicked up all of the spores and infected these people.
Why might people with histoplasmosis have symptom resolution after 2-3 weeks but relapse after decades?
The initial infection gets into the alveolar macrophages which then migrate out to the lymph nodes, spleen liver and bone marrow. 2-3 weeks after the infection macrophages become fungicidal, form granulomas and calcify. A small number of yeast molecules remain viable in the granulomas and can relapse when the immune system becomes weakend.
What type of patient is most likely to manifest symptoms of histoplasmosis and exhibit more granuloma formation on chest x-ray?
People with T-cell deficiency.
What clinical manifestations should you specifically be aware of with histoplasmosis?
Pulmonary manifestations, mediastinal disease and disseminated histoplasmosis
How are pulmonary presentations in histoplasmosis divided into categories?
Acute (pneumonia symptoms, mediastinal/hilar lymph node spread), Subacute (continued fever, productive cough and sweats with spleen lymphadenopathy) and Chronic (dense consolidations and scarring within the lung)
A 34 year old male with Crohn’s disease is taking a TNF-alpha inhibitor and symptoms get better. Shortly thereafter he starts getting fevers and lymphadenopathy. His chest x-ray is seen below. Why might this patient need to be treated for histoplasmosis ASAP?
Note diffuse infiltrates in his lungs. Progressive disseminated histoplasmosis can spread to the bone marrow, GI tract and adrenal glands.
Why are patients with histoplasmosis at risk for cardiac tamponade?
Acute pericarditis from histoplasmosis can lead to scarring and rupture of cardiac tissue.
When should you always consider histoplasmosis in your differential diagnosis?
Tuberculosis, they present almost the same way due to granuloma formation.
What are the different modes of diagnosing histoplasmosis?
Gold standard = culture (takes a while and misses a lot), fungal stain (misses a lot), serology (lots of false-positives from cross reactivity) and antigen test in urine, blood or bronchoalveolar lavage (high sensitivity in disseminated histoplasmosis)
How do you treat histoplasmosis?
Itraconazole for moderate disease and IV amphotericin B for sever disease.
What does blastomycosis look like as a mold? The yeast?
Mold = The spores look like tear drops on the end of hyphae. Yeast = really thick double-contoured walls.
A 54 year old male was working out in the yard last week and got sick. The next day his dog died. What fungal infection could have infected the man and his dog?
Blastomycosis. It is 10x more potent in dogs. People usually get infected by kicking up of dust and inhalation of spores…this guy was doing yard work.
Where is histoplasmosis most prevalent?
Central states
Where is blastomycosis most prevalent?
South central states
What are the most common clinical manifestations of blastomycosis?
Pulmonary disease, skin lesions (verrucous), osteomyelitis and genitourinary infections (prostatitis, epididymoorchitis).
A 54 year old male was working out in the yard last week and his dog died the next day. Over the next month or so he has experienced fatigue, fevers, sweats and weight loss. He goes to the doctor and gets a chest x-ray. What finding may the radiologist see if this patient has blastomycosis?
Mass-like pulmonary lesions.
Why is blastomycosis referred to as the great pretender?
They often get misdiagnosed as cancer or bacterial infections.
How do you diagnose blastomycosis?
Biopsy and blood culture.
How do you treat blastomycosis?
Mild disease = itraconazole. Severe disease = IV amphotericin B.
How do people get exposed to coccidioidomycosis?
When times get hard, the tubular hyphae of the mold segment into spores (arthrocondia). These are then inhaled and people are infected.
How does a coccidioidomycosis infection spread once it is inside the host?
The yeast forms endospores that rupture to form more yeast colonies with more endospores.
Where is coccidioidomycosis most often found in the US?
California
A 31 year old male comes to you complaining of fever, cough, dyspnea, weight loss and chest pain that has lasted for the past 4 months. History only reveals travel to California in the past year. What might labs show on this patient if you think he has coccidioidomycosis?
Eosinophilia and peripheral thin-walled cavities or nodules on x-ray.
What are patients who are immunocompromised at risk for if they are infected by coccidioidomycosis?
Dissemination to skin, bone and meninges. This is very uncommon in immunocompetent hosts.
How do you diagnose coccidioidomycosis?
Microscopic evaluation of sputum or tissue. Note that the lab must know because they can never open the culture outside of a hood or risk being infected.
How do you treat coccidioidomycosis?
Mild= fluconazole or itraconazole. Severe = IV amphotericin B.
A 21 year old male presents with a cough and chest pain for the past two weeks. He was given azithromycin for pneumonia. Later he developed fevers, sweats and green sputum production. He had trained in camp Pendelton California. He also notes a raised, reddish rash on his skin. His chest x-ray is shown below. What might you expect to see on biopsy of the lung?
Note the dense oval infiltrate in his left lung. This is indicative of coccidioidomycosis. You would expect to see endospores on biopsy.
A 61 year old female immigrant from South America comes to see you in clinic. She says she has had multiple episodes of pneumonia over the past year. On physical exam you note non-healing ulcers in her mouth. Her CXR is shown below. What is your diagnosis? How do you diagnose and treat this patient?
These findings are all consistent with paracoccidiooidomycosis. This is endemic in South America and is a yeast present in the soil. You diagnose this with tissue biopsy and culture. You treat it with itraconazole or amphotericin. Sulfa drugs can prevent reactivation.
