Histoplasmosis

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Histoplasmosis is caused when patients have inhaled Histoplasma capsulatum spores. The spores contain a fungus called dimorphic saprophytic fungus, which is often found within the feces of animals such as birds, chickens, and bats. The disease is transmitted by inhaling these spores from disturbed soil areas, as a result of excavation or construction in the area. Histoplasmosis causes to skin legions and/or pulmonary pneumonia and are most detrimental to those with a compromised immune system. Instances of the disease are commonly found in the central states of the U.S. but are also endemic to areas in the Southeast regions of Mexico, Africa, and Asia.  

Histoplasmosis can also be referred to as "Cave disease" or "Darling's disease” (Rapini, et. Al, 2007).The names "Ohio valley disease”,"Reticuloendotheliosis,""Spelunker’s Lung" and Caver's disease have also been used as alternative names for this pathology (Rapini, et. Al, 2007). The cave and valley references relate to the areas in which bats and disease carrying animals typically inhabit, causing the infected soil.

For those with acute pulmonary histoplasmosis, about 90% of patients fail to have symptoms (Ha Kirsten Do, 2010). Those that do may experience coughing and flu-like symptoms within 12 to 14 days of initial exposure. Others who do develop symptoms must address skin legions on varied and multiple parts of their bodies, including their eyes and private areas. Chronic pulmonary histoplasmosis seems to occur most in patients which have already developed and underlying lung disease. Immunosuppressed patients often develop progressive disseminated histoplasmosis, which can result in skin legions. It also affects the eyes of about 10% of patients, resulting in eye disease developed from ocular histoplasmosis. This can lead to permanent damage of the retina as a result of calcified scar tissue. Cutaneous histoplasmosis can also occur, creating skin legions in the pelvic region as well as the legs and hands of the patient. 

While those with a strong immune system can limit the spread of Pneumonia within their bodies, children, the elderly, those with HIV, and other people with weak immune systems often suffer from dissemination of the disease to their liver, bones, lungs, nodes, and the spleen (Ha Kirsten Do, 2010).  This development of the disseminated disease is common among patients that are living with AIDS because of their significantly compromised immune system. When this occurs, patients experience high fever and rapid weight loss, as well as spleen enlargement. As it affects the internal organs and interrupts normal body function, it can be deadly if not treated.  Skin legions can develop as ulcers, papules, or nodules, and can also progress to macules, vesicles, or pustules, which are less common (Ha Kirsten Do, 2010).

Histoplasmosis is not contagious and requires inhalation of the spores from the disturbed droppings or infected droppings. The fungus itself is considered to be thermally dimorphic, meaning it can reproduce yeast like pathogenic fungi through the body (Ha Kirsten Do, 2010). This occurs specifically by the alveoli’s ingestion of the microbiota in the spores. The spores are able to survive inside the phagosome, allowing it to be turned into a type of yeast as the result of its exposure to the body’s internal temperature. This causes the fungus to grow and multiply, circulating and spreading the disease to multiple different organs.  While those with strong cellular immunity can fight the disease within, those with compromised immune systems suffer from increased spread of it.

Diagnostic Methods 

Medical Biological imaging makes use of radiology, nuclear medicine, microscopy, medical photography, endoscopy and thermography. Radiology comprises the use of X rays, ultrasounds, and magnetic resonance (MRI) scanning which can transmit and produce relevant images to be reviewed by health professionals. For the purposes of reviewing human pathological investigations, microscopy is most appropriate for the review and diagnosis of disease and cultures. Branches of microscopy include optical, electron, and scanning probe microscopy (Pluta, 1988). The optical and electron branches use diffraction, reflection, or refraction of electromagnetic radiation as it interacts with the culture. This radiation is collected to create a signal and image visible through the microscope. This can be accomplished by using a transmission electron microscopy to illuminate the sample or by scanning a beam over it using a laser. Scanning probe microscopy uses a probe to scan the surface of the culture, which is used to form images. These medical imaging procedures provide detailed and clear images which health professionals can use to properly diagnose and review disease.

When viewing Histoplasmosis through medical imaging the culture will show a hairy or wooly mold that is tan or brown in color. It is visible between 25-30Celcius on Sabouraud dextrose agar, which helps to cultivate the fungus for viewing and proper diagnosis.  The organisms will show to have delicate septate hyhae with cross-walls connecting to other sells. The thickness will be the width of one or two microns and contain a large and rough wall of macroconidia consisting of anywhere from five to fifteen microns. Medical imaging can further be used to confirm existence of the disease by completing follow up imaging studies using sheep blood agar to test its reversion of yeast when it reaches 37 degrees Celsius. The image will show two to four microns of yeast in a single, budding nucleus which is oval shaped with rigid, yet thin walls.

As Histoplasmosis is not contagious, the pathology of the disease does not significantly alter how imaging professionals’ image the samples. However, because there are multiple different forms of the disease, procedures may be altered to compare and contrast one form of Histoplasmosis with the other to determine if there is a difference in the samples which cause skin legions and that which causes eye irritation.

Treatment & Prognosis 

Those with the discussed healthy immune systems who have mild cases will not require treatment because their bodies will develop a process to fight off the spread of the disease. However, for those who have compromised immune systems, or for those who have severe cases, antifungal drugs are used to manage it. In immunocompetent patients, the drug Itraconazole will be prescribed for use over about nine months. In those with suppressed immune systems, Itraconazole will be followed by IV Amphotericin B in order to properly treat it.  

Itraconazole is an anti-fungal drug that will affect the pathology of the disease and prevents fungi growth by preventing fungi from producing protective membranes around its cells. It is effective against Histoplasmosis as well as other fungal infections.  It can also be used for treatment in patients who have low white cell blood counts in order to prevent a potential fungal infection (Ogbru, n.d). IV Amphotericin B is disseminated intravenously and also works as an antifungal drug (Khan, Rawlings & Caffrey, 2011). This drug affects the pathology of Histoplasmosis by binding with the ergosterol found in fungi. It forms a transmembrane around the cell which helps to manage the fungus and its growth.

Conclusion

In conclusion, Histoplasmosis can be effectively diagnosed with proper medical imaging, which helps doctors and physicians understand the pathology of the disease. In addition, antifungal drugs can help mitigate and prevent new fungal growth. Understanding of the treatment and cause of the disease is supported by medical imaging which allows comprehensive review of the disease and its effect on the body. It helps to improve diagnostic methods as well as treatment and prognosis of the disease. 

(Figures 1 & 2 omitted for preview. Available via download) 

References

Al-Hameed, F.  (2013) Thoracic Histoplasmosis Imaging. Retrieved from http://emedicine.medscape.com/article/356401-overview 

Charles Kuhn, C. (n.d.). Histoplasmosis. Brown Medical School. Retrieved from http://www.brown.edu/Courses/Digital_Path/systemic_path/pulmonary/histo.html 

Ha Kirsten Do, M.D. (2010). Skin-nontumor / Clinical Dermatology Infectious disorders Fungi - Histoplasma capsulatum PathologyOutlines.com, Inc. Retrieved from http://ultius.com/component/myorders/?view=writerorderdetail&order_id=3623&client_order_id=3623&client_id=1206 

Khan N, Rawlings B, Caffrey P (2011). "A labile point in mutant amphotericin polyketide synthases". Biotechnol Lett. 33 (6): 1121–6. doi:10.1007/s10529-011-0538-3.

Ogbru, O. (n.d) Itraconazole, sporanox. Medicine net. Retrieved from http://www.medicinenet.com/itraconazole/article.htm 

Pluta, Maksymilian (1988). Advanced Light Microscopy vol. 1 Principles and Basic Properties. Elsevier. ISBN 978-0-444-98939-0.

Rapini, Ronald P.; Bolognia, Jean L.; Jorizzo, Joseph L. (2007). Dermatology: 2-Volume Set. St. Louis: Mosby. ISBN 1-4160-2999-0.