A letter to the public in regards to specific health and awareness:

by NS

Image 1 from Ref 5

Within the central river valleys of Midwest US, the belt of the Southern Central US, and the upper regions of Central US, there is a microbe that poses an issue for 500,000 individuals per year. Histoplasma capsulatum is a virulent and airborne fungus associated with mild to severe respiratory infections among individuals (3). With 5 – 20% of lifetime residents in these areas showing exposure, as well as a very high mortality rate upon untreated systemic infections, H. capsulatum is a microbe of necessary awareness for public health (2).

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H. capsulatum primarily resides in moist rich soil within the regions of infection. Soil that of which is infected by bird and bat fecal matter are of primary risk for contamination. Notably soil near livestock populations, such as chickens, are also at a higher risk (5). Within the soil, the fungus begins its transition to infectious stages at temperatures of 77 degrees Fahrenheit. Upon the surrounding environment reaching this temperature and fungal formation of short stalks completed, disturbance of the fungi through any means, such as walking, will release its infectious agents, spores, for potential infection of individuals(2) (4) (6). Construction sites are at high risk of outbreak due to them containing wind-blown dust that carries the infectious agents. H. capsulatum is not infectious from person to person, which remains an advantage for dealing with outbreaks (5).

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The environment H. capsulatum is encountered in determines it’s primary growth stage, of 3 total stages. While residing in soil, H. capsulatum is in its first stage of growth. Formation of infectious agents such as macro and microconidia, both a form of spores, are key to this stage, with the latter hypothesized to be the more infectious form (2). Upon the release of spores from its short stalk formation which lead to subsequent infection, H. capsulatum is able to transition to its next stage from within the human body due to the temperature shift from an environment of 77 degrees to human body temperature of 98.6 degrees Fahrenheit (3) (4). Spores inhaled from the environment of stage one are lodged in the mucus membrane of the lungs where they’re devoured by host immune cells. Contrarily, chronic but mostly harmless infections occur when they stay within the pulmonary calcifications, healed lung tissue, and are not detected by immune cells. After host immune cells engulf H. capsulatum, it begins to transition to an oval budding yeast from within its own safe bubble in the immune cell. After 4 – 6 days of being in stage two, which can be accelerated in abundance of cysteine and iron, the microbe transitions to stage three of growth. Within this stage, the newly formed yeast keeps a constant safe environment of homeostasis around it to perform cellular process (4) (6). H. capsulatum will require cysteine and iron to be successful, which it has counter mechanisms for due to low free iron levels within hosts. Cysteine is vital for yeast stage transition and growth, this is due to yeast requiring a high demand of cysteine and iron for nutrition (2).

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Detection is tricky but varies depending on severity. As with stated that some chronic but mostly harmless infections do occur, these types do not show symptoms. These are dangerous due to the potentiality of eventual immune compromisation, meaning the random chance your immune system becomes weakened; the infection will flare up and cause major issues. When it flares back up, symptoms will include ones mirroring pneumonia (1) (6). These would be troubled breathing, light-headedness, dizziness, chronic sweating, and cold chills. Within worsening systemic, whole body, infections symptoms to be aware of include those linked to Superior vena cava syndrome such as shortness of breath as well as facial and arm swelling. Inflammation and chronic pain from within the chest cavity is also a symptom linked to systemic infections due to its association with peripheral tissue inflammations such as Mediastinitis. Contrary to asymptomatic chronic infections, symptomatic infections will arise 3 to 17 days post infection. The symptoms will range from fever, dry cough, chest pains, and a general sick feeling (3) (5).  As with any detection of symptomatic infections, subsequent contact of a doctor is highly advised for overall wellness of patient.

Post detection treatment varies on the stage and type of infection. With chronic infections that flare up after secondary immune compromise events, prolonged treatments with antifungals will occur for about a year (1) (5). Chronic infections have different styles, however treatment will stay the same for all chronic infections with any variance being on medication dosage levels (3) (6). The worse stage of chronic infection is when the yeast becomes disseminated and spreads through the blood to other organs and tissues, which is known as a systemic infection. This stage is very lethal if left untreated due to potential systemic organ failure, however treatment in patients that do not suffer irreversible damage to their tissue is extremely successful (5) (6). Subsequent medications of balancers might be utilized for later stages of this, however antifungals of the same style will be utilized. Due to the reclusive nature of the microbe in undetected stages, it remains hard to detect and subsequently treat it (6). A good reference is that in cases of greater infection, symptoms from H. capsulatum will occur which allows for detection and subsequent treatment.

A key reminder is that the elderly and adolescents pose a higher risk of acute infections due to structurally weaker immune systems. Awareness of the microbe and its symptoms can lead to proper detection and subsequent treatment of such individuals at higher risk.

Prevention of infections is a seemingly coordinated effort for H. capsulatum. Prevention of accumulated bird or bat droppings near opportune soil environments is a combined effort. Within working environments with higher risk, utilization of greater personal protective equipment (PPE) is vital to preventing potential infections. Awareness of areas containing high concentrations of bats and birds is a great advantage in the field of prevention. Contrary to land birds, aquatic birds such as gulls, provide no threat to infection. As with most infections that spike in immune-compromisation, keeping a healthy immune system is vital in preventing more harmful and serious infections (5) (7). Proper diet, sleep patterns, and proper actions within the state of being sick are crucial for preventing a weakening of the immune system. A key thing to note in this is that infections leading to sickness can weaken an immune system to the point where different subsequent microbes, such as H. capsulatum, are allowed to have a more opportune impact on a host. Proper health measures during illness, such as sleeping enough and eating well are crucial for preventing subsequent infections from other microbes (5). With acquired immune deficiency syndrome (AIDS) at pandemic levels, and fungal vaccines still in developmental stages, proper preventative measures prove highly effective for preventing such a microbe from having a high impact on the population. (1)

To summarize, H. capsulatum resides in the central US with 5 – 20% of lifetime residents obtaining chronic infections. Soil frequented by birds, bats, and livestock pose a higher risk, so be aware with frequenting these areas in the ideal temperature range (77 degrees), since any walking can release spores. Infection will occur in the lungs and can eventually progress to a systemic infection. Asymptomatic chronic infections are frequent and these are problematic if your immune system is weakened by future infections. Symptomatic infections will result fairly recent after infection and seeking of a physician is important to prevent a systemic infection. The key factor with infection of H. capsulatum is prevention of a systemic infection, which can be avoided by being aware of symptoms and seeking of medical assistance.  Be aware that elderly, adolescent, and immune-compromised individuals (AIDS) are at a higher risk of infection, and observe symptoms in those individuals if they arise while encouraging seeking medical treatment. Keeping a healthy immune system through sleeping, eating, and exercising properly is a key factor in managing infections and should be done regardless.

References:

(1)      Medici, Natasha P., and Maurizio Del Poeta. "New Insights on the Development of Fungal Vaccines: From Immunity to Recent Challenges." Mem. Inst. Oswaldo Cruz Memórias Do Instituto Oswaldo Cruz 110.8 (2015): 966-73. Web.

(2)      Bossche, Hugo, Frank Odds, and David Kerridge. Dimorphic Fungi in Biology and Medicine. 1st ed. New York and London: Plenum Press, 1993

(3)       Chang, Ryan. "Histoplasmosis." 19 Sep 2005. emedicine. 25 Aug 2007 <http://www.emedicine.com/MED/topic1021.htm>.

(4)      Heitman, Joseph, Scott G. Filler, Aaron P. Mitchell, and John E. Edwards, Jr.Molecular Principles of Fungal Pathogenesis. 1st ed. New York: ASM Press, 2006. (Heitman et al. 611-626)

(5)       "Histoplasmosis." Centers for Disease Control and Prevention. 12 Oct 2005. Centers for Disease Control and Prevention. 25 Aug 2007 <http://www.cdc.gov/ncidod/dbmd/diseaseinfo/histoplasmosis_g.htm>.

(6)      Kobayashi, George S.. "Molecular Basis of Adaptation in Histoplasma capsulatum ." Washington University School of Medicine. 25 Aug 2007 <http://research.medicine.wustl.edu/OCFR/Research.nsf/Abstracts/64ABA9996B650C50862567ED00029E69?OpenDocument&VW=Infectious+Diseases>.

(7)      Lai, Chung-Hsu, Chun-Kai Huang, Chuen Chin, Ya-Ting Yang, and Hsiu-Fang Lin. "Indigenous Case of Disseminated Histoplasmosis, Taiwan." Emerging Infectious Diseases Jan 2007 127-129.