Histoplasmosis

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American crow

Histoplasmosis is a fungal infection caused by Histoplasma capsulatum. This fungus grows primarily in soil that has been contaminated with bat or bird droppings. Typically, H. capsulatum is most viable in areas with large concentrations of feces and often does not result in an infection. However, this disease has become endemic to some regions of the U.S and is zoonotic, meaning it can transfer from animals to humans. Infections can be mild to severe chronic conditions depending on several factors including the number of spores inhaled and individual immune capacities. While this disease is mediated by animals, it is not contagious or zoonotic (transferrable from animals to humans). This is not to say that animals cannot become infected by histoplasmosis, but that it cannot spread once contracted like WNS or SFD can.

Mechanism of Action

H. capsulatum spores are released into the air once contaminated soil is disturbed. In a  person with a compromised immune system or an area with high concentrations of spores, an infection is likely to occur from inhalation of disturbed spores. Although infections are typically acute, there are chances of systemic spread to other parts of the body. This occurs after the spores in the lungs are allowed to form into yeast. The yeast would then travel into the lymph nodes and then to the bloodstream. The blood could then carry the infection to other organs of the body.

Species of Concern

  • American crows
  • Rock pigeons
  • European starlings
  • Gregarious bats (big brown, tricolored, etc.)
  • Flocking birds

Symptoms

Symptoms can appear between 3 and 17 days after first inhalation of spores. Most acute cases may result in:

  • Mild fever/chills
  • Cough
  • Chest/joint/body pain
  • Red bumps on lower legs
  • Fatigue

More severe cases may result in:

  • Excessive sweating
  • Shortness of breath
  • Coughing blood
  • Serious chest pain
  • High fever
  • Stiff neck and headaches

Range

H. capsulatum can be found anywhere in the world, but is most common in North and Central America, with particularly high concentrations in southeastern and central U.S. The Ohio and Mississippi River Valleys are the areas of highest concern.

histoplasmosis-lifecycle-maps-300px

Prevention

Those with known suppressed immune systems should avoid doing activities cohesive with histoplasmosis infection. Some activities include disturbing soil with droppings on it, cleaning chicken coops, exploring caves, construction or remodeling houses. Some occupations may be high risk such as construction, farming, pest control, demolition, roofer or landscaper. A respirator should be used when working in situations where infection is likely to occur.

Significance

Although histoplasmosis often does not result in serious infection, there are still locations in America where histoplasmosis is highly endemic. It can infect pets as well as humans and can be very problematic for those with weakened immune systems. Many people are at risk of infection, even in urban areas where flocking birds like pigeons and crows are highly common. Although breathing in spores often does not result in symptomatic infection, there are still easily avoided risks surrounding this disease. Histoplasmosis is opportunistic and may infect up to 30% of HIV/AIDS patients, resulting in more serious, systemic infections. Small children and seniors may also have high risk of infection and are at a greater risk for serious infection.

Sources

Delgado, A. (2016, January 19). Histoplasmosis (D. Weatherspoon Ph.D, Ed.). Retrieved April 20, 2017, from http://www.healthline.com/health/histoplasmosis#risk-factors5

CDC. (2015, November 21). Fungal Diseases. Retrieved April 20, 2017, from https://www.cdc.gov/fungal/diseases/histoplasmosis/index.html

Kauffman, C. A. (2007). Histoplasmosis: a Clinical and Laboratory Update. Clinical Microbiology Reviews, 20(1), 115-132. Retrieved April 20, 2017, from http://cmr.asm.org/content/20/1/115.short

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