Histoplasmosis

What is Histoplasmosis?

Histoplasmosis is caused by Histoplasma spp., which are dimorphic fungi found across the globe, often as a mould in soil or animal droppings.^1,2 They can also exist in a yeast-like form at human body temperature.¹

Pathogenesis

Histoplasmosis generally affects the lungs, but can spread to the central nervous system, or to other parts of the body via the bloodstream.¹ While most people who inhale Histoplasma spp. do not become ill, or they recover without requiring medication, some may develop disseminated disease. Patients who are critically ill or immunocompromised are more likely to develop disseminated disease.¹

Epidemiology

Histoplasmosis is an endemic mycosis, with higher incidence rates occurring in the Americas and Africa compared with the rest of the world.^1–3 In Europe, there have been reports of an increasing number of autochthonous cases.⁴ Recorded trends in recent years appear stable.¹ Global estimates for the incidence of histoplasmosis and disseminated histoplasmosis are ~500,000 and ~100,000 cases per year, respectively.⁵

Mortality rates for histoplasmosis range from 21 to 53% in patients who are human immunodeficiency virus (HIV) positive to 9–11% in patients who are immunosuppressed and solid organ transplant recipients.¹

Patients who are hospitalised with histoplasmosis tend to remain in hospital for 5–7 days, although this is highly variable.¹ The incidence of complications and sequelae is unknown.¹

Histoplasma spp. are able to persist chronically for years in an immunocompetent host and not result in any symptoms of disease, and acute infection can be reactivated if the host immune system becomes compromised.⁶

Risk factors

Known risk factors for histoplasmosis include:^1,7

• HIV infection
• Corticosteroid therapy
• Malignancy
• Transplantation
• Travel to or resident in known endemic areas

Pathogenic species

Histoplasma capsulatum is the causative agent of histoplasmosis.⁷