histoplasmosis

see also:

• fungi
• antifungal agents

• histoplasmosis is a fungal infection caused by Histoplasma capsulatum which grows as a yeast at mammalian body temperatures
• it is mainly found in soils of organic rich river valleys between latitudes between 45° north and 30° south, and is spread via droppings from birds and bats
• it is the most common endemic fungal infection seen in humans
• ~80% of young adults in endemic areas have been infected
• human outbreaks of infection can arise when this soil is disrupted as in earthworks at construction sites
• humans can also become infected by travelling through endemic areas as airborne spores can travel hundreds of metres
• 90% infections are asymptomatic
• patients at risk of clinical disease are mainly the immunocompromised or those who have a large inoculum of spores
• histoplasma may also remain latent in healed granulomas and become clinical once immunocompromised

• acute pulmonary histoplasmosis
  • incubation period 3-14 days
  • fever
  • headache
  • myalgia
  • abdominal pain
  • may develop cough, haemoptysis, SOB, chest pains
  • most resolve spontaneously but large inoculums may cause severe resp. distress or other complications
  • 5-6% develop joint pains, erythema multiforme, or erythema nodosum
  • 5-10% develop hilar and mediastinal lymphadenopathy
  • 15% have +ve sputum cultures
  • exudative pericarditis
    • in 5% of symptomatic patients
    • 40-60% of these patients also develop pleural effusions
  • granulomatous mediastinitis
    • due to necrosis of mediastinal lymphadenopathy
  • fibrosing mediastinitis
    • uncommon complication, particularly in young women
• ocular histoplasmosis syndrome
  • occurs in up to 10% of asymptomatic patients
  • macular involvement may cause blindness
• chronic pulmonary histoplasmosis
  • mainly in those with chronic lung disease
  • cavitating lesions
  • mild anaemia
  • >60% have +ve sputum cultures
  • may develop pulmonary fibrosis
  • up to 50% mortality if untreated, reduces to half this if treated
• progressive disseminated histoplasmosis
  • 1 in 2000 immunocompetent adults who are infected
  • 4-27% of children, elderly or immunocompromised adults
  • if untreated may be fatal in weeks (or up to 2 years in the subacute form)
  • 70-90% develop pancytopenia
  • raised AP
  • blood cultures are +ve in > 50%
  • 5-20% of these patients develop CNS infection such as meningitis or mass lesions
  • superior vena cava syndrome may occur
  • 10% develop skin lesions
  • hepatosplenomegaly may occur