histoplasmosis

introduction

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

clinical features

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