Both tobacco and marijuana are commonly contaminated with fungi and aspergillus - antibodies to aspergillus in blood samples from marijuana smokers do occur. It is uncertain whether the exposure to aspergillus comes from handling the marijuana or from inhaling spores which may survive the burning process.
A recent publication has described 2 cases of chronic pulmonary aspergillosis associated with extensive medicinal use of marijuana (Gargani et al 2011).
One patient aged 47 was already a heavy smoker but his breathlessness was considerably worse once he commenced marijuana smoking (5 joints per day), for relief of rheumatoid arthritis. He was coughing up thick mucous and noticed unusual weight loss.
His lungs contained a number of bullae - these are like air filled holes in the lung tissue - he had surgery removing part of his lung and one bullae was found to contain an aspergilloma 7 cm across. After surgery his lung function did not improve and and the other lung was seen to contain a number of these bullae or "holes". After antifungal treatment for 4 months with posaconazole his cough and sputum production improved, he also stopped using marijuana. He was monitored for 4 years and showed no recurrence of symptoms.
The second patient had smoked around 20 joints a day from the age of 10 - initially for pain relief. At 35 he was diagnosed with emphysema but at 43 years old - he suffered respiratory failure - he gave up cannabis smoking aged 44- but by this time he needed long term oxygen therapy and could only walk 10 metres on the flat. Radiology of his lungs showed complex cavitary lesions and a probable aspergilloma. Sputum samples revealed the presence of Aspergillus fumigatus with positive antibody tests - all consistent with CPA. His lungs deteriorated so much he needed a lung transplant - but the presence of Aspergillus was a contraindication to a lung transplant. He was given antifungal treatment but died within a few months.
Marijuana usage has been implicated in some cases of Aspergillus infections -but evidence from these 2 patients indicates that development of aspergilloma and CPA may also be linked to smoking this substance.
The method of smoking marijuana is different to tobacco - usually there is no filter, the breathe is held for longer, exhalation aginst closed airways- all this maximises intake of psychoactive substances, but increases tar and carbon monoxide content and increases pressure changes in the lungs.
An understanding of the full health risk in smoking marjuana is difficult to assess since the lack of disclosure by patients of their smoking habits - for fear of legal issues - does not permit clinicians to fully assess the results of smoking this drug.