Aspergillosis: Aspergillus infections

Aspergillosis: definition

The term "aspergillosis" defines a group of diseases caused by molds belonging to the genus Aspergillus. Aspergillosis are diseases affecting the respiratory system, with a pathogenesis that is partly infectious and partly allergic.
Let us briefly remember that Aspergilli are commensal fungi normally present in the organism, especially on the skin, oral cavity and digestive system: only under certain conditions, these microorganisms can become pathogenic and cause damage, mostly affecting the respiratory tract.
Aspergillus fumigatus and Aspergillus niger they are probably the two species of greatest pathological interest, therefore the most involved in aspergillosis.

For further information: Aspergillosis Symptoms

Classification

The most common aspergillosis are classified into:

ALLERGIC or bronchial ASPERGILLOSIS: a very widespread form of aspergillosis, the result of a violent hypersensitivity reaction triggered by the inhalation of the Aspergillus spores. This form manifests itself with:
- asthma
- allergic bronchopneumonia → fibrosis of the lung segments, dyspnoea and bronchiectasis

This variant of aspergillosis is manifested above all in previously sensitized patients, who make contact with the conidia of the aspergillus again. The tissue damage is subordinated to the immune reaction of the host.

Allergens → IgE production → antigen-antibody complex activates the mastocells → release of histamine → bronchospasm and mucus production in the bronchioles

Allergic aspergillosis is frequent especially in patients with cystic fibrosis and severe asthma. The clinical and symptomatic picture is manifested by intense dyspnea, bronchospasm, malaise and cough.
When not carefully treated, allergic bronchopulmonary aspergillosis can cause permanent lung damage (pulmonary fibrosis).

NON-INVASIVE LOCAL ASPERGILLOSIS (there is no invasion of contiguous tissues):
- Pulmonary / sinus aspergilloma (or mycetoma) or intracavitary aspergillosis. Aspergilloma consists of the formation of hyphae inside the lung cavity. Initially asymptomatic, aspergilloma subsequently manifests itself with chronic cough, weakness, loss of appetite, anorexia and hemoptysis.
- Otomycosis: the most involved etiopathological agent is Aspergillus niger. The symptomatic picture is characterized by pain, edema, erythema and itching. Aspergillus grows on debris and ear wax in the outer ear.
- Onychomycosis: similar to otomycosis, also in onychomycosis the most responsible causal agent is Aspergillus niger. The most common symptoms are: pain, edema, erythema and itching.
- Eye infections (e.g. conjunctivitis)
- Primary cutaneous aspergillosis: typical of patients with pressure sores / burns and paraplegics; the distinctive signs of this aspergillosis are comparable to a dermatomycosis.

The signs and symptoms that distinguish non-invasive aspergillosis are cough and hemoptysis.

INVASIVE or diffuse ASPERGILLOSIS: the invasion of blood by the hyphae can cause blood clots, heart attacks and hemorrhages. Typical of the severely immunocompromised patient, this form of aspergillosis is probably the most dangerous, and presents a high mortality.
- Disseminated invasive aspergillosis: causes gastrointestinal, brain, liver, kidney, skin and eye problems. It appears particularly common among immunocompromised patients, especially if undergoing solid organ transplantation. The mycelium develops in the lung and then spreads to the brain, skin and heart.
- Invasive pulmonary aspergillosis (probably the most common form)
- Invasive rhino-sinus and tracheo-bronchial aspergillosis

Invasive aspergillosis occurs mainly among leukemia patients, transplant recipients and AIDS patients. Patients on prolonged therapy with high-dose corticosteroids are also at risk of Aspergillus infections.
The symptomatic picture is characterized by rather vague and non-specific symptoms: dyspnoea, chest pain, fever, hemoptysis, cough (generally non-productive).

Diagnosis

If aspergillosis is suspected, the patient undergoes general diagnostic tests, such as chest x-rays and computed tomography. When the tests show unmistakable signs of infection, a more specific investigation is carried out to isolate the fungus starting from samples of pleural exudate, bronchial secretions or from samples performed by bronchoscopy. Broncho-alveolar lavage or endotracheal aspirate are further investigations used for cultural examination and for microscopic observation.

For the cytological examination, the presence of calcium oxalate crystals is an indicator of aspergillosis. The culture test, useful for accurately detecting the etiological agent, is performed on sabourad agar medium, while the histological diagnosis uses staining hematoxylin-eosin.

It should not be forgotten, however, that the search for "Aspergillus in the sputum" can give false positivity: in fact, some commensal species of Aspergillus can coexist within the oral cavity.

Care

Unfortunately, invasive aspergillosis gives a poor prognosis in the vast majority of cases: in order to avoid such consequences, it is recommended to consult a doctor even if only in case of suspected aspergillosis.
Let us briefly recall that in healthy subjects, aspergillus infections should not be too alarming: in fact, aspergillosis tends to occur almost exclusively in immunocompromised patients.

Mild forms of aspergillosis (allergic variants) are easily treatable.
The drugs most used in therapy for the treatment of aspergillosis are antifungals (eg voriconazole, posaconazole, caspofungin and Amphotericin B). In order to exert an "intense anti-inflammatory action, corticosteroids can also be useful in the case of aspergillosis associated with asthma. and / or cystic fibrosis.