An Overview Of Aspergillosis And Its Effects Biology Essay

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Aspergillosis is the collective name that refers to a group of diseases caused by the fungi belonging to the Aspergillus variety. These diseases primarily affect the lungs. Aspergillus fumigatus is the most common type of Aspergillus fungus to cause aspergillosis.

The Aspergillus variety is found in soil and decaying vegetation. These fungi are the causative agents of opportunistic infections in people having a weak immune system. People with a normal immune system rarely suffer from the disease.

Diagnosis depends upon immunodetection of antigens or histopathology, and prophylaxis (prevention) consists of isolating high-risk individuals. Different types of aspergillosis affect different age groups. Aspergillosis is associated with significant morbidity and mortality.

CAUSES

As mentioned before, aspergillosis is primarily caused by the fungus named Aspergillus fumigatus.

Fungi of this type are found in soil and decaying vegetation.

The fungus enters the body via inhalation of its spores.

Clinical manifestations of the disease depend upon the immunologic state of the patient, and range from non-invasive colonisation of the previously damaged tissue to rapidly progressive invasive disease.

Aspergillosis affects different organs of the body; thus, it presents itself in the following forms:

Pulmonary aspergilloma

Acute broncho-pulmonary aspergillosis (ABPA)

Chronic necrotizing pulmonary aspergillosis (CNPA)

Invasive pulmonary aspergillosis (IPA)

When the spores of Aspergillus are inhaled, mucous layer and ciliary action form the first line of defence in the respiratory tract of the human host. The toxic metabolites produced by Aspergillusproduces toxins which, however, sometimes inhibit macrophage and neutrophil phagocytosis (the process by which invading microorganisms are engulfed and digested by a cell). Thus aspergillus escapes defence mechanism and then proceed to colonise the body.

Different individuals react differently to such an invasion of Aspergillus:

An individual with a normal immune system undergoes no further impairment.

One with a cavitary lung disease may develop pulmonary aspergilloma.

A person with a chronic lung disease may develop CNPA (Chronic necrotizing pulmonary asperigillosis).

Someone with asthma may contract ABPA (Acute broncho-pulmunory aspergillosis) .

An immuno-compromised host may fall victim to IPA (Invasive pulmonary Asperigillosis).

RISK FACTORS

Individuals taking immunosuppressive drugs or those who have undergone organ transplant are prone to this infection because of a weakened immune system.

Aspergillus is readily found in a hospital, e.g. on bedrails, plants, surgical instruments, air conditioning, etc. Seriously ill patients are, thus, prone to contracting aspergillosis.

This disease also affects people with a low white-blood-cell count, such as those undergoing hemotherapy and organ transplant.

Individuals with long-standing lung problems such as asthma, cystic fibrosis and lung cavities are also susceptible.

Individuals undergoing long-term corticosteroid therapy are likely to be infected as such a treatment suppresses their immunity.

SIGNS AND SYMPTOMS

Aspergilloma is a fungus ball that typically occurs in patients with a pre-existing cavitary lung disease. It usually manifests as an asymptomatic radiological abnormality. Pulmonary aspergilloma is common in patients with HIV. It occurs in cystic areas resulting from prior pneumonia. The ball of fungus does not invade the cavity wall, but may move within. The most common symptom is haemoptysis, which may be massive and life threatening. Less commonly, coughs and fever may also occur.

Chronic necrotizing pulmonary aspergillosis is not a common form of aspergillosis. It is a slowly progressive necrotizing pneumonia-having duration of more than one month-which produces cavitary pulmonary infiltrate. Usually, people with a compromised immune system fall prey to this infection. It manifests as sub-acute pneumonia that is unresponsive to antibiotic therapy. People with CNPA may also be associated with an underlying lung disease, chronic steroid therapy or alcoholism. Middle-aged and older individuals show a predisposition towards this illness. Individuals suffering from CNPA exhibit fever, dyspnoea, cough and haemoptysis, and weight loss. Recurrent or relapsing infections are common in this type of aspergillosis.

Acute broncho-pulmonary aspergillosis usually occurs in children and young adults. Most patients may have other allergic disorders such as asthma, rhinitis, conjunctivitis and atopic dermatitis. It occurs either at the onset or after the onset of asthma. The affected individual displays a hypersensitive reaction to the fungal colonisation of the tracheobronchial tree. He/she may have a cough with purulent sputum, and produce mucous plugs that may form bronchial casts. Coughing usually increases and the person may suffer from chest pain and haemoptysis. Asthma may also progress from mild form to corticosteroid-dependant asthma. It may occur in conjunction with allergic fungal sinusitis, with symptoms including chronic sinusitis with purulent sinus drainage.

ABPA usually has the following five stages:

Acute stage (characterised by fever, cough, sputum, chest pain and haemoptysis)

Remission stage (asymptomatic)

Exacerbation (either symptoms of acute stage or asymptomatic)

Corticosteroid-dependant asthma (severe asthma)

Fibrosis (characterised by cyanosis and severe dyspnoea)

Invasive pulmonary aspergillosis is a condition observed in people who have a suppressed immune system, especially those who have undergone organ transplant and bone marrow transplant, and those with haematological malignancy, neutropenia and HIV. This form of aspergillosis is characterised by a fungal invasion of blood vessels. Via the bloodstream, it spreads to the brain, the heart, the liver and the kidneys. The affected individual typically displays symptoms such as fever, cough, dyspnoea and pleuritic chest pain. Sometimes, patients with prolonged neutropenia or immunosuppression also exhibit haemoptysis. As it is a rapidly progressive condition, this form of aspergillosis is often fatal.

DIAGNOSIS

The diagnosis of this disease depends upon microscopy and culture examination.

Microscopy: Characteristic branching at an angle of 45 degrees is seen. Biopsy specimens are treated with H and E, and PAS stains.

Culture: Different species of Aspergillus show different coloured colonies, e.g. A.fumigatus shows green-coloured colonies. The colonies have a velvety surface. Lacto phenol cotton blue colonies show branching and septet hyphen.

Chest radiography may also be conducted to detect cavitary lesions.

CT scan is helpful for confirming bronchiectasis in ABPA.

An intradermal skin test can be done for ABPA. In this test, an Aspergillus antigen is injected in the skin, and a positive reaction confirms the diagnosis.

TREATMENT

Aspergillosis is treated by antifungal therapy, with the aid of antifungal agents such as itraconazole, amphoterecin a and b, voriconazole and posaconazole. Usually, oral itraconazole is preferred and is the drug of choice.

In case of allergic aspergillosis that is caused by asthma, oral corticosteroids are beneficial.

Laminar airflow (LAF) or high-efficiency particulate air (HEPA) filtration of patient rooms helps prevent aspergillosis in patients who receive bone marrow transplants, and other high-risk patients.

Surgical treatment is considered when patients fail to respond to antifungal therapy. However, before surgical intervention, pulmonary-function tests should be carried out to assess operative risk.

COMPLICATIONS

Invasive aspergillosis causes the infection to spread to other organs in the body. Since it is a rapidly progressive condition, this form of aspergillosis is often fatal. Invasive aspergillosis can also cause fatal lung bleeds.

If sinuses are infected, then the facial bones may also be damaged. Further, the infection may spread to other parts, thereby leading to a life-threatening condition.

PREVENTION

Aspergillosis as such cannot be prevented. However, people with a weakened immune system should wear face masks to avoid catching any infection. Those who are severely ill or have undergone a surgery should try and avoid high-risk areas such as construction sites and grain storages.

PROGNOSIS

The prognosis of aspergillosis depends upon its severity and type. Allergic aspergillosis can be treated effectively. Invasive aspergillosis, on the other hand, is difficult to treat and is associated with significant morbidity and mortality.

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