Pneumonia is a condition characterized by inflammation of the alveoli present on one or both the lungs. It occurs when one or both the lungs of a person get infected by bacteria, fungi or virus. The alveoli are microscopic sac-like structures in the lungs that absorb oxygen. These sacs become inflamed and get filled with fluid. It can result in swelling, irritation and congestion of lungs. Pneumonia is quite a common health condition that can affect anyone, irrespective of age and gender. The nature and severity depends on the cause of pneumonia. However, the condition is more dangerous for infants, elderly and people with an impaired immune system. There can be several causative factors based on the different types of pneumonia. Causes of Pneumonia As stated earlier, pneumonia can be caused due to different pathogenic agents, out of which, bacterial and viral pneumonia are the most common. These pathogens find entry in the body through food or through the contaminated air that we breathe. When a person breathes, the immune system of the body fails to prevent the entry of these pneumonia-causing agents and they reach the lungs of the person directly. These microorganisms settle in the alveoli and start multiplying there. Now, this triggers the immune system to send antibodies to fight the infection, due to which the alveoli or the air sacs in the lungs get filled with fluid, ultimately resulting in pneumonia. Bacterial Pneumonia Streptococccus pneumoniae is one of the most common bacterial pneumonia causes in adults. Klebsiella pneumoniae and Haemophilus influenzae are the bacteria responsible for causing pneumonia in people suffering from chronic obstructive pulmonary disease or alcoholism. Atypical pneumonia is caused by the bacterium, Mycoplasma pneumoneae. Another bacterium Legionella pneumophila causes Legionnaire's disease, which is an uncommon form of pneumonia. Clamydophila psicatti causes another rare form of pneumonia known as psittacosis pneumonia. Viral Pneumonia Viral pneumonia is generally caused by the virus affecting the respiratory system. It is one of the common causes in children. Respiratory syncytial virus, parainfluenza and adenoviruses are the primary causes, however, infection of influenza A or B virus or chickenpox virus (Varicella zoster) can also progress to pneumonia if left untreated. Fungal Pneumonia Fungal pneumonia is common in the United States, however, it rarely occurs in other parts of the world. Fungi infections generally occur in people who have a weak immune system. The various fungal infections that can lead to pneumonia are as follows:

• Histoplasmosis
• Blastomycosis
• Asperigillosis
• Coccidiomycosis
• Cryptococcosis

Parasitic Pneumonia Pneumonia can also be caused by certain parasites. These parasites enter the body through skin or through the food we eat. Once they are ingested, they travel to the lungs and start growing in number. They cause damage to the cells of the lungs and adversely affect the working of the lungs. This stimulates immune response and can result in inflammation of the lungs, causing pneumonia. Some example of parasites that cause such type of pneumonia include Strongyloides stercoralis, Toxoplasma gondii and Ascariasis. Aspiration Pneumonia Aspiration pneumonia, also known as anaerobic pneumonia, is a condition characterized by inflammation of the bronchial tube and lungs, caused by inhalation of some foreign material. Inhalation of harmful chemical or smoke can also cause irritation of the bronchial tube lining and result in inflammation of the lungs. Proper knowledge of the signs and symptoms of pneumonia is necessary for early diagnosis of this condition. It is advisable to consult your health care provider as soon as you observe any of the pneumonia symptoms. This can help in effective treatment of pneumonia. You could also ask your doctor about the different measures for preventing this disease.