Symptoms of infectious pneumonia caused by the invasion of the lungs by microorganisms and the immune system's response to infection. Although more than one hundred types of microorganism can cause pneumonia, only a few are responsible for most cases. The most common causes of pneumonia are viruses and bacteria. Less common causes of infectious pneumonia are fungi and parasites.
Virus
The virus attacks the cells to reproduce. Typically, a virus reaches the lungs when airborne droplets are inhaled through the mouth and nose. Once in the lungs, the virus invades the cells lining the airways and alveoli. This invasion often leads to cell death, either when the virus directly kills the cells, or by the type of cell apoptosis controlled self-destruction called. When the immune system responds to viral infections, lung damage even more the case. White blood cells, particularly lymphocytes, activate certain chemical cytokines which allow fluid to leak into the alveoli. The combination of cell destruction and fluid-filled alveoli disrupt normal transportation of oxygen into the bloodstream.
As well as damaging the lungs, many viruses affect other organs and thus disrupt many body functions. Viruses can also make the body more susceptible to bacterial infections, bacterial pneumonia reason that often complicate pneumonia.
Viral pneumonia is commonly caused by viruses such as influenza virus, respiratory syncytial virus (RSV), adenovirus, and metapneumovirus. Herpes simplex virus is a rare cause of pneumonia except in newborns. People with weakened immune systems are also at risk of pneumonia caused by cytomegalovirus (CMV).
Bacterium
Bacteria typically enter the lung when airborne droplets are inhaled, but can also reach the lung through the bloodstream when there is an infection in another part of the body. Many bacteria live in the upper respiratory tract, including the nose, mouth and sinuses, and can easily be inhaled into the alveoli. Once inside, the bacteria can invade the space between cells and between alveoli through connecting pores. This invasion triggers the immune system to send neutrophils, a type of defensive white blood cells, to the lungs. Neutrophils engulf and kill the offending organisms, and also release cytokines, causing a general activation of the immune system. It causes fever, chills, and fatigue common in bacterial and fungal pneumonia. Neutrophils, bacteria, and fluid from surrounding blood vessels fill the alveoli and interrupt normal oxygen transportation.
Bacteria often travel from infected lungs into the bloodstream, causing serious or even fatal illness such as septic shock, with low blood pressure and damage to some parts of the body including the brain, kidneys, and heart. Bacteria can also travel to the area between the lungs and the chest wall (the pleural cavity) causing a complication called empyema.
The most common causes of bacterial pneumonia are Streptococcus pneumoniae'''' and "atypical" bacteria. Atypical bacteria are intracellular parasitic bacteria that live or do not have a cell wall. In addition, they cause generally less severe pneumonia, thus atypical symptoms, and respond to different antibiotics than other bacteria.
Types of Gram-positive bacteria that cause pneumonia can be found in the nose or mouth of many healthy people. Streptococcus pneumoniae'''', often called "pneumococcus", is the most common bacterial cause of pneumonia in all age groups except newborns. Pneumococcus kills approximately one million children each year, mainly in developing countries. Other causes important Gram-positive Staphylococcus aureus pneumonia is'''','''' Streptococcus agalactiae to be an important cause of pneumonia in newborns. Gram-negative bacteria cause pneumonia less frequently than gram-positive bacteria. Some gram-negative bacteria that cause pneumonia include Haemophilus influenzae'''','''' Klebsiella pneumoniae, Escherichia coli'''','' Pseudomonas aeruginosa'' and'' Moraxella catarrhalis''. These bacteria often live in the stomach or intestines and can enter the lungs if inhaled vomit. "Atypical" bacteria which cause pneumonia include Chlamydophila pneumoniae'''','''' Mycoplasma pneumoniae, and Legionella pneumophila''''.
Mushrooms
Fungal pneumonia is rare, but can occur in individuals with immune system problems due to AIDS, immunosuppresive drugs, or other medical problems. Pathophysiology of pneumonia caused by fungi is similar to bacterial pneumonia. Fungal pneumonia is most often caused by Histoplasma capsulatum'''', blastomyces,'' Cryptococcus neoformans'','' Pneumocystis jiroveci'', and'''' Coccidioides immitis. Histoplasmosis is most common in the Mississippi River basin, and coccidioidomycosis in the southwestern United States.
Parasite
A variety of parasites can affect the lungs. These parasites typically enter the body through the skin or swallowed. Once inside, they travel to the lungs, usually through the blood. There, as in other cases of pneumonia, a combination of cellular destruction and immune response causes disruption of oxygen transportation. One type of white blood cell, eosinophil, it responds vigorously to parasite infection. Eosinophils in the lungs can lead to eosinophilic pneumonia, making it difficult for the underlying parasitic pneumonia. The most common parasites causing pneumonia'' Toxoplasma gondii'','' Strongyloides stercoralis'', and'''' ascariasis.
Idiopathic
Idiopathic interstitial pneumonia (IIP) is a class of diffuse lung disease. In some types of IIP, eg some types of usual interstitial pneumonia, the cause, indeed, is unknown or idiopathic. In some types of IIP known to cause pneumonia, interstitial pneumonia Desquamative instance caused by smoking, and the name is a misnomer.
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