Classifying pneumonia. Bacterial pneumonia is one of several types of pneumonia. One type is called mycoplasma pneumonia. It is also called atypical or walking pneumonia because the symptoms are so mild in some patients that they do not know that they are sick. It is caused by a organism called Mycoplasma pneumoniae, a small bacteria that is not like other bacteria. The deadly pneumonic plague is caused by the plaque bacteria, Yersinia pestis.
Viral pneumonia is caused by viruses such as the parainfluenza virus. It can even be caused by the herpes simplex virus, but this is rare. Fungal pneumonia is not as common as viral or bacterial pneumonia, and it mostly strikes people whose immune systems are compromised. These would include people with AIDS or who are taking drugs to suppress their immune system. Among the fungi that cause fungal pneumonia are histoplasmosis, blastomyces, Histoplasma capsulatum and Cryptococcus neoformans.
Parasitic pneumonia is caused by parasites such as the Toxoplasma gondii and even plasmodium malariae, the parasite that causes malaria. These parasites don’t directly attack the lungs but cause a sickness that eventually involves the lungs. Other types of noninfectious pneumonia are due to conditions that damage the lungs. Respiratory bronchiolitis interstitial lung disease, for example, is a consequence of smoking.