Pneumocystis jiroveci (carinii). Pneumocystis jiroveci – previously known as Pneumocystis carinii (classified as a protozoon at that time) is a fungus causing pneumacystosis. It affects people with a weaker immunity like: children and the elderly but these are rather occasional cases. Most cases of Pneumocystis jiroveci infections constitute as AIDS infection symptoms. The fungus occurs in the digestive system of most pets and domestic animals (dog, cats, cattle and horses) however they very rarely infect healthy organisms. Generally, this germ infects persons suffering from AIDS, large bowel cancer or people having thier immune systems handicapped in some sort of way. Pneumacytosis is detected by colouring the sputum with silver.