There are many kinds of opportunistic infections common to AIDS, the common ones are Pneumocystis carinii which can cause Pneumocystis carinii pneumonia; Cryptococcus, Candida, etc. which can cause mucosal infections; Herpes simplex virus which can cause herpes simplex and herpes zoster in patients; and other Mycobacterium tuberculosis which can easily cause tuberculosis. Cytomegalovirus infections and sporozoite infections can cause patients to get other diseases such as meningitis. Normally, these pathogens can exist in the normal body with very low pathogenic ability, but AIDS patients are different because HIV virus mainly attacks the patient’s immune cells and after a long time the patient’s immune function will be severely impaired, so the normal and viruses that reside in the human body can also cause the patient to get the disease and lead to opportunistic infections.