原虫感染主要引起T细胞介导的免疫应答反应。艾滋病患者的原虫感染,如利什曼原虫、弓形虫和隐孢子虫,比免疫机能健全的病人危害性更为严重,尤其是弓形虫和隐孢子虫在艾滋病患者中特别普遍。艾滋病患者的大脑弓形虫病通常是隐性感染的复发,患者T辅助细胞(CD4~+)的耗竭使包囊中释放出来的缓殖子在脑中存活。在免疫功能丧失的情况下,缓殖子转变为速殖子进而分裂增殖,迅速导致组织坏死性脑炎。艾滋病患者坏死性脑炎中多数是由于弓形虫感染,表现为大脑局部脓肿或弥漫性脑膜脑炎。大约10～80%的艾滋病患者患弓形虫脑炎;相比之下其他免疫功能低下的人群,如皮肤移植者等,产生弓形虫脑炎情况就相当少。另外免疫功能低下病人弓形虫感染并不 Protozoan infections primarily cause T cell-mediated immune response. Protozoal infections in people with AIDS, such as Leishmania, toxoplasma and cryptosporidiosis, are even more devastating than immunocompetent patients, with Toxoplasma gondii and cryptosporidiosis being particularly prevalent in AIDS patients. Toxoplasmosis in AIDS patients is usually a recurrence of a latent infection. The depletion of T helper cells (CD4 +) in patients with HIV allows bradyzoites released in the cyst to survive in the brain. In the event of a loss of immune function, the gonorrhea transforms into tachyzoites to divide and proliferate, rapidly causing tissue necrotizing encephalitis. Most patients with AIDS necrotizing encephalitis is due to Toxoplasma infection, manifested as local brain abscess or diffuse meningoencephalitis. About 10 to 80% of AIDS patients have toxoplasma encephalitis; in contrast, other immunocompromised people, such as skin transplant recipients, produce relatively few toxoplasma encephalitis. In addition, immunocompromised patients do not have toxoplasma infection