三、感染在发达国家,由感染所致的MR随感染性疾病的控制而减少,在MR的致病因素中所占比例很小。而在发展中国家,感染性疾病仍是小儿智能发育的严重威胁。由细菌、病毒和寄生虫感染所致的脑膜炎和脑膜脑炎特别易发生于生活在不良社会环境中的营养不良儿童。例如,结核和麻疹在发达国家是预后相对较好的疾病,很少并发脑膜脑炎,但在发展中国家,这些疾病仍常常并发脑膜脑炎。一些病毒可引起进行性中枢 Third, the infection In developed countries, MR caused by infection with the control of infectious diseases and reduce the proportion of MR in the risk factors is small. In developing countries, however, infectious diseases are still a serious threat to children’s intellectual development. Meningitis and meningoencephalitis caused by bacterial, viral and parasite infections are particularly prevalent in undernourished children living in poor social settings. For example, tuberculosis and measles are relatively well-prognosed diseases in developed countries and rarely occur meningoencephalitis, but in developing countries these diseases are often complicated by meningoencephalitis. Some viruses can cause progressive centers