Pittella J E
Department of Pathology and Legal Medicine, School of Medicine, Federal University of Minas Gerais, Belo Horizonte, Brazil.
Brain Pathol. 1997 Jan;7(1):649-62. doi: 10.1111/j.1750-3639.1997.tb01080.x.
Schistosomiasis is an infection caused by digenetic trematode platyhelminths of the genus Schistosoma. These blood flukes use man and other mammals as definitive hosts and aquatic and amphibious snails as intermediate hosts. Of the schistosomal species, S. mansoni, S haematobium and S. japonicum are the most important to man and the most widely distributed. The infection affects about 200 million individuals in 74 countries of Latin America, Africa and Asia. Far less commonly, schistosomes reach the central nervous system (CNS). This may occur at any time from the moment the worms have matured and the eggs have been laid. For this reason, CNS involvement may be observed with any of the clinical forms of schistosomal infection. The presence of eggs in the CNS induces a cell-mediated periovular granulomatous reaction. When eggs reach the CNS during the early stages of the infection or during evolution of the disease to its chronic forms, large necrotic-exudative granulomas are found. In-situ egg deposition following the anomalous migration of adult worms appears to be the main, if not the only, mechanism by which Schistosoma may reach the CNS in these stages. The mass effect produced by the heavy concentration of eggs and the presence of large granulomas in circumscribed areas of the brain and spinal cord explains, respectively, 1) the signs and symptoms of increased intracranial pressure and focal neurological signs; and 2) the signs and symptoms of rapidly progressing transverse myelitis, usually affecting the lumbosacral segments of the spinal cord. Most of the cases of CNS involvement associated with the hepatosplenic and cardiopulmonary chronic forms, or with severe urinary schistosomiasis, though more frequent, are asymptomatic. In the patients with these clinical forms, the random and sparse distribution of eggs in the CNS indicates that the embolization of eggs from the portal mesenteric system to the brain and spinal cord constitutes the main route of CNS invasion by Schistosoma. The discrete inflammatory reaction elicited by the sparsely distributed eggs in the CNS explains the lack of neurological symptoms that could be produced by egg deposition.
血吸虫病是由血吸虫属的复殖吸虫扁形虫引起的一种感染。这些血吸虫以人和其他哺乳动物为终宿主，以水生和两栖蜗牛为中间宿主。在血吸虫种类中，曼氏血吸虫、埃及血吸虫和日本血吸虫对人类最为重要且分布最广。这种感染影响着拉丁美洲、非洲和亚洲74个国家的约2亿人。血吸虫极少会侵入中枢神经系统（CNS）。从蠕虫成熟并产卵的那一刻起，这种情况在任何时候都可能发生。因此，在血吸虫感染的任何临床形式中都可能观察到中枢神经系统受累。中枢神经系统中虫卵的存在会引发细胞介导的围卵性肉芽肿反应。当虫卵在感染早期或疾病发展为慢性形式时进入中枢神经系统，会发现大量坏死性渗出性肉芽肿。成虫异常迁移后虫卵在原位沉积似乎是血吸虫在这些阶段进入中枢神经系统的主要（如果不是唯一的）机制。大脑和脊髓特定区域大量虫卵聚集和大肉芽肿的存在所产生的占位效应分别解释了：1）颅内压升高的体征和症状以及局灶性神经体征；2）通常影响脊髓腰骶段的快速进展性横贯性脊髓炎的体征和症状。与肝脾和心肺慢性形式或严重泌尿血吸虫病相关的大多数中枢神经系统受累病例，虽然更常见，但没有症状。在患有这些临床形式的患者中，虫卵在中枢神经系统中随机且稀疏分布表明，虫卵从门静脉肠系膜系统栓塞到大脑和脊髓是血吸虫侵入中枢神经系统的主要途径。中枢神经系统中稀疏分布的虫卵引发的离散炎症反应解释了虫卵沉积可能不会产生神经症状的原因。
