Diseases caused by different infect

Diseases caused by different infectious disease pathogens for which no effective vaccines exist, such as HIV, malaria, tuberculosis and parasitic helminths remain uncontrolled.19 Attempts at developing vaccines for these diseases have proved challenging for a number of reasons.19 Obstacles that must be overcome include the need for the elicitation of an immune response greater than that induced by natural infection as well as an understanding of mechanisms of protective immunity in humans. Vaccine development against parasitic helminths in particular has been hampered by a poor understanding of the complex interactions between the human host and parasites, including the mechanisms behind protective immunity.

An effective vaccine against a complex metazoan schistosome parasite can be developed. This belief is based on the following: (1) the immunization of mice with one dose of irradiated cercariae results in 50% - 70% reduction in adult worm burden which can be increased to over 80% with two or three immunizations20; (2) in non-permissive animal models (e.g., rats and rhesus macaques), worm elimination proceeds via a coordinated immune response by the host21,22; and (3) human populations following exposure in endemic areas invariably develop some degree of protection naturally.23,24 Moreover, this belief is strongly reinforced by the successful introduction of several effective anti-parasite vaccines (both against protozoa and helminths) in veterinary practice.25

Vaccinology for human helminth infections is defined by a paradigm that differs from that for bacterial or viral infections. Namely, sterile immunity is likely not achievable, but immunotherapy should confer sufficient levels of protection to reduce worm burdens to an intensity associated with healthy growth and development of children.26 A vaccine that would limit cercariae penetration and/or adult worm maturation would reduce egg accumulation, and thus, control pathology, the major source of morbidity. Additionally, the prevailing opinion is that a vaccine that confers an initial 50% protection in humans should be effective in reducing overall morbidity and mortality,10,15,27 and in all likelihood would be an appropriate first generation schistosomiasis vaccine.28

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Possible mechanisms of protectio

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由没有有效的疫苗存在不同传染病病原体引起的疾病，如艾滋病，疟疾，肺结核和寄生蠕虫仍然uncontrolled.19试图在这些疾病的疫苗已被证明是具有挑战性的一些原因。必须克服的19个障碍，包括诱导的免疫反应，比自然感染引起的免疫反应的需要，以及在人类的保护性免疫机制的理解。寄生蠕虫的疫苗一直是由人类宿主和寄生虫之间复杂的相互作用的认识不足阻碍了，包括在免疫保护机制。

对复杂的多细胞动物血吸虫的有效疫苗可以开发。这种信念是基于以下几点：（1）用一个剂量的辐照尾蚴结果50%在成虫负担可增加到两个或三个immunizations20 80%减少70%免疫小鼠；（2）在非许可的动物模型（例如，大鼠和猕猴），消灭蠕虫通过协调免疫反应的host21,22；和（3）的人群暴露在流行地区往往会形成一定程度的保护，自然有此外，这种信仰是由几种有效的抗寄生虫疫苗成功引进强钢筋（包括对原生动物和蠕虫）在兽医实践。25

疫苗人体寄生虫感染的定义是一个范例，不同于细菌或病毒感染。即不可能实现无菌免疫，但免疫治疗应该给予足够的保护水平减少蠕虫负担和健康成长和发展children.26疫苗会限制尾蚴穿透和/或成虫成熟会降低鸡蛋的积累，因此，相关的强度控制的病理，发病的主要来源。另外，普遍的看法是，一种疫苗，赋予初始50%保护人类应该在降低总体发病率和死亡率的有效，10,15,27十有八九会是一个合适的第一代疫苗。28

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的保护机制