Evidence that the Human Pathogenic Fungus Cryptococcus neoformans var. grubii May Have Evolved in Africa

Most of the species of fungi that cause disease in mammals, including Cryptococcus neoformans var. grubii (serotype A), are exogenous and non-contagious. Cryptococcus neoformans var. grubii is associated worldwide with avian and arboreal habitats. This airborne, opportunistic pathogen is profoundly neurotropic and the leading cause of fungal meningitis. Patients with HIV/AIDS have been ravaged by cryptococcosis – an estimated one million new cases occur each year, and mortality approaches 50%. Using phylogenetic and population genetic analyses, we present evidence that C. neoformans var. grubii may have evolved from a diverse population in southern Africa. Our ecological studies support the hypothesis that a few of these strains acquired a new environmental reservoir, the excreta of feral pigeons (Columba livia), and were globally dispersed by the migration of birds and humans. This investigation also discovered a novel arboreal reservoir for highly diverse strains of C. neoformans var. grubii that are restricted to southern Africa, the mopane tree (Colophospermum mopane). This finding may have significant public health implications because these primal strains have optimal potential for evolution and because mopane trees contribute to the local economy as a source of timber, folkloric remedies and the edible mopane worm.

多数可引发哺乳动物疾病的真菌物种，包括新生隐球菌格鲁比变种（Cryptococcus neoformans var. grubii，血清型A），均为外源性且无传染性。新生隐球菌格鲁比变种在全球范围内均与鸟类及树栖生境相关联。该空气传播的机会致病性病原体具有高度嗜神经性，是真菌性脑膜炎的首要致病病原体。艾滋病（HIV/AIDS）患者群体深受隐球菌病（cryptococcosis）的危害：据估算，每年新增隐球菌病病例约100万例，病死率接近50%。
本研究通过系统发育与群体遗传分析，证实新生隐球菌格鲁比变种或许起源于非洲南部的一个多样化种群。我们的生态学研究支持以下假说：其中部分菌株获得了新型环境储存宿主——野生原鸽（Columba livia）的排泄物，并通过鸟类与人类的迁徙在全球范围内扩散。本研究还发现了仅局限于非洲南部的高多样性新生隐球菌格鲁比变种菌株的新型树栖储存宿主——mopane树（Colophospermum mopane）。这一发现具有重要的公共卫生意义：这些原始菌株具备极佳的进化潜力，且mopane树作为木材来源、民间药用原料以及可食用的mopane毛虫的宿主，对当地经济具有重要贡献。