Baylisascaris schroederi, a roundworm (ascaridoid) parasite specific to the bamboo-feeding giant panda (Ailuropoda melanoleuca), represents a leading cause of mortality in wild giant panda populations. Here, we present a 293-megabase chromosome-level genome assembly of B. schroederi to infer its biology, including host adaptations. Comparative genomics revealed an evolutionary trajectory accompanied by host-shift events in ascaridoid parasite lineages after host separations, suggesting their potential for transmission and rapid adaptation to new hosts. Genomic and anatomical lines of evidence, including expansion and positive selection of genes related to the cuticle and basal metabolisms, indicate that B. schroederi undergoes specific adaptations to survive in the sharp-edged bamboo-enriched gut of giant pandas by structurally increasing its cuticle thickness and efficiently utilizing host nutrients through gut parasitism. Additionally, we characterized the secretome of B. schroederi and predicted potential drug and vaccine targets for new control strategies. Overall, this genome resource provides new insights into the host adaptation of B. schroederi to the giant panda as well as the host-shift events in ascaridoid parasite lineages. Our findings on the unique biology of B. schroederi will also aid in the development of prevention and treatment measures to protect giant panda populations from roundworm parasitism.

Baylisascaris schroederi是一种以竹子为食的大熊猫( Ailuropoda melanoleuca )特有的蛔虫（蛔虫）寄生虫，是导致野生大熊猫种群死亡的主要原因。在这里，我们展示了B. schroederi的 293 兆碱基染色体级基因组组装，以推断其生物学，包括宿主适应性。比较基因组学揭示了蛔虫寄生虫谱系在宿主分离后伴随宿主转移事件的进化轨迹，表明它们具有传播和快速适应新宿主的潜力。基因组和解剖学证据，包括与角质层和基础代谢相关的基因的扩展和阳性选择，表明B. schroederi通过在结构上增加其角质层厚度并通过肠道寄生有效利用宿主养分，经历了特定的适应性，以在大熊猫锋利的富含竹子的肠道中生存。此外，我们对B. schroederi的分泌蛋白组进行了表征，并预测了新控制策略的潜在药物和疫苗靶标。总的来说，这个基因组资源为B. schroederi对大熊猫的宿主适应以及蛔虫寄生虫谱系中的宿主转移事件提供了新的见解。我们对B. schroederi独特生物学的发现也将有助于制定预防和治疗措施，以保护大熊猫种群免受蛔虫寄生。