Data from: Campylobacter jejuni infection associated with relatively poor condition and low survival in a wild bird

Campylobacter jejuni is the most common foodborne pathogen in industrialized countries. Most human infections come from contaminated poultry, but wild birds are also known to harbor C. jejuni. Wild birds are often described as asymptomatic carriers, but this assumption is based on domestic poultry research. We studied the effects of C. jejuni infection on body condition and survival of adult and nestling American crows Corvus brachyrhynchos in Davis, California. Previous work demonstrated that more than half of the crows in this population are infected with C. jejuni and that at least some of the isolates carried by crows are similar to those found in domestic animals and humans. In this study, we compared the body condition of infected and uninfected individuals at the time of capture among adults (n = 44; 52% infected) and nestlings (n = 97; 77% infected). We subsequently monitored these banded individuals for up to 3 yr and used mark–recapture survival analysis to estimate relationships between infection status and later survival. We found that adult crows infected with C. jejuni were in poor condition relative to uninfected adults: average body mass of infected birds was 12% lower, whereas average body size did not differ between the two groups. Likewise, apparent survival probability was lower for infected adults. In contrast, nestling body condition, fledging success, and survival did not differ by infection status. This is the first study to document adverse effects of C. jejuni infection in a free-living, wild bird. If these effects are widespread, C. jejuni exposure may be a cause of conservation concern for some species, especially when human activities increase exposure to infections or introduce novel strains to wild bird populations. Our results add to the growing body of work demonstrating hidden long-term costs of seemingly mild infections in wild populations.

空肠弯曲杆菌（Campylobacter jejuni）是工业化国家中最常见的食源性致病菌。多数人类感染源于受污染的家禽，但已知野生鸟类也可携带空肠弯曲杆菌。野生鸟类常被描述为无症状携带者，但这一推论仅基于家禽的相关研究。本研究针对加利福尼亚州戴维斯市的美洲鸦（Corvus brachyrhynchos），探究空肠弯曲杆菌感染对成体及雏鸟身体状况与存活率的影响。前期研究显示，该种群中超半数美洲鸦感染有空肠弯曲杆菌，且至少部分由美洲鸦携带的菌株与家畜及人类分离得到的菌株具有相似性。本研究中，我们分别对比了成体（样本量n=44，感染率52%）与雏鸟（样本量n=97，感染率77%）在捕获时的感染个体与未感染个体的身体状况。随后，我们对这些佩戴脚环的个体进行了长达3年的监测，并采用标记-重捕存活分析法，估算感染状态与后续存活率之间的关联。研究结果显示，感染空肠弯曲杆菌的成体美洲鸦身体状况劣于未感染个体：感染个体的平均体重较未感染个体低12%，但两组的平均体型无显著差异。同样，感染成体的表观存活率也更低。与之相反，雏鸟的身体状况、出巢成功率及存活率均未因感染状态出现显著差异。本研究是首个证实空肠弯曲杆菌感染对自由生活的野生鸟类存在不利影响的研究。若此类影响具有普遍性，则空肠弯曲杆菌暴露可能成为部分野生鸟类物种的保护关切因素，尤其是当人类活动加剧了感染暴露风险，或向野生鸟类种群引入新型菌株时。本研究结果进一步丰富了相关研究成果，证明野生种群中看似轻微的感染往往存在隐蔽的长期代价。