Department of Emerging and Infectious Diseases, United States Army Medical Research Directorate-Africa, Kenya Medical Research Institute/Walter Reed Project, Kisumu, Kenya.
Medical Research Council, Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Imperial College London, London, UK.
Lancet Microbe. 2021 Apr;2(4):e141-e150. doi: 10.1016/S2666-5247(21)00009-4. Epub 2021 Mar 2.
The epidemiology and severity of non-falciparum malaria in endemic settings has garnered little attention. We aimed to characterise the prevalence, interaction, clinical risk factors, and temporal trends of non-falciparum Plasmodium species among symptomatic individuals presenting at health-care facilities in endemic settings of Kenya.
We diagnosed and analysed infecting malaria species (Plasmodium falciparum, Plasmodium ovale curtisi, Plasmodium ovale wallikeri, and Plasmodium malariae) via PCR in clinical samples collected between March 1, 2008, and Dec 31, 2016, from six hospitals located in different regions of Kenya. We recruited patients aged 6 months or older who presented at outpatient departments with symptoms of malaria or tested positive for uncomplicated malaria by malaria rapid diagnostic test. Descriptive statistics were used to describe the prevalence and distribution of Plasmodium species. A statistical model was designed and used for estimating the frequency of Plasmodium species and assessing interspecies interactions. Mixed-effect linear regression models with random slopes for each location were used to test for change in prevalence over time.
Samples from 2027 symptomatic participants presenting at care facilities were successfully analysed for all Plasmodium species. 1469 (72·5%) of the samples were P falciparum single-species infections, 523 (25·8%) were mixed infections, and only 35 (1·7%) were single non-falciparum species infections. 452 (22·3%) were mixed infections containing P ovale spp. A likelihood-based model calculation of the population frequency of each species estimated a significant within-host interference between P falciparum and P ovale curtisi. Mixed-effect logistic regression models identified a significant increase in P ovale wallikeri (2·1% per year; p=0·043) and P ovale curtisi (0·7% per year; p=0·0002) species over time, with a reciprocal decrease in P falciparum single-species infections (2·5% per year; p=0·0065). The frequency of P malariae infections did not significantly change over time. Risk of P falciparum infections presenting with fever was lower if co-infected with P malariae (adjusted odds ratio 0·43, 95% CI 0·25-0·74; p=0·0023).
Our results show a prevalence of non-falciparum species infections of 27·5% among symptomatic individuals presenting at care facilities, which is higher than expected from previous cross-sectional surveys. The proportion of infections with P ovale wallikeri and P ovale curtisi was observed to significantly increase over the period of study, which could be due to attenuated responsiveness of these species to malaria drug treatment. The increase in frequency of P ovale spp could threaten the malaria control efforts in Kenya and pose increased risk of malaria to travellers.
Armed Forces Health Surveillance Branch and its Global Emerging Infections Surveillance Section.
在流行地区，非恶性疟原虫疟疾的流行病学和严重程度尚未得到充分关注。本研究旨在描述肯尼亚流行地区医疗机构就诊的有症状个体中非恶性疟原虫种的流行率、相互作用、临床危险因素和时间趋势。
我们在 2008 年 3 月 1 日至 2016 年 12 月 31 日期间，从肯尼亚六个不同地区的六家医院采集的临床样本中，通过 PCR 诊断和分析了感染的疟原虫种类（恶性疟原虫、卵形疟原虫 curtisi、卵形疟原虫 wallikeri 和间日疟原虫）。我们招募了年龄在 6 个月或以上的患者，这些患者在门诊就诊时出现疟疾症状或疟疾快速诊断检测呈阳性。采用描述性统计方法描述疟原虫种的流行率和分布情况。设计了一个统计模型来估计疟原虫种的频率，并评估种间相互作用。采用具有每个位置随机斜率的混合效应线性回归模型来检验随时间变化的流行率。
对 2027 名在就诊设施就诊的有症状参与者的样本进行了所有疟原虫种的成功分析。1469 份（72.5%）样本为恶性疟原虫单一物种感染，523 份（25.8%）为混合感染，仅 35 份（1.7%）为单一非恶性疟原虫种感染。452 份（22.3%）为含有卵形疟原虫种的混合感染。基于似然的种群频率计算估计，恶性疟原虫和卵形疟原虫 curtisi 之间存在显著的宿主内干扰。混合效应逻辑回归模型发现卵形疟原虫 wallikeri（每年 2.1%；p=0.043）和卵形疟原虫 curtisi（每年 0.7%；p=0.0002）的时间变化呈显著增加趋势，而恶性疟原虫单一物种感染呈相反的每年 2.5%（p=0.0065）的减少趋势。间日疟原虫感染的频率随时间变化无显著变化。如果同时感染间日疟原虫，恶性疟原虫感染发热的风险较低（调整后的优势比 0.43，95%CI 0.25-0.74；p=0.0023）。
我们的结果显示，在就诊设施就诊的有症状个体中非恶性疟原虫种的感染率为 27.5%，高于以往的横断面调查预期。卵形疟原虫 wallikeri 和卵形疟原虫 curtisi 的感染比例在研究期间观察到显著增加，这可能是由于这些物种对疟疾药物治疗的反应减弱所致。卵形疟原虫种频率的增加可能会威胁肯尼亚的疟疾控制工作，并增加旅行者患疟疾的风险。
武装部队健康监测处及其全球新发传染病监测科。
