PNG Institute of Medical Research, Madang, Papua New Guinea.
PLoS One. 2010 Feb 4;5(2):e9047. doi: 10.1371/journal.pone.0009047.
Where P. vivax and P. falciparum occur in the same population, the peak burden of P. vivax infection and illness is often concentrated in younger age groups. Experiences from malaria therapy patients indicate that immunity is acquired faster to P. vivax than to P. falciparum challenge. There is however little prospective data on the comparative risk of infection and disease from both species in young children living in co-endemic areas.
METHODOLOGY/PRINCIPAL FINDINGS: A cohort of 264 Papua New Guinean children aged 1-3 years (at enrolment) were actively followed-up for Plasmodium infection and febrile illness for 16 months. Infection status was determined by light microscopy and PCR every 8 weeks and at each febrile episode. A generalised estimating equation (GEE) approach was used to analyse both prevalence of infection and incidence of clinical episodes. A more pronounced rise in prevalence of P. falciparum compared to P. vivax infection was evident with increasing age. Although the overall incidence of clinical episodes was comparable (P. falciparum: 2.56, P. vivax 2.46 episodes / child / yr), P. falciparum and P. vivax infectious episodes showed strong but opposing age trends: P. falciparum incidence increased until the age of 30 months with little change thereafter, but incidence of P. vivax decreased significantly with age throughout the entire age range. For P. falciparum, both prevalence and incidence of P. falciparum showed marked seasonality, whereas only P. vivax incidence but not prevalence decreased in the dry season.
CONCLUSIONS/SIGNIFICANCE: Under high, perennial exposure, children in PNG begin acquiring significant clinical immunity, characterized by an increasing ability to control parasite densities below the pyrogenic threshold to P. vivax, but not to P. falciparum, in the 2(nd) and 3(rd) year of life. The ability to relapse from long-lasting liver-stages restricts the seasonal variation in prevalence of P. vivax infections.
当间日疟原虫和恶性疟原虫同时存在于同一人群中时，间日疟原虫感染和发病的高峰负担往往集中在年龄较小的人群中。从疟疾治疗患者的经验来看，针对间日疟原虫的免疫比针对恶性疟原虫的免疫更快获得。然而，在同时流行地区，年幼儿童感染两种疟原虫的风险以及感染后发病的情况，几乎没有前瞻性数据。
方法/主要发现：对巴布亚新几内亚 264 名 1-3 岁（入组时）的儿童进行了一项队列研究，对他们进行了为期 16 个月的间日疟原虫和恶性疟原虫感染和发热性疾病的主动随访。每隔 8 周和每次发热时，通过光镜和 PCR 确定感染状况。使用广义估计方程（GEE）方法分析感染率和临床发作的发病率。随着年龄的增长，间日疟原虫感染的流行率明显高于恶性疟原虫感染。虽然临床发作的总发病率相当（恶性疟原虫：2.56 例/儿童/年，间日疟原虫 2.46 例/儿童/年），但恶性疟原虫和间日疟原虫的感染性发作具有强烈但相反的年龄趋势：恶性疟原虫的发病率在 30 个月之前增加，此后变化不大，但间日疟原虫的发病率随着年龄的增长在整个年龄范围内显著下降。对于恶性疟原虫，恶性疟原虫的流行率和发病率均具有明显的季节性，而只有间日疟原虫的发病率在旱季下降，而流行率没有下降。
结论/意义：在高、常年暴露的情况下，巴布亚新几内亚的儿童开始获得显著的临床免疫力，其特征是控制间日疟原虫寄生虫密度低于发热阈值的能力逐渐增强，但对恶性疟原虫的控制能力则没有增强，这一情况在儿童 2 岁和 3 岁时尤为明显。来自长期肝期的复发能力限制了间日疟原虫感染的季节性变化。
