Studies on the transmission model for vivax malaria and its simulations

我们提出了一个定量描述间日疟传播的数学模型，并将其调整到所罗门群岛的瓜达尔卡纳尔岛疫区。传播模型的模拟将有助于规划疟疾控制战略。间日疟原虫生活史的一个特征是，被蚊子叮咬注入血流的子孢子有时会作为催眠虫留在肝细胞内。因此，我们将复发引起的新的感染现象纳入了传播模型。此外，通过模拟，我们还试图评估选择性大规模药物管理(MDA)和媒介控制计划(如二氯氰菊酯处理蚊帐的分布)导致的流行率下降。模拟表明，每隔一周集中重复一次丙二醛，可在初期迅速降低间日疟的患病率，并可在几年内将间日疟原虫率保持在1%以下，但此后患病率将上升。相反，如果一次或两次丙二醛试验伴随着通过加强媒介控制而降低媒介容量，寄生率将长期保持在1%以下。无论如何，重要的是要警惕复发病例，因为即使在执行了丙二醛之后，也需要很长时间才能减少催眠药携带者的比例。

We have proposed a mathematical model describing the transmission of Plasmodium vivax malaria quantitatively, which is adjusted to the infected region, Guadalcanal, in the Solomon Islands. The simulation of a transmission model will be instrumental in planning the malaria control strategy. A characteristic of the life cycle of P. vivax parasites is that a sporozoite injected into the blood stream by a mosquito bite may sometimes stay in a hepatocyte as a hypnozoite. Therefore we have incorporated a phenomenon of renewed infections caused by a relapse into the transmission model. Also through the simulations we have attempted to evaluate the decline in prevalence caused by the programs of selective mass drug administration (MDA) and vector control such as the distribution of permethrin-treated bednets. The simulations have indicated that the concentrated repetition of MDA at one week intervals would reduce the prevalence of vivax malaria swiftly in the beginning and would keep the parasite rate below 1% for a few years but the prevalence would increase thereafter. In contrast the parasite rate would remain below 1% for a long time if a trial of one or two times MDA is accompanied with some reduction of the vectorial capacity by the enforcement of vector control. In any case, it is important to beware of relapse cases because even after the execution of MDA it takes a long time to decrease the proportion of hypnozoite carriers.