A mathematical model for the transmission of Plasmodium vivax malaria.

We have proposed a mathematical model for 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 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 1-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 1 or 2 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.

School-based helminthiases control: I. A baseline study of soil-transmitted helminthiases in Nakhon Si Thammarat Province, Thailand.

A baseline study of soil-transmitted helminthiases was carried out in Nakhon Si Thammarat Province, southern Thailand. The study sites were Wat Krou Chou Primary School and nearby villages in Sichon district, and Wat Thang Phoon Primary School and nearby villages in Chalerm Phrakiat District. Surveys of the schoolchildren's stools were conducted by the Kato-Katz technique. The results showed that 23.7% of schoolchildren in Wat Krou Chou and 24.7% of those in Wat Thang Phoon were infected with soil-transmitted helminths, with a 24.1% overall infection rate. The major infection was hookworm (22.2% and 19.6%) and the minor one was trichuriasis, (2.9% and 8.7% respectively). The intensity of infection was similar in both schools, 85.7% and 90.2% respectively for light intensity hookworm. Schoolchildren with hookworm infection were not anemic. The hemoglobin value of children with hookworm infection was not significantly different from that of uninfected children. Data regarding the health behavior of children's parents in both schools were reported.