Preservation of Wild Isolates of Human Malaria Parasites in Wet Ice and Adaptation Efficacy to In Vitro Culture

Wild isolates of malaria parasites were preserved in wet ice for 2–12 days and cultivated by a candle jar method. In four isolates of <i>Plasmodium falciparum</i> collected from Myanmar and preserved for 12 days, all failed to grow. In 31 isolates preserved for 5–10 days, nine were transformed to young gametocytes, but 22 isolates grew well. From Ranong, Thailand, nine isolates preserved for 7 days were examined, and six grew well. On the other hand, all of the 59 isolates collected from eastern Indonesian islands failed to establish as culture-adapted isolates, even most of them were preserved only for 2–3 days: 10 isolates stopped to grow, and 49 isolates were transformed to sexual stages by Day 10. These results indicated that a great difference in adaptation to in vitro culture may exist between wild isolates distributed in continental Southeast Asia and in eastern Indonesia and that gametocytogenesis might be easily switched on in Indonesian isolates. In wild isolates of <i>P. vivax</i>, <i>P. malariae</i> and <i>P. ovale</i> preserved for 2–9 days, ring forms or young trophozoites survived, but adaptation to in vitro culture failed. These results indicate that wild isolates can be preserved in wet ice for 9–10 days.

MALARIA ENDEMIC PATTERNS ON LOMBOK AND SUMBAWA ISLANDS, INDONESIA

Nusa Tengara Barat (NTB) province consists of two main islands, Lombok and Sumbawa, to the east of Bali Island, Indonesia. Most of the area is known to be moderately malaria endemic, but the exact malaria epidemiology has not been elucidated. At least 30 deaths per year are thought to be caused by falciparum malaria in Lombok alone, judging from the hospital data. According to the Gebrak Malaria Team in West Lombok, the annual incidence in the district of West Lombok from 1996 to 1999 was consistently over 40‰.<BR>In the present report, we describe the small malaria endemic foci in the West Lombok and Sumbawa districts. Falciparum malaria is predominant over vivax malaria and other types of malaria. There are 11 species of <I>Anopheles</I> vector, but three of these species, <I>An. subpictus, An. maculates</I> and <I>An. barbirostris,</I> are of primary importance in malaria transmission and An. sundaicus and An. aconitus are of secondary importance. Our data from Sekotong, West Lombok, and Sumbawa supported the importance of <I>An. subpictus</I> in coastal areas but suggested the existence of different transmission peaks according to environmental conditions. The usual transmission peak comes in the dry season but is affected by climatic and geographical conditions. Although there were many malaria endemic foci along the coast, the width and grade of the foci varied widely. The presence of malaria endemic foci inland, although likely, has not been definitively reported to date.