Malaria Attack Rates Research Articles

Malaria Vaccine Study Site in Irian Jaya, Indonesia: Plasmodium falciparum Incidence Measurements and Epidemiologic Considerations in Sample Size Estimation

Malaria epidemiologic and entomologic studies were performed during both the high transmission and low transmission seasons to characterize the Plasmodium falciparum malaria transmission at a proposed malaria vaccine trial site in Irian Jaya, Indonesia. The study population consisted of two subsets: native Irianese men with lifelong exposure to malaria and transmigrants who arrived from a nonmalarious area 2.5 years before the start of the study. All subjects received a radical cure for malaria and were then monitored weekly by blood film. Both P. falciparum malaria attack rates and incidence densities were calculated; transmigrants had a significantly higher rate (P = 0.003) than the Irianese during the low transmission season study (20-weeks long) but not during the high transmission season study (12-weeks long). Lack of exposure-induced immunity left the transmigrants at a minimum 17-25% greater relative risk of becoming parasitemic compared with the Irianese during the low transmission season study. During the high transmission season study, 50% of the transmigrants were P. falciparum positive by week 6 and 50% of the Irianese by week 9. During the low transmission season, 50% of the transmigrants were positive by week 10 and 43% of the Irianese were positive by week 17. Entomologic studies showed that Anopheles koliensis was the predominant vector (> 98% of anopheline catch). Entomologic inoculation rates for P. falciparum were 0.018 and 0.39 infective bites/person/night for the low and high transmission seasons, respectively. New P. vivax cases represented between 16% and 42% of all initial malaria cases.(ABSTRACT TRUNCATED AT 250 WORDS)

The Changing Pattern of Imported Malaria in British Visitors to Kenya 1987–1990

Following a sudden increase of imported malaria from Kenya in December 1989-January 1990, an investigation was set up to identify risk factors for travellers' malaria. A questionnaire asking for details of travel patterns and compliance with prophylaxis was sent to cases reported over the 6-month Kenyan winter period. Quarterly malaria attack rates between January 1987 and June 1991 were calculated and linked to meteorological conditions in Mombasa. The number of travellers to Kenya has doubled in the 4 years studied and the quarterly rates varied 4-fold over this period. There was no clear seasonal pattern of malaria in travellers, nor was there any clear relation of malaria to coastal rainfall. Compliance with chemoprophylaxis was poor, with only 16% of cases using currently advised regimens. While the annual malaria attack rate per 10,000 travellers decreased by 37% over the study period, the total numbers of malaria cases imported from Kenya rose by 61%, reflecting the increase in the numbers of travellers to the region. As the popularity of East Africa as a tourist destination continues to increase, Kenya will remain an important and significant source of malaria imported into the UK.

CHEMOPROPHYLAXIS OF MALARIA IN NON-IMMUNE RESIDENTS IN DAR ES SALAAM, TANZANIA

The malaria infection rates in non-immune residents of Dar es Salaam on various chemoprophylactic regimens were compared with that (37·1%) in those not taking prophylactic antimalarials. Among 647 people resident in Dar es Salaam for 1-6 years the two groups with the lowest infection rates by person-episodes (2·0% and 1·5%) were those taking proguanil 200 mg daily alone or with chloroquine base 300 mg weekly. Infection rates (16·9% and 14·0%) were also significantly lower than in the no-prophylaxis group in those taking chloroquine base 300 mg weekly combined with 'Fansidar', 'Maloprim' (each one tablet weekly), or proguanil 100 mg daily. No significant reduction in the malaria attack rate was found in those taking chloroquine base 300 mg or 600 mg weekly (31·2%), pyrimethamine 25 mg weekly (27·3%), proguanil 100 mg daily (46·4%), maloprim one tablet weekly (40·4%), or a combination of chloroquine base 300 mg weekly and pyrimethamine 25 mg weekly (27·1%). Similar results were obtained when the infection rates per year of exposure were compared. Proguanil was associated with fewest user complaints and fansidar with most.

Malaria as understood by soldiers.

Abstract : Questionnaires about malaria were administered to 194 American, 182 Australian, and 280 Korean soldiers serving in Vietnam. Analysis of their responses indicate that the Australians had the best understanding of malaria and very high standards of malaria discipline. Although over two-thirds of American and Korean troops are adequately instructed about malaria and practice good malaria discipline, there is room for significant improvement if the malaria attack rates current at the time of this report continue to occur. Such improvement might be achieved by a better understanding of practical epidemiology by the troops; correction of lapses in protective clothing discipline; and assiduous attention by commanders to the logistics of antimalaria chemoprophylaxis, particularly during operations.

Malaria among prisoners of war in Siam (“F” Force)

1. 1. The 7,000 British and Australian prisoners of war who formed “F” force, left Changi camp on Singapore Island in April, 1943, and 3,122 returned in December, 1943. They had spent the intervening 8 months in the hilly jungle country of Siam, about 200 miles north-west of Bangkok near the Three Pagodas pass on the Siam-Burma border, constructing a section of a new railway to link Bangkok and Moulmein. 2. 2. Few had had malaria before leaving Changi. Those who returned had a malaria parasite rate of 25·7 per cent. (801/3,122), and a malaria attack rate during 7 weeks of January to February, 1944, of 18·8 per thousand men per day. 3. 3. Field's rapid stain proved of great value. Its independence of alcohol and the pH of the water available, and its extreme economy in use, made it ideal for our purpose. 4. 4. Plasmodium vivax was at all times the commonest species of parasite; in the later months it completely outnumbered P. falciparum, and the picture presented was that of chronic relapsing vivax malaria in a debilitated population. 5. 5. Quinine, when available in sufficient quantity, effectively cured attacks of malaria, but recurrences in a few weeks were commonplace. 6. 6. Malaria was recorded as a cause in 11 per cent. of all deaths (338/3,087), but there is reason to think that it was contributory to many more. 7. 7. Anopheles maculatus and A. minimus were considered to be the principal vectors, though A. leucosphyrus may also have played some part in transmission; these judgements, however, are based on larval surveys only, and lack the definite proof afforded by trapping and dissection of adult mosquitoes. 8. 8. Larvae of Anopheles aitkeni and A. barbumbrosus were found. These species do not appear to have been reported from Siam before. 9. 9. We confirm Anigstein's opinion of the malarious nature of hilly regions in Siam, but differ from him by suggesting that the season of greatest transmission in this particular region is more likely to be the wet season than the dry. He thought that agriculture in the hilly regions, which involved irrigation, usually made the malaria worse. This is in line with our findings that the two camps situated near abandoned rice fields were the most malarious.