Entomological evaluation of community-wide use of lambdacyhalothrin-impregnated bed nets against malaria in a border area of north-west Thailand.

This paper reports 2 studies. (i) After a year of baseline data collection, lambdacyhalothrin-treated bed nets were introduced into 3 of 5 villages in north-west Thailand, the remaining 2 being treated with placebo. Human bait collections were carried out in each village on 2 nights per month, for 8 months of each year, and the biting densities were compared between the first year and the second year. The treated bed nets did not have any significant impact on the density or parous rates of Anopheles sawadwongporni and A. maculatus s.s. populations. The results for A. dirus s.l. were not conclusive because of the low number caught. Significant reductions in biting and parous rates of A. minimus species A were observed in only one of the 3 treated villages, and there was no overall difference between treated and control groups. However, the trial suffered from the washing of nets by villagers and the low rate of reimpregnation. (ii) A short-term study involved 4 villages in a cross-over design, and lasted 48 d. For the first 24 d, residents of 2 villages were given new treated nets while the other 2 villages retained their own untreated nets. For the second 24 d, this situation was reversed. Daily light-trapping revealed no significant difference in the indoor densities or parous rates of A. minimus species A between the periods with treated or untreated nets.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of folk healers in the malaria volunteer program in Thailand.

In the Malaria Control Program of Thailand, villagers were recruited as village malaria volunteers to assist and participate in passive case detection at the community level by preparation of blood smears and provision of presumptive treatment to suspected cases. Among these volunteers, there were some folk healers. This study was intended to investigate the role of the folk healer volunteer in the Malaria Control Program in the northern area under the responsibility of the Malaria Zone 1, Region 2 in Fang, Mae Ai and Chiang Dao Districts of Chiang Mai Province. The combination of qualitative and quantitative research methodologies (participant and non-participant observations and structured questionnaires) were used to get information from 246 volunteers, of whom 113 were folk healers. Most of the volunteers were male and more than half were in the age group 30-50 years. Almost all volunteers had completed the compulsory education and farming was their main occupation. Folk healer volunteers were older and had been in the service longer than the non-folk healer volunteers. Both groups of volunteers shared some negative attitudes towards the Malaria Control Program, such as the interference with their occupation and the waste of time. However, the folk healer volunteers had more positive attitudes towards the program in terms of gaining social respect and the willingness to stay on. It was also found that the folk healer volunteers performed their assignment better than the non-folk healer volunteers.(ABSTRACT TRUNCATED AT 250 WORDS)

Seroepidemiology of malaria in northern Thailand: II. Focal and temporal variations in endemicity.

Four population groups from regions of Northern Thailand were surveyed for the presence of antibodies to Plasmodium falciparum using the indirect immunofluorescent antibody (IFA) test. Each of the four populations was selected from areas known to represent different patterns of malaria transmission. Group 1 was from an area where there had been no malaria transmission for approximately 30 years. Individuals in this group below age 40 showed an extremely low prevalence of malaria antibodies. Group 2 was chosen from an area where low levels of transmission have continued despite more than 30 years of DDT spraying. In this group the age related pattern of malaria antibodies varied from village to village but in all villages there was a sharp increase in the prevalence of IFA positive tests in individuals over 30. The third group has had continuously high levels of transmission. Although there are differences in the age related prevalence of IFA positives when individual villages are compared, there is a greater prevalence at all ages than in the first two groups. The fourth group was selected from an area where transmission had recently resumed after freedom from indigenous cases for approximately six years. There was little difference in the prevalence of IFA positive individuals below the age of 25 but above that there was a steady increase in prevalence with age. The correlation of IFA antibody positives with known patterns of malaria transmission in these four areas demonstrates the usefulness of this serological technique in assessing malaria endemicity and the effectiveness of control measures as well as in the interpretation of other malaria statistics.

An epidemiological early warning system for malaria control in northern Thailand.

Parasitological data for the years 1973-81 were examined to determine the years of "acceptable" or "normal" transmission of malaria, for every district of northern Thailand. The monthly mean number of cases and the mean plus 2 standard deviations (SD) were calculated for the selected years and plotted on log-linear graph paper. The resulting graphs were distributed to the Malaria Sector Offices. Sector Chiefs were then responsible for plotting the monthly observed number of cases of malaria as the data became available; if the observed incidence was more than 2 SD greater than the "normal" mean for that month, the Zone and Regional Malaria Offices were informed. Retrospective analysis of data from districts where malaria outbreaks had occurred indicated that the method provides an effective warning of impending epidemics. It is expected that the resulting earlier implementation of appropriate remedial control measures will lead to a reduction in malaria incidence in the region.

Seroepidemiology of malaria in northern Thailand.

The seroepidemiology of malaria in two areas of Northern Thailand was studied by means of the indirect immunofluorescent antibody tests (IFAT). In one transmission has been interrupted completely for over 30 years, but in the other area transmission still occurs at a low level. Results of the survey for antibodies confirm existing parasitological findings and reflect both the recent and past history of malaria in both areas. The IFAT is less sensitive to recent malaria infection in very young people in an area of low endemicity than is the number of reported slide proven cases, but as age and cumulative exposure increase the IFAT reflects period prevalence in adults of ages 20--40. Thus, the serological data are complementary to other available information. This study also confirms the observation that malaria antibodies may last for over 30 years in people who formerly lived in hyperendemic areas and had multiple infections with the malaria parasite.