Dengue vector mosquitos at a tourist attraction, Ko Samui, in 1995

On Ko Samui, Thailand there were two epidemics of dengue hemorrhagic fever (DHF) in 1966 and 1967, followed by endemics up to 1994. Aedes aegypti and Aedes albopictus were the vectors. From January to July 1995, 51 cases of DHF were reported, out of these were many foreigners who still suffer from dengue fever and return home with negative impression. We carried out an entomological survey around the island and collected the mosquitos to detect dengue virus by digoxigenin-cDNA probe. The data revealed that Aedes aegypti and Aedes albopictus still were abundant and some were infected with dengue virus. Visual larval survey indices (HI, CI and BI) were 90.4, 61.3 and 301.3 respectively. Biting rate (BR) of Aedes mosquitos was high, the average indoor and outdoor BR were 9.7 and 100.8 mosquitos/man-hour. From 13 pools of mosquitos, 8 strains of dengue virus were detected (61.5%). The results may encourage the local authorities to improve vector surveillance and control before the famous island becomes an unpleasant island.

House dust mite fauna in Thailand

House dust mites have been shown to be the most important source of allergen in Thailand. The results of our initial mite survey were in conflict with previous data reported 20 years ago. To evaluate the current condition of mite fauna in Thailand, we conducted a larger scale survey of house dust mites in dusts from three different parts of the country. A total of 630 mattress dust samples was collected from various types of housing from central, northern and northeastern parts of Thailand. House dust mites were identified and enumerated by standard techniques and 388 dust samples were analysed further for group I antigen by a two-site monoclonal antibody enzyme-linked immunosorbent assay. House dust mites were identified in 555/630 (88.1%) of dust samples collected; 27.6% of these 555 samples contained over 100 mites per gram of fine dust. Dermatophagoides pteronyssinus was the most abundant species found with a mean count of 87.2 mites per gram of dust (range 1-1460). Group I antigen was detected in 380/388 (97.9%) samples analysed and 330 of which (86.8%) contained over 2 micrograms/gm of group I antigen. The highest density of mites was found in dusts from northern Thailand whereas dusts with highest amount of antigen were those collected from the northeastern part. Some degree of correlation between mite count and mite allergen was observed (r2 = 0.133, P < 0.001). No significant difference in the mite count and mite allergen was found among various types of housings. House dust mites are the source of allergens ubiquitously found all over Thailand.(ABSTRACT TRUNCATED AT 250 WORDS)

Control of Culex pipiens fatigans(W) by the larvivorous fish Poecillia reticulata and by removal of debris from the breeding habitat

Twice weekly removal of floating debris from two polluted ponds in Bangkok resulted in 75% reduction of immature populations of C.p. fatigans for seven weeks. Subsequent introduction of the guppy Poecilia reticulata at 10 fish per m2 further reduced the aquatic population to 2% of the pretreatment level during 12 weeks. When debris removal was discontinued, partial recovery of the larval density was observed. When fish were introduced in a plot without prior debris removal, there was no reduction of the mosquito population, and when only part of the debris was removed from one plot, the reduction was immediate.