Control of Mansonia mosquitos, vectors of brugian filariasis in Sarawak, Malaysia.

Two field trials in the control of subperiodic brugian filariasis vectors, mainly Mansonia bonneae and Mansonia dives were carried out in Sarawak, East Malaysia. In the first trial, malathion ultra-low volume (ULV) spray was used to control the Mansonia mosquitos in two filariasis endemic villages. Six spray rounds were applied at biweekly intervals at Kampung Rasau and two spray rounds were applied at monthly intervals in Kampung Triboh. ULV malathion spray reduced biting Ma. bonneae population for 3 days after spraying. The biting density decreased to 50% of the pre-treatment level by the 12th - 13th day and reached the pre-treatment level by the 24th - 25th day. Contact bioassay tests on caged Mansonia mosquitos revealed considerable penetration of the malathion aerosol indoors and relatively adequate coverage outdoors. The estimated number of bites per case per day was 1.09 to 4 times less in the sprayed kampung than in an unsprayed control kampung. The parous and daily survival rates of Mansonia mosquitos were not significantly affected by the spraying. In a second trial, chemotherapy with diethylcarbamazine citrate (DEC) was combined with vector control through indoor residual spraying in Kampung Ampungan. The results were compared with the use of only DEC mass treatment in Kampung Sebangkoi and Kampung Sebamban. The combined control measures in Kampung Ampungan reduced the MfD-50 to 44% of the pre-treatment level over a period of 4 years. In the other two kampungs where only mass DEC therapy was applied, the microfilarial rate and MfD-50 declined significantly in the second blood survey but increased gradually in two subsequent follow-up blood surveys. The total insecticidal impact for Ma. bonneae was 3.9 to 1 indoors and 2.7 to 1 outdoors. These results indicated that quarterly pirimiphos-methyl indoor spraying used in integrated control could reduce indoor transmission by 3.9 times. The infective rate from the Ma. bonneae dissected in all three kampungs after the interventions, irrespective of DEC treatment alone or in combination with pirimiphos-methyl residual spraying were reduced by two fold. However the infection rate of brugian filarial larvae in Kampung Ampungan was significantly reduced after the use of DEC and insecticide. Annual Transmission Potential (ATP) showed a high significant reduction in Kampung Ampungan (p > 0.001) compared with Kampungs Sebangkoi and Schambam. In Ampungan, the ATP was reduced by 8.5 times indoors after the MDA and insecticidal application and 3 times outdoors. The reduction rate for Sebangkoi and Sebamban both indoors and outdoors were less than 2 fold.(ABSTRACT TRUNCATED AT 400 WORDS)

Course of antibody production by the DIG-ELISA method in neonatally infected and juvenile infected rats after primary infection with Breinlia booliati (Filarioidea: Onchocercidae).

The course of antibody production in Wistar neonatal and juvenile rats after primary infection with Breinlia booliati was studied by the DIG-ELISA technique using filter papers impregnated with capillary blood drawn from the infected rat tails at 7, 14, 28, 60 and 90 days post infection. Sera of neonatally infected rats did not react with adult worm antigen until day 7 and the titers of antibody remained at very low levels for the next 7 days. There was little tendency to eliminate the filarial larvae during this time. The antibody levels then rose rapidly throughout the next fortnight and increased to a maximum at day 60 after which the titer leveled out at a constant high value until early patency at day 90. On the other hand, antibodies could be detected in sera of juvenile infected rats as early as day 7 and the levels of antibody rose markedly to a maximum at day 28. During the period from day 60 to day 90 at early patency, the antibodies declined gradually to lower levels. The humoral immune responses of 42 neonatally infected rats and 53 juvenile infected rats of 3 strains (Lewis, Wistar and Sprague Dawley) were tested against soluble B. booliati antigens from both female (1:50) and male (1:10) worm extracts by the DIG-ELISA method. Antibodies were detected in sera from all the microfilaremic and amicrofilaremic rats belonging to neonatally and juvenile infected groups. Sera of clean neonatal rats did not give a positive reaction zone.

The effect of Bacillus thuringiensis israelensis [H-14] on emergence of Mansonia mosquitos from natural breeding habitat.

The measurement of the ultimate effects of the microbial insecticides on mosquito density is best obtained by assessment of adult populations. The main aims of this study are: (1) to assess the effect of Bacillus thuringiensis israelensis (Bti) FC Skeetal and Bactimos briquettes on the emergence rate of Mansonia bonneae developed from the introduced first-instar stage larvae and (2) to measure the effect of these two formulations of insecticides on Mansonia adult populations emerging from the natural breeding plots. Bti Skeetal and Bactimos briquettes at the lower applied dosages of 2.3 kg/ha and 1 briquette case/20 m2 respectively achieved 39-40% pupation rates and 31.5-34.2% adult emergence rates. At these low applied dosages, there was little or no direct effect on pupation from the surviving larvae and thereafter on the emergence of adults from the pupae. A two-fold increase in dosage, however, produced a drastic decline in the pupation rate and adult emergence rate. The rates dropped to 6.5% (pupation) and 4.3% (adult emergence) of the total larvae for Bactimos briquettes and to merely 1.5% (pupation) and 1.3% (adult emergence) of the total larvae for Skeetal. In studying the effect of Bti on the field populations of Mansonia mosquitos, two plots each were treated with Bactimos at 1 briquette case/10 m2 and Skeetal at 4.6 kg/ha. A wooden pyramid-shaped screened cage was placed on a cluster of host plants for a period of 2 weeks to trap the emerging adult mosquitoes. There were a total of 24 clusters of host plants in each plot.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on filariasis in Singapore: immunodiagnosis using indirect immunofluorescence.

Filarial antibodies were detected by the indirect fluorescent antibody (IFA) technique using sonicated microfilariae of Brugia malayi as antigen. Of the 324 sera of patients with clinical symptoms suggestive of filarial infection, 90 (28%) had detectable antibodies with titres ranging from 1 : 4 to 1 : 4096. Forty-six percent of patients with eosinophilic lung were positive with titres ranging from 1 : 4 to 1 : 1024. Highest rates of positives were seen in Indians (48%) with lower rates in Malays (36%) and Chinese (15%).

Studies on human filariasis in Malaysia: immunodiagnosis using indirect immunofluorescence.

The indirect immunofluorescence test using sonicated microfilariae of Brugia malayi has been evaluated on 173 sera from patients and persons exposed to Wuchereria bancrofti and B. malayi in endemic areas of Peninsular Malaysia. In the microfilaria-negative group, without signs and symptoms of filariasis 55/62 sera (89%) had titers of 1:16 and less. In the microfilaremic groups and in the amicrofilaremic cases with clinical filariasis, all the sera tested were positive, with the antibody titers ranging generally from 1:16 - 1:256. Cross-reaction tests were done on 16 samples of onchocerciasis sera from West Africa using sonicated antigen as well as antigen-coated CNB1-activated sepharose. Antibody titers were detected in all the sera. The usefulness of the sonicated microfilarial antigen in serodiagnosis of filariasis is discussed.

Distribution and ecological consideration of Breinlia booliati infecting wild rodents in Malaysia.

Seven of the 18 species of lowland forest terrestrial and semi-arboreal murids were found naturally infected with Breinlia booliati. Of these, two species, Rattus sabanus and R. cremoriventer, were found to be the most preferred hosts. None of the murids from the highland, field or human-inhabited areas was infected. This could have been due more to the greater scarcity of the vectors in these habitats than to the susceptibility of the hosts. The absence of this parasite in the squirrels examined may be attributed either to host specificity or to the normal activity cycles or vertical stratification of the vectors, separating them in space and/or time from the squirrels. The pattern of dispersion of the parasite is influenced by the wide distribution of suitable hosts, and the hypothesis that the parasite is of forest origin is discussed.