Vector mosquitoes of Wuchereria bancrofti at Bicol region in the Philippines. 1. Transmission capability.

Mosquitoes were surveyed for the capability of filaria transmission at Sitio Bacolod and Barrio Salvacion, in Bicol region, Luzon, Philippines. The results of indoor collections and experimental infections showed that the infective rates and the median density of infective larvae per infected mosquito were significantly higher in Aedes poicilius than in Culex quinquefasciatus. Aedes poicilius was found to be the principal vector of bancroftian filariasis in this region.

Comparison of the blood film, Millipore filter and Nuclepore filter techniques for the detection of microfilaremia in a field survey in the Philippines.

The blood film, Millipore filter and Nuclepore filter techniques were applied in a filariasis field survey at a village in the Philippines. venous blood from each person was examined by the three techniques to compare their efficacy of microfilariae detection. Overall positive rate was 16.1% by the combined techniques. Microfilaria positive rate was highest in Nuclepore filter method (15.6%) followed by Millipore technique (13.6%) and blood film (11.5%), but their difference was not significant statistically. The ratio of the total microfilaria counts by the three techniques was 1:29.8:30.3, which seems to reflect the ratio of the blood volumes used. There was no significant difference between the microfilaria counts by the three techniques adjusted to the same volume of 30 microliter and examined by F-test. It is considered that the blood film is still of practical value in field surveys.

Bancroftian filariasis in a Philippine village: entomological findings.

Bancroftian filariasis in an isolated Philippine village has been intensively investigated; this paper reports the entomological findings. Surveys were carried out six months apart in the driest and wettest months. Significant transmission was demonstrated only during the wet season. Aedes poicillius was the major vector of Wuchereria bancrofti. Ae. poicilius accounted for 58% of larvae found in the axils of banana plants and 31% of those in abaca axils; negligible numbers of larvae of this species were found in pandanus and gabi axils. Mosquitoes were collected from indoor harbourages twice weekly for five weeks during the wet season; 615 mosquitoes were caught of which 80% were Ae. poicilius and 9% were Culex quinquefasciatus. 11% of the former and 13% of the latter contained filariae; whereas all stages of development were seen in Ae. poicilius, no development beyond the first stage was seen in Cx. quinquefasciatus. Human bait trapping was used for 110 manhours; 371 mosquitoes were caught of which 58% were Ae. poicilius and 24% were Culex summorosus. Filarial larvae were seen only in Ae. poicilius; 3.7% of mosquitoes were positive and all stages of filarial development were seen. The mean landing/biting rate between 1900 and 0500 hours was 3.37 mosquitoes per man-hour with a maximum of almost seven mosquitoes per man-hour at midnight. Overall, 2.26% of vectors collected in the human studies were infective. There was an average of 3.38 third-stage larvae per infective mosquito. The efficiency of transmision was estimated as 6.1 x 10-5, or one new case of microfilaraemia for every 16, 400 bites by infective mosquitoes in the village population. In contrast to the human studies, large numbers of mosquitoes were caught by animal bait trapping in both the wet and dry seasons. The distribution of mosquito species was similar in the two seasons. Ae. poicillius represented only 1.0-1.5% of all mosquitoes seen. No filarial larvae were seen. It was concluded that transmission of filariasis in the village was inefficient and postulates were advanced to explain the increased intensity and severity of filariasis inmen as compared to women.

Bancroftian filariasis in a Philippine village: clinical, parasitological, immunological, and social aspects.

PIP: The distribution and effects of Bancroftian filariasis in 535 inhabitants of a Philippine village were investigated. Clinical, parasitiological, immunological, and socioeconomic assessments were made. A history of acute lymphatic inflammation and the presence of inguinal lymphadenopathy were common. Lymphatic obstructive disease, defined as leg edema, hydrocele, or an epididymal cyst, was more common in men than women and increased progressively with age. The prevalence and intensity of microfilaremia rose with age in males, whereas the prevalence but not the intensity of infection increased with age in females. The prevalence of immunological responsiveness, as assessed by skin reactivity to microfilarial antigen and serum antibodies to adult filarial worms, increased with age in both males and females. There was no relationship between either microfilaremia or obstructive disease and the ability to work or have children, but both were more common in heads of households with the lowest socioeconomic scores. Epidemiological factors which may have contributed to these findings are discussed. (author's modified)^ieng

Sensitivity and specificity of skin reactivity to Brugia malayi and Dirofilaria immitis antigens in Bancroftian and Malayan filariasis in the Philippines.

Saline antigen extracts of microfilariae, adult worms and third-stage larvae of subperiodic Brugia malayi maintained in gerbils were prepared for use as skin test reagents. Patients were studied on three different islands in the Philippines, one endemic for Bancroftian filariasis (Sorsogon, Luzon), another endemic for Malayan filariasis (Palawan) and the third without endemic filariasis (Cebu). A dose-response curve was established initially in patients with Bancroftian filariasis: thereafter 1.0 microng of the B. malayi antigens and 0.05 microng of Dirofilaria immitis FST antigen (obtained from Dr. T. Sawada) were used. Sizes of reactions were measured by recording the diameters of wheals at 20 minutes, 24 and 48 hours. There was a very high correlation in immediate hypersensitivity reactions among the three B. malayi antigens. Reaction sizes followed a normal distribution. When an area of an antigen-induced wheal 3 X that of the saline control was considered a positive reaction, 99% of 150 patients with Bancroftian filariasis and 96% of 45 subjects with Malayan filariasis reacted to B. malayi larval antigen. Only 68% of patients with Bancroftian filariasis but 90% of those with Malayan filariasis reacted to D. immitis FST antigen. There was no relationship between skin reactivity and age, sex, microfilaremia or severity of clinical disease. Approximately half of 50 patients who lived in an endemic area for W. bancrofti but had neither patent infection nor clinical disease reacted to B. malayi antigens. A maximum of 7% of 120 age- and sex-matched controls from Cebu gave false positive reactions with any of the antigens. Only a small proportion of patients gave 24- and 48-hour reactions. It is concluded that the use of antigens prepared from a human parasite, subperiodic B. malayi, which is easily maintained in a laboratory animal host, improves the ability to diagnose filarial infections by immunological means.