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A blood survey for filariasis was carried out in the Kepu District of Jakarta. Examination of stained 20 c.mm finger-prick blood thick films and membrane filter concentration (MFC) of 1 ml venous blood. The youngest age group examined, 5-9 years old revealed a mf rate of 17% of which 71% were of a low density character detected by MFC only. The mf rate appears to remain relatively constant from the 10-14 year old group onward, approximately 35%, but at all age groups at least half the infections were of low density. The highest mf rate and density was observed present in the 15-20 year old group.
A blood survey employing membrane filter concentration (MFC) and examination of stained 20 c.mm thick blood films as diagnostic methods was carried out in Banjar Regency of South Borneo, an area of endemic B. malayi filariasis. In untreated populations the mf rate, as revealed by MFC, ranged from 23.2% for the 5-9 year old group to 43.7% for the greater than 50 year old group. For all age groups approximately one half of the microfilaraemias were of a low grade nature, diagnosed by MFC only. In a population that had been subjected to mass DEC administration 1 1/2 years prior to this survey, the MFC-diagnosed rate was 15%. Approximately two thirds of these infections were of very low density, the average density being 2.2 mf/ml.
In a Bancroftian filariasis survey on the coast of Tanzania microfilaria rates rose with age reaching 53% in the 60-69 year group followed by a slight fall above this age. The most important clinical manifestations were hydrocoele, funiculitis and elephantiasis, with hydrocoele presenting the most serious public health problem. Hydrocoele rates increased with age reaching 90% above the age of 70. The highest proportion of large hydrocoeles were also in the older age groups. A satisfactory methodology was established for the planning of future surveys leading to control.
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From 1956, when filariasis control was first listed in our national program, up to 1991, a cumulative total of 677,931,521 person-time blood examinations and 217,472,045 person-time diethylcarbamazine treatments were made in the whole country, and 835 (96.6%) out of the 864 endemic counties achieved the criterion for control of filariasis. Surveillance data collected in various provinces, autonomous regions and municipalities starting from the second year after they reached the criterion for control of filariasis demonstrated that in 1991 the microfilarial rate in human populations and natural infection of filarial larvae in mosquito vector populations in previous endemic areas had already declined to a very low level, even zero, without resurgence in quite a number of villages. In some places where filariasis was brought under control relatively early, the anti-filarial antibody positive rate of the human population has fallen to a level the same as or similar to that in nonendemic areas. Therefore, the data suggest that in most places where filariasis has been controlled, the transmission of bancroftian filariasis and periodic malayan filariasis has been interrupted. However, filariasis is still endemic in 29 counties in China at present, the danger of introduction of sources of infection by the floating population hasn't been extinguished yet, and there are still a few areas with weak links in filariasis control. Therefore, control work still needs to be strengthened and systematic surveillance must be pursued until the elimination of filariasis in the whole country.
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.
A study was undertaken to define the sensitivity and specificity of serological tests in bancroftian and malayan filariasis and correlate the findings with clinical disease. Sera were collected from subjects on three different islands in the Philippines: one endemic for bancroftian filariasis, another endemic for malayan filariasis and the third without endemic filariasis. Antibodies were measured, using rugia malayi as the source of antigen. Antibodies against adult worms measured by indirect immunofluorescence were found at a titer of 1:8 or greater in all patients with bancroftian or malayan filariasis but not in the control subjects. There was no relationship of antibody titer to clinical status. Antibodies against microfilariae were measured by indirect immunofluorescence and microfilarial agglutination. A high correlation was observed between the two methods. These antibodies were found in only one quarter, approximately, of patients with filariasis. Microfilarial antibodies were found more commonly in those patients with chronic lymphatic obstruction. It is concluded that measurement of antibodies to adult worms is a useful indicator of infection while microfilarial antibodies are correlated with disease.
Further studies on malayan filariasis were made at Bangluke canton of Chumphon province of South Thailand, where mass drug treatment was not applied. It was found after 9 years that there was a marked reduction in filariasis in the area. The filariasis infection rate being decreased from 14.1 to 1.9 per cent, the microfilarial rate from 10.8 to 0.9 per cent, and the elephantiasis rate from 3.3 to 1.0 per cent, and the mean microfilarial density among positive cases being decreased from 27.6 to 6.6 per 20 c.mm blood. Dissection of 1,893 Mansonia mosquitoes revealed the finding of only stage I and stage II larvae of B. malayi in seven M. annulifera and M. indiana. The reduction in the filariasis infection was assumed to be due to the interruption of transmission of filariasis cycle in the mosquitoes resulting from DDT spraying operation of the Malaria Eradication Programme of the Thai Government. There were also some positive cases moving out of the area. The rural development programme of the Thai Government also played another important role in the reduction in the prevalence of malayan filariasis in this area.
In 1984-1990 longitudinal or sectional serological surveillance on filariasis by ELISA with Brugia malayi adult antigen was carried out in 6 villages, Yuhang County, Zhejiang Province, where malayan filariasis had been under control. During that period the microfilaraemia rate of inhabitants had been declining continuously till nil, the positive rate and mean optical density (OD) value in ELISA for positive inhabitants concurrently declined year by year, especially for children under age of 10. By the 5th year after control both the positive rate and mean OD value were close to those of healthy persons living in nonendemic areas of filariasis, no positivity was found in children. In the meantime, ELISA was used to detect serum antibodies in members of a family who were infected with bancroftian filariasis and inhabitants living around them in 1990. Positive rate of ELISA was higher in these inhabitants (8.33%) than in healthy persons (2.53%), and positive ones were detected from children under age of 10. The results suggest that the detection of antifilarial antibody by using ELISA is an effective method for the surveillance of filariasis.
Immunological function in Filipino patients with bancroftian filariasis, manifested as either asymptomatic microfilaraemia or chronic obstructive disease, was compared with that found in healthy control subjects living in the same area. As a group, patients with filariasis had raised serum IgG levels, impairment of antibody responses to tetanus and typhoid vaccines, and suppression of delayed hypersensitivity skin reactions to heterologous antigens. This immunosuppression in filariasis may result from antigenic competition and may contribute to the development of secondary infections.
The main vectors of bancroftian filariasis in Kwale, Tanzania, were Anopheles gambiae complex and Culex p. quinquefasciatus. After vector control by the insecticides Dursban (chlorpyrifos) or Abate (temephos), the number of all man-biting mosquitoes was reduced by 94.8%, and that of house-resting mosquitoes by 95.3%. Anopheles gambiae complex were highly exophilic, possibly due to a high proportion of Anopheles merus in this village. The infection rate of A. gambiae complex rose significantly in the post-control samples (P less than 0.05), but nevertheless the overall reduction in filariasis transmission was 87.2%. The infection rate of A. gambiae complex caught off human bait was significantly higher than that of the spray-caught sample (P less than 0.05). It was suggested that the former sample contained a higher proportion of A. merus. This species may be a better vector of filariasis than freshwater forms.
Diethylcarbamazine (DEC)-medicated salt was used to control bancroftian filariasis in 20 endemic counties and cities of Fujian Province in China. The population was 5,189,126 and the microfilaria (mf) rates were between 1.56 and 11.81%. The total dose of DEC was 6-10.5 g per person over a period of 2-4 months. Six to 9 months after treatment the mf rate was reduced to 0-0.57% with a mean of 0.07% (621/823,796). In 184 villages sampled one year post treatment the mf rate was 0.22% (371/171,067) and in 29 villages 2-4 years after treatment the mf rate was 0.05% (31/56,459). In a region of endemic Malayan filariasis, with a population of 67,778 and mf rate of 3.82-4.36%, treatment with DEC-medicated salt to a dosage of 3.2 g DEC per person was administered for 2 months. Six months after treatment the mean mf rate was reduced from 4.08 to 0.26% (10/3841). Filariasis in all the villages controlled with DEC-medicated salt reached the basic criteria of elimination (mf rate below 1%).
A survey was carried out among persons residing in 8 villages in the Province of West Kalimantan, Indonesia to determine the prevalence of filariasis. Finger tip blood smears were obtained at night from over 3,000 people and microfilariae of Brugia malayi were found in 108 (3.5%) and Wuchereria bancrofti in 10 (0.3%). Most B. malayi (96 carriers) was found in Kakap, a village near the coast, 20 km from the provincial capital of Pontianak. Nine of 10 cases of W. bancrofti were located in Pahauman, a village 130 km northeast of the provincial capital. Periodicity studies indicate the strain of B. malayi to be subperiodic. In Kakap 18% of 226 persons examined had a clinical history of filariasis and elephantiasis was seen in 13%. This is the first report of rural bancroftian filariasis in the area. A few Mansonia species of mosquitoes were examined but none were infected with filarial larvae.
A blood and clinical survey for bancroftian filariasis was made in the Kepu District of Central Jakarta in June 1976. About 90% of 614 inhabitants in the survey area was examined. The microfilarial rate was 4.5%; 5.8% in males and 3.3% in females. Most of the carriers were asymptomatic. The microfilarial density was low. There were 15 persons (2.7%) with signs and symptoms of filariasis; 11 males and 4 females. The total filariasis infection rate was 6.7%. The percentage of infected persons increased with years of residency. Persons living in poorly built houses had approximately 9 times higher microfilarial rate and 5 times higher disease rate than those living in modern houses.
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.
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.
Five cases of reaction in leprosy with filariasis have been presented to emphasise the coexistance of the two conditions in the areas endemic to filariasis and leprosy. One may modify the clinical features of the other. Necessity of recognising filariasis as an important precipitating factor for lepra reaction in tropical countries has been highlighted for proper management of rather protracted and resistant cases.