The significant scale up and success of Transmission Assessment Surveys 'TAS' for endgame surveillance of lymphatic filariasis in Bangladesh: One step closer to the elimination goal of 2020.

BACKGROUND: Bangladesh had one of the highest burdens of lymphatic filariasis (LF) at the start of the Global Programme to Eliminate Lymphatic Filariasis (GPELF) with an estimated 70 million people at risk of infection across 34 districts. In total 19 districts required mass drug administration (MDA) to interrupt transmission, and 15 districts were considered low endemic. Since 2001, the National LF Programme has implemented MDA, reduced prevalence, and been able to scale up the WHO standard Transmission Assessment Survey (TAS) across all endemic districts as part of its endgame surveillance strategy. This paper presents TAS results, highlighting the momentous geographical reduction in risk of LF and its contribution to the global elimination target of 2020. METHODOLOGY/PRINCIPAL FINDINGS: The TAS assessed primary school children for the presence of LF antigenaemia in each district (known as an evaluation unit-EU), using a defined critical cut-off threshold (or 'pass') that indicates interruption of transmission. Since 2011, a total of 59 TAS have been conducted in 26 EUs across the 19 endemic MDA districts (99,148 students tested from 1,801 schools), and 22 TAS in the 15 low endemic non-MDA districts (36,932 students tested from 663 schools). All endemic MDA districts passed TAS, except in Rangpur which required two further rounds of MDA. In total 112 students (male n = 59; female n = 53), predominately from the northern region of the country were found to be antigenaemia positive, indicating a recent or current infection. However, the distribution was geographically sparse, with only two small focal areas showing potential evidence of persistent transmission. CONCLUSIONS/SIGNIFICANCE: This is the largest scale up of TAS surveillance activities reported in any of the 73 LF endemic countries in the world. Bangladesh is now considered to have very low or no risk of LF infection after 15 years of programmatic activities, and is on track to meet elimination targets. However, it will be essential that the LF Programme continues to develop and maintain a comprehensive surveillance strategy that is integrated into the health infrastructure and ongoing programmes to ensure cost-effectiveness and sustainability.

Progress and impact of 13 years of the global programme to eliminate lymphatic filariasis on reducing the burden of filarial disease.

BACKGROUND: A Global Programme to Eliminate Lymphatic Filariasis was launched in 2000, with mass drug administration (MDA) as the core strategy of the programme. After completing 13 years of operations through 2012 and with MDA in place in 55 of 73 endemic countries, the impact of the MDA programme on microfilaraemia, hydrocele and lymphedema is in need of being assessed. METHODOLOGY/PRINCIPAL FINDINGS: During 2000-2012, the MDA programme made remarkable achievements - a total of 6.37 billion treatments were offered and an estimated 4.45 billion treatments were consumed by the population living in endemic areas. Using a model based on empirical observations of the effects of treatment on clinical manifestations, it is estimated that 96.71 million LF cases, including 79.20 million microfilaria carriers, 18.73 million hydrocele cases and a minimum of 5.49 million lymphedema cases have been prevented or cured during this period. Consequently, the global prevalence of LF is calculated to have fallen by 59%, from 3.55% to 1.47%. The fall was highest for microfilaraemia prevalence (68%), followed by 49% in hydrocele prevalence and 25% in lymphedema prevalence. It is estimated that, currently, i.e. after 13 years of the MDA programme, there are still an estimated 67.88 million LF cases that include 36.45 million microfilaria carriers, 19.43 million hydrocele cases and 16.68 million lymphedema cases. CONCLUSIONS/SIGNIFICANCE: The MDA programme has resulted in significant reduction of the LF burden. Extension of MDA to all at-risk countries and to all regions within those countries where MDA has not yet reached 100% geographic coverage is imperative to further reduce the number of microfilaraemia and chronic disease cases and to reach the global target of interrupting transmission of LF by 2020.

Population migration: implications for lymphatic filariasis elimination programmes.

Human population migration is a common phenomenon in developing countries. Four categories of migration-endemic to nonendemic areas, rural to urban areas, non-MDA areas to areas that achieved lymphatic filariasis (LF) control/elimination, and across borders-are relevant to LF elimination efforts. In many situations, migrants from endemic areas may not be able to establish active transmission foci and cause infection in local people in known nonendemic areas or countries. Urban areas are at risk of a steady inflow of LF-infected people from rural areas, necessitating prolonged intervention measures or leading to a prolonged "residual microfilaraemia phase." Migration-facilitated reestablishment of transmission in areas that achieved significant control or elimination of LF appears to be difficult, but such risk can not be excluded, particularly in areas with efficient vector-parasite combination. Transborder migration poses significant problems in some countries. Listing of destinations, in endemic and nonendemic regions/countries, and formulation of guidelines for monitoring the settlements and the infection status of migrants can strengthen the LF elimination efforts.

Surveillance of lymphatic filariasis after stopping ten years of mass drug administration in rural communities in south India.

BACKGROUND: While various studies provided insight into the impact of mass drug administration (MDA), information on the dynamics of the post-MDA threshold level lymphatic filariasis (LF) infection facilitates understanding its disappearance pattern and determining the duration of post-MDA monitoring and evaluation. METHODS: The changes in microfilaraemia (Mf) prevalence and vector infection rates were monitored for four (2005-2008) and six years (2005-2010) respectively after stopping ten rounds of annual mass diethylcarbamazine (DEC) administration in a group of five villages located in South India. Four years after stopping MDA, circulating filarial antigenaemia (Ag) status among children and adults was also assessed in two villages. RESULTS: Overall Mf prevalence (n = 700) and vector infection rates (n=803-3520) showed a declining trend. Two villages maintained zero Mf status in each of the four years, vector infection rate was zero from the third year onwards and Ag prevalence in adults was 0.4% (n = 226). In two other villages despite persistence of Mf and vector infection there was zero vector infectivity rate during the third to sixth year and Ag prevalence among children (n = 50) was nil. In the fifth village Mf prevailed at <1.0% and Ag prevalence among 1-7 year old children was 4.6% (n = 44) and vector infectivity rate during the sixth year was 0.1% (n = 852). CONCLUSION: The incidence of sporadic new infections is evident in highly endemic communities such as the fifth village. However, there is uncertainty on the potential of the Ag positive children to reestablish infection. Six years of post-MDA monitoring and evaluation appears to be adequate to discern the status of transmission interruption and appropriate decision making.

Effect of annual mass administration of diethylcarbamazine and albendazole on bancroftian filariasis in five villages in south India.

Annual mass drug administration (MDA) is the recommended strategy for lymphatic filariasis (LF) elimination. We assessed the effect of six rounds of mass administration of diethylcarbamazine (DEC) and albendazole (ALB) on microfilaria (Mf) prevalence and intensity and vector infection and infectivity rates and circulating filarial antigenaemia (CFA) in a group of five villages in south India, endemic for Culex-transmitted bancroftian filariasis. During different rounds of MDA, 60-70% of the eligible population (>15 kg body weight) was treated. The MDA reduced the Mf prevalence from 8.10% (CI 6.18-10.01) to 1.01% (CI 0.31-1.71) (P<0.05) and geometric mean intensity of Mf from 0.31 (CI 0.22-0.40) to 0.02 (CI 0.00-0.04) (P<0.05), equivalent to a fall of 86% and 94% respectively. The vector infection and infectivity rates declined from 13.11% (CI 11.52-14.70) to 0.78% (CI 0.16-1.40) (P<0.05) and 1.04% (CI 0.56-1.52) to 0.13% (CI 0.00-0.39) (P<0.05), respectively. Four out of the five villages recorded <0.5% Mf prevalence and 0% vector infection rate. Circulating filarial antigenaemia (CFA) fell by 86% in the total population and 100% in 1-10 year old children. One of the five villages, which showed the highest baseline vector infection rate, showed >1.0% Mf rate. The results suggest that six rounds of mass administration of DEC and ALB, with 60-70% treatment coverage, is likely to achieve total interruption of transmission and elimination of LF in the majority of villages.

Prolonged persistence of residual Wuchereria bancrofti infection after cessation of diethylcarbamazine-fortified salt programme.

A diethylcarbamazine (DEC)-fortified salt intervention programme was implemented between 1982 and 1986 in Karaikal district, Union territory of Pondicherry, south India, to control Culex transmitted bancroftian filariasis. The intervention reduced the microfilaria (Mf) rate from 4.49% to 0.08%. To eliminate the residual microfilaraemia, the health department detected and treated Mf carriers from 1987 to 2005 and mass-administered drugs in 2004 and 2005. Surveillance from 1987 to 2005 revealed persistent microfilaraemia in 0.03-0.42% of the population. In 2006, we conducted a more detailed Mf survey and a child antigenaemia (Ag) survey in 15 urban wards and 17 rural villages. These surveys showed an overall Mf rate of 0.46% in the high-risk urban areas and 0.18% in the rural areas; none of the sampled children was positive for Ag. All detected Mf carriers were >20 years old. The age of the youngest Mf carrier was 30 years in urban and 21 years in rural areas, which suggests that transmission was interrupted and there was no incidence of new Mf case after cessation of DEC salt programme. Eleven of 15 urban and 15 of 17 villages were totally free from microfilaraemia. Nevertheless, three of 15 surveyed urban localities and two of 17 villages showed >1% Mf rate. Thus, it seems that (i) post-intervention very low levels of microfilaraemia can continue as long as 20 years; (ii) 0.60-0.70% Mf rate is a safe level and at this level recrudescence of infection may not occur; (iii) there can be isolated localities with >1% Mf rate and their detection for further intervention measures could be challenging in larger control/elimination programmes and (iv) the residual infection mostly gets concentrated in the adult population, in underdeveloped urban areas and in historically highly endemic or large endemic rural areas. These groups and areas should be targeted with rigorous intervention measures such as mass drug administration to eliminate the residual infection.

Usage of personal-protection measures against mosquitoes and the low prevalences of Wuchereria bancrofti microfilaraemia in the Indian city of Chennai.

The usage of personal-protection measures against mosquitoes and the prevalence of Wuchereria bancrofti microfilaraemia were assessed in different areas of the city of Chennai, a large urban area in southern India. Most of the households investigated (75% to 92%, depending on socio-economic status) used some form of personal protection (such as mosquito coils, vaporizing mats and liquids and mosquito nets). The study households spent a mean (S.D.) of 109.45 (141.65) Indian rupees/month on personal protection, such expenditure increasing significantly with increasing household income (F=2.95; P=0.03). Over the last three decades the prevalence of W. bancrofti microfilaraemia has been slowly declining in Chennai. Most of the 'moderate-income' areas of the city investigated in the present study appeared free of such microfilaraemia, and the prevalences recorded in about half of the low- and very-low-income study areas did not exceed 1.0%. The mean prevalences recorded in the moderate-, low- and very-low-income areas were 0.51%, 1.15% and 1.30%, respectively. Given their very low prevalences of microfilaraemia, relatively good housing, sanitation and health care and extensive use of personal-protection measures, the 100 million Indians living in (mostly urban) moderate- and high-income areas may not require active mass drug administrations (MDA) against lymphatic filariasis. The need to develop simple methods to stratify urban areas, into those that require and those that do not require active MDA, remains. If lymphatic filariasis is to be eliminated from India in a reasonable time-frame, at least as a public-health problem, MDA should now be focused on the poorer localities.

Impact of seven rounds of mass administration of diethylcarbamazine and ivermectin on prevalence of chronic lymphatic filariasis in south India.

OBJECTIVE: To evaluate the impact of seven rounds of mass administration of diethylcarbamazine (DEC) and ivermectin on the prevalence of chronic lymphatic filariasis and to compare it with that observed in a placebo arm in a community-level trial. METHODS: Cross-sectional clinical surveys were carried out before and after seven rounds of mass drug administration (MDA). About 54-75% of the target population were treated at each round of MDA. RESULTS: After seven rounds, the hydrocele prevalence had declined from the pre-intervention level of 20.5-5.1% (P < 0.05) in the DEC arm, from 23.9% to 10.4% (P < 0.05) in the ivermectin arm and from 20.4% to 10.9% (P < 0.05) in the placebo arm, equivalent to reductions of 75.3%, 56.6% and 46.6%, respectively. The lymphoedema/elephantiasis prevalence declined only marginally and without statistical significance from 3.7% to 3.2%, 4.6% to 3.9% and 2.9% to 2.3% in the DEC, ivermectin and placebo arm. After the seventh MDA, none of the sampled people in the 0-20 age group was found with hydrocele and there was a statistically significant decline in hydrocele prevalence in all other age groups in the communities treated with DEC, the drug known to have macrofilaricidal effect. The impact was relatively less in ivermectin arm. CONCLUSION: Repeated DEC administration has the potential to prevent incidence of new hydrocele cases and may resolve the manifestation at least in a proportion of affected people. Apart from reducing the microfilaraemia prevalence and transmission of infection, MDA also results in significant public health benefits by reducing the burden of hydrocele in treated communities.

Impact of 10 years of diethylcarbamazine and ivermectin mass administration on infection and transmission of lymphatic filariasis.

The potential of repeated mass administration of diethylcarbamazine (DEC) and ivermectin to eliminate lymphatic filariasis has been examined in a study implemented in 10 villages with a population of 18415 in south India. During ten rounds of mass drug administration, 49-84% of the eligible population received treatment in different villages. Ten rounds of mass administration of DEC alone reduced the microfilaria (mf) prevalence and intensity by 93% and 97%, respectively, and the vector infection and infectivity rates by 91% and 89%, respectively. The corresponding figures with nine rounds of administration of ivermectin alone were 83%, 90%, 89% and 79%. Out of five villages in each treatment arm, the mf rate declined to

Changes in Wuchereria bancrofti infection in a highly endemic community following 10 rounds of mass administration of diethylcarbamazine.

Mass drug administration (MDA) is the principal strategy of the programme to eliminate lymphatic filariasis (LF). Evaluation of MDA in highly endemic 'sentinel' communities is necessary to understand its impact on LF infection. This study examined the changes in Wuchereria bancrofti infection following 10 rounds of annual mass administration of diethylcarbamazine (DEC) in a highly endemic community. The mean number of DEC treatments received per adult in the community was 7.4+/-2.0. Following 10 rounds of DEC administration, the number of microfilaria (mf) carriers fell from 565 to 55. None of the pre-MDA amicrofilaraemic individuals showed circulating filarial antigen (CFA). However, 54.5% of the pre-MDA microfilaraemic individuals were positive for CFA. All the pre-MDA high intensity mf carriers continued to be positive for CFA, and some of them also showed blood mf. These patients are the most difficult to be cured by MDA and were distributed in 8.2% of the households. All the children born during the last 7 years of the MDA programme were negative for CFA. The study suggests that six to seven DEC treatments per individual suppresses microfilaraemia, except in some people with heavy infection, and repeated MDA has very good potential to prevent infection in children.

A campaign of "communication for behavioural impact" to improve mass drug administrations against lymphatic filariasis: structure, implementation and impact on people's knowledge and treatment coverage.

In the mass drug administrations (MDA) that form the principal strategy of the Global Programme to Eliminate Lymphatic Filariasis, treatment coverages of at least 65%-80% will be needed if the programme is to be successful. In the Indian state of Tamil Nadu, where treatment coverages were typically <65%, a comprehensive strategy of advocacy and communication, called the "communication for behavioural impact" (COMBI) campaign, has been developed and implemented, in an attempt to improve treatment coverage. This strategy combined advocacy, aimed at state-, district- and village-level administrations, with communication activities targeted at individual communities. The main aim was to alter the behaviour of many of those included in the rounds of MDA, so that they would be more likely to accept and consume the diethylcarbamazine tablets offered to them. The COMBI campaign had two variants, COMBI(+) and the more intensive COMBI(+ +), each of which has been implemented in six districts. Both the variants included the "personal selling" of treatment, via door-to-door visiting by a total of 113,500 filaria-prevention assistants. These assistants were able to visit 34%-49% of the households in each target community. In the COMBI(+ +) districts, up to 44% and 38% of households received information on lymphatic filariasis and its elimination via television commercials and posters, respectively. Overall, 78% of the villages in the COMBI(+ +) districts and 33% of those in the COMBI(+) districts were considered to have had good exposure to the communication campaign. At the end of this campaign about 30% more people (than pre-campaign) believed that lymphatic filariasis could be eliminated and many of those targeted considered lymphatic filariasis to be a dreadful disease, knew that a particular day had been designated "Filaria Day", and thought that the tablets offered in MDA should be consumed to prevent or eliminate the disease. Apparently as the result of the COMBI campaign, drug consumption increased, from 33% of those living in endemic communities, to 37% in the COMBI(+) districts and to 49% in the COMBI(+ +). Coverages as high as 65%-73% were recorded among those who had had the maximum exposure to the communication campaign. These results indicate that the COMBI campaign favourably changed the perception and behaviour of the people towards the elimination of lymphatic filariasis. The costs of the COMBI(+) and COMBI(+ +) strategies were only U.S.$0.002 and U.S.$0.009 per capita, respectively.

Pattern of community compliance with spaced, single-dose, mass administrations of diethylcarbamazine or ivermectin, for the elimination of lymphatic filariasis from rural areas of southern India.

Current programmes to eliminate lymphatic filariasis (LF) are largely based on annual mass administrations of single doses of antifilarial drugs. The level and pattern of compliance by the target population are important determinants of the success of such mass drug administrations (MDA). Community compliance was therefore investigated during a study in southern India of the effects, on Wuchereria bancrofti microfilaraemia and transmission, of spaced MDA based on diethylcarbamazine (DEC) or ivermectin (IVM). During six rounds of MDA, the frequency of compliance in the target populations, in the five study villages given DEC and the five given IVM, ranged from 55%-77%. Analysis of the relevant cohort data indicated that about 30% of the villagers had complied with treatment during all six rounds, but 3.5% of those in the DEC arm and 4.0% of those in the IVM arm had never complied with treatment. Most of the villagers (>90%) had received treatment at least once, however, and >60% had each received treatment in at least four of the six rounds. Overall, there was a significant negative correlation (r=-0.78; P=0.008) between the size of the village, in terms of the number of villagers, and the mean frequency of compliance over the six rounds of MDA. The pattern of community compliance was found to be 'semi-systematic', laying between random and systematic. In terms of the elimination of LF, a semi-systematic pattern of compliance is worse than random compliance but better than systematic. The relevance of the levels and patterns of compliance to LF control or elimination is discussed.

Situation analysis in a large urban area of India, prior to launching a programme of mass drug administrations to eliminate lymphatic filariasis.

The main strategy now adopted for the elimination of lymphatic filariasis (LF) is based on mass drug administrations (MDA). Annual administration of antifilarial drugs to 65%-80% of the population at risk of the disease is believed to be necessary if LF is to be eliminated, at least as a public-health problem, within a reasonable time-frame. To facilitate the development of drug-delivery strategies that are sufficient to ensure such high treatment coverages in large urban areas, a situation analysis was undertaken in the Indian city of Chennai. The subjects interviewed came from households with high, moderate, low or very low incomes. A lack of information on the prevalence and socio-economic impact of the disease meant that LF was not viewed as a major pubic-health problem in the study area, even though cases of elephantiasis and hydrocele were detected in 2%-8% and 7%-20% of the households investigated. Overall, 40% of the interviewees from very-low-income households and 78% of those from middle-income households knew that (the parasite causing) elephantiasis was transmitted by mosquitoes. Only 4% of the subjects from high-income areas and 1% of those from low-income areas were aware that filarial infection was a major cause of hydrocele. Most of the subjects (>55% of each of the four socio- economic groups considered) felt that they were not at risk of developing elephantiasis. When specifically asked, only 35% of the subjects from high-income households but 84% of those from low-income households said that they would be willing to consume tablets of an antifilarial drug (diethylcarbamazine) in MDA to eliminate LF. It is therefore unclear whether high-income households in urban areas should be included in MDA programmes. The interviewees felt that an intensive campaign of information, education, communication and advocacy would be necessary if an effective MDA-based programme were to be implemented. Drug distribution through the health services was the most preferred option.Clearly, factors such as a lack of appreciation of the socio-economic impact of LF, a general belief that the risk of elephantiasis is low, doubts about the need to include all sectors of the eligible population in MDA, and a common dependence on private practitioners make successful MDA against LF in urban areas a challenging task. On the positive side, however, an urban population is often covered by a huge network of colleges, private practitioners, non-governmental organizations and residents' associations, and such networks provide new opportunities in the development of effective drug-delivery strategies.

Meta-analysis of age-prevalence patterns in lymphatic filariasis: no decline in microfilaraemia prevalence in older age groups as predicted by models with acquired immunity.

The role of acquired immunity in lymphatic filariasis is uncertain. Assuming that immunity against new infections develops gradually with accumulated experience of infection, models predict a decline in prevalence after teenage or early adulthood. A strong indication for acquired immunity was found in longitudinal data from Pondicherry, India, where Mf prevalence was highest around the age of 20 and declined thereafter. We reviewed published studies from India and Subsaharan Africa to investigate whether their age-prevalence patterns support the models with acquired immunity. By comparing prevalence levels in 2 adult age groups we tested whether prevalence declined at older age. For India, comparison of age groups 20-39 and 40+ revealed a significant decline in only 6 out of 53 sites, whereas a significant increase occurred more often (10 sites). Comparison of older age groups provided no indication that a decline would start at a later age. Results from Africa were even more striking, with many more significant increases than declines, irrespective of the age groups compared. The occurrence of a decline was not related to the overall Mf prevalence and seems to be a chance finding. We conclude that there is no evidence of a general age-prevalence pattern that would correspond to the acquired immunity models. The Pondicherry study is an exceptional situation that may have guided us in the wrong direction.

The dynamics of Wuchereria bancrofti infection: a model-based analysis of longitudinal data from Pondicherry, India.

This paper presents a model-based analysis of longitudinal data describing the impact of integrated vector management on the intensity of Wuchereria bancrofti infection in Pondicherry, India. The aims of this analysis were (1) to gain insight into the dynamics of infection, with emphasis on the possible role of immunity, and (2) to develop a model that can be used to predict the effects of control. Using the LYMFASIM computer simulation program, two models with different types of immunity (anti-L3 larvae or anti-adult worm fecundity) were compared with a model without immunity. Parameters were estimated by fitting the models to data from 5071 individuals with microfilaria-density measurement before and after cessation of a 5-year vector management programme. A good fit, in particular of the convex shape of the age-prevalence curve, required inclusion of anti-L3 or anti-fecundity immunity in the model. An individual's immune-responsiveness was found to halve in approximately 10 years after cessation of boosting. Explanation of the large variation in Mf-density required considerable variation between individuals in exposure and immune responsiveness. The mean life-span of the parasite was estimated at about 10 years. For the post-control period, the models predict a further decline in Mf prevalence, which agrees well with observations made 3 and 6 years after cessation of the integrated vector management programme.

The impact of six rounds of single-dose mass administration of diethylcarbamazine or ivermectin on the transmission of Wuchereria bancrofti by Culex quinquefasciatus and its implications for lymphatic filariasis elimination programmes.

Lymphatic filariasis (LF) is targeted for global elimination. Transmission interruption through repeated annual single-dose mass administration of anti-filarial drugs is the mainstay of the LF elimination strategy. This study examined the ability of six rounds of mass administration of diethylcarbamazine (DEC) or ivermectin (IVM) to interrupt transmission of Wuchereria bancrofti by Culex quinquefasciatus, the predominant parasite and vector species, respectively. After six rounds of mass drug administration (MDA), received by 54-75% of the eligible population (> or =15 kg body weight), the resting vector infection and infectivity rates fell by 83% and 79% in the DEC arm, 85% and 84% in the IVM arm and 31% and 45% in the placebo arm, respectively. The landing vector infection and infectivity rates fell by 83% and 94% in the DEC arm, 63% and 75% in the IVM arm and 1% each in the placebo arm, respectively. The filarial larval load per resting mosquito declined by 92% and 93% and per landing mosquito by 83% and 69% in the DEC and IVM arms, respectively. The annual infective biting rate (AIBR) fell from 735 to 93 (87%) in the DEC arm, 422 to 102 (76%) in the IVM arm and 472 to 398 (16%) in the placebo arm. The annual transmission potential (ATP) declined from 2514 to 125 (95%), 1212 to 241 (80%) and 1547 to 1402 (9%) in the DEC, IVM and placebo arms, respectively. However, mosquitoes with infection [microfilaria/larva 1/larva 2 (Mf/L1/L2)] were found in all study villages. Three of five villages in the IVM arm and two of five in the DEC arm recorded no resting mosquitoes with infective-stage (L3) larva. Although the ATP, after six rounds of MDA, fell substantially and remained at 125 and 241 in the DEC and IVM arms, respectively, the cumulative exposure to infective stage larvae (ATP) during the treatment period of 6 years was as high as 2995 in the DEC arm and 1522 in the IVM arm, because of considerable level of transmission during the initial (1-3) rounds of MDA. We conclude that (i) six rounds of MDA, even with 54-75% treatment coverage, can reduce LF transmission very appreciably; (ii) better treatment coverage and a few more rounds of MDA may achieve total interruption of transmission; (iii) high vector densities may partly nullify the reductions achieved in vector infection and infectivity rates by MDA and (iv) achievement of 'true zero' Mf prevalence in communities and 0% infection rate (mosquitoes with Mf/L1/L2) in mosquitoes may be necessary to totally interrupt Culex-transmitted LF.

The prevalences of Wuchereria bancrofti antigenaemia in communities given six rounds of treatment with diethylcarbamazine, ivermectin or placebo tablets.

The ICT filariasis card test was used to determine the prevalences of Wuchereria bancrofti antigenaemia among villagers in India. Prior to the tests, those living in the 15 study villages had been treated six times, in six rounds of mass treatment (with 54%-75% coverage) spread over 6 years, with single doses of diethylcarbamazine (five villages), ivermectin (five villages) or placebo (five villages). The corresponding overall prevalences (and ranges) of filarial antigenaemia were 20.2% (13.7%-28.6%), 22.6% (15.3%-34.3%) and 25.9% (22.6%-29.3%), respectively. The overall prevalence of antigenaemia in the villages where diethylcarbamazine (DEC) had been distributed (but not that in the 'ivermectin' villages) was significantly lower than that recorded in the 'placebo' villages (z =2.56; P <0.05). The prevalences of antigenaemia among the villagers aged 1-5 years (18.9%, 15.6% and 22.4% in the DEC, ivermectin and placebo villages, respectively) did not differ significantly with treatment (P >0.05). The results indicate that annual mass treatments based on DEC or ivermectin, with 54%-75% treatment coverage, may have only a limited effect on the prevalence of infection with adult W. bancrofti. The possible reasons for the antigenaemias observed are discussed.

The mosquito problem and type and costs of personal protection measures used in rural and urban communities in Pondicherry region, South India.

Personal protection measures have become an important tool against mosquito nuisance. The severity of mosquito nuisance and the type and costs of personal protection measures in the Pondicherry region in South India have been investigated, using a structured questionnaire. The number of respondents sampled was 300 in the urban area and 100 in rural areas. 87 and 63% of the urban and rural respondents, respectively, felt that mosquito nuisance was severe in their locality. 83% of the urban and 27% of the rural respondents are aware that mosquitoes transmit diseases and were able to name at least one mosquito-borne disease. All the neighbourhood shops in urban and a majority in rural areas stocked personal protection products. As many as 99.3 and 73% of the urban and rural respondents, respectively, were found to use personal-protection measures during some or all seasons of the year. Mosquito coils were the most widely used measure in both urban and rural areas, followed by vaporising mats in the former and electric fans in the latter areas. 48 and 40% in urban and rural areas, respectively, used personal-protection measures daily. In urban areas 46% used the measures in more than one room. Only a small proportion (3-14%) used bed nets. The average monthly expenditure on the measures was Rupees (Rs.) 62.17 (US$ 1.30) (range: Rs. 0.00-500.00) in urban areas and Rs. 8.03 (US$ 0.17) (range Rs. 0.00-45.00) in rural areas. Annual expenditure on personal protection measures in urban areas amounted to 0.63% of the per capita income. 73.7% of the respondents in urban areas expressed satisfaction with the protective effect of the measures used by them. However, 46.3% of the urban and 15% of the rural respondents felt that the personal-protection measures are harmful to health. Some of the perceived harmful effects are allergy, breathing problems, cough and head ache.