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Tanzania filariasis project: studies on microfilaraemia and selected clinical manifestations of Bancroftian filariasis.

In a total of 1977 males aged 5 years and over examined in 21 cluster samples on the coast of Tanzania, the overall rate for microfilariae of Wuchereria bancrofti was 32%. Hydrocoele and elephantiasis rates were 39% and 3%, respectively. The rates and severity of these 2 clinical manifestations increased in the older age groups. Both the microfilarial density and prevalence increased rapidly in the early age groups, followed by a levelling off and then a slight fall in old age. There was no association between microfilarial densities or rates and the overall prevalence of hydrocoele, but a negative association was demonstrated between microfilaraemia and hydrocoeles and elephantiasis. A comparison between the length of residence in an endemic area and the microfilarial and clinical sign rates showed evidence for the long incubation period for W. bancrofti and for the slow development of hydrocoeles and elephantiasis.

Adolescent↗

[Study on the transmission threshold of filariasis. Collaborating Research Group on the Transmission Threshold of Filariasis].

Twenty-one villages from ten provinces and one autonomous region with different mf rates in population and different levels of mean mf density per 60 microliters blood in positive cases and representative species of filaria and vector after DEC treatment were selected as study sites. In these villages a longitudinal investigation for a period of 3-5 years was carried out without adopting any control measure. The main results were: 1. Among 279 residual microfilaremia cases, 235 (84.2%) turned negative spontaneously and successively. The negative conversion rates were 86.6% (46/53) in malayan cases, 60.8% (28/46) in bancroftian cases after 3 years' follow-up, and 100% (29/29) in malayan cases, 87.4% (132/151) in bancroftian cases after 4-5 year's follow-up. Among 110 bancroftian cases followed-up to seven years, 109 (99.1%) turned negative. 2. Twenty-two new microfilaremia cases were detected, of which, 18 might be missed in previous blood examination, 4 might be new infection. 3. Mf rate in the population in twenty villages has been trending down, whereas in one village fluctuated around the original level. Among the 20 villages, no microfilaremia case was found in 7 villages. 4. The natural infection rates of filarial larvae and infective rates in mosquito vectors were in descending trend in most of these villages, and no filarial larva was found in 12 villages.(ABSTRACT TRUNCATED AT 250 WORDS)

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The argument for integrating vector control with multiple drug administration campaigns to ensure elimination of lymphatic filariasis.

BACKGROUND: There is a danger that mass drug administration campaigns may fail to maintain adequate treatment coverage to achieve lymphatic filariasis elimination. Hence, additional measures to suppress transmission might be needed to ensure the success of the Global Program for the Elimination of Lymphatic Filariasis. DISCUSSION: Vector control successfully eliminated lymphatic filariasis when implemented alone or with mass drug administration. Challenges to lymphatic filariasis elimination include uncertainty of the exact level and duration of microfilarial suppression required for elimination, the mobility of infected individuals, consistent non-participation of some infected individuals with mass drug administration, the possible development of anti-filarial drug resistance and treatment strategies in areas co-endemic with loasis. Integration of vector control with mass drug administration can address some of these challenges. The potential benefits of vector control would include: (1) the ability to suppress filariasis transmission without the need to identify all individual 'foci of infection'; (2) minimizing the risk of reestablishment of transmission from imported microfilaria positive individuals; and (3) decreasing the risk of dengue or malaria transmission where, respectively, Aedes or Anopheles are lymphatic filariasis vectors. SUMMARY: With adequate sustained treatment coverage, mass drug administration should meet the criteria for elimination of lymphatic filariasis. However, it may be difficult to sustain sufficiently high mass drug administration coverage to achieve lymphatic filariasis elimination in some areas, particularly, where Aedes species are the vectors. Since vector control was effective in controlling and even eliminating lymphatic filariasis transmission, integration of vector control with mass drug administration will ensure the sustainability of transmission suppression and thereby better ensure the success of national filariasis elimination programs. Although trials of some vector control interventions are needed, proven vector control strategies are ready for immediate integration with mass drug administration for many important vectors. Vector control is the only presently available additional lymphatic filariasis control measure with the potential for immediate implementation.

Journal Article↗

Filariasis surveillance at the post-control stage in China.

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.

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The spectrum of disease in lymphatic filariasis.

Lymphatic filariasis affects predominantly the poorer sector of a community, who can least afford to have the disease. According to an estimate by the World Health Organization in 1984, more than 90 million people are currently infected. It is postulated that the different disease manifestations of filariasis are caused by different host immune responses. An understanding of the clinical spectrum of lymphatic filariasis is essential for the effective treatment and control of the disease, and for correctly correlating clinical status with host immune responses. The disease should be divided into lymphatic filariasis caused by adult worms and occult filariasis due to hyper-responsiveness of the host against microfilariae. The acute stage of filariasis is characterized by episodic adenolymphangitis, followed by obstructive lesions one or more decades later. In brugian filariasis, adenolymphangitis is most commonly observed at the inguinal region, and elephantiasis predominantly involves the leg below the knee. In bancroftian filariasis, the lymphatics of the male genitalia are frequently affected, leading to epididymo-orchitis and hydrocele. Lymphatic filariasis runs an accelerated clinical course in previously unexposed adult migrants. Occult filariasis is not a disease of public health importance. It is characterized by lymphadenopathy, asthmatic bronchitis, hypereosinophilia, and an increase in the production of antibodies, especially immunoglobulin, against microfilarial antigens.

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The Elimination of Lymphatic Filariasis: A Strategy for Poverty Alleviation and Sustainable Development - Perspectives from the Philippines.

BACKGROUND: Within the Philippines areas endemic for lymphatic filariasis are in regions with the highest incidence of poverty. Out of a total of 79 provinces, 39 have a higher poverty incidence than the national average and 30 of these 39 provinces are endemic for lymphatic filariasis. DISCUSSION: Recognizing that provinces endemic for lymphatic filariasis (LF) are also the poorest provinces, the elimination of lymphatic filariasis in these areas presents significant opportunities to reduce poverty and inequalities in health. The implementation of an effective national programme for the elimination of lymphatic filariasis will provide means for sustainable development at national, local and community levels. SUMMARY: The elimination of lymphatic filariasis as a public health problem is a 20-year strategic plan for the world community, with the vision of all endemic communities free of transmission of lymphatic filariasis by 2020 and with the commitment to ensure the delivery of quality technologies and human services to eliminate lymphatic filariasis worldwide through a multi-stakeholder global alliance of all endemic countries. This global goal of elimination of lymphatic filariasis is a significant opportunity for partnerships - a world with less poverty through sustainable development and free from the scourge of lymphatic filariasis.

Journal Article↗

[Epidemiological characteristics and control of filariasis in Hunan Province].

Of 98 counties or cities in Hunan Province, 55 were endemic areas of filariasis. The average microfilaria rate was 5.64% (180,046/3,194,102), and the incidence of advanced filariasis, including elephantiasis and hydrocele was 3.29%. The number of filariasis patients in the whole province was estimated to be 1.63 million, comprising 1.25 million of microfilaremia cases, Culex fatigans and Anopheles hyrcanus sinensis were the major vectors of bancroftian and malayan filariasis respectively in the province. Control strategies concentrated on the elimination of infection source were implemented on the basis of extensive investigations, and the ensuing examination and treatment of filariasis cases in pilot areas prior to the implementation of province-wide filariasis control. Repeated blood examinations and medications for 3-4 times were carried out in hypo-endemic areas of malayan filariasis, whereas mass treatment with hetrazan-medicated salt containing 0.2% to 0.5% DEC was carried out in meso- and hyper-endemic areas of bancroftian filariasis as well as those situated in remote mountainous regions for six months. Subsequent evaluation and clearance checking showed that microfilaria rate of the whole province has already dropped to less than 1%. That filariasis was basically eliminated in Hunan was recognized by the Evaluation Mission Group sent by the Ministry of Public Health in 1986.

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The use of grid sampling methodology for rapid assessment of the distribution of bancroftian filariasis.

The recent World Health Assembly Resolution to eliminate lymphatic filariasis as a public health problem once more brings to the fore the need for reliable data for the effective planning of disease control programmes. Most countries do not have data on the distribution of lymphatic filariasis and are therefore not in the position to initiate control programmes based on sound baseline data. We tested in Ghana in 1998-99 a method for the Rapid Assessment of the Geographical Distribution of Bancroftian Filariasis (RAGFIL) that uses a spatial sampling grid with 50 km between sampled villages, rapid assessment surveys for filariasis prevalence in the sampled villages and spatial analysis to estimate the geographical distribution of filariasis throughout the study area. The prevalence contours obtained with the 50 x 50-km sampling grid were operationally similar to those obtained with a 25 x 25-km grid. The predicted prevalence was not statistically different from the sample survey prevalence in 57 independent villages and the 50 x 50-km grid appears adequate for rapid mapping of filariasis. For the purpose of filariasis mapping, the antigen test would seem a better diagnostic test than clinical examination for hydrocoele. We recommend that a regional approach to mapping be used because of the importance of cross-border foci as demonstrated by our findings from the north of Ghana. Application of the method will provide the minimal information required for effective planning of treatment programmes, and will facilitate estimation of the number of people to be treated. It will also help improve estimates of the number of people at risk and affected, and of the burden of disease due to lymphatic filariasis in Africa.

Adolescent↗

Differences in the frequency of cytokine-producing cells in antigenemic and nonantigenemic individuals with bancroftian filariasis.

Individuals with clinical manifestations of lymphatic filariasis may be currently infected or not. Twenty-five individuals from a Wuchereria bancrofti-endemic area of Brazil were classified as being asymptomatic microfilaremic individuals, antigenemic individuals with clinical filariasis, or nonantigenemic individuals with clinical filariasis. Intracellular cytokine staining of mitogen-stimulated peripheral blood mononuclear cells (PBMC) showed that the frequency of either gamma interferon (IFN-gamma)- or interleukin-4 (IL-4)-producing cells was higher in the nonantigenemic individuals with clinical filariasis than in the asymptomatic microfilaremic individuals (geometric means, 22.1 versus 10.7% [P = 0.02] and 2.9 versus 1.4% [P = 0.01], respectively). When the asymptomatic microfilaremic individuals and antigenemic individuals with clinical filariasis were grouped together to constitute all actively infected individuals, the frequency of IFN-gamma-producing cells was also lower than in the nonantigenemic individuals with clinical filariasis (P = 0.04). Likewise, the frequency of IL-4-producing cells in the actively infected individuals was also lower than in the nonantigenemic individuals with clinical filariasis (P = 0.02). No differences in the frequency of IFN-gamma-, IL-4-, or IL-5-producing cells in purified CD4 T lymphocytes were found among the groups. These findings suggest that the presence of antigenemia, which is an indicator of current active infection, is closely associated with the frequency of IFN-gamma- and IL-4-producing cells in lymphatic filariasis. The differences found in the frequency of cytokine-producing cells among the three groups appear to be due to a subset of cells other than CD4 T cells.

Adolescent↗