Planning an implementation programme
Review existing literature
In most filariasis-endemic countries, some information on the occurrence of the disease already exists. This information may be found in:
• historical records;
• published and unpublished reports of filaria surveys;
• medical and health department records;
• theses and dissertations in university libraries, and
• hospital discharge data on repair of surgical hydrocoele.
• The existence and recognition of local names for hydrocoele and lymphoedema of the leg may also point to the occurrence of lymphatic filariasis within a particular area.
• Documentation on the vector(s) responsible for LF transmission in the country can be derived from studies by other vector control programmes or research or academic institutes; the distribution of the filaria vectors can aid in the development of the filaria endemicity map.
• Where appropriate, mapping for filariasis should be integrated with other health-related geographical information system (GIS) data.
The above steps should help identify areas which are definitely endemic and those for which more data are required, especially in areas bordering the definitely endemic areas. Further steps need to be taken to define endemicity in the grey areas. This can be undertaken rapidly and at low cost by administering a questionnaire.
Decide on an implementation unit (IU)
The degree of centralization of health services within a country will influence this decision. Therefore, even before developing a strategy to assess the geographical distribution of filarial infection, the national government should identify the smallest (lowest-level) administrative unit that will be responsible for implementing mass treatment (district, town, city block), within which everyone will be treated, regardless of infection status. The larger the IU, proportionately the fewer the resources that will be needed in the initial epidemiological assessment. Resources can thus be conserved for implementing the programme. However, if very large administrative units are chosen and the disease is confined to small areas of the administrative units, drugs and effort may be spent unnecessarily. The choice of the size of the IU is important, but when in doubt choose the larger IU. In most situations, the district would be the most feasible size for the IU.
Assessing distribution
Once Implementation Units are designated, the next step is to identify the units in which LF is endemic and in which mass chemotherapy is to be undertaken. This can be done in three steps:
• Reviewing the existing information on the distribution of LF.
• Collecting new information through a questionnaire and mapping implementation units according to three categories:- confirmed filaria-endemic units (red areas)
- confirmed non-endemic units (green areas)
- units contiguous to the confirmed filaria-endemic units and units for which adequate information is not available [categorized as doubtful units (grey areas)].
• Carrying out a survey in the grey areas to detect the presence of filarial antigenaemia in order to establish boundaries of filaria-endemic areas.
Diagnosis
To diagnose, the Filariasis Test Strip (FTS) is simple, sensitive and specific. The FTS, developed by AlereTM is a rapid diagnostic tool used for the qualitative detection of Wuchereria bancrofti antigen in human blood samples collected by finger stick. Both tests can detect infection within minutes and, unlike blood smears, can be carried out at any time of day.
Community treatment (mass drug administration)
The current strategy for interrupting transmission is an annual single co-administration of two drugs for at least five years. The two alternative regimens are: single doses of albendazole (400mg) plus Mectizan® (150-200 mg/kg/body wt) or single doses of albendazole (400mg) plus DEC (6mg/kg/body wt).
Albendazole, donated by GSK for LF prevention, is a well-established anti-parasitic treatment, given to an estimated 500-800 million people, mostly children, for intestinal infections over the past 20 years. The combination of albendazole with either Mectizan® or DEC has been proven to enhance the efficacy of the individual-drug treatments in reducing the numbers of parasites in the blood.
Mectizan® (generic name: ivermectin) is an oral anti-parasitic drug, discovered and developed by Merck & Co. Inc. which is effective against both LF and onchocerciasis. Mectizan® is provided free of charge by Merck & Co. Inc. for the treatment of onchocerciasis in all endemic countries and for LF in African countries where onchocerciasis and LF co-exist.
DEC, developed over 50 years ago, is an inexpensive and effective anti-filarial drug which is used to treat LF in many countries. However, DEC cannot be used in most of Africa because severe side reactions can occur when other infections, such as onchocerciasis (river blindness) are also present. DEC is now donated by Eisai Co. Ltd.
Alternative strategies are under investigation for specific situations. For example, in areas co-endemic with Loa loa where DEC and ivermectin cannot be used, twice yearly albendazole and the use of bednets is an already approved strategy and early studies have shown it to be effective. A further strategy recently recommended by WHO is triple drug therapy (IDA - Ivermectin, DEC and albendazole) to accelerate the global elimination of lymphatic filariasis where there is no onchocerciasis. Other strategies that are being considered to enhance the elimination of transmission include the use of different dose regimens of the above medicines.link is external