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Lymphatic filariasis elimination programme in Assam, India, needs change in mass drug administration strategy to target the focus of infection

© 2018 Indian Journal of Medical Research, published by Wolters Kluwer Medknow for Director-General, Indian Council of Medical Research In spite of commendable progress made by India towards the elimination of lymphatic filariasis (LF), the envisaged target 2015 could not be achieved. In 2004, LF elimination programme was launched in 255 endemic districts of 16 States and five Union Territories of India. Initially diethylcarbamazine (DEC) was given under MDA and later on in 2006 albendazole was added with DEC in MDA. In December 2015, of the 255 endemic districts under MDA, 222 districts have reported microfilaria (mf) rate below one per cent, and in 53 districts, MDA was stopped as they reported a break in the transmission cycle of the parasite successfully and passed Transmission Assessment Survey (TAS)1. Sixty eight endemic districts are ready to enter into TAS, whereas others are still tackling with poor drug compliance and other operational issues2.

LF is endemic in the State of Assam 3 . The situation of LF in the remaining seven northeastern States (Arunachal Pradesh, Manipur, Meghalaya, Mizoram, Nagaland, Sikkim and Tripura) is not known. No LF survey has been carried out except in some parts of Tripura and Sikkim. Although limited survey report of Tripura could not confirm indigenous transmission, findings of Sikkim confirmed LF prevalence and possibility of local transmission in the eastern district of the State 4 .
Earlier reports reveal the presence of bancroftian as well as brugian filariasis in Assam [5][6][7][8] . Several studies on LF prevalence, intervention, transmission, drug trial and mf periodicity have been conducted by the ICMR-Regional Medical Research Centre, Dibrugarh, at Assam, and have documented the problem of LF in the State 9-16 . Findings indicated that LF was mostly confined amongst tea garden workers of Assam.
As per national guidelines of lymphatic filariasis elimination programme 17 , site selection process for MDA is based on line listing (i.e. searching for elephantiasis, lymphoedema and hydrocele cases by trained health workers) from each district. Normally, this is done on the basis of feedback received from health workers of each Community Health Centres (CHC)/Primary Health Centres (PHCs)/ mini PHCs of the district. Based on the finding/reporting of the clinical cases, district will be declared as endemic or non-endemic for LF. From each endemic district, accordingly, four sentinel sites (where clinical cases were reported) and four spot check (random) sites without consideration of clinical cases of LF are chosen. In Assam, drug coverage in MDA was poor (25.42%, 2004) initially but improved in subsequent rounds (90.66%, 2014) 19 . The reported drug coverage includes drugs given directly to the people during the visit of drug distributor and also drugs given to the family members for those who were not present at the time of drug distribution. In this process, it is difficult to estimate the actual intake/consumption of drug at the community level. However, drug compliance survey on post-MDA done has reported improvement in the actual drug compliance 20  In Assam, mf rate is low (below 1%) in urban population. Moreover, rural population other than the tea garden workers also shows low mf rate (<1%) similar to the urban population. However, tea garden workers' population accounts for 96.39 per cent of total mf positive cases, whereas non-tea garden rural population contributes only 3.61 per cent 23 . This situation creates two important issues to LF elimination programme of Assam. Initially, what could be the implementation unit of MDA? Then how the actual target population can be enumerated and ensured for MDA coverage?
As per the national guidelinesof LF elimination 2 , district is the implementation unit of MDA. A district will only be considered eligible for MDA if it records mf rate >1 per cent in night blood survey in any of the selected sites (four sentinel and four random sites covering 500 participants for each site making a total of 4000 blood smears). The selection of sentinel sites is done on the basis of clinical cases reported during the line listing of filariasis cases (elephantiasis and hydrocele) and will not be changed throughout the monitoring, whereas random sites are chosen without consideration of the presence of clinical case from the study locations and will be changed at each time of survey. The chance of inclusion of tea garden workers in the process of selection of random site is fifty per cent.
Let us look at this approach taking an example of a district of Assam which has typical urban and rural population. In urban population (negligible tea worker population), situation of LF prevalence is very low (<1%). The rural population is comprised of people of mixed communities including local people and tea worker community. The tea garden workers which are a part of rural population account for a maximum number of mf carriers 23,24 . This tea garden population which is scattered in the district constitutes hotspot locations often remained undetected during the filaria survey. Therefore, while considering the eligibility of a district for MDA, this tea garden worker population (hotspot) is a vital factor. In this regard, during the selection process for night blood survey, if tea garden workers do not fall in the selected sites (eight locations), and as a result, a district may report quite low mf rate (below 1%) and will not be eligible for MDA. However, tea garden worker population of the same district was found to possess as high as 7.41 per cent mf rate even after six rounds of MDA 24 . Now, the point of concern is that, though such a district will not qualify for MDA, a sizeable population (22.88%) of the district such as Tinsukia (not under MDA) will require MDA 25 .
This situation is unlike of the LF hotspot areas of other States of India where a few places report such a situation and can be dealt with focal MDA 26,27 . Districts such as Tinsukia, Dibrugarh, Charaideo, Sivasagar, Jorhat, Biswanath, Golaghat and Sonitpur are the main tea cultivating districts of upper Assam and possess plenty of tea gardens which deploy more than 10 lakhs of tea garden workers in tea industry. In Assam, a total number of big tea gardens are over 767, and if small tea gardens (84577) are also included, total workforce engaged in tea industry will be over 30 lakhs 28 . This distribution of tea garden population (15-20%) is not confined to a particular geographical area of the State, but it is scattered in the districts, and as such, all these areas may not be included in the mf survey. Thus, it may not contribute significantly to keep the mf rate above one per cent at district level although many tea gardens may continue to harbour mf rate more than one per cent 24 . Instead of geographically defining focus of LF hotspot in Assam, we intend to consider the high-risk tea garden population as foci irrespective to their distribution in the State.
The currently available data from the State Government of Assam as well as Government of India may depict that LF elimination programme in Assam is in the state of completion as out of nine districts under MDA only two have shown mf rate >1 per cent during 2014 18 . Moreover, in a recent TAS, these two districts may also report low antigenemia level in 6-7 yr old children, and thus MDA might have been discontinued. However, real situation may differ from these observations because of heterogeneous distribution of LF in tea garden and non-tea garden populations. In case TAS was conducted in non-tea garden population, it may pass the TAS, but infection may remain >one per cent in tea garden worker population. Therefore, it is high time to target whole tea garden population irrespective of endemicity status. Almost all the big tea estates possess hospital facility for their workers. Utilization of this facility for MDA programme will not incur any drug distribution cost. Mop-up rounds may also be effectively tackled by the tea garden management that will not only reduce the cost of the drug distribution but also ensure high drug compliance rate amongst tea garden workers. A quick decision on site-specific strategy is required for tea garden worker population of Assam, and if it is found successful, this could be advocated in similar situations elsewhere in the country for successful LF elimination programme.
In conclusion, the following strategy may be adapted for successful elimination of LF in Assam: (i) Instead of district as implementation unit, PHCs may be regarded as implementation unit for LF elimination; (ii) Involvement of tea estate owners and worker community in the MDA programme; (iii) Programme managers must ensure covering of all tea garden worker population under MDA irrespective to the endemicity status of the PHC; and (iv) Biannual dose of MDA with DEC and albendazole may be adapted as it has shown better compliance and will also reduce the span of MDA 29 .

Conflicts of Interest:
None.