Molecular xenomonitoring as a post-MDA surveillance tool for global programme to eliminate lymphatic filariasis: Field validation in an evaluation unit in India

Abstract

Background Lymphatic filariasis (LF) is targeted for elimination by the year 2020. As of 2017, 67 of the 72 endemic countries have implemented annual Mass Drug Administration (MDA) for interrupting LF transmission. Transmission Assessment Survey (TAS) is the recommended protocol to evaluate the impact of MDA and to decide when to stop MDA in an Evaluation Unit (EU, population �2 million). As the human infection levels go down with repeated MDA rounds, it becomes a challenge to select the appropriate survey methods to assess transmission interruption. This study validates a standard protocol for molecular xenomonitoring of infection in vectors (MX) at an EU as a complementary tool for TAS to stop MDA and its utility for post-MDA or post-validation surveillance. Methodology The study was conducted in Cuddalore district, Tamil Nadu, India, which was found eligible for TAS after 15 annual rounds of MDA (4 with DEC alone and 11 with DEC plus albendazole). The district was divided into two EUs as per the TAS protocol and one EU was randomly selected for the study. A two-stage cluster design vector sampling, developed and validated at a sub-district level, was implemented in 30 randomly selected clusters in the EU. Female Culex quinquefasciatus were collected placing gravid traps overnight (1800-0600 hrs) inside the premises of systematically selected households. Pools of 20-25 bloodfed, semi-gravid and gravid Cx. quinquefasciatus were subjected to real-time quantitative PCR (polymerase chain reaction) assay for detecting Wuchereria bancrofti DNA. Pool infection rate (% of pools positive for W. bancrofti DNA), and the estimated prevalence of W. bancrofti DNA in mosquitoes and its 95% confidence interval were calculated. Additionally, in these 30 clusters, microfilaria (Mf) survey among individuals >5 years old was carried out.

Lymphatic filariasis epidemiology in Samoa in 2018: Geographic clustering and higher antigen prevalence in older age groups

“…Heterogeneity (clustering) observed between and within PSUs and households also leads to consideration of different sampling strategies including spatially explicit sampling and prediction [42], adaptive or snowball sampling [43], and the use of markers that are potentially more sensitive than Ag or Mf e.g. anti-filarial antibodies [27,41,44], molecular xenomonitoring of mosquitoes [45][46][47][48], or combinations of these.…”

Potential strategies for strengthening surveillance of lymphatic filariasis in American Samoa after mass drug administration: Reducing ‘number needed to test’ by targeting older age groups, hotspots, and household members of infected persons

“…opportunistic screening at workplaces or clinics [4]), it is potentially possible to achieve the desirable combination of low NNTest and low cost. In American Samoa [16], Sri Lanka [8], and India [47], molecular xenomonitoring of mosquitoes has also been shown to potentially provide earlier and more sensitive signals of transmission than TAS, and could be useful for informing more targeted surveillance. However, molecular xenomonitoring requires access to entomological expertise for mosquito identification and a laboratory for molecular testing, which may be beyond the reach of many developing countries.…”

Molecular xenomonitoring of diurnally subperiodic Wuchereria bancrofti infection in Aedes (Downsiomyia) niveus (Ludlow, 1903) after nine rounds of Mass Drug Administration in Nancowry Islands, Andaman and Nicobar Islands, India

“…However, most of the Nicobarese go into the forest daily to collect forest products like firewood and their availability for blood sampling during the daytime remains uncertain. In such situations, monitoring LF infection in the population at risk via mosquitoes (MX) offers a key pathway for illustrating possible transmission as it has been recommended as an instrument for observing the impact of MDA on LF transmission [5,6,[16][17][18][19]. MX protocol has already been developed for W. bancrofti parasite and other vector combinations [16,17,19].…”

“…This study carried out MX as a supplementary measure to assess the impact of MDA. Mf prevalence <1% would provide better yield for surveillance by methods like MX when it is difficult to sample human blood [5,7,18]. There are two components of MX, collection of vector mosquitoes and performing molecular assay.…”

“…Transmission Assessment Survey (TAS) is the recommended protocol to evaluate the impact of the programme and take a decision on stopping the intervention [4]. Recently, molecular xenomonitoring (MX) has been demonstrated to be a potential surveillance tool to supplement TAS for different parasite and vector combinations [5][6][7].…”