Presence of Filarial DNA in Vectors

Xenomonitoring of black flies to confirm serologic threshold for onchocerciasis elimination mapping

To determine the appropriate serologic threshold(s) to be used to initiate MDA for onchocerciasis.

Countries: Ethiopia
Diseases: Onchocerciasis

Xenomonitoring of black flies to confirm serologic threshold for onchocerciasis elimination mapping

To determine the appropriate serologic threshold(s) to be used to initiate MDA for onchocerciasis

Countries: Malawi
Diseases: Onchocerciasis

Impact of Malaria Vector Control & Status of Lymphatic Filariasis Transmission in the Lake Zone of Tanzania

To assess filarial exposure in the study population and mosquito infection status prior to and after the start of intensified malaria control interventions.

Countries: Tanzania

TAS Strengthening in American Samoa

To evaluate strategies to improve the sensitivity of the TAS for detecting evidence of recent lymphatic filariasis transmission in an evaluation unit (EU). The TAS Strengthening Study in American Samoa is designed to assess additional indicators that may be added to the current TAS platform in order to strengthen the resulting stopping or surveillance decisions. A comprehensive analysis will be conducted to understand the correlation between antigen and antibody in adults and children with the mosquito data. A spatial analysis looking at microfoci of infection will also be conducted.  Xenomonitoring work to assess Aedes mosquitoes is underway.

Preliminary Findings and Lessons Learned

The ultimate goal of this study is to strengthen the existing TAS platform so that the programs can be more confident with their stopping and surveillance decisions.   In order to strengthen the existing TAS platform we need to better understand which target population(s) and diagnostic indicator(s) are best-suited for identifying areas with persistent transmission that is not expected to cease on its own, knowing that the answer may vary according the primary vector and stage of the program.  In the selected sites a community-based TAS was conducted using the standard sampling of 6-7 year olds while a community TAS (individuals >8 years) was conducted concurrently.  All samples were tested via FTS and DBS (for Wb123 ELISA).  In these same communities a molecular xenomonitoring study will take place and the mosquitoes will be tested for filarial DNA to relate back to the human specimens.  To date human sampling has been completed in all sites and laboratory analysis of the specimens is complete. Mosquito collection has been completed in Haiti and Tanzania and the PCR analysis has been completed in Haiti and is planned for Tanzania (pending the arrival of a new PCR machine).  In American Samoa xenomonitoring has been delayed due to weather conditions and arbovirus outbreaks; work is expected to commence spring 2018.

Countries: American Samoa

TAS Strengthening in Haiti

To evaluate strategies to improve the sensitivity of the TAS for detecting evidence of recent lymphatic filariasis transmission in an evaluation unit (EU). The TAS Strengthening Study in Haiti is designed to assess additional indicators that may be added to the current TAS platform in order to strengthen the resulting stopping or surveillance decisions. A comprehensive analysis will be conducted to understand the correlation between antigen and antibody in adults and children with the mosquito data. A spatial analysis looking at microfoci of infection will also be conducted.  Xenomonitoring work to assess Culex mosquitoes will be conducted in the same sites as the human sampling. 

Preliminary Findings and Lessons Learned

The ultimate goal of this study is to strengthen the existing TAS platform so that the programs can be more confident with their stopping and surveillance decisions.   In order to strengthen the existing TAS platform we need to better understand which target population(s) and diagnostic indicator(s) are best-suited for identifying areas with persistent transmission that is not expected to cease on its own, knowing that the answer may vary according the primary vector and stage of the program.  In the selected sites a community-based TAS was conducted using the standard sampling of 6-7 year olds while a community TAS (individuals >8 years) was conducted concurrently.  All samples were tested via FTS and DBS (for Wb123 ELISA).  In these same communities a molecular xenomonitoring study will take place and the mosquitoes will be tested for filarial DNA to relate back to the human specimens.  To date human sampling has been completed in all sites and laboratory analysis of the specimens is complete. Mosquito collection has been completed in Haiti and Tanzania and the PCR analysis has been completed in Haiti and is planned for Tanzania (pending the arrival of a new PCR machine).  In American Samoa xenomonitoring has been delayed due to weather conditions and arbovirus outbreaks; work is expected to commence spring 2018.

Countries: Haiti

TAS Strengthening in Tanzania

To evaluate strategies to improve the sensitivity of the TAS for detecting evidence of recent lymphatic filariasis transmission in an evaluation unit (EU). The TAS Strengthening Study in Tanzania is designed to assess additional indicators that may be added to the current TAS platform in order to strengthen the resulting stopping or surveillance decisions. A comprehensive analysis will be conducted to understand the correlation between antigen and antibody in adults and children with the mosquito data. A spatial analysis looking at microfoci of infection will also be conducted. Because the EU is also endemic for onchocerciasis, the new Ov16 monoplex RDT was used in the field. The Wb123 and Ov16 antibodies were assessed via ELISA in the NIMR lab in Tanga and the results will soon be compiled.  Xenomonitoring work to assess Culex and Anopheles mosquitoes, as well as black flies, is underway.

Preliminary Findings and Lessons Learned

The ultimate goal of this study is to strengthen the existing TAS platform so that the programs can be more confident with their stopping and surveillance decisions.   In order to strengthen the existing TAS platform we need to better understand which target population(s) and diagnostic indicator(s) are best-suited for identifying areas with persistent transmission that is not expected to cease on its own, knowing that the answer may vary according the primary vector and stage of the program.  In the selected sites a community-based TAS was conducted using the standard sampling of 6-7 year olds while a community TAS (individuals >8 years) was conducted concurrently.  All samples were tested via FTS and DBS (for Wb123 ELISA).  In these same communities a molecular xenomonitoring study will take place and the mosquitoes will be tested for filarial DNA to relate back to the human specimens.  To date human sampling has been completed in all sites and laboratory analysis of the specimens is complete. Mosquito collection has been completed in Haiti and Tanzania and the PCR analysis has been completed in Haiti and is planned for Tanzania (pending the arrival of a new PCR machine).  In American Samoa xenomonitoring has been delayed due to weather conditions and arbovirus outbreaks; work is expected to commence spring 2018.

Countries: Tanzania

Molecular Xenomonitoring for Lymphatic Filariasis in Bangladesh

Mass drug administration (MDA) programs have dramatically reduced lymphatic filariasis (LF) incidence in many areas around the globe, including Bangladesh. Post-treatment surveillance activities as recommended by WHO include repeated transmission assessment surveys (TAS) among children and ongoing surveillance to detect new foci of transmission and collect data on infection trends in the general population. The contribution of molecular xenomonitoring (MX, or detection of filarial DNA in mosquitoes) to confirm the interruption of transmission during the post-treatment surveillance phase has not been well defined. There is also a need to better understand the relationship between the prevalence of W. bancrofti DNA in mosquitoes and infection in humans.

Countries: Bangladesh

Correlation of Xenomonitoring and LF-Antibody Responses as Measures of Transmission in American Samoa

Determine the utility of xenomonitoring and serological assessments for the detection of residual transmission

Countries: American Samoa

Development and validation of sampling strategies for xenomonitoring of infection in Culex vector by PCR as a surveillance tool for assessing post-MDA lymphatic filariasis transmission

Develop and validate sampling strategies for monitoring vector infection that would be useful to evaluate the success of LF-elimination programmes.

Findings and Lessons Learned:

This represents a follow-up to a longitudinal study with data collection in 2010 and 2012 (previous funding) and now with a third time point in 2015. At all 3 time points a rigorous mosquito sampling protocol was applied and the results were analyzed to detect filarial DNA by PCR. To test the reproducibility of the results, at each time point the survey teams conducted two independent, sequential samples of approximately 11,000 mosquitoes each. In addition to surveying the entire PHC area, a nested hotspot survey was conducted in areas where there has been historically high transmission. One very important outcome of this study is the development of a standardized protocol for sampling culex mosquitoes that is statistically rigorous and reproducible. The study showed that MX can be a valuable tool for monitoring decreasing prevalence over-time. The authors propose a threshold of 0.5% in culex be used to measure 0% Ag prevalence in children for stopping MDA.

Countries: India