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The impact of residual infections on Anopheles-transmitted Wuchereria bancrofti after multiple rounds of mass drug administration.

de Souza DK, Ansumana R, Sessay S, Conteh A, Koudou B, Rebollo MP, Koroma J, Boakye DA, Bockarie MJ - Parasit Vectors (2015)

Bottom Line: Thus, this study was undertaken to assess the importance of these areas in implementation units (districts) where microfilaria (MF) positive individuals could not be found during the mid-term assessment after three rounds of mass drug administration.The results indicated the presence of MF infected children in Pujehun district.Nevertheless, our results showed that the transmission was contained in a small area.

View Article: PubMed Central - PubMed

Affiliation: Noguchi Memorial Institute for Medical Research, University of Ghana, Legon, Ghana. ddesouza@noguchi.ug.edu.gh.

ABSTRACT

Background: Many countries have made significant progress in the implementation of World Health Organization recommended preventive chemotherapy strategy, to eliminate lymphatic filariasis (LF). However, pertinent challenges such as the existence of areas of residual infections in disease endemic districts pose potential threats to the achievements made. Thus, this study was undertaken to assess the importance of these areas in implementation units (districts) where microfilaria (MF) positive individuals could not be found during the mid-term assessment after three rounds of mass drug administration.

Methods: This study was undertaken in Bo and Pujehun, two LF endemic districts of Sierra Leone, with baseline MF prevalence of 2 % and 0 % respectively in sentinel sites for monitoring impact of the national programme. Study communities in the districts were purposefully selected and an assessment of LF infection prevalence was conducted together with entomological investigations undertaken to determine the existence of areas with residual MF that could enable transmission by local vectors. The transmission Assessment Survey (TAS) protocol described by WHO was applied in the two districts to determine infection of LF in 6-7 year old children who were born before MDA against LF started.

Results: The results indicated the presence of MF infected children in Pujehun district. An. gambiae collected in the district were also positive for W. bancrofti, even though the prevalence of infection was below the threshold associated with active transmission.

Conclusions: Residual infection was detected after three rounds of MDA in Pujehun--a district of 0 % Mf prevalence at the sentinel site. Nevertheless, our results showed that the transmission was contained in a small area. With the scale up of vector control in Anopheles transmission zones, some areas of residual infection may not pose a serious threat for the resurgence of LF if the prevalence of infections observed during TAS are below the threshold required for active transmission of the parasite. However, robust surveillance strategies capable of detecting residual infections must be implemented, together with entomological assessments to determine if ongoing vector control activities, biting rates and infection rates of the vectors can support the transmission of the disease. Furthermore, in areas where mid-term assessments reveal MF prevalence below 1 % or 2 % antigen level, in Anopheles transmission areas with active and effective malaria vector control efforts, the minimum 5 rounds of MDA may not be required before implementing TAS. Thus, we propose a modification of the WHO recommendation for the timing of sentinel and spot-check site assessments in national programs.

No MeSH data available.


Related in: MedlinePlus

Modification of the WHO recommendation [1] for timing of sentinel and spot-check site assessments in national programmes. * Likely, but not necessary, to be conducted regardless of assessment results
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Related In: Results  -  Collection

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Fig2: Modification of the WHO recommendation [1] for timing of sentinel and spot-check site assessments in national programmes. * Likely, but not necessary, to be conducted regardless of assessment results

Mentions: From this study and other reports from elsewhere, we conclude that the existence of areas of residual transmission will not necessarily lead to the spread of Anopheles transmitted LF infection, where the vectors exhibit facilitation. What should be emphasized is the value of xenomonitoring in determining if ongoing vector control activities, biting rates and infection rates of the vectors can support the transmission of the disease. Additional control strategies may then be implemented based on the evidence obtained from the xenomonitoring surveys in these areas. Furthermore, it may not be necessary to complete the minimum 5 rounds of MDA before implementing TAS, when mid-term assessments reveal MF prevalence below 1 % or 2 % antigen level, in Anopheles transmission areas with active and effective malaria vector control efforts. Implementing 2 additional rounds of MDA before TAS in these areas will require significant resources that can better be directed to other areas with more pressing needs. Thus we propose a modification (Fig. 2) of the WHO recommendation for the timing of sentinel and spot-check site assessments in national programs [1], depending on whether LF endemic areas have a history of Ivermectin treatment and/or implement vector control strategies which may differ in various countries, through ITN/LLIN distribution or Indoor Residual Spray.Fig. 2


The impact of residual infections on Anopheles-transmitted Wuchereria bancrofti after multiple rounds of mass drug administration.

de Souza DK, Ansumana R, Sessay S, Conteh A, Koudou B, Rebollo MP, Koroma J, Boakye DA, Bockarie MJ - Parasit Vectors (2015)

Modification of the WHO recommendation [1] for timing of sentinel and spot-check site assessments in national programmes. * Likely, but not necessary, to be conducted regardless of assessment results
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4581406&req=5

Fig2: Modification of the WHO recommendation [1] for timing of sentinel and spot-check site assessments in national programmes. * Likely, but not necessary, to be conducted regardless of assessment results
Mentions: From this study and other reports from elsewhere, we conclude that the existence of areas of residual transmission will not necessarily lead to the spread of Anopheles transmitted LF infection, where the vectors exhibit facilitation. What should be emphasized is the value of xenomonitoring in determining if ongoing vector control activities, biting rates and infection rates of the vectors can support the transmission of the disease. Additional control strategies may then be implemented based on the evidence obtained from the xenomonitoring surveys in these areas. Furthermore, it may not be necessary to complete the minimum 5 rounds of MDA before implementing TAS, when mid-term assessments reveal MF prevalence below 1 % or 2 % antigen level, in Anopheles transmission areas with active and effective malaria vector control efforts. Implementing 2 additional rounds of MDA before TAS in these areas will require significant resources that can better be directed to other areas with more pressing needs. Thus we propose a modification (Fig. 2) of the WHO recommendation for the timing of sentinel and spot-check site assessments in national programs [1], depending on whether LF endemic areas have a history of Ivermectin treatment and/or implement vector control strategies which may differ in various countries, through ITN/LLIN distribution or Indoor Residual Spray.Fig. 2

Bottom Line: Thus, this study was undertaken to assess the importance of these areas in implementation units (districts) where microfilaria (MF) positive individuals could not be found during the mid-term assessment after three rounds of mass drug administration.The results indicated the presence of MF infected children in Pujehun district.Nevertheless, our results showed that the transmission was contained in a small area.

View Article: PubMed Central - PubMed

Affiliation: Noguchi Memorial Institute for Medical Research, University of Ghana, Legon, Ghana. ddesouza@noguchi.ug.edu.gh.

ABSTRACT

Background: Many countries have made significant progress in the implementation of World Health Organization recommended preventive chemotherapy strategy, to eliminate lymphatic filariasis (LF). However, pertinent challenges such as the existence of areas of residual infections in disease endemic districts pose potential threats to the achievements made. Thus, this study was undertaken to assess the importance of these areas in implementation units (districts) where microfilaria (MF) positive individuals could not be found during the mid-term assessment after three rounds of mass drug administration.

Methods: This study was undertaken in Bo and Pujehun, two LF endemic districts of Sierra Leone, with baseline MF prevalence of 2 % and 0 % respectively in sentinel sites for monitoring impact of the national programme. Study communities in the districts were purposefully selected and an assessment of LF infection prevalence was conducted together with entomological investigations undertaken to determine the existence of areas with residual MF that could enable transmission by local vectors. The transmission Assessment Survey (TAS) protocol described by WHO was applied in the two districts to determine infection of LF in 6-7 year old children who were born before MDA against LF started.

Results: The results indicated the presence of MF infected children in Pujehun district. An. gambiae collected in the district were also positive for W. bancrofti, even though the prevalence of infection was below the threshold associated with active transmission.

Conclusions: Residual infection was detected after three rounds of MDA in Pujehun--a district of 0 % Mf prevalence at the sentinel site. Nevertheless, our results showed that the transmission was contained in a small area. With the scale up of vector control in Anopheles transmission zones, some areas of residual infection may not pose a serious threat for the resurgence of LF if the prevalence of infections observed during TAS are below the threshold required for active transmission of the parasite. However, robust surveillance strategies capable of detecting residual infections must be implemented, together with entomological assessments to determine if ongoing vector control activities, biting rates and infection rates of the vectors can support the transmission of the disease. Furthermore, in areas where mid-term assessments reveal MF prevalence below 1 % or 2 % antigen level, in Anopheles transmission areas with active and effective malaria vector control efforts, the minimum 5 rounds of MDA may not be required before implementing TAS. Thus, we propose a modification of the WHO recommendation for the timing of sentinel and spot-check site assessments in national programs.

No MeSH data available.


Related in: MedlinePlus