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

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de Souza, Dziedzom K., Ansumana, Rashid, Sessay, Santigie, Conteh, Abu, Koudou, Benjamin, Rebollo, Maria P., Koroma, Joseph, Boakye, Daniel A. and Bockarie, Moses (2015) 'The impact of residual infections on Anopheles-transmitted Wuchereria bancrofti after multiple rounds of mass drug administration'. Parasites & Vectors, Vol 8, e488.

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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.

Item Type: Article
Additional Information: The electronic version of this article is the complete one and can be found online at: http://www.parasitesandvectors.com/content/8/1/488
Subjects: QX Parasitology > Helminths. Annelida > QX 203 Nematoda
QX Parasitology > Insects. Other Parasites > QX 515 Anopheles
WA Public Health > Preventive Medicine > WA 110 Prevention and control of communicable diseases. Transmission of infectious diseases
WA Public Health > Health Problems of Special Population Groups > WA 395 Health in developing countries
WC Communicable Diseases > Tropical and Parasitic Diseases > WC 880 Filariasis and related conditions (General)
Faculty: Department: Biological Sciences > Department of Tropical Disease Biology
Biological Sciences > Vector Biology Department
Digital Object Identifer (DOI): https://doi.org/10.1186/s13071-015-1091-z
Depositing User: Lynn Roberts-Maloney
Date Deposited: 20 Oct 2015 10:21
Last Modified: 06 Feb 2018 13:10
URI: https://archive.lstmed.ac.uk/id/eprint/5364

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