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Loa loa vectors Chrysops spp.: perspectives on research, distribution, bionomics, and implications for elimination of lymphatic filariasis and onchocerciasis

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ABSTRACT

Background: Loiasis is a filarial disease caused Loa loa. The main vectors are Chrysops silacea and C. dimidiata which are confined to the tropical rainforests of Central and West Africa. Loiasis is a mild disease, but individuals with high microfilaria loads may suffer from severe adverse events if treated with ivermectin during mass drug administration campaigns for the elimination of lymphatic filariasis and onchocerciasis. This poses significant challenges for elimination programmes and alternative interventions are required in L. loa co-endemic areas. The control of Chrysops has not been considered as a viable cost-effective intervention; we reviewed the current knowledge of Chrysops vectors to assess the potential for control as well as identified areas for future research.

Results: We identified 89 primary published documents on the two main L. loa vectors C. silacea and C dimidiata. These were collated into a database summarising the publication, field and laboratory procedures, species distributions, ecology, habitats and methods of vector control. The majority of articles were from the 1950–1960s. Field studies conducted in Cameroon, Democratic Republic of Congo, Equatorial Guinea, Nigeria and Sudan highlighted that C. silacea is the most important and widespread vector. This species breeds in muddy streams or swampy areas of forests or plantations, descends from forest canopies to feed on humans during the day, is more readily adapted to human dwellings and attracted to wood fires. Main vector targeted measures proposed to impact on L. loa transmission included personal repellents, household screening, indoor residual spraying, community-based environmental management, adulticiding and larviciding.

Conclusions: This is the first comprehensive review of the major L. loa vectors for several decades. It highlights key vector transmission characteristics that may be targeted for vector control providing insights into the potential for integrated vector management, with multiple diseases being targeted simultaneously, with shared human and financial resources and multiple impact. Integrated vector management programmes for filarial infections, especially in low transmission areas of onchocerciasis, require innovative approaches and alternative strategies if the elimination targets established by the World Health Organization are to be achieved.

Electronic supplementary material: The online version of this article (doi:10.1186/s13071-017-2103-y) contains supplementary material, which is available to authorized users.

No MeSH data available.


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Picture of Chrysops silacea. Source: https://www.cdc.gov/parasites/loiasis/
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Fig2: Picture of Chrysops silacea. Source: https://www.cdc.gov/parasites/loiasis/

Mentions: Information on species identification were not commonly documented, however, from the articles published, both C. silacea and C. dimidiata have only been identified and distinguished from each other by morphological features [54, 61]. Overall, the two species are similar with a characteristic colour, longitudinal black stripes on abdomen, mottled wings and large head and eye (Fig. 2). In some parts of West Africa, C. silacea is known as the ‘Red Fly’ [61, 66, 102] due to its bright orange abdomen with short black stripes, which was considered distinct from C. dimidiata with its paler colour and broader longer stripes. Field workers were found to have no problem distinguishing them apart with noted typical ‘silacea’ and ‘dimidiata’ characteristics [21, 23, 66].Fig. 2


Loa loa vectors Chrysops spp.: perspectives on research, distribution, bionomics, and implications for elimination of lymphatic filariasis and onchocerciasis
Picture of Chrysops silacea. Source: https://www.cdc.gov/parasites/loiasis/
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5382514&req=5

Fig2: Picture of Chrysops silacea. Source: https://www.cdc.gov/parasites/loiasis/
Mentions: Information on species identification were not commonly documented, however, from the articles published, both C. silacea and C. dimidiata have only been identified and distinguished from each other by morphological features [54, 61]. Overall, the two species are similar with a characteristic colour, longitudinal black stripes on abdomen, mottled wings and large head and eye (Fig. 2). In some parts of West Africa, C. silacea is known as the ‘Red Fly’ [61, 66, 102] due to its bright orange abdomen with short black stripes, which was considered distinct from C. dimidiata with its paler colour and broader longer stripes. Field workers were found to have no problem distinguishing them apart with noted typical ‘silacea’ and ‘dimidiata’ characteristics [21, 23, 66].Fig. 2

View Article: PubMed Central - PubMed

ABSTRACT

Background: Loiasis is a filarial disease caused Loa loa. The main vectors are Chrysops silacea and C. dimidiata which are confined to the tropical rainforests of Central and West Africa. Loiasis is a mild disease, but individuals with high microfilaria loads may suffer from severe adverse events if treated with ivermectin during mass drug administration campaigns for the elimination of lymphatic filariasis and onchocerciasis. This poses significant challenges for elimination programmes and alternative interventions are required in L. loa co-endemic areas. The control of Chrysops has not been considered as a viable cost-effective intervention; we reviewed the current knowledge of Chrysops vectors to assess the potential for control as well as identified areas for future research.

Results: We identified 89 primary published documents on the two main L. loa vectors C. silacea and C dimidiata. These were collated into a database summarising the publication, field and laboratory procedures, species distributions, ecology, habitats and methods of vector control. The majority of articles were from the 1950–1960s. Field studies conducted in Cameroon, Democratic Republic of Congo, Equatorial Guinea, Nigeria and Sudan highlighted that C. silacea is the most important and widespread vector. This species breeds in muddy streams or swampy areas of forests or plantations, descends from forest canopies to feed on humans during the day, is more readily adapted to human dwellings and attracted to wood fires. Main vector targeted measures proposed to impact on L. loa transmission included personal repellents, household screening, indoor residual spraying, community-based environmental management, adulticiding and larviciding.

Conclusions: This is the first comprehensive review of the major L. loa vectors for several decades. It highlights key vector transmission characteristics that may be targeted for vector control providing insights into the potential for integrated vector management, with multiple diseases being targeted simultaneously, with shared human and financial resources and multiple impact. Integrated vector management programmes for filarial infections, especially in low transmission areas of onchocerciasis, require innovative approaches and alternative strategies if the elimination targets established by the World Health Organization are to be achieved.

Electronic supplementary material: The online version of this article (doi:10.1186/s13071-017-2103-y) contains supplementary material, which is available to authorized users.

No MeSH data available.


Related in: MedlinePlus