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A crossover study to evaluate the diversion of malaria vectors in a community with incomplete coverage of spatial repellents in the Kilombero Valley, Tanzania.
Parasit Vectors. 2016 08 15; 9:451.PV

Abstract

BACKGROUND

Malaria elimination is unlikely to occur if vector control efforts focus entirely on transmission occurring indoors without addressing vectors that bite outdoors and outside sleeping hours. Additional control tools such as spatial repellents may provide the personal protection required to fill this gap. However, since repellents do not kill mosquitoes it is unclear if vectors will be diverted from households that use spatial repellents to those that do not.

METHODS

A crossover study was performed over 24 weeks in Kilombero, Tanzania. The density of resting and blood-engorged mosquitoes and human blood index (HBI) of malaria vector species per household was measured among 90 households using or not using 0.03 % transfluthrin coils burned outdoors under three coverage scenarios: (i) no coverage (blank coils); (ii) complete coverage of repellent coils; and (iii) incomplete coverage of repellent and blank coils. Mosquitoes were collected three days a week for 24 weeks from the inside and outside of all participating households using mosquito aspirators. Paired indoor and outdoor human landing collections were performed in three random households for six consecutive nights to confirm repellent efficacy of the coils and local vector biting times.

RESULTS

The main vectors were Anopheles arabiensis and Anopheles funestus (sensu stricto), which fed outdoors, outside sleeping hours, on humans as well as animals. Anopheles arabiensis landings were reduced by 80 % by the spatial repellent although household densities were not reduced. The HBI for An. arabiensis was significantly higher among households without repellents in the incomplete coverage scenario compared to houses in the no coverage scenario (Odds ratio 1.71; 95 % CI: 1.04-2.83; P = 0.03). This indicated that An. arabiensis mosquitoes seeking a human blood meal were diverted from repellent users to non-users. The repellent coils did not affect An. funestus densities or HBI.

CONCLUSIONS

Substantial malaria vector activity is occurring outside sleeping hours in the Kilombero valley. Repellent coils provided some protection against local An. arabiensis but did not protect against local (and potentially pyrethroid-resistant) An. funestus. Pyrethroid-based spatial repellents may offer a degree of personal protection, however the overall public health benefit is doubtful and potentially iniquitous as their use may divert malaria vectors to those who do not use them.

Authors+Show Affiliations

Swiss Tropical and Public Health Institute, Socinstr. 57, Basel, CH-4002, Switzerland. mmaia@ihi.or.tz. University of Basel, St. Petersplatz 1, CH-4002, Basel, Switzerland. mmaia@ihi.or.tz. Ifakara Health Institute, P.O. Box 74, Bagamoyo, Pwani, United Republic of Tanzania. mmaia@ihi.or.tz.Ifakara Health Institute, P.O. Box 74, Bagamoyo, Pwani, United Republic of Tanzania. University of Glasgow, Institute of Biodiversity Animal Health and Comparative Medicine, Glasgow, G12 8QQ, UK.Ifakara Health Institute, P.O. Box 74, Bagamoyo, Pwani, United Republic of Tanzania.Ifakara Health Institute, P.O. Box 74, Bagamoyo, Pwani, United Republic of Tanzania.Ifakara Health Institute, P.O. Box 74, Bagamoyo, Pwani, United Republic of Tanzania.Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, 46556, USA.Swiss Tropical and Public Health Institute, Socinstr. 57, Basel, CH-4002, Switzerland. University of Basel, St. Petersplatz 1, CH-4002, Basel, Switzerland.Swiss Tropical and Public Health Institute, Socinstr. 57, Basel, CH-4002, Switzerland. University of Basel, St. Petersplatz 1, CH-4002, Basel, Switzerland. Ifakara Health Institute, P.O. Box 74, Bagamoyo, Pwani, United Republic of Tanzania.

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

27527601

Citation

Maia, Marta Ferreira, et al. "A Crossover Study to Evaluate the Diversion of Malaria Vectors in a Community With Incomplete Coverage of Spatial Repellents in the Kilombero Valley, Tanzania." Parasites & Vectors, vol. 9, 2016, p. 451.
Maia MF, Kreppel K, Mbeyela E, et al. A crossover study to evaluate the diversion of malaria vectors in a community with incomplete coverage of spatial repellents in the Kilombero Valley, Tanzania. Parasit Vectors. 2016;9:451.
Maia, M. F., Kreppel, K., Mbeyela, E., Roman, D., Mayagaya, V., Lobo, N. F., Ross, A., & Moore, S. J. (2016). A crossover study to evaluate the diversion of malaria vectors in a community with incomplete coverage of spatial repellents in the Kilombero Valley, Tanzania. Parasites & Vectors, 9, 451. https://doi.org/10.1186/s13071-016-1738-4
Maia MF, et al. A Crossover Study to Evaluate the Diversion of Malaria Vectors in a Community With Incomplete Coverage of Spatial Repellents in the Kilombero Valley, Tanzania. Parasit Vectors. 2016 08 15;9:451. PubMed PMID: 27527601.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - A crossover study to evaluate the diversion of malaria vectors in a community with incomplete coverage of spatial repellents in the Kilombero Valley, Tanzania. AU - Maia,Marta Ferreira, AU - Kreppel,Katharina, AU - Mbeyela,Edgar, AU - Roman,Deogratius, AU - Mayagaya,Valeriana, AU - Lobo,Neil F, AU - Ross,Amanda, AU - Moore,Sarah Jane, Y1 - 2016/08/15/ PY - 2016/03/15/received PY - 2016/08/03/accepted PY - 2016/8/17/entrez PY - 2016/8/17/pubmed PY - 2017/11/29/medline KW - Anopheles arabiensis KW - Anopheles funestus KW - Diversion KW - Kilombero Valley KW - Malaria KW - Mosquito coils KW - Resistance KW - Spatial repellents KW - Tanzania KW - Transfluthrin KW - Vector bionomics SP - 451 EP - 451 JF - Parasites & vectors JO - Parasit Vectors VL - 9 N2 - BACKGROUND: Malaria elimination is unlikely to occur if vector control efforts focus entirely on transmission occurring indoors without addressing vectors that bite outdoors and outside sleeping hours. Additional control tools such as spatial repellents may provide the personal protection required to fill this gap. However, since repellents do not kill mosquitoes it is unclear if vectors will be diverted from households that use spatial repellents to those that do not. METHODS: A crossover study was performed over 24 weeks in Kilombero, Tanzania. The density of resting and blood-engorged mosquitoes and human blood index (HBI) of malaria vector species per household was measured among 90 households using or not using 0.03 % transfluthrin coils burned outdoors under three coverage scenarios: (i) no coverage (blank coils); (ii) complete coverage of repellent coils; and (iii) incomplete coverage of repellent and blank coils. Mosquitoes were collected three days a week for 24 weeks from the inside and outside of all participating households using mosquito aspirators. Paired indoor and outdoor human landing collections were performed in three random households for six consecutive nights to confirm repellent efficacy of the coils and local vector biting times. RESULTS: The main vectors were Anopheles arabiensis and Anopheles funestus (sensu stricto), which fed outdoors, outside sleeping hours, on humans as well as animals. Anopheles arabiensis landings were reduced by 80 % by the spatial repellent although household densities were not reduced. The HBI for An. arabiensis was significantly higher among households without repellents in the incomplete coverage scenario compared to houses in the no coverage scenario (Odds ratio 1.71; 95 % CI: 1.04-2.83; P = 0.03). This indicated that An. arabiensis mosquitoes seeking a human blood meal were diverted from repellent users to non-users. The repellent coils did not affect An. funestus densities or HBI. CONCLUSIONS: Substantial malaria vector activity is occurring outside sleeping hours in the Kilombero valley. Repellent coils provided some protection against local An. arabiensis but did not protect against local (and potentially pyrethroid-resistant) An. funestus. Pyrethroid-based spatial repellents may offer a degree of personal protection, however the overall public health benefit is doubtful and potentially iniquitous as their use may divert malaria vectors to those who do not use them. SN - 1756-3305 UR - https://www.unboundmedicine.com/medline/citation/27527601/A_crossover_study_to_evaluate_the_diversion_of_malaria_vectors_in_a_community_with_incomplete_coverage_of_spatial_repellents_in_the_Kilombero_Valley_Tanzania_ L2 - https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-016-1738-4 DB - PRIME DP - Unbound Medicine ER -