Changing patterns of malaria epidemiology between 2002 and 2010 in western kenya: The fall and rise of malaria

Guofa Zhou, Yaw A. Afrane, Anne M. Vardo-Zalik, Harrysone Atieli, Daibin Zhong, Peter Wamae, Yousif E. Himeidan, Noboru Minakawa, Andrew K. Githeko, Guiyun Yan

Research output: Contribution to journalArticle

92 Citations (Scopus)

Abstract

Background: The impact of insecticide treated nets (ITNs) on reducing malaria incidence is shown mainly through data collection from health facilities. Routine evaluation of long-term epidemiological and entomological dynamics is currently unavailable. In Kenya, new policies supporting the provision of free ITNs were implemented nationwide in June 2006. To evaluate the impacts of ITNs on malaria transmission, we conducted monthly surveys in three sentinel sites with different transmission intensities in western Kenya from 2002 to 2010. Methods and Findings: Longitudinal samplings of malaria parasite prevalence in asymptomatic school children and vector abundance in randomly selected houses were undertaken monthly from February 2002. ITN ownership and usage surveys were conducted annually from 2004 to 2010. Asymptomatic malaria parasite prevalence and vector abundances gradually decreased in all three sites from 2002 to 2006, and parasite prevalence reached its lowest level from late 2006 to early 2007. The abundance of the major malaria vectors, Anopheles funestus and An. gambiae, increased about 5-10 folds in all study sites after 2007. However, the resurgence of vectors was highly variable between sites and species. By 2010, asymptomatic parasite prevalence in Kombewa had resurged to levels recorded in 2004/2005, but the resurgence was smaller in magnitude in the other sites. Household ITN ownership was at 50-70% in 2009, but the functional and effective bed net coverage in the population was estimated at 40.3%, 49.4% and 28.2% in 2010 in Iguhu, Kombewa, and Marani, respectively. Conclusion: The resurgence in parasite prevalence and malaria vectors has been observed in two out of three sentinel sites in western Kenya despite a high ownership of ITNs. The likely factors contributing to malaria resurgence include reduced efficacy of ITNs, insecticide resistance in mosquitoes and lack of proper use of ITNs. These factors should be targeted to avoid further resurgence of malaria transmission.

Original languageEnglish (US)
Article numbere20318
JournalPloS one
Volume6
Issue number5
DOIs
StatePublished - May 27 2011

Fingerprint

Epidemiology
Kenya
Insecticides
malaria
Malaria
epidemiology
insecticides
Parasites
Ownership
parasites
ownership
bed nets
Anopheles funestus
Insecticide Resistance
Anopheles
school children
insecticide resistance
Health Facilities
Culicidae
households

All Science Journal Classification (ASJC) codes

  • Biochemistry, Genetics and Molecular Biology(all)
  • Agricultural and Biological Sciences(all)

Cite this

Zhou, Guofa ; Afrane, Yaw A. ; Vardo-Zalik, Anne M. ; Atieli, Harrysone ; Zhong, Daibin ; Wamae, Peter ; Himeidan, Yousif E. ; Minakawa, Noboru ; Githeko, Andrew K. ; Yan, Guiyun. / Changing patterns of malaria epidemiology between 2002 and 2010 in western kenya : The fall and rise of malaria. In: PloS one. 2011 ; Vol. 6, No. 5.
@article{1d8b3776e1bf4738aee93757d91fc48e,
title = "Changing patterns of malaria epidemiology between 2002 and 2010 in western kenya: The fall and rise of malaria",
abstract = "Background: The impact of insecticide treated nets (ITNs) on reducing malaria incidence is shown mainly through data collection from health facilities. Routine evaluation of long-term epidemiological and entomological dynamics is currently unavailable. In Kenya, new policies supporting the provision of free ITNs were implemented nationwide in June 2006. To evaluate the impacts of ITNs on malaria transmission, we conducted monthly surveys in three sentinel sites with different transmission intensities in western Kenya from 2002 to 2010. Methods and Findings: Longitudinal samplings of malaria parasite prevalence in asymptomatic school children and vector abundance in randomly selected houses were undertaken monthly from February 2002. ITN ownership and usage surveys were conducted annually from 2004 to 2010. Asymptomatic malaria parasite prevalence and vector abundances gradually decreased in all three sites from 2002 to 2006, and parasite prevalence reached its lowest level from late 2006 to early 2007. The abundance of the major malaria vectors, Anopheles funestus and An. gambiae, increased about 5-10 folds in all study sites after 2007. However, the resurgence of vectors was highly variable between sites and species. By 2010, asymptomatic parasite prevalence in Kombewa had resurged to levels recorded in 2004/2005, but the resurgence was smaller in magnitude in the other sites. Household ITN ownership was at 50-70{\%} in 2009, but the functional and effective bed net coverage in the population was estimated at 40.3{\%}, 49.4{\%} and 28.2{\%} in 2010 in Iguhu, Kombewa, and Marani, respectively. Conclusion: The resurgence in parasite prevalence and malaria vectors has been observed in two out of three sentinel sites in western Kenya despite a high ownership of ITNs. The likely factors contributing to malaria resurgence include reduced efficacy of ITNs, insecticide resistance in mosquitoes and lack of proper use of ITNs. These factors should be targeted to avoid further resurgence of malaria transmission.",
author = "Guofa Zhou and Afrane, {Yaw A.} and Vardo-Zalik, {Anne M.} and Harrysone Atieli and Daibin Zhong and Peter Wamae and Himeidan, {Yousif E.} and Noboru Minakawa and Githeko, {Andrew K.} and Guiyun Yan",
year = "2011",
month = "5",
day = "27",
doi = "10.1371/journal.pone.0020318",
language = "English (US)",
volume = "6",
journal = "PLoS One",
issn = "1932-6203",
publisher = "Public Library of Science",
number = "5",

}

Zhou, G, Afrane, YA, Vardo-Zalik, AM, Atieli, H, Zhong, D, Wamae, P, Himeidan, YE, Minakawa, N, Githeko, AK & Yan, G 2011, 'Changing patterns of malaria epidemiology between 2002 and 2010 in western kenya: The fall and rise of malaria', PloS one, vol. 6, no. 5, e20318. https://doi.org/10.1371/journal.pone.0020318

Changing patterns of malaria epidemiology between 2002 and 2010 in western kenya : The fall and rise of malaria. / Zhou, Guofa; Afrane, Yaw A.; Vardo-Zalik, Anne M.; Atieli, Harrysone; Zhong, Daibin; Wamae, Peter; Himeidan, Yousif E.; Minakawa, Noboru; Githeko, Andrew K.; Yan, Guiyun.

In: PloS one, Vol. 6, No. 5, e20318, 27.05.2011.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Changing patterns of malaria epidemiology between 2002 and 2010 in western kenya

T2 - The fall and rise of malaria

AU - Zhou, Guofa

AU - Afrane, Yaw A.

AU - Vardo-Zalik, Anne M.

AU - Atieli, Harrysone

AU - Zhong, Daibin

AU - Wamae, Peter

AU - Himeidan, Yousif E.

AU - Minakawa, Noboru

AU - Githeko, Andrew K.

AU - Yan, Guiyun

PY - 2011/5/27

Y1 - 2011/5/27

N2 - Background: The impact of insecticide treated nets (ITNs) on reducing malaria incidence is shown mainly through data collection from health facilities. Routine evaluation of long-term epidemiological and entomological dynamics is currently unavailable. In Kenya, new policies supporting the provision of free ITNs were implemented nationwide in June 2006. To evaluate the impacts of ITNs on malaria transmission, we conducted monthly surveys in three sentinel sites with different transmission intensities in western Kenya from 2002 to 2010. Methods and Findings: Longitudinal samplings of malaria parasite prevalence in asymptomatic school children and vector abundance in randomly selected houses were undertaken monthly from February 2002. ITN ownership and usage surveys were conducted annually from 2004 to 2010. Asymptomatic malaria parasite prevalence and vector abundances gradually decreased in all three sites from 2002 to 2006, and parasite prevalence reached its lowest level from late 2006 to early 2007. The abundance of the major malaria vectors, Anopheles funestus and An. gambiae, increased about 5-10 folds in all study sites after 2007. However, the resurgence of vectors was highly variable between sites and species. By 2010, asymptomatic parasite prevalence in Kombewa had resurged to levels recorded in 2004/2005, but the resurgence was smaller in magnitude in the other sites. Household ITN ownership was at 50-70% in 2009, but the functional and effective bed net coverage in the population was estimated at 40.3%, 49.4% and 28.2% in 2010 in Iguhu, Kombewa, and Marani, respectively. Conclusion: The resurgence in parasite prevalence and malaria vectors has been observed in two out of three sentinel sites in western Kenya despite a high ownership of ITNs. The likely factors contributing to malaria resurgence include reduced efficacy of ITNs, insecticide resistance in mosquitoes and lack of proper use of ITNs. These factors should be targeted to avoid further resurgence of malaria transmission.

AB - Background: The impact of insecticide treated nets (ITNs) on reducing malaria incidence is shown mainly through data collection from health facilities. Routine evaluation of long-term epidemiological and entomological dynamics is currently unavailable. In Kenya, new policies supporting the provision of free ITNs were implemented nationwide in June 2006. To evaluate the impacts of ITNs on malaria transmission, we conducted monthly surveys in three sentinel sites with different transmission intensities in western Kenya from 2002 to 2010. Methods and Findings: Longitudinal samplings of malaria parasite prevalence in asymptomatic school children and vector abundance in randomly selected houses were undertaken monthly from February 2002. ITN ownership and usage surveys were conducted annually from 2004 to 2010. Asymptomatic malaria parasite prevalence and vector abundances gradually decreased in all three sites from 2002 to 2006, and parasite prevalence reached its lowest level from late 2006 to early 2007. The abundance of the major malaria vectors, Anopheles funestus and An. gambiae, increased about 5-10 folds in all study sites after 2007. However, the resurgence of vectors was highly variable between sites and species. By 2010, asymptomatic parasite prevalence in Kombewa had resurged to levels recorded in 2004/2005, but the resurgence was smaller in magnitude in the other sites. Household ITN ownership was at 50-70% in 2009, but the functional and effective bed net coverage in the population was estimated at 40.3%, 49.4% and 28.2% in 2010 in Iguhu, Kombewa, and Marani, respectively. Conclusion: The resurgence in parasite prevalence and malaria vectors has been observed in two out of three sentinel sites in western Kenya despite a high ownership of ITNs. The likely factors contributing to malaria resurgence include reduced efficacy of ITNs, insecticide resistance in mosquitoes and lack of proper use of ITNs. These factors should be targeted to avoid further resurgence of malaria transmission.

UR - http://www.scopus.com/inward/record.url?scp=79956353796&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=79956353796&partnerID=8YFLogxK

U2 - 10.1371/journal.pone.0020318

DO - 10.1371/journal.pone.0020318

M3 - Article

C2 - 21629783

AN - SCOPUS:79956353796

VL - 6

JO - PLoS One

JF - PLoS One

SN - 1932-6203

IS - 5

M1 - e20318

ER -