Population Dynamics of Major Malaria Vectors and the

1363
Population Dynamics of Major Malaria Vectors and the Impact
of Indoor Residual Spraying on Entomological Inoculation Rate
in Nasarawa State, North Central Nigeria
November 2014
Petrus U. Inyama , Lazarus M. Samdi , Henry Nsa , Nduka O. Iwuchukwu , Lena Kolyada , Aklilu Seyoum , Dereje Dengela , Bradford Lucas , Funto Adewusi , Joseph Ifeanyi Okeke , Christen Fornadel
1
1
1
1
1
1
1
1
1
1
2
President’s Malaria Initiative (PMI) Africa Indoor Residual Spraying (AIRS) Project, Abt Associates; 2USAID/President’s Malaria Initiative
1
Abstract
The President’s Malaria Initiative Africa Indoor Residual Spraying (PMI AIRS) Project, implemented by
Abt Associates, carried out spray operations for two years in Nasarawa Eggon and Doma Local
Government Areas of Nasarawa State, Nigeria, from 2012-2013. Taxonomic keys and molecular tools
were used to identify the predominant vectors responsible for malaria transmission in the study area,
and entomological inoculation rates (EIRs) were calculated before and after intervention. Mosquitoes
were identified morphologically and by molecular methods using polymerase chain reaction (PCR).
The Plasmodium falciparum circumsporozoïte indexes were measured by Enzyme-Linked
Immunosorbent Assay (ELISA) and the EIRs were calculated for the three areas. A total of 2,539 Anopheles mosquitoes were caught in intervention and control sites. A subsample of 1,265 Anopheles mosquitoes was randomly selected for PCR analysis. Morphological analysis indicated
that 1,174 (92.8%) were An. gambiae s.l., while the remaining were An. funestus (3.6%), An. pharoensis (2.8%) and An. squamosus (0.8%). PCR analysis of the Anopheles gambiae s.l. revealed a
predominance of An. gambiae s.s (68.5%), while 29.9% were An. arabiensis. At baseline, ELISAs
showed that P. falciparum sporozoite infection rates were 1.7% in An. gambiae s.s. and 0.6% in An.
arabiensis. There was a significant difference between the sporozoite rate of An. gambiae s.s. and An.
arabiensis (χ2=8.696, p<0.0032, df=1). Baseline EIR was 1.31 infective bites/person/night (bpn) in
Doma, 0.16 in N/Eggon and 0.13 in Lafia, including both indoor and outdoor collections. After the IRS
intervention, EIR was reduced to 0.9 in Doma and 0.11 in N/Eggon, while it remained the same at the
control area in Lafia at 0.13 bpn. There was a significant difference in EIR reduction (p<0.0001)
between the intervention and control sites. Although ELISA tests incriminated An. gambiae s.s. as the
predominant vector responsible for transmission of malaria in the study area, An. arabiensis was also
found to be sporozoite positive. An. funestus group were not incriminated in malaria transmission
possibly due to small sample size. After intervention, EIRs significantly decreased in the intervention
areas. These findings provide information on the relative roles of the main malaria vectors in the
study areas and the impact of indoor residual spraying on malaria transmission.
Results and Discussion
Table 1. Species Composition, CSP, and EIRs in Doma, Nasarawa Eggon and Lafia LGAs, Nasarawa State, North Central Nigeria.
(MBR–man biting rate)
Background
The PMI AIRS Project conducted indoor residual spraying (IRS) in
Nasarawa Eggon and Doma Local Government Areas (LGA) of
Nasarawa State, Nigeria, to reduce malaria-associated morbidity
and mortality. A total of 62,592 structures were sprayed in the
second year. To measure IRS program impact on malaria vectors,
the sibling species composition, proportion infected with
Plasmodium sporozoites and entomological inoculation rates
(EIRs) were determined in the two intervention and control areas.
Intervention
Area
Intervention
Area
Materials and Methods
Morphological keys were used to identify the vectors responsible
for malaria transmission, and EIRs were calculated before and after
intervention. Predominant sibling species were identified by
molecular methods using polymerase chain reaction (PCR). The
Plasmodium falciparum circumsporozoïte protein (CSP) indexes
were measured by Enzyme-Linked Immunosorbent Assay (ELISA)
and the EIRs were calculated.
Intervention
Area
Intervention
Area
From March 2013 to April 2014, a total of 29,849 mosquitoes were collected
from the three LGAs. Of these, 19,483 were morphologically identified as
Anopheles mosquitoes which indicated that 18,930 (97.2%) were An. gambiae
s.l., 80 (0.4%) were An. funestus, 120 (0.6%) were An. pharoensis, 81 (0.4%)
were An. squamosus, 165 (0.8%) were An. coustani, 105 (0.5%) were An. nili, 1
(0.01%) was An. rufipes and 1 (0.01%) was An. azani. A proportionally
representative subsample of 3,293 mosquitoes were analyzed using PCR out of
which 2,341 mosquitoes were further analyzed using ELISA. PCR Results
indicated that 2,760 (83.8%) were An. gambiae s.s, with an average sporozoite
rate of 3.2% as the predominant vector in all three LGAs while 313 (9.5%) were
An. arabiensis with a sporozoite rate of 0.63% present only in Doma LGA.
About 6.7% of the samples analyzed were PCR negative with no diagnostic
bands. A significant difference was observed between An. gambiae s.s. and An.
arabiensis in the area (χ2 = 113.38 df = 1 P< 0.0001). EIR was significantly higher
in the control area (Lafia) compared to both intervention areas of Nassarawa
Eggon and Doma (χ2= 48.1, df=1, P<0.0001; χ2 = 386.7 , df=1, P<0.0001). Of the
two intervention areas EIR was significantly higher in Doma compared to
Nassarawa Eggon (χ2 = 180.5 , df=1, P<0.0001). Although ELISA tests found An.
gambiae s.s. to be the predominant vector responsible for malaria transmission
in the study area, An. arabiensis was also found to be sporozoite positive.
Conclusions
EIR were significantly reduced in the intervention areas post-spraying compared to pre-spraying unlike in the control area which was unchanged. These findings
provide information on the relative roles of the main malaria vectors found in the study areas and the impact of indoor residual spraying on malaria transmission.
Acknowledgments
We wish to thank all technicians who participated in the entomological surveillance activities as well as the Nigeria Institute of Medical Research, Yaba, Lagos, for conducting the molecular analysis.
This work was funded by the President’s Malaria Initiative.
www.pmi.gov
www.africairs.net
[email protected]
www.abtassociates.com

Download Report