Background
Why the entomological inoculation rate (EIR)?
Index | What is Measured | Advantages | Disadvantages |
---|---|---|---|
Entomological Inoculation Rate (EIR)
| Infectious bites per unit time (usually per year) | Direct reflection of vector control and antigametocytocidal drugs | - No standard protocols - Variability in methodologies - Few trained specialists |
Parasite Rate (PR)
| Proportion of the population found to carry asexual parasites in RBCs; can also assess gametocyte rates; by age group | Direct reflection of inoculations, immunity, and treatment effectiveness in humans | - Microscopy "gold standard"; lacks sensitivity - Prone to technical efforts - Changes may occur following environmental and control factors |
Annual Parasite Index (API)
| Number of parasite infections in a well-defined geographical area; usually per 1,000 persons per year | Direct reflection of all prevention and control effects on humans | - Depends on active case detection system, which is often poor |
Spleen Rate (SR)
| Proportion of children 2-9 years of age with a palpable spleen | Non-invasive, indirect way of measuring impact of malaria on spleen | - Variability in examiners; many causes of splenomegaly - Point prevalence measurements can vary/change rapidly |
What is the EIR and how is it measured?
Vector control interventions against malaria
Methods for evaluating the effect of vector control on EIRs
Results
Insecticide-treated nets (ITN)
Location/Year Study Done/Reference | Insecticide | Mosquito | Method | EIR | Parasite Rate |
---|---|---|---|---|---|
Tanzania: highland hamlets (altitudes 784 - 1148 m) and lowland hamlets (199-300 m) October 1998-August 2000 [20] | [0.02] g alphacypermethrin/m2 nets not re-treated during study | An. gambiae s.l., An. funestus and An.marshallii s.l. | light traps, pyrethrum spray, window exit traps and ELISA | Infectious bites/person/year Highland: Control = 10.4 ITN = 3.2 Lowland: Control = 148.6 ITN = 37.5 Highland =
69% Reduction
Lowland =
75% Reduction
| Highlands: 6 months-2 years: Control = 54.1% ITN = 31.4% 2-5 years: Control = 73% ITN = 44.3% 6-12 years: Control = 67.7% ITN = 49.4% Lowlands: 6 months-2 years: Control = 82.9% ITN = 63.1% 2-5 years: Control = 88.8% ITN = 78.3% 6-12 years: Control = 83.3% ITN = 80.6% Highlands = 36% Reduction Lowlands = 13% Reduction |
Lake Victoria shore in Western Kenya January 1997-February 2000 [19] | [0.5] g permethrin/m2 nets re-treated every 6-11 months | An. gambiae and An. funestus | pyrethrum spray sheet collection and ELISA | Infectious bite/person/month Control = 0.93 ITN = 0.08
91% Reduction
|
Not reported
|
North East Tanzania 1997-1998 [21] | [0.02] g alphacypermethrin/m2 or [0.1] g lambdacyhalothrin/m2 | An. gambiae s.l., An. funestus, An. marshallii and cx. quinquefasciatus | light traps and ELISA | Infectious bites/person/night Control = 3.24 alphacypermethrin = 0.153 lambdacyhalothrin = 0.140 alphacypermethrin = 95% Reduction lambdacyhalothrin = 97% Reduction | Rates of re-infection with asexual malaria parasites after treatment with chlorproguanil-dapsone: Control = 30.8% alphacypermethrin = 8.0% lambdacyhalothrin = 7.5% alphacypermethrin = 74% Reduction lambdacyhalothrin = 76% Reduction |
North-east Tanzania 1995-1996 [25] | [0.01] g lambdacyhalothrin/m2 for two villages [0.02] g lambdacyhalothrin/m2 for two villages nets re-treated after 7 months | An. gambiae and An. Funestsus | light traps, window exit traps, pyrethrum spray collection and ELISA | Infectious bites/person/night 1995: Control = 1.04 ITN = 1.48 1996: Control = 0.773 ITN = 0.08 1995 = 42% Increase 1996 = 90%Reduction |
Not reported
|
Western Kenya March-June 1990 and 1991 (high transmission season) [22] | [0.5] g permethrin/m2 nets re-treated October 1990 |
An. Gambiae s.s.
| night biting collections and ELISA | Infectious bites/person/night 1990 high transmission season: Control = 0.47 ITN = 0.21 1991 high transmission season: Control = 0.36 ITN = 0.09 1990 = 55% Reduction 1991 = 75% Reduction | Incidence of Plasmodium falciparum parasitemia ≥ 2,500/mm2 in children less than six years old 1990 high transmission season: Control = 135 (94) ITN = 77 (53) 1991 high transmission season: Control = 64(82) ITN = 51(64) 1990 = 43% Reduction 1991 = 20% Reduction |
Northern Guadalcanal, Solomon Islands November 1987-June 1988 [26] | [0.5] g permethrin/m2 nets re-treated August 1987 | An. farauti and An. Puctulatus | Human landing catch and ELISA | Infectious bites/person/night Control = 2.204 ITN = 0.129
94% Reduction
|
P. falciparum
Control = 29% ITN = 21%
P. vivax
Control = 12% ITN = 14% P. falciparum = 28% Reduction P. vivax = 17% Increase |
Indoor residual spraying (IRS)
Location/Year Study Done/Reference | Insecticide | Mosquito | Method | EIR | Parasite Rate |
---|---|---|---|---|---|
North-east Tanzania 1995-1996 [25] | [0.03] g lambdacyhalothrin/m2 re-sprayed 7-8 months after initial spray | An. gambiae and An. funestsus | light traps, window exit traps, pyrethrum spray collection and ELISA | Infectious bites/person/night 1995: Control = 1.04 IRS = 0.98 1996: Control = 0.773 IRS = 0.057 1995 = 5.7% Reduction 1996 = 93% Reduction |
Not reported
|
Northern Guadalcanal, Solomon Islands November 1987-June 1988 [26] | [2] g DDT/m2 | An. farauti and An. puctulatus | Human landing catch and ELISA | Infectious bites/person/night Control = 2.204 IRS = 0.9675
56% Reduction
|
P. falciparum
Control = 29% IRS = 46%
P. Vivax
Control = 12% IRS = 9% P. falciparum =
59% Increase
P. vivax =
25% Reduction
|
Garki, Nigeria September 1969-February 1976 [23] | [2] g propoxur/m2 re-sprayed every 2 months | An. Gambiae s.l. and An. funestus | Human landing collection, pyrethrum spray collection, exit trap collection, outdoor resting collection and ELISA | Infectious bites/person/wet season (wet season 1972: May 22-Oct. 22 1973: June 18-Nov. 4) Control: Village 1: 1972 = 17 1973 = 21 Village 2: 1972 = 25 1973 = 28 IRS: Village 3: 1972 = 0 1973 = 10 Village 4: 1972 = 3 1973 = 4 1972 = 93% Reduction 1973 = 71.4%Reduction |
P. falciparum
Control 1972 = 43.3% 1973 = 47.5% IRS 1972 = 36.8% 1973 = 35.0%
P. malariae
Control 1972 = 13.0% 1973 = 11.19% IRS 1972 = 13.3% 1973 = 13.3%
P. falciparum
1972 =
15% Reduction
1973 =
26% Reduction
P. malariae
1972 = 2.3% Increase 1973 = 19% Increase |
Source reduction (larval control)
EIR analysis
Integrated vector management (IVM)
Conclusions
Conclusions and future research directions
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Researchers should conduct more EIR studies in relation to vector control interventions; there are only nine studies that measure the impact of vector control interventions on the EIR.
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Researchers must standardize EIR methods to allow comparisons between studies. EIR percent changes were calculated for comparisons of different studies. If researchers agreed on a standard EIR time frame measurement, then individuals could directly compare different studies.
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Researchers should include background information about communities in their studies. The EIR is influenced by factors such as altitude, population density, rainfall, socio-cultural attitudes and behaviour, as well as current malaria control actions and their impact on human infection and disease. Additionally, researchers should include information about the coverage in intervention groups. Among the studies in this paper, the Garki project was the only study that reported level of coverage. These details are often missing from articles on EIR studies and they are essential for comparing different studies.
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It is necessary to conduct long term (>1 year) studies to measure the sustainability of the intervention's impact. If researchers had conducted the Garki project for only one year, they would have a false sense of confidence in the impact of IRS for their site.
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Increased research in source reduction and integrated vector management studies are strongly advised, particularly for urban, peri-urban, and epidemic-prone areas. Integrated vector management provides an approach that makes the most use out of existing tools. Only two studies were found that used ITNs and SR, one of which was a theoretical analysis [5, 31]. Researchers should conduct an IVM study with all three vector control interventions to measure their additive or synergistic effect.
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Measurement of the EIR should also be coordinated with parasitological, clinical, and meteorological indices, assessed at the same time and in the same place to reflect the most accurate picture of transmission. These factors are interrelated, however, researchers have yet to conduct a study that takes all these factors into account.
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There must be a focus on building entomological operational and research capacity. Figure 5 illustrates vector surveillance capacities in national malaria control programmes and research institutions in 38 African countries. Only South Africa, Algeria, and Cameroon have a high entomology capacity [32]. This figure is based on data from 2006, so there may have been improvements since then. The President's Malaria Initiative (PMI), the Global Fund for AIDS, Tuberculosis and Malaria, and other public health programmes have made major investments in vector control interventions, yet we lack trained researchers to conduct the work. Accomplishing the goals defined by these ambitious programmes requires a highly skilled, supervised, and supported team of entomology and vector control specialists in addition to a large cadre of scientists, public health, and operational specialists in all malaria disciplines.