Am. J. Trop. Med. Hyg., 78(2), 2008, pp. 248–250
Copyright © 2008 by The American Society of Tropical Medicine and Hygiene
Short Report: Rapid Control of Malaria by Means of Indoor Residual Spraying of
Alphacypermethrin in the Democratic Republic of São Tomé and Príncipe
Lien Fen Tseng, Wen Chun Chang, Maria Conceição Ferreira, Cheng Hua Wu, Herodes Sacramento Rampão,
and Jih Ching Lien*
The Anti-Malaria Team of Taiwan, Medical Mission to São Tomé and Príncipe, São Tomé and Príncipe; Centro Nacional de
Endemias (CNE), Democratic Republic of São Tomé and Príncipe; Institute of Preventive Medicine, National Defense Medical
Center, Sanhsia, Taipei County, Taiwan 237
Abstract. A nationwide yearly cycle of indoor residual spraying (IRS) with a pyrethroid, alphacypermethrin, at a
dosage of 50 mg/m2 was instituted in 2004 in the Democratic Republic of São Tomé and Príncipe. Rates of IRS
acceptance were high, varying from 82% to 95% for dwellings and outhouses. Epidemiologic surveys of the children < 9
years of age before and after the first IRS cycle revealed a rapid reduction in malaria. Overall prevalence of malaria
parasitemia for all districts was lowered from 20.1% to 2.8% at 12 months after the first IRS and reached 0.7% at 8
months after the second IRS. Longer insecticidal persistence was found on wood than on cement with alphacypermethrin.
United States, the Soviet Union, Europe, and Taiwan, and it
also reduced the malaria incidence rate significantly in Southeast and South Asia, southern Africa, and South America.6
At present, IRS is still considered as one of the most effective
and economical measures of malaria control in the world.6 In
Pakistan, a single round of IRS with alphacypermethrin at a
dosage of 25 mg active ingredient per square meter of surface
area was demonstrated to be effective for the entire transmission season.7
We report herein the achievements so far made by means
of IRS with alphacypermethrin for effective control of malaria in DRSTP. Yearly cycles of nationwide IRS campaigns
with the pyrethroid insecticide, alphacypermethrin (10% suspension concentrate), at 50 mg/m2, were initiated in DRSTP.
São Tomé Island is administratively divided into 6 districts,
and Príncipe Island is an autonomous region (Figure 1). For
IRS, 48 workers were recruited and trained for the operation
in Príncipe, and 42 workers, including foremen, were recruited and trained for the operation in São Tomé. The first
yearly cycle of spraying campaign was initiated on October 25
and was completed on November 11, 2004, in Príncipe, and
various districts of São Tomé were treated between December 2004 and October 2005 as shown in Table 1. The acceptance rate of IRS for dwellings and outhouses varied from
81.9% to 94.7% (av. 87.24%) with population coverage of
93.8%.
For parasitological assessment, thick and thin blood smears
were taken immediately before spraying from random
samples of children < 9 years of age without reference to any
malaria symptoms at a selected locality for each district. The
assessment was carried out once every 4 months. In addition
to this active surveillance, clinical records were also collected
by Centro Nacional de Endemias (CNE) for general understanding of the epidemiology of malaria in the country.
The results of parasitological assessment of the children < 9
years of age regardless of presence of any malaria symptoms
before the IRS campaign and 12 months after the first spraying showed that the overall prevalence of malaria parasitemia
for all districts was reduced from 20.1% to 2.8% at 12 months
after the first IRS, which was reduced further to 0.7% at 8
months after the second IRS (Table 1).
Bioassays showed the residual efficacy of alphacypermethrin to last for at least 424 days when the pyrethroid was
The Democratic Republic of São Tomé and Príncipe
(DRSTP) is situated 220 km off the Africa continent, west of
Gabon in the Gulf of Guinea, with a total land area of 1001
km2 and a population of 150,000 inhabitants. Malaria has
been endemic, with ≈71% of the human population infected
with malaria parasites in some districts, and malaria accounted for 32% of national morbidity in 2000 and 47.8% in
2002. All 4 species of human malaria are present at different
levels.1 In 1979 hematological surveys showed that 74% of
malaria infections were from Plasmodium falciparum, 15.8%
from Plasmodium vivax, 0.6% from Plasmodium malariae,
and 9.6% from P. vivax + P. falciparum.2 The only vector is
Anopheles gambiae s.s., the forest cytoform, and it is largely
confined to coastal areas, being virtually absent at altitudes
> 200 m.3 In the early 1980s, the malaria control campaign
with IRS using DDT successfully reduced malaria prevalence
from 19.2% to 0.6%1,4; however, because of financial and
administrative problems, the IRS campaign was suspended,
and malaria outbreaks occurred in 1985 and 1986, causing
high malaria prevalence and mortality.1,4
There is no ideal solution to the problem of malaria control;
DDT house spraying has its limitations, and there is a continuing need for operational research to improve the costeffectiveness of this approach.5 To institute more active ways
of vector control to fight malaria in São Tomé and Principe,
authorities from DRSTP and Taiwan agreed to initiate a pilot
study. The study was carried out in 2003 with 3 methods of
intervention, that is, indoor residual spraying (IRS) with alphacypermethrin at a dosage with 50 mg/m2, nocturnal fogging of pirimiphos-methyl at 100 g/hectare, and larval control
with an insect growth regulator (IGR), pyriproxyfen, at 2
g/m3. Unpublished data of the pilot study demonstrate that
IRS is an effective method for malaria control in DRSTP.
Thus, it was then determined to carry out a nationwide IRS
campaign with alphacypermethrin once per year, commencing from 2004.
Although IRS with DDT has been criticized because of
supposed environmental damage, it is indeed an effective
method to eliminate malaria in many countries, such as the
* Address correspondence to Jih Ching Lien, Institute of Preventive
Medicine, National Defense Medical Center, P.O. Box 90048-700
Sanhsia, Taipei County, Taiwan 237. E-mail: [email protected]
248
20.1% N ⳱ 1354
5.3% N ⳱ 1143
3.3% N ⳱ 997
2.8% N ⳱ 1077
1.4% N ⳱ 1016
0.7% N ⳱ 975
0.6% N ⳱ 687
2.0% N ⳱ 200
2.5% N ⳱ 161
2.3% N ⳱ 132
3.0% N ⳱ 101
0% N ⳱ 172
0% N ⳱ 73
Not done
May/Oct. ’05
Jul./Dec. ’06
6.3% N ⳱ 207
4.0% N ⳱ 151
0% N ⳱ 100
1.0% N ⳱ 100
1.4% N ⳱ 74
0% N ⳱ 107
0% N ⳱ 81
Mar./May ’05
Apr./Jul. ’06
24.6% N ⳱ 187
7.0% N ⳱ 186
3.7% N ⳱ 136
1.0% N ⳱ 196
0.9% N ⳱ 217
1.8% N ⳱ 171
0.8% N ⳱ 120
Feb./Mar. ’05
Mar./Apr. ’06
35.4% N ⳱ 223
6.8% N ⳱ 147
4.3% N ⳱ 188
1.7% N ⳱ 180
4.6% N ⳱ 152
0% N ⳱ 173
1.1% N ⳱ 88
Feb. ’05
Mar. ’06
35.4% N ⳱ 198
7.1% N ⳱ 169
3.5% N ⳱ 115
5.3% N ⳱ 131
0% N ⳱ 134
0% N ⳱ 103
0% N ⳱ 109
Dec. ’04
Jan./Feb. ’06
10.3% N ⳱ 174
1.0% N ⳱ 197
3.2% N ⳱ 189
2.9% N ⳱ 208
0% N ⳱ 121
0.5% N ⳱ 192
0% N ⳱ 171
Oct./Nov. ’04
Oct./Nov. ’05
Before 1st
4 mo. after 1st
8 mo. after 1st
12 mo. after 1st
4 mo. after 2nd
8 mo. after 2nd
12 mo. after 2nd
1st IRS date
2nd IRS date
25.5% N ⳱ 165
10.6% N ⳱ 132
5.1% N ⳱ 137
5.0% N ⳱ 161
2.7% N ⳱ 146
1.9% N ⳱ 156
1.7% N ⳱ 118
Dec. ’04/Feb. ’05
Feb./Mar. ’06
Gamboa, Agua Grande
Trindade, Me-Zoxi
Ribeira Afonso, Cantagalo
Angolares, Caue
Micolo, Lobata
Neves, Lemba
Príncipe
applied to plywood, plastic-coated plywood, and wrapping
paper at dosages of 20, 30, and 50 mg of active ingredient per
square meter of surface area.8 However, the insecticidal effect
of alphacypermethrin sprayed on cement walls persisted for
only a few weeks. In DRSTP, most houses are built of
wooden materials, especially in the rural areas where malaria
is highly endemic.
The IRS campaign with alphacypermethrin has already
been shown to have effectively lowered the prevalence of
malaria parasitemia and achieved a rapid reduction of malaria
infection in DRSTP. IRS with alphacypermethrin for malaria
control was highly acceptable to the people in São Tomé and
Príncipe due to the following facts: 1) no visible residue remained on the sprayed walls, 2) no domestic livestock died,
even if they ingested moribund household pests, such as cockroaches etc., and 3) no cats died.9 Thus it has shown that IRS
with alphacypermethrin is an effective measure for malaria
control in São Tomé and Príncipe. In Zanzibar, similar recent
success was demonstrated with the pyrethroid lamdacyhalothrin.10 Records from hospitals and health centers showed
that malaria declined immediately following a 54-day IRS
effort.10 Successful use of pyriproxyfen against malaria was
demonstrated in Sri Lanka.11 This chemical persists much
longer in water than does Bacillus thuringiensis israelensis
(Bti). With the aim of preventing development of insecticide
resistance by vector mosquitoes, we are planning to commence larval control, using IGR or Bti as an alternative to the
Before/after spraying
FIGURE 1. Map showing districts and major localities in the
Democratic Republic of São Tomé and Prı́ncipe.
TABLE 1
Malaria parasitemia before and after IRS in blood samples taken without regard to malaria symptoms in random samples of children < 9 years of age
Totals/all districts
RAPID CONTROL OF MALARIA IN SÃO TOMÉ AND PRÍNCIPE
249
250
TSENG AND OTHERS
IRS campaign, after completion of 3 yearly cycles of IRS with
alphacypermethrin.
3.
Received April 10, 2007. Accepted for publication September 28,
2007.
Acknowledgments: We are grateful to the Ministry of Foreign Affairs of Taiwan for financial support, to the International Cooperation and Development Fund of Taiwan (ICDF) for administrative
support, and to the Center for Disease Control of Taiwan for technical assistance. Many thanks also go to the staff of CNE for their
close cooperation in field operations, to the short-term assistants
from the CDC of Taiwan for their technical assistance in the laboratory, and to Chang Chi Lin, the Department of Microbiology and
Immunology, National Defense Medical Center, for his PCR tests to
determine the vector mosquito identity and insecticide resistance.
Authors’ addresses: Lien Fen Tseng, Wen Chun Chang, Cheng Hua
Wu, and Jih Ching Lien, The Anti-Malaria Team of Taiwan Medical
Mission to São Tomé and Príncipe, C.P. 839, São Tomé e Príncipe.
Maria Conceição Ferreira and Herodes Sacramento Rampão, Centro
Nacional de Endemias (CNE), República Democrática de São Tomé
e Príncipe. Jih Ching Lien, Institute of Preventive Medicine, National Defense Medical Center, Sanhsia, Taipei County, Taiwan 237,
Telephone: +886-2-25944651, Fax: +886-2-25947988, E-mail:
[email protected].
4.
5.
6.
7.
8.
9.
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