Transactions of the Royal Society of Tropical Medicine and Hygiene (2006) 100, 45—47

Biting time of Anopheles darlingi in the BolivianAmazon and implications for control of malaria

Angela F. Harrisa,∗, Abrahan Matias-Arnezb, Nigel Hill a

a Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine,Keppel Street, London WC1E 7HT, UKb Proyecto de Salud Integral (PROSIN), Av. Unzaga de la Vega s/n, Guayaramerin, Beni, Bolivia

Received 30 November 2004; received in revised form 24 June 2005; accepted 6 July 2005Available online 9 September 2005

KEYWORDSMalaria;Anopheles darlingi Root;Peak biting time;Human landing catch;Insecticide-treated bednets;Bolivian Amazon

Summary Malaria is a growing problem in the Bolivian Amazon where there hasbeen a four-fold increase between 1991 and 1998, largely owing to forest clearancebringing human and vector into closer association. The principle vector in this regionis Anopheles darlingi Root, the behaviour of which has been little studied in this partof South America. The peak time of biting of A. darlingi was studied over a seriesof nights in July 2003 during the dry season in the town of Riberalta in the BolivianAmazon. Peak biting occurred between 19:00 and 21:00 hours, when 48% of the totalnight’s biting took place. This early biting habit has implications regarding controlof malaria via the use of insecticide-treated bed nets. Anopheles darlingi was themost prevalent vector in the study, although A. albitarsis s.l. and A. braziliensiswere also present.© 2005 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd.All rights reserved.

1. Introduction

Since the early 1990s malaria has re-emerged asa problem in Bolivia. This is predominantly owingto Plasmodium vivax infection, although P. falci-parum has also markedly increased. Approximately50% of the malaria cases in Bolivia are in the Amazonregion in the north bordering Brazil and they occurup to an altitude of 2500 m (Warrell and Gilles,2002). In this region, malaria is associated with

∗ Corresponding author: Tel.: +44 20 7927 2646;fax: +44 20 7927 2918.

E-mail address: angi harris@hotmail.com (A.F. Harris).

settlement of previously forested areas by non-immune immigrants (Moore et al., 2002).

The primary vector of malaria in the Amazonis Anopheles darlingi Root, which is widespreadthroughout much of Central and South Amer-ica, favouring lowland rural areas close to rivers(Hudson, 1984) and remaining closely associatedwith humans and human activity (Tadei et al.,1998). Anopheles darlingi is very effective as avector of malaria because it is highly anthro-pophilic and relatively long lived (Charlwood, 1996;Zimmerman, 1992). Peak time of biting varies inthis species in different parts of South America(Charlwood, 1996; Guarda et al., 1999; Hudson,

0035-9203/$ — see front matter © 2005 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved.doi:10.1016/j.trstmh.2005.07.001

46 A.F. Harris et al.

1984; Klein and Lima, 1990; Pates and Curtis, 2005;Roberts et al., 1987; Rozendaal, 1989; Tadei andThatcher, 2000). There may be a complex of dif-ferent sibling species. The present study aimed todetermine the biting time of A. darlingi in theBolivian Amazon. Peak biting time will presumablyinfluence the effectiveness of insecticide-treatedbed nets (ITN) against malaria transmission (Patesand Curtis, 2005).

2. Methods

The study took place in the El Prado district of Rib-eralta, Vaca Diez, in the Beni Province of the Ama-zon region. The Bolivian Comite Impulsor de Etica YBioetica granted ethical approval for the study andprophylaxis was offered to the local entomologicalstaff who carried out the human landing catches todetermine peak biting time. The catches took placenightly from 18:00—06:00 hours (i.e. from approxi-mately half an hour before sunset to half an hourafter sunrise) for 12 nights between 8 July and 23July 2003.

The two volunteers, supplied with an aspirator

braziliensis (4); the latter two species are alsoknown to be malaria vectors (Zimmerman, 1992).

Hourly data from all the catches were pooled andthe average number of bites per hour was obtained.Figure 1 shows that biting peaked between 19:00and 21:00 hours and that 83% of the night’s bitinghad occurred by 22:00 hours when most local peoplego to bed (Population Services International, 2001).After this time, numbers declined, with little or noactivity between 02:30 and 05:00 hours, althoughtwo mosquitoes were recorded after 05:00 hours.

4. Discussion

Biting activity may be affected by seasonal changesin temperature and population density. This studytook place during the dry season in Riberalta and itis possible that at different times of the year bit-ing behaviour may vary. Anopheles darlingi feedsindoors as well as outdoors (Guarda et al., 1999;Hudson, 1984; Klein and Lima, 1990); our landingcatches took place outdoors and it is possible thatindoor biting time may be somewhat different.

Approximately 94.4% of the population of Riber-

and torch, were seated next to each other in anopen area near the river (an established anophe-line breeding site), approximately 10 m from thenearest dwelling where biting had previously beenreported (A. Matias-Arnez, personal observation).Mosquitoes caught were transferred to containerslabelled in half hour time intervals and the follow-ing morning catches were identified to species levelusing the key of Faran and Linthicum (1981).

3. Results

The following Anopheles species were caught:A. darlingi (272), A. albitarsis s.l. (16) and A.

Figure 1 Percentage of night’s biting by Anopheles dar-lingi, by hour. The dotted line indicates the approximatetime when the local people go to bed.

alta claim to own and regularly use ITNs (PopulationServices International, 2001). Studies showing theefficacy of ITNs for malaria control have beenextensive in Africa where sporozoite-positive vec-tors generally bite at hours in the night when mostpeople are in bed (Maxwell et al., 1998). In Bolivia,ITNs may prove inappropriate for control owing toearly biting by A. darlingi. However, in Guatemalawhere the vector A. albimanus bites predominantlyearly in the night, ITNs have proved surprisinglyeffective (Richards et al., 1993).

To deal with the problem of early-biting malariavectors, repellents could have an important roleand there is now evidence from Bolivia for reducedmalaria incidence using a plant-based repellent(Lemon Eucalyptus) in addition to ITNs (N. Hill, per-sonal observation).

Conflicts of interest statementThe authors have no conflicts of interest concerningthe work reported in this paper.

Acknowledgements

This project was funded by the London Schoolof Hygiene and Tropical Medicine travel scholar-ship and the Gates Malaria Partnership (GMP) atLSHTM. We thank the staff of PSI, Riberalta, forsupport in the field and local advice; the District

Malaria control and biting time of Anopheles darlingi in Bolivia 47

Health Department for supplying transport, staffand laboratory facilities; and Jorge Carvajal andRafael Gonzales for their expertise in human land-ing catches and extensive local knowledge. Wealso thank Sarah Moore and Cheryl Whitehornfor their advice on Anopheles identification andtaxonomy.

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