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Malaria Vectors and Transmission Dynamics in Coastal South-Western Malaria Journal BioMed Central Research Open Access Malaria vectors and transmission dynamics in coastal south-western Cameroon Jude D Bigoga1,2, Lucien Manga3, Vincent PK Titanji4, Maureen Coetzee*5,6 and Rose GF Leke2,7 Address: 1Department of Biochemistry, Faculty of Science, University of Yaounde I, Cameroon, 2The Biotechnology Center, University of Yaounde I, P.O. Box 3851-Messa, Yaounde, Cameroon, 3Vector Biology and Control Unit, WHO Regional Office for Africa, Brazzaville, Congo, 4Department of Life Sciences, Faculty of Science, University of Buea, Cameroon, 5Vector Control Reference Unit, National Institute for Communicable Diseases, NHLS, Johannesburg, South Africa, 6Division of Virology and Communicable Disease Surveillance, School of Pathology of the National Health Laboratory Service and the University of the Witwatersrand, Johannesburg, South Africa and 7Faculty of Medicine and Biomedical Sciences, University of Yaounde I, Cameroon Email: Jude D Bigoga - [email protected]; Lucien Manga - [email protected]; Vincent PK Titanji - [email protected]; Maureen Coetzee* - [email protected]; Rose GF Leke - [email protected] * Corresponding author Published: 17 January 2007 Received: 09 November 2006 Accepted: 17 January 2007 Malaria Journal 2007, 6:5 doi:10.1186/1475-2875-6-5 This article is available from: http://www.malariajournal.com/content/6/1/5 © 2007 Bigoga et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Background: Malaria is a major public health problem in Cameroon. Unlike in the southern forested areas where the epidemiology of malaria has been better studied prior to the implementation of control activities, little is known about the distribution and role of anophelines in malaria transmission in the coastal areas. Methods: A 12-month longitudinal entomological survey was conducted in Tiko, Limbe and Idenau from August 2001 to July 2002. Mosquitoes captured indoors on human volunteers were identified morphologically. Species of the Anopheles gambiae complex were identified using the polymerase chain reaction (PCR). Mosquito infectivity was detected by the enzyme-linked immunosorbent assay and PCR. Malariometric indices (plasmodic index, gametocytic index, parasite species prevalence) were determined in three age groups (<5 yrs, 5–15 yrs, >15 yrs) and followed-up once every three months. Results: In all, 2,773 malaria vectors comprising Anopheles gambiae (78.2%), Anopheles funestus (17.4%) and Anopheles nili (7.4%) were captured. Anopheles melas was not anthropophagic. Anopheles gambiae had the highest infection rates. There were 287, 160 and 149 infective bites/person/year in Tiko, Limbe and Idenau, respectively. Anopheles gambiae accounted for 72.7%, An. funestus for 23% and An. nili for 4.3% of the transmission. The prevalence of malaria parasitaemia was 41.5% in children <5 years of age, 31.5% in those 5–15 years and 10.5% in those >15 years, and Plasmodium falciparum was the predominant parasite species. Conclusion: Malaria transmission is perennial, rainfall dependent and An. melas does not contribute to transmission. These findings are important in the planning and implementation of malaria control activities in coastal Cameroon and West Africa. Page 1 of 12 (page number not for citation purposes) Malaria Journal 2007, 6:5 http://www.malariajournal.com/content/6/1/5 Background serious environmental modifications over the years owing Malaria is a major public health problem in Cameroon [1- to rapid growth in population, urbanization and the agro- 3]. Over 900,000 clinical cases occur yearly and are industrial activities of the Cameroon Development Cor- responsible for 40–45% hospital consultations, 20% hos- poration (CDC), the largest agricultural scheme in central pital admissions and 35–40% deaths. Children less than Africa. Such modifications can lead to ecological changes five years old are the most affected [4]. Despite efforts that affect the vector population structure, distribution made by the National Malaria Control Programme to curb and density, all of which would impact on the efficiency the disease burden, the prevalence is seemingly on the in transmitting malaria. Thus, this paper describes the increase. Previous studies have attributed this to the anopheline species composition and malaria transmis- increasing spread of drug resistance in the parasite, insec- sion dynamics in three localities (Tiko, Limbe and Ide- ticide resistance in the vectors, inadequate and inconsist- nau) along the Atlantic coast of south-western Cameroon. ent allocation of resources for control [5,6] and the presence of very efficient mosquito vectors of Plasmodium Methods falciparum [7-9]. Description of the study area The study was conducted in Tiko (Small Ikange) 4° 04'N, Malaria vector control activities in Cameroon focus 9°17'E – a rural setting; Limbe (Middle Farm) 4°02'N, mainly on the use of insecticide-treated bed nets. How- 9°11'E – a cosmopolitan town; and Idenau (Bibunde- ever, the implementation of effective vector control strat- Scipio) 4°01'N, 9°03'E – a semi-urban vicinity situated egies requires requisite information on the vector along the Atlantic coast of Cameroon. Idenau borders the population structure, their distribution and efficiency in Atlantic Ocean; while Tiko is situated 20 km from Limbe, malaria transmission. Previous studies in Cameroon have 50 km from Idenau and 19 km from the coastline. Limbe shown that the intensity and duration of transmission, as is situated 30 km from Idenau and 8 km from the coast- well as the vector species, vary greatly between different line. The area lies within the tropical rain forest region of eco-zones of the country, from perennial transmission in Central Africa and harbours the largest agro-industrial the southern forested regions to seasonal and unstable scheme in the country and sub region, the Cameroon transmission in the northern Sudano-savannah and Sahe- Development Corporation (CDC). Crops grown in the lian savannah regions [8-13]. At least 14 out of the 45 spe- plantations include rubber (Fiscus elastica) and banana cies of Anopheles described in Cameroon are capable of (Musa spp.) in Tiko, and oil palm (Elaies Spp.) in Tiko, transmitting malaria. The most common and efficient vec- Limbe and Idenau. Plantation workers are housed in tor species are Anopheles gambiae, Anopheles. arabiensis camps with few medical facilities at their disposal. The Anopheles funestus, Anopheles nili and Anopheles moucheti population is highly heterogeneous comprising people [14]. Species such as Anopheles paludis, Anopheles pharoensis from almost every ethnic community in Cameroon, some and Anopheles hankocki play only minor, secondary roles parts of neighbouring Nigeria, Niger and Ghana. The cli- in malaria transmission [8,15]. mate is typically equatorial with a mean annual tempera- ture of 26°C, mean annual rainfall of 2,000–10,000 mm Although Anopheles melas, a member of the An. gambiae and 88% relative humidity. There are two seasons; the dry complex, is purported to be an important malaria vector season from November to February and the wet season along the coast of many West African countries, its impor- from March to October. tance in malaria transmission in Cameroon is not clear. Although few studies have reported on the occurrence of Study design and ethical considerations An. melas in Cameroon [16], currently there is insufficient A longitudinal study was carried out for 12 months from information on its abundance and infection rates. This August 2001 to July 2002. Permission to carry out this may be due, in part, to the fact that early studies on An. study was obtained from the Human Resources and gambiae s.l. relied on morphological identification only Health departments of the Cameroon Development Cor- and more recent studies have not used modern methods poration (CDC), and an ethical clearance obtained from like PCR because they are expensive and expertise the National Ethical Review Committee of Cameroon. A demanding. sensitization rally was organized with the population dur- ing which the purpose of the study was clearly explained. Unlike in the southern forested and northern savannah Participation in the study was voluntary. All diagnosed regions of Cameroon, where the epidemiology of malaria cases of malaria were treated for free, following recom- has been better studied prior to the implementation of mendations set by the national malaria control program. malaria control activities, very little is known about the vectors and their contribution to malaria transmission in Collection and processing of adult mosquitoes specimens the coastal areas. The coastal area of south-west Cam- For two consecutive nights (6:00 pm–6:00 am) every eroon is a characteristic ecological area. It has undergone month, at each site (total 72 nights), mosquitoes were Page 2 of 12 (page number not for citation purposes) Malaria Journal 2007, 6:5 http://www.malariajournal.com/content/6/1/5 captured indoors on six human volunteer collectors using sporozoites by PCR [25,26]. To minimize having false the human landing catch method. These were sorted and positive ELISA [27,28] only PCR confirmed specimens the anophelines morphologically identified to groups were used to determine the infection rates.
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