(Finlaya) Poicilius, Putative Vector of Bancroftian Filariasis on Panay Island, the Philippines
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SOUTHEAST ASIAN J TROP MED PUBLIC HEALTH INVESTIGATION OF MOSQUITOES WITH EMPHASIS ON AEDES (FINLAYA) POICILIUS, PUTATIVE VECTOR OF BANCROFTIAN FILARIASIS ON PANAY ISLAND, THE PHILIPPINES 1 1 1 1 2 Wilfredo Aure , Majhalia Torno , Richard P Malijan , Estrella Cruz , Leda Hernandez , Mario Baquilod2, Michael J Bangs3,4 and Ferdinand V Salazar1 1Research Institute of Tropical Medicine, Filinvest City Cpd, Muntinlupa City; 2Infectious Disease Office, Department of Health, Manila, The Philippines;3 Public Health and Malaria Control, Kuala Kencana, Papua, Indonesia; 4Department of Entomology, Faculty of Agriculture, Kasetsart University, Bangkok, Thailand Abstract. Entomological investigations were conducted in four remaining lym- phatic filariasis endemic provinces of Panay Island, The Philippines to determine mosquito species present in these areas and to identify host preference and biting activity of Aedes (Finlaya) poicilius Theobald, primary vector of nocturnal periodic Wuchereria bancrofti in The Philippines. Sampling techniques targeted nocturnally active mosquito species using a carabao-baited trap (CBT) and human-landing collection (HLC), the latter taking place from 06:00 to 12:00 PM. A total of 25,536 mosquitoes comprising 42 species and 7 genera were collected from CBT, whilst HLC acquired 6,486 mosquitoes comprising 28 species and 5 genera. Three known or potential vectors of human filarial were collected, namely, Aedes poicilius, Culex quinquefasciatus and Mansonia uniformis. The peak landing (biting) activity for Ae. poicilius was between 09:00 and 11:00 PM. Comparisons between CBT and HLC yields showed this species to be more zoophilic. Based on observed mosquito behavior and interviews with residents, vector-host contact was promoted by the local practice of staying overnight in makeshift shelters in high risk areas without adequate protection against mosquito bites. Results of this survey will augment information for integrating vector control and mass drug administration into an island-wide lymphatic filariasis elimination program. Keywords: Aedes poicilius, behavior, lymphatic filariasis, mosquito species, Panay Island, The Philippines INTRODUCTION brera and Arambulo, 1973; Cabrera and Valeza, 1978; Hernandez, 1993, Amarillo Despite decades of efforts to control et al, 2008; DOH, 2008). Both Wuchereria lymphatic filariasis, it still remains a pub- bancrofti and Brugia malayi are present in lic health concern in The Philippines (Ca- the country; however, only autochthonous Correspondence: Ferdinand V Salazar, Research Bancroftian filariasis is known to occur Institute of Tropical Medicine, Filinvest City in Panay Island. Since 2015, there were Cpd, Alabang 1781, Muntinlupa City, Republic 44/81 provinces in the country that have of the Philippines. been designated as ‘filarial-free’ while E-mail: [email protected] the remaining 33 provinces are currently 912 Vol 47 No. 5 September 2016 AEDES POICILIUS IN PANAY, THE PHILIPPINES under an elimination phase. The remain- mentioned provinces were conducted ing four provinces from Region VI, which from September 2011 to October 2012 with comprises the remaining four provinces the following objectives: (1) identification on Panay Island, namely, Aklan, Antique, of potential filariasis mosquito vectors in Capiz and Iloilo, are under a control cat- areas with positive human cases, (2) deter- egory (DOH, 2013). mination of distribution of mosquito spe- In 2007, a serendipitous detection of cies with emphasis on filariasis vectors, microfilaria from a patient in Iloilo City and (3) determination of vector behavior subsequently resulted in blood surveys and bionomics contributing to filariasis among residents in areas suspected of transmission in each area. residual infection or active transmission Entomological surveys of this type (Pendon, 2012; DOH, 2013). The surveys contribute substantially to the Philippine yielded several patent human infec- National Filariasis Elimination Program tions in three municipalities of Iloilo, towards the development of site-specific, ie, Concepcion, Janiuay and Lambunao. evidence-based, integrated vector control Nighttime blood surveys were extended strategies (DOH, 2013). Although the to other provinces of Panay Island and vector species on Panay Island may be additional filaria cases were detected similar to other areas in The Philippines, in the municipalities of Bugasong and site-specific spatial variation in mosquito Valderama in Antique Province; Libacao, behavior may be present, which might Madalag and Malinao in Aklan Province; be critical to the understanding of dis- and Tapaz in Capiz Province (http://balita. ease transmission and implementation ph/2009/11/27/health-authorities-strength- of cost-effective vector control measures. en-campaign-vs-lympathic-filariasis/, Moreover, a better understanding of local 2009). All filarial infections revealed only community activities, which may promote W. bancrofti. transmission could be targeted to mini- Aedes (Finlaya) poicilius Theobald mize vector-human contact. (Knight and Stone, 1977; Wilkerson et al, 2015) is the principal vector of Bancroftian MATERIALS AND METHODS filariasis in The Philippines, especially in areas where abaca and banana cultiva- Study sites and activities tions are abundant (Suguri et al, 1985; The island of Panay (11° 09’N, 122° Schultz, 1988; Hernandez, 1993; Walker 29’E) is in Western Visayas Region of The et al, 1998). As for other mosquito-borne Philippines and comprises four provinces, diseases of importance, with the exception namely, Aklan, Antique, Capiz and Iloilo, of Antique Province (Semirara Island), on the main island and Guimaras Island, Panay Island is regarded as malaria-free southeast of Panay Island. Panay is sur- with no reported indigenous cases in the rounded by various bodies of sea and the previous 5-10 years, placing Panay Island land mass is characterized by relatively in the pre-elimination phase of control wide stretches of coastal lowlands com- (DOH, 2014). bined with rugged hills and mountains In order to further investigate the risk in the interior. Panay possesses a diverse of filariasis transmission on Panay Island, marine life, inland fisheries and various entomological surveys in the four above- agricultural products. Its large agricul- Vol 47 No. 5 September 2016 913 SOUTHEAST ASIAN J TROP MED PUBLIC HEALTH Fig 1–Map of mosquito collection sites in the four provinces of Panay Island, The Philippines. tural areas produce high quantities of were sampled for 2 nights per month rice, coconut, mango, pineapple, banana, from September 2011 to October 2012. various root crops, vegetables and sugar. Entomological sampling was conducted Abaca and rattan crafts are also important in locations that were identified as filarial industries. positive by active case detection surveys Collection sites were chosen based completed in 2007-2009 (Pendon, 2012; on the presence of filariasis positive DOH, 2013). These included Aklan Prov- cases, accessibility and security. Working ince (Barangays Loctuga and Rosal from closely with the regional entomology staff the municipality of Libacao and Brgy and the Filaria Program Coordinator of Mamba from the municipality of Ma- Department of Health, Regional Health dalag); two municipalities from Antique Office - Region VI, candidate collection Province, namely Bugasong (Brgy. Zara- sites were identified and representative goza) and Valderama (Brgy. Buluangan mosquito collection sites in Aklan, An- I); the municipality of Tapaz in Capiz tique, Capiz and Iloilo Provinces (Fig 1) Province (Brgy. Artuz and Bacahan); and 914 Vol 47 No. 5 September 2016 AEDES POICILIUS IN PANAY, THE PHILIPPINES municipalities of Concepcion (Sitio Dadoy within the vicinity of primary residences and Sitio Puntalis from Brgy. Nipa) and of filaria-positive cases (DOH, 2013). Lambunao (Barangays Jayobo and Ca- Known filariasis vector species in the batangan) from Iloilo Province. country belong within four genera (Aedes, The primary goal was to conduct vec- Anopheles, Culex, and Mansonia), each with tor collections in and around the primary specific breeding site preferences; therefore residence and/or work area of known all possible sources of mosquito larvae filariasis-positive cases and interview key were inspected using various techniques informants, such as local health work- (WHO, 1975). Inspected breeding sites ers, barangay (village) health workers, include margins of slow moving creeks, kagawads (elected councilor for the small- streams, irrigation canals, ponds, ground est political unit in The Philippines, the pools, roots of aquatic plants and natural barangay), and midwives to gain a better containers. Particular attention was paid understanding of the local cultural habits to sampling plant leaf axils, such as abaca, and behavioral patterns. banana, Pandanus, taro (Colocasia esculenta) All mosquito collections were per- and other similar plants that are the pre- formed in locations that are relatively ferred breeding habitats of Aedes poicilius. flat landscapes between hills with open Collection of mosquitoes by carabao-baited canopy transition forest. Other vegeta- traps (CBT) tion types in the near vicinity of collec- Animal-baited traps generally collect tions included grass, rice , low shrub, a wider diversity and number of mosquito bamboo, scattered trees, abaca (‘manila species than most other collection meth- hemp’, Musa textilis), banana (Musa spp), ods per trapping session and is dependent and Pandanus.