Author: Kazemi, S H Moosa
Date published: June 1, 2010
Mosquito-borne diseases such as malaria, West Nile and Sindbis viruses, Japanese encephalitis, RiftValley fever as well as Dirofilaria immitis (dog heart worm) and D. repens (dirofilariasis) are a major public health threat in Asian countries, including Iran1-3. Malaria transmission in this area occurs in summer, most of the malaria cases were observed on borderline with Iraq4. Numerous semi-permanent and permanent aquatic habitats in irrigation and drainage systems offer excellent conditions for mosquito development. Consequently, the inhabitants of the surrounding villages suffer a periodical, but long-lasting mosquito nuisance from May to the end of July.
Seven species of Anopheles have been recorded in Kurdistan province, namely An. algeriensis Theobad, An. claviger Meigen, An. maculipennis Meigen s.l., An. marteri sogdianus Keshishian, An. sacharovi Favre, An. sergentii Theobald, and An. superpictus Grassi4. About 64 species, three subspecies and seven genera of mosquitoes have been reported in Iran3. Two genera of Culex, and Culiseta and eight species of the Culicinae subfamily have been reported in Kurdistan province5. Three genera of Aedes, Ochlerotatus and Uranotaenia have not been found in Sanandaj previously5. Zaim and Cranston5 did not mention this species in their checklist of Iranian Culicinae. Zaim6 mentioned two genera and eight species of the subfamily Culicinae (Diptera: Culi cidae) in Kurdistan province, namely Culex hortensis Ficalbi, Cx. perexiguus Theobald, Cx. pipiens Linnaeus,Cx. mimeticus Noe, Cx. theileri Theobald, Cx. tritaeniorhynchus Giles, Culiseta longiareolata Macquart and Cs. subochrea Edwards. There is only one recent study on the mosquitoes in the county in relation to malaria and anophelines4. While it is necessary to study mosquitoes in Sanandaj, there are no more references on the Culicine mosquitoes of the district. This paper presents the first survey of larvae and adults of Culicinae mosquito samples captured from different sites in Sanandaj county, Kurdistan province, western Iran.
Material & Methods
A field trial was conducted in four randomly selected rural villages in Sanandaj district (35°37'N, 36°16'E) in May, June and July 2009 in Kurdistan province. The district is bounded by the Iraq in the west, Hamedan province in the east, Kermansha province in the south, and western Azerbayjan province in the north. In 2009, the maximum and minimum mean monthly temperatures were 30°C and -1°C in July and February respectively. The total annual rainfall was 800 mm, the minimum of 3.9 mm in April and maximum of 126.2 mm in November. The mean annual relative humidity was 39%. The main economic activity of the people is agriculture and husbandry of cow and goats. On the basis of available epidemiological data from the Sanandaj Health Centre, four villages with 1118 houses and 5513 population were selected.
Sampling was carried out using dipping method for collecting larvae and night catch using suction tubes from animal baited traps for adult mosquitoes. The specimens were collected from three villages in different topographical areas of the district, including Hassan-Abad-e-Sofla, Hassan-Abad-e-Olia and Hossain-Abad. Night catch mosquito collection was conducted from 2000 to 0300 hrs monthly in fixed animal shelter randomly in each village. All collected mosquitoes were pinned and then identified using the keys of Zaim and Cranston5, Harbach7, and Darsie and Samanidou-Voyadjoglou8. Mosquitoes name abbreviations are cited based on Reinert9.
Larval habitats present within 500 m radius of each village were identified and sampled for mosquito larvae twice a month. Three randomly selected breeding places located within a 500 m radius of the study site were also included. All larvae were collected from natural habitats, generally feeding with seepage water, such as swamps, seepages, streams, river banks, drying river beds, pools, and grasslands. Up to 20 dipper samples were taken at intervals along the edge of each larval breeding place using a standard mosquito dipper (350 ml) depending on the size of the habitat.
The larvae for each habitat were placed separately in whirl-pak bags and transported to the laboratory where they were sorted by genus and instar counted and recorded. All III and IV instars of Culicinae subfamily were preserved in 100% lactophenol solution and later identified morphologically into species5. Samples for each habitat type were pooled together in each site irrespective of the collection date. Physical characteristics of the larval habitats including habitat stability, water depth, turbidity, presence of other aquatic invertebrates, and presence of floating, emergent, and submerged vegetation were recorded. Water depth was measured using a metal ruler. The habitat was recorded as unstable if it did not contain water during the next weekly sampling visit. The larvae were preserved in lactophenol and the microscopic slides of the preserved larvae were prepared using Berlese medium. The Culicinae larvae along with the description of their breeding sites were sent to the Department of Medical Parasitology, School of Medicine, Kurdistan University of Medical Sciences. In order to reconfirm the species, specimens were also sent to the School of Public Health, Tehran University of Medical Sciences.
The number of Culicinae mosquito species at the ecological station of Sanandaj is shown in Table 1. A total of 1862 adult and 3785 larvae of Culicinae mosquitoes were collected, of which four genera and eight species of Culicinae were recognized, namely Aedes vexans, Ochlerotatus caspius s.l. (indicating new occurrence records for the province), Culex hortensis, Cx. pipiens, Cx. mimeticus, Cx. theileri, Culiseta longiareolata and Cs. subochrea.
A total of 1862 adult Culicinae mosquitoes were collected using night catch from cow bait and bait net trap in living quarters and stables. Overall, Culex theileri predominated (50.5%), followed by Oc. caspius s.l. (23.2%), Ae. vexans (9.5 %), Cx. pipiens (8.8%), Cs. subochrea (4.2%), Cx. mimeticus (2.6%), Cx. hortensis (1.1%), and Cs. longiareolata (0.07%).
In the larval collection, of 3785 Culicinae larvae collected, Cs. longiareolata and Cs. subochrea predominated (19.5%), followed by Cx. pipiens (13.6%), Cx. theileri (8.3%), Oc. caspius s.l.(6.5%), Cx. mimeticus (4.1%), Ae. vexans (2.4%) and Cx. hortensis (1.3%) (Table 1). Two species including Cx. theileri, and Oc. caspius s.l., accounted for 50.5 and 23.2% of the adult collection respectively. The other species are less frequent, each accounting for less than 27% of the total (Table 1).
Culex theileri was the most frequent culicine mosquito collected at the Sanandaj, with total of 934, and 418 specimens, using night catch and larval collection, respectively. Aedes vexans and Oc. caspius s.l. are recorded for the first time in Sanandaj, Kurdistan province. The number and prevalence of Culicinae mosquito catches by animal bait trap through night are presented in Table 2. Feeding activity of Oc. caspius s.l. was increased from 2000 to 2300 hrs and decreased slowly from 2300 to 0200 hrs, whereas blood feeding activity of Cs. subochrea was increased from 2300 to 0200 hrs and then decreased from 0200 to 0500 hrs. Culex theileri was active throughout the night and other culicine mosquitoes species such as Cx. pipiens, Cx. hortensis, Cx. mimeticus, and Ae. vexans were active during 2300 to 0200 hrs. Two species including Cx. theileri, and Oc. caspius s.l. accounted for 83% of the adult collection after the sunset in the animal bait trap collection whereas during 2300 to 0200 hrs these spe- cies with Cx. pipiens were predominant and accounted for 79% of the adult collection. In this study, Cx. theileri, Oc. caspius s.l. and Ae. vexans were active during 0200 to 0500 hrs and formed about 89% of the total mosquito catches.
Four genera and eight species of Culicinae mosquitoes were identified from Sanandaj and Kurdistan province, including the first record of Ae. vexans and Oc. caspius s.l. in this area. Among eight species reported in this study, six species had previously been recorded5, and only two species are new. Culex perexiguus and Cx. tritaeniorhynchus have not been found throughout this investigation. The occurrence of Ae. vexans and Oc. caspius s.l., in the province was not mentioned before5, although these were reported in many parts of Iran10 .Two species of Ae. vexans and Oc. caspius s.l. were differentiated from each other in the larval stage8. There is no information about the Oc. caspius sibling species (A or B) in the country3.
The species of Cs. longiareolata was one of the most frequent culicine mosquito collected at the Sanandaj, with total number of 982 specimens, by larval collection, however, this species was collected in low numbers in adult collections. Culex pipiens can be separated from Cx. torrentium and Cx. vegans by Harbach's key using seta 1-III-V, seta 1-M, seta 1- X, seta 1-C, and some other characters11. Based on this key, in the current survey only Cx. pipiens was identified.
Results of this survey are almost the same as those of previous study in Kurdistan province5. It should be mentioned that in this study, other culicine mosquitoes were collected being potential vectors of human and domesticated animal pathogens, such as Oc. caspius s.l. and Ae. vexans7,11. Culex theileri was one of the culicinae mosquitoes collected and is the more prevalent species at higher altitudes and in rural areas of Isfahan12, Zanjan13and East Azerbaijan provinces14.
In this study, peak blood feeding activity of Oc. caspius s.l. was around 2000 to 2300 hrs. Our findings conform with those of a previous study in Zarrin- Shar and Mobarakeh areas in Isfahan province, in the central part of Iran12. Results of this research are in line with those of Mousa kazemi who reported that the Cx. theileri was active during the night, whereas Ae. vexans and Cs. subochrea were active from 0200 to 0500 hrs.
Observations made during the present study agree with those of Simsek who noted that Cx. theileri in Turkey prefers large natural larval habitats that are generally present in rural areas15. Presence of river can lead to explore new sites like pools, swamps and grasslands that permit the recognition of a large number of Culicinae mosquitoes. It is worth to note that another study also reported formation of pools, swamps and grasslands which can lead to proliferation of new species of culicinae16.Therefore, as environmental factors keep on changing, monitoring should be done constantly and their ecology needs to be studied extensively.
The authors are grateful to Dr G. Zamini, Department of Medical Parasitology, Faculty of Medicine, Kurdistan University of Medical Sciences, for his valuable suggestions. The authors are also grateful to Dr Kalantar Enayat for his review of the manuscript. The authors also would like to express appreciation to the people of villages of Hassan Abad, Sanandaj for their kind cooperation throughout the study, many thanks also for dedicated efforts of field staff of the Medical Parasitology Department.
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S.H. Moosa Kazemia, F. Karimiana & B. Davarib
aDepartment of Medical Entomology and Vector Control, School of Public Health, Tehran University of Medical Sciences, Tehran; bDepartment of Medical Entomology and Parasitology, School of Medicine, Kurdistan University of Medical Sciences, Sanandaj, Iran
Corresponding author: Dr B. Davari, Department of Medical Entomology and Parasitology, School of Medicine, Kurdistan University of Medical Sciences, Pasdaran Street, Sanandaj, P.O. Box: 61177-13446, Iran.
Received: 19 January 2010 Accepted in revised form: 25 April 2010