Mosquitoes ( Diptera : Culicidae ) in El Gharbia Governorate , Egypt : their spatial distribution , abundance and factors affecting their breeding related to the situation of lymphatic filariasis

Mosquitoes were surveyed (March May, and November 2007) in all centers of the El Gharbia Governorate. Seven mosquito species (6 culicine and 1 anopheline) were collected. These are Culex pipiens, Cx. perexiguus, Cx. antennatus, Cx. theileri, Ochlerotatus detritus, Culiseta longiareolata and Anopheles tenebrosus. Cx. pipiens, the main filariasis vector was the most common or predominating species (ca. 45%, 15 adult/room and 86%, 63 larva/SU, P<0.01). Cx. antennatus (ca. 38%, 13 adult/room) was also common species (P<0.01). For the three common species, Cx, pipiens, Cx. perexiguus and Cx. antennatus the relation of their larval and adult indoor densities with the environmental factors (water temperature and pH; indoorand outdoortemperature and RH) were examined. No infection with Wuchereria bancrofti were found in 1493 blood sample examined. Only one Elephantiasis case was reported from El Santa center (1/ 196 examined sample).


INTRODUCTION
El Gharbia Governorate locates in the center of the Nile Delta bordering with Kafr El Sheikh Governorate to its north, El Menoufia Governorate to the south, and Damietta and Rosetta branches of the Nile to the east.The capital of El Gharbia is Tanta City that locates about 90 km² from Cairo.The governorate encompasses eight administrative centers in addition to a large number of cities, towns, and villages.El Gharbia with a population of around 4,000,000 and covers about 25,400 km², the majority of which are agricultural lands.The major economic resources for the governorate are agriculture and food and textile industries.The most important crops in it are wheat, rice and cotton in addition to some fruits and flowers.Extended irrigation water network and various water collections are found in the governorate which has its impact on the occurrence and abundance of the mosquitoes (Kenawy et al., 1996).
In only one occasion, the mosquitoes were surveyed in the governorate by El-Said and Kenawy (1983) in 4 localities in two centers (Tanta and El Mahla El Kobra) and seven mosquito species were reported, of which Cx. pipiens was the most common species (in all surveyed localities).Culicine mosquitoes in Egypt are vectors of filariasis (Southgate, 1979), Rift valley fever (RVF) virus (Meegan et al., 1980), West Nile virus (Taylor et al. 1956) and several other viruses (Darwish and Hoogstraal, 1981).Anopheles pharoensis is the proven malaria vector, An. multicolor is suspected as a vector while An.tenebrosus has no role in malaria Yousrya M. Abdel-Hamid et al. (El Said et al., 1986 andkenawy, 1988) The present study was planned to update and provide further observations on the mosquito fauna of the governorate.This is important for planning a vector control program based on solid biological and ecological information of mosquito fauna mainly the disease vectors.

MATERIALS AND METHODS The Study Areas:
The survey was carried out (March -May and November 2007) in three localities representing each of the eight centers of the governorate (Table 1).Locations (longitude and latitude) of these centers were recorded using a global positioning system (GPS) navigator.

Mosquito Survey
Mosquito Larvae were collected by netting and adults were collected from inside houses by hand collection and space spraying (0.2% pyrethroid in kerosene) as described by Abdel-Hamid et al. (2009).Keys (Harbach, 1988 andGlick, 1992) were used for mosquito identification.

Filariasis Survey
The AMRAD-ICT Filariasis card Test (ICT-Fil, Immunochromatographic Diagnostic Tests Company, Balgowlah, New South Wales, Australia) was used to detect the Wuchereria bancrofti antigen in the whole blood (Ramzy et al., 1999).Finger prick blood samples were drawn onto the card (El-Setouhy et al., 2007) and the results were read visually (negative/positive) after 15 minutes.

Statistical Analysis
Means and Standard Errors were calculated for larval and adult densities of the reported mosquito species.Means were compared by the one-way ANOVA and if significantly different, they were exposed to pairwise comparison by Tukey test.Multiple Regression analysis was used to examine the relation of larval density to the temperature and pH of the breeding water and of the indoor adult density to the indoor-and outdoortemperature and relative humidity (RH).The slopes of the regression equations were tested for deviation from 0 by t-test.The PAST (PAleontological Statistics Version 2.08, Hammer et al. 2001) computerized program was used for statistical analysis
Results based on the percentage of each mosquito species from total collected in each center revealed that: (1) in larval collection, Cx. pipiens was the most common species in all districts (47.3-100%) except in El Santa where Cx antennatus was the most common (74.0%), (2) In adult collections: Cx. pipiens was also the most common species in all centers (40.1-52.5%)except in El Santa and El Mahalla El Kobra where Cx. antennatus was the most common (63.2 and 51.2%, respectively).In general, for all species (Fig. 2) larvae were most common in El Mahlla El Kobra (29.6%) while adults were most common in Zefta (29.6%) than in the other centers.Larvae and adults were most common in the eastern part (65.7 and 63.8%, respectively) than the western part (34.3 and 36.2%,respectively) of the governorate.However, For all species, mean densities of both adults (3.28±1.76-20.42±8.69adult/room) and larvae (1.14±0.62-55.40±53.10larva/SU) were insignificantly different among the study centers (F = 1.80 and 0.49, respectively.d.f.= 7, 24.P>0.05).

Factors Affecting Breeding and Abundance 1. Effect of Water Temperature and pH On the Larval Density
Breeding water was mostly alkaline (pH= 6.8-8.2) and have a temperature range of 21-34 o C. Multiple regression analysis (Table 3) for the three common species, revealed that larval density of Cx. pipiens increases (P>0.05) as temperature increased and decreases as pH (P>0.05) increased.Densities of Cx. antennatus and Cx.perexiguus increase as both temperature and pH increased (P>0.05).In general for all reported larvae, density increases as temperature increased and decreases as pH increased (P>0.05).3) revealed that: (1) Cx. pipiens and Cx.perexiguus densities increase as indoor temperature (range=21.9-29.3o C), outdoor RH (range=43.9-80.0%)while they decrease as outdoor temperature (range= 20.7 -29.5 o ) and indoor RH (range=46.1-76.8%-)increased, (2) Cx.antennatus density increases as indoortemperature and RH increased, while it decreases as outdoor-temperature and RH increased (P>0.05) and ( 3) Generally for all adults, density increases as indoor temperature and outdoor RH increased, while it decreases as outdoor temperature and indoor RH increased (P>0.05).

Filariasis Infection
In a total of 1493 blood sample examined from the eight centers, no infection with Wuchereria bancrofti was found.Only one Elephantiasis case was reported from El Santa center (1/ 196 examined sample).

DISCUSSION
Seven mosquito species were collected of which Cx. pipiens, Cx. perexiguus, and Cx.antennatus were collected as larvae and adults from all surveyed centers.Except for Cx.theileri, the other species were previously reported in the only occasion (El-Said and Kenawy, 1983) where mosquitoes were surveyed in this governorate.An. pharoensis was missed in this study.This may be due to missing of the rice growing period, the main breeding habitat for such malaria vector.Based on this and the previous study, the mosquito fauna can be represented by Cx. pipiens, Cx. antennatus, Cx. perexiguus, Cx. theileri, Oc. caspius, Cs. longiareolata, An. tenebrosus and An.(Cellia) pharoensis Theobald.Among the study centers, mean densities of both larvae and adults were similar (P>0.05).
Culex pipiens, the main filariasis vector (Harb et al., 1993) was the most common or the predominating species (ca.45%, 15 adult/room and 86%, 63 larva/SU, P<0.01) in agreement with the previous observations by El-Said and Kenawy (1983).Cx. antennatus (ca.38%, 13 adult/room) was also common species (P<0.01).Due to the facts that our collected samples were limited (1493 blood sample) and that the governorate is covered by the Mass Drug Administration (MDA) national programme of Ministry of Health to eliminate lymphatic filariasis (Ramzy et al., 2005 andEl-Setouhy et al., 2007), no Wuchereria bancrofti infections were detected.However, the detection of one elephantiasis case indicates old history of disease transmission in this governorate.This is different from the situation in the adjacent El Menoufia Governorate where lymphatic filariasis is circulating (ca.5% infection, range= 2-14%) associated mainly with the abundance of Cx. pipiens adults (Abdel-Hamid et al., 2011) and El Sharqiya Governorate (Abdel Hamid et al., 2009).Culex pipiens was also the chief vector of RVF virus during the 1977-78 epizootics in Egypt (Hoogstraal et al., 1979 andMegan et al., 1980).In addition, Cx. pipiens, Cx. antennatus, and Cx.perexiguus were also potential vectors during 1993 outbreak (Turell, 1996).The governorate has a history of RVF transmission as during 1993, the disease was documented among persons residing in such governorate and other 9 governorates (Arthur et al., 1993).
Five types of breeding habitats for mosquito larvae were detected during the study of which the irrigation drains were the most productive and the least productive one was the streams in agreement with the finding of Kenawy et al. (1996) in El Sharqiya Governorate.Breeding water was mostly alkaline (pH= 6.8-8.2) as previously reported in El Ismailia (kenawy andEl Said, 1990 andAbdel Hamid et al., 2011) Kenawy and El-Said (1990) in El Ismailia and Kenawy et al. (1996) (Sinha, 1976;Saxena et al. 1992 andWanji et al. 2009).
Multiple regression analysis for the relation of temperature and RH with the density of mosquito adults revealed that generally for all adults of the three common species, density increases as indoor temperature and outdoor RH increased, while it decreases as outdoor temperature and indoor RH increased (P>0.05).Different relations were observed for the same mosquito species in El Sharqiya (Abdel Hamid et al., 2009) and El Menufia (Abdel-Hamid et al., 2011) governorates.
It can be concluded that the prevalence and abundance of culicine mosquito species mainly the Cx.pipiens the main filariasis vector in El Gharbia with its history of filariasis as indicated by detecting one elephantiasis case may pause a risk of such disease transmission in this area.

Fig. 1 :
Fig. 1: Distribution of the reported mosquito species in El Gharbia Governorate

Fig. 3 :
Fig. 3: Relative productivity (Number and % of collected larvae) of the different breeding habitats 2. Effect of Temperature and Relative Humidity on the indoor adult Density Multiple regression analysis for the relation of temperature and RH with the indoor density of mosquito adults (Table3) revealed that: (1) Cx. pipiens and Cx.perexiguus densities increase as indoor temperature (range=21.9-29.3o C), outdoor RH (range=43.9-80.0%)while they decrease as outdoor temperature

Table 1 :
Coordinates of the surveyed centers in El Gharbia Governorate.

Yousrya M. Abdel-Hamid et al. 12Table 2 :
Relative abundance of the reported mosquito species in El Gharbia Governorate Density: larva/10 net and adult/room; in each column, means with different letters are significantly different (pair wise comparison by Tukey test, P <0.01).
Fig. 2: Percentages of the collected mosquito larvae and adults (all species) in the eight centers of Gharbia Governorate
in El Sharqiya.Other authors had different relations in the other governorates such as Abdel Hamid et al. (2009) In Sharqiya and Abdel-Hamid et al. (2011) in El Menufia.Several other physicochemical factors, e.g.salinity and free ammonia are known to affect the survival and abundance of mosquito larvae