Prediction of villages at risk for filariasis transmission in the nile delta using remote sensing and geographic information system technologies

Remote sensing and geographic information system [GIS] technologies were used to discriminate between 130 villages in the Nile Delta, at high and low risk for filariasis, as defined by microfilarial prevalence. Landsat Thematic Mapper [TM] data were digitally processed to generate a map of land-cover as well as spectral indices such as NDVI and moisture index. A Tasseled Cap transformation was also carried out on the TM data which produced 3 more indices [brightness, greenness and wetness]. GIS functions were used to extract information on land-cover and spectral indices within 1 km buffers around the study villages. The relationship between satellite data and prevalence was investigated using discriminant analysis. The analysis indicated that the most important landscape elements associated with prevalence were water and marginal vegetation, while wetness and moisture index were the most important indices. Discriminant functions generated for these variables were able to predict correctly 80% and 74% of high and low prevalence villages, respectively, with an overall accuracy of 77%. The present approach provided a promising tool for regional filariasis surveillance and helps direct control efforts

Spatial analysis of lymphatic filariasis distribution in the nile delta in relation to some environmental variables using geographic information system technology

Geographic information system [GIS] was used to analyze the spatial distribution of filariasis in the Nile Delta. The study involved 201 villages belonging to Giza, Qalyoubia, Monoufia, Gharbia, and Daqahlia governorates. Villages with similar microfilarial [mf] prevalence rates were observed to cluster within 1-2 km distance, then clustering started to decrease significantly with distance up to 5 km [Pearson correlation coefficient = -0.98]. The likelihood of negative and high prevalence villages being contiguous was very low [1.8%, n = 612 village-pairs] indicating homogeneity in disease processes within the defined spatial scales. Of the villages located within 2 km from the main Nile branches [n = 46], 95% exhibited low prevalence. In addition, the spatial pattern of mf prevalence was shown to be negatively associated with annual rainfall and relative humidity, while it was positively associated with annual daily temperature. Average mf prevalence in warmer, relatively drier areas receiving 25 mm of rain was significantly higher [3.9%] than that in less warmer but more humid areas receiving 50 mm of rain [1.6%] [P <0.0001]. Based on the results of the present study, GIS was used to generate a filariasis risk map that could be used by health authorities to efficiently direct surveillance and control efforts. This investigation identified some of the factors underlying filariasis spatial pattern, quantified clustering and demonstrated the potential of GIS application in vector-borne disease epidemiology

Effect of juvenile hormone and ecdysone on initiating blood meal-dependent vitellogenic ovarian cycles in autogenous and anautogenous culex pipiens [Diptera: culicidae]

The effect of juvenile hormone [JH] and ecdysone on initiating blood meal - stimulated ovarian cycles was studied in autogenous [2[nd] ovarian cycle] and anautogenous [1[st] ovarian cycle] Cx. pipiens. Although vitellogenesis was initiated in both mosquitoes in response to ecdysone, JHI and sequential JHI-ecdysone treatments induced vitellogenesis in anautogenous females only. JHI treatment initiated vitellogenesis in Ca. 30% of anautogenous females and only half of those were able to form mature eggs. Sequential JHI- ecdysone treatment triggered vitellogenesis in 10 out of 25 anautogenous females and mature eggs were formed in three females only. In response to ecdysone, vitellogenesis in 10 out of 18 autogenous females and mature eggs were formed in two individuals. In Ca. 70% of anautogenous siblings vitellogenesis was initiated and in most of those females mature eggs were developed. Our data suggests that differences in hormone - dependent events of vitellogenesis in autogenous and anautogenous Cx. pipiens seem to be related to the regulation of ecdysteroide release

In vitro transmission of Wuchereria bancrofti L3-stage larvae by experimentally infected culex pipiens L [Diptera: culicidae]

Females of Culex pipiens L. experimentally infected with Wuchereria bancrofti were tested for in vitro transmission of infective stage L[3] larvae using a capillary tube technique. Of the females harbouring L[3] larvae, 60.7% [34/56] transmitted a geometric mean of 2.84 L[3] larvae [range 1- 35]. Transmitting Cx. pipiens contained significantly more L[3] larvae than non-transmitters. Both the probability of transmission and the number of L[3] larvae transmitted were related to the total number of L[3] larvae/mosquito. Almost all females with L[3] loads >/= 10 transmitted larvae in vitro. The possibility is discussed that the detection of L[3] larvae in field collected mosquitoes by dissection may overestimate the proportion capable of parasite transmission and the proportion of L[3] larvae deposited on host skin by Ca. 40%

Vector competence of autogenous and anautogenous culex pipiens mosquitoes for wuchereria bancrofti

Vector competence of autogenous and anautogenous Culex pipiens derived from North Sinai Governorate, Egypt, for the human filaria parasite Wuchereria bancrofti was studied. After feeding on the same microfilaremic volunteers both biotypes were readily infected with the parasite [infection rates > 80%] and supported its development to the infective stage within 11 - 12 days. Infective rates of both autogenous and anautogenous mosquitoes were similar [> 95%]. However, autogenous Cx. pipiens developed significantly less number of infective stage larvae [4.7 +/- 1.4 1.3 / female] than did anautogenous siblings [6.7 +/- 3.6 L[3]/ female] [P < 0.05]. Moreover, autogenous females were observed to contain twice the number of L[3] larvae in the thoracic muscles and less larvae in the head region compared to autogenous counterparts. Vector competence characteristics of Cx. pipiens derived from a filariasis endemic area in Qalubiya Governorate were similar to those of anautogenous mosquitoes of North Sinai. These findings indicate that autogenous Cx. pipiens may be less efficient vector of W. bancrofti in endemic areas of Egypt

Transmission of rift valley fever virus by different geographic strains of culex pipiens in Egypt

Previous investigations have delt with colonized Cx. pipiens and RVF virus interactions. This study evaluated the vector competence of parental Cx. pipiens populations for RVF virus and investigated variations in the vector competence among different geographic strains of this mosquito in Egypt. Cx. pipiens females were fed on viremic hamsters circulating 9.4 - 10.5 log[10] SMICLD[50] of virus. Mosquito samples were freezed at different intervals extending between 0-12 days of extrinsic incubation [E1].Transmission experiments started at day 5 of E1 when individual females were allowed to refeed on normal hamsters. The infection rates for the geographic strains tested ranged between 85% and 100% and the transmission rates ranged between 6% and 35%.Transmission of RVF virus to normal hamsters took place at days 9, 12, 15 and 18 of E1 by the different tested Cx. pipiens strains. Transmitter females contained significantly more virus than the non-transmitters except for the strain of Giza. Most of the infected Cx. pipiens individuals were of the non-transmitting type even those with high titers. Barriers at the salivary gland level competing RVF virus transmission are probably present in Egyptian Cx. pipiens. RVF virus infection was observed to adversly affect Cx pipiens. The present investigation revealed no geographic variations in the vector competence of Egyptian Cx. pipiens for RVF virus

colonization and biology of Egyptian culex univittatus [theobald]

Culex univittatus has been associated with several diseases in Egypt; however, its colonization procedures have not been described nor has its life cycle been studied in the laboratory. We found that all stages of this mosquito could be transported successfully over long distances in twilly bags stored in cooled water in a thermos. Immature stages survived well in distilled water and adult females fed on immobilized pigeon as well as giunea pigs and people. Fecundity was variable. Two third of eggs hatched when derived from the first gonotrophic cycle but this decreased in later gonotrophic cycles. Adult females were long lived and passed through several gonotrophic cycles. Blood feeding began one day after oviposition. Colonization will enable further study of this potential disease vector

Ecology of anopheles [cellia] sergent II theiobald in the Eastern Desert, Red sea Governorate, Egypt

During a mosquito survey of the inland water sources of the Red Sea Governorate, several larvae and pupae of Anopheles sergentii were collected from a breeding place located 8 km west of El-Quseir town in the Eastern Desert. This finding represents the south-eastern most boundary for this species in Africa. A full description of the ecology of the recorded area as well as of the breeding place is given in this study. In addition, preliminary laboratory observations indicated that An. sergentii females were able to oviposit both fertile and infertile eggs in small cages. This may indicate that this species consisted of stenogamous and eurygamous subpopulations