GIS-based prediction of malaria risk in Egypt.

Environmental variables in a malaria geographic information system (GIS) database were analysed to discriminate between governorates at high and low risk of malaria. Only Fayoum governorate was categorized as a high risk area for malaria during the last 2 decades. Discriminant models correctly classified 96.3% of the risk categories and indicated that the most important predictor of risk is hydrogeology. Further GIS spatial analysis indicated that the high malaria risk in Fayoum is associated with a unique environmental envelope of biotic (presence of both efficient malaria vectors) and abiotic (hydrogeology and soil) variables. Recommendations for surveillance and control are discussed.

GIS-based prediction of malaria risk in Egypt

Environmental variables in a malaria geographic information system [GIS] database were analysed to discriminate between governorates at high and low risk of malaria. Only Fayoum governorate was categorized as a high risk area for malaria during the last 2 decades. Discriminant models correctly classified 96.3% of the risk categories and indicated that the most important predictor of risk is hydrogeology. Further GIS spatial analysis indicated that the high malaria risk in Fayoum is associated with a unique environmental envelope of biotic [presence of both efficient malaria vectors] and abiotic [hydrogeology and soil] variables. Recommendations for surveillance and control are discussed

Preliminary observations on cross-mating of the malaria vector, Anopheles sergentii from two Egyptian oases.

Intra- and inter-strain crosses were made between randomly collected adults Anopheles sergentii originated from Tersa village (El-Faiyum Governorate) and Siwa oasis (Matruh Governorate). The success of such crosses and their effects on fecundity and fertility of the parental females and on survival and development velocities of the F1 immatures were examined. No overall heterosis effects on such attributes were detected suggesting absence of genetic differences between the vector populations in these two malarious areas.

Characterization of rice field mosquito habitats in Sharkia Governorate, Egypt.

The characteristics of the breeding water, interspecific association and seasonal abundance of 3 mosquito species within rice fields were examined in 6 districts. Larvae of Cx. antennatus were dominant (83.71% collected larvae), of An pharoensis were common (12.29%) and of Cx perexiguus were uncommon (4.0 = .0%). Breeding water has pH of 6-8, salinity of 0.05-0.35 gm Cl/L. and temperature of 21-29 degrees C. Although the relation of larval density (for each species) was positive with pH and negative with salinity and temperature however, no interaction (regression analysis) was existed among the variables (R = 0.26-0.40, P > 0.05). Significant and complete associations (CAB = 1.0, P < 0.01) were detected for Cx. antennatus with other species. During rice growing period (June to October), Cx perexiguus larvae were quite short lasting (June to August). Larval abundance varied monthly in relation to the plant growth stage. No larvae of any species were collected in short plant (< 20 cm, beginning of June) or in very long ones (130 cm in October). Higher numbers of larvae were often associated with the moderate plant growth (50-80 cm) with a peak in plants of 70 cm height in August (161.50 larvae/10 net dips for the 3 species). The highest larval density for Cx antennatus (132.50 larvae) and An pharoensis (22.25 larvae) were during August (70 cm plant) and for Cx. perexiguus (7.67 larvae) was in July (60 cm plant). So, rice fields are potential habitats for these disease vectors. The plant height and irrigation scheme are major factors affecting the abundance of these species.

The ecological characteristics of Anopheles mosquitoes associated with low malaria transmission in Siwa oasis, Egypt.

The ecology of Anopheles sergentii and An. multicolor was investigated over eight months to examine the entomological factors maintaining the low Plasmodium vivax transmission in Siwa oasis. The two species were encountered as larvae while the dominant species, Anopheles sergentii was also collected as adults. Breeding sites were characterized for the two species in six localities. Larvae of both species were common during June and November. In Bahi El Din as an indicator village with a higher endemicity, An. sergentii females were endophilic but more common inside animal sheds than in houses, attracted more to donkey-baited traps than to human hosts, more endophagic as human biters and were more common in May/June and November. Female survivorship was higher in November than in the other months. Vector potential of An. sergentii was predicted and revealed that the species characteristics (low human contact, short survival and zoophilic feeding behavior) are responsible for maintaining such low and unstable malaria in Siwa oasis.

Anopheles sergentii (Diptera: Culicidae): seasonal variation in the development rates of immatures from El Faiyum and Siwa Oasis, Egypt.

Three colonies of An. sergentii from El Faiyum (Tersa and El Nazlah) and Siwa oasis were maintained for one year under the circulating room conditions to examine the rates of immature development and survival. For each colony, the egg incubation periods and immature developmental periods (P 50 and E 50) were significantly longer at low temperatures (mean = 13.4 degrees C) during winter. Egg hatch rates and survivorships of the different immature stages did not significantly differ among seasons except for Siwa colony where rates of immature survival decreased during summer (mean = 28.5 degrees C). No differences in such estimates were observed among the three colonies. With the exception of Tersa eggs, the developmental velocity (V = 1/period)--temperature relationships were linear (r2 = 0.94-0.98). The temperature thresholds (to) were 8.64 and 7.35 degrees C with thermal constants (K) of 38.61 and 42.74 degree--days (DD) for eggs of El Nazlah and Siwa, respectively. For adult emergence (male or female) of the three colonies, the to's were 8.02-9.41 degrees C and K's were 212.34-223.71, DD required above the to to complete development. The study indicated that seasons of higher temperatures (mean = > 20 degrees C) are optimal for the development and survival of An. sergentii immatures.

Comparison of the life table characteristics of Anopheles sergentii (Diptera: Culicidae) from two malarious areas in Egypt.

Life table characteristics were examined for the malaria vector, An. serenti from two Faiyum villages: Tersa (T) and El Nazlah (N) from Siwa oasis (Sw) under constant laboratory conditions at 25 degrees C and 70% RH. Females of T, N and Sw completed 4, 5, and 2 gonotrophic cycles (gc) respectively. The first gc required a significantly longer period (p<0.05) than the subsequent ones. Development times for Sw immatures were longer (p<0.05) than for the other colonies. Life expectancies at emergence for males of the 3 colonies were significantly shorter than for their respective females. Generation time was shorter (p<0.05) for T (mean = 31.15 days) than for Sw (37.81 days) or N (43.64 days) colonies. The birth rate of Sw colony (mean = 0.33 female female/female) was significantly higher (p

Development and survival of Anopheles pharoensis and An. multicolor from Faiyum, Egypt.

Adults of Anopheles pharoensis and An. multicolor were held under cycling environmental conditions in the laboratory to examine the duration of the gonotrophic cycles, survival and life expectancy, and to examine the life table characteristics of F1 larvae. The first gonotrophic cycle took 6.14 and 7.37 days for An. pharoensis and An. multicolor, respectively. Subsequent gonotrophic cycles for the 2 species were shorter. Daily survival rates of An. pharoensis and An. multicolor in the laboratory were 0.95 and 0.93, respectively. The parity rate of field-collected females and estimates of the duration of the gonotrophic cycle yielded daily survivorship estimates of 0.89 and 0.80 for An. pharoensis and An. multicolor, respectively. Mean life expectancy at emergence was 19.0 days for An. pharoensis compared with 17.9 days for An. multicolor. Survivorship from egg eclosion to adult emergence and development time were similar for both species. Both the duration of gonotrophic cycles and mean life expectancies indicated that An. pharoensis had a greater potential to serve as a malaria vector than An. multicolor.

Selection for fenitrothion--resistance in Culex pipiens L larvae (Diptera: Culicidae).

Laboratory selection of Culex pipiens larvae by fenitrothion pressure for 24 generations resulted in 25.67 fold increase in resistance to this compound. Adults resulted from the selected larvae also acquired resistance (32.3 fold) to fenitrothion. Stability of resistance was tested and indicated that regression in resistance only occurred at lower level that regression in resistance only occurred at lower level of selection. Cross resistance to malathion and DLD slightly increased by 2.1-fold and 1.25-fold respectively that may be manifestations of vigour tolerance. It is considered that the positive results obtained here increase the probability of development of such resistance in the field. However, results of cross-resistance are encouraging as they indicate that eventual development of resistance to fenitrothion does not preclude the use of other insecticides against the resistant population.

Adult diet as a factor affecting biology of the sandfly Phlebotomus papatasi (Diptera: Psychodidae).

The effects of adult nutrients on egg retention, immature development and adult survival of P. papatasi, the important vector of leishmaniasis in Egypt were investigated. The tested nutrients were distilled water, overripe fig fruits, guinea pig blood, sucrose solution and alternative meals of blood and sucrose. Egg retention was observed in females irrespective to the type of offered nutrient (r = 0.21) but higher proportion (47%) of blood fed females had retained eggs. Duration of the life cycle was higher for the progeny of fig fed females (P less than 0.05) and mean generation time was longer for sucrose fed females (P less than 0.05). Such nutritional effect on life cycle was observed only for pre-oviposition periods and no extend effect on larval or pupal durations. The survivorship rates for eggs through adults were similar (P greater than 0.05). It is estimated that the population would increase by Ca. 15, 11, 10 and 7 folds if the mother female was fed blood, sucrose, fig or distilled water respectively. The mean life time differed significantly (P less than 0.05) among females fed on different nutrients with the highest co (life expectancy at emergence) value (14.98 +/- 2.75 days) for sucrose fed females. Males fed on distilled water, fig fruits or sucrose solution were with similar longevities P greater than 0.05). In respect to leishmania transmission, the calculated expectancies for female life beyond the infective age indicated that blood-sucrose fed females have higher capability than those fed on sucrose blood or blood alone.

The mode of inheritance of fenitrothion resistance in Culex pipiens L. larvae (Diptera:Culicidae).

The genetics of fenitrothion resistance in Cx. pipiens larvae was studied to determine its mode of inheritance. A laboratory susceptible and fenitrothion-resistant larval strains were used. Reciprocal crosses between the resistant and susceptible strains showed an F1 generation of partial dominance with slight cytoplasmic effect. The F2 generation underwent segregation into three genotypes, viz. susceptible, hybrid and resistant in the ratio of 1:2:1. The progenies of backcrosses to resistant and susceptible parents were in a 1:1 ratio of the same phenotypes as the parents and hybrids involved. After selection, the progeny of the back-crosses to resistant parent exhibited full resistance. It is concluded that fenitrothion resistance in Cx. pipiens larvae is due to monofactorial inheritance with partial dominance and slight cytoplasmic effect.

Factors affecting the human-feeding behavior of anopheline mosquitoes in Egyptian oases.

Blood meals were tested by a direct enzyme-linked immunosorbent assay (ELISA) for 424 Anopheles sergentii and for 63 An. multicolor collected in Siwa, Farafra and Bahariya oases in the Western Desert of Egypt. Both species were highly zoophilic. Human blood-feeding by An. sergentii was less common in Bahariya (2.3%) and Farafra (1.3%) than in Siwa (15.3%). A likely explanation is that large domestic animals are held at night inside houses in Bahariya and in Farafra whereas in Siwa, animals are usually housed outdoors in sheds. These patterns of An. sergentii human-feeding behavior may contribute to the persistence of low-level Plasmodium vivax transmission in Siwa in contrast to negligible or no transmission in Bahariya and Farafra.

Interpretation of low-level Plasmodium infection rates determined by ELISA for anophelines (Diptera: Culicidae) from Egyptian oases.

Plasmodium infection rates determined by enzyme-linked immunosorbent assay (ELISA) were compared for Anopheles sergentii (Theobald) and An. multicolor Cambouliu in Siwa Oasis, Egypt, an area with low-level Plasmodium vivax transmission, and in Bahariya and Farafra, two other Egyptian oases which appear to be free of malaria. Initial testing indicated that 4.4% (23 of 518) and 0.8% (4 of 518) of the An. sergentii were positive for P. vivax and P. falciparum, respectively, and that 1.4% (1 of 71) of the An. multicolor were positive for P. falciparum. However, after two confirmational tests, only 1.2% (6 of 518) of the An. sergentii remained consistently positive for P. vivax. Initial ELISA absorbance was not a useful predictor of potential false positive reactions in the P. vivax assay. Paradoxically, the six ELISA-positive An. sergentii were from the two malaria-free oases. This study raises the question of whether ELISA-positive reactions for anopheline vector species provides unequivocal evidence for transmission in areas of low malaria endemicity.

Fauna of anopheline mosquitoes (Diptera: Culicidae) in A.R. Egypt. "Historical background and present situation".

Based on the available reports of the mosquito surveys carried out over eighty years starting from 1903, the author reviewed and updated the information on distribution and abundance of the anopheline mosquito fauna of Egypt. The present status of twelve reported species are discussed.

Sandflies (Diptera: Psychodidae) in Mersa Matruh and Siwa oasis, A.R. Egypt.

Sandflies were surveyed 3 times during 1989 in Mersa Matruh city and Siwa oasis to investigate their status. Only Phlebotomus papatasi was identified from inside houses and outdoor sites. More flies were collected in Mersa Matruh than in Siwa. Results document for the first time the presence of P. papatasi in Mersa Matruh and verify its presence in Siwa oasis.

Feeding patterns of Phlebotomus papatasi and Phlebotomus langeroni (Diptera: Psychodidae) in El Agamy, Egypt.

Blood meals from 602 Phlebotomus papatasi (Scopoli) and 49 Phlebotomus langeroni Nitzulescu were collected in El Agamy, Egypt, and were identified using counterimmunoelectrophoresis. Blood meals were tested against specific antisera of eight vertebrate hosts (human, cat, dog, rat, sheep, goat, general avian, and general bovine). Of 597 P. papatasi collected indoors, 594 contained human blood and three had mixed blood meals (human-dog, human-rat, and human-avian). Four of five P. papatasi collected outdoors contained human blood and one contained avian blood. All 39 P. langeroni collected indoors had fed on humans. Six of 10 outdoor-collected P. langeroni had fed on human blood, 2 on dog, 1 on cat, and 1 on rat blood. Both P. papatasi and P. langeroni feed predominantly on humans in El Agamy, Egypt. The documented feeding on humans and dogs by P. langeroni supports the role of this species as the primary vector of visceral leishmaniasis at the El Agamy focus.

Anopheles sergenti (Theobald) a potential malaria vector in Egypt.

Two immunoassays for malaria sporozoite detection and identification, the immunoradiometric assay (IRMA) and the enzyme-linked immunosorbent assay (ELISA) using the species-specific monoclonal antibodies are routinely performed in our laboratory. We analyzed (573) anopheline mosquitoes of A. sergenti (463), A. pharoensis (81) and A. multicolor (29) collected from Siwa-oases and Faiyum Governorate (two known active malaria foci in Egypt), for detection of P. falciparum and P. vivax sporozoites. P. falciparum sporozoites were detected by both IRMA and ELISA tests in two A. sergenti mosquitoes (one from Siwa 1/389 = (0.26%) and one from Faiyum Governorate 1/74 = (1.35%)). No P. vivax sporozoites were detected. This finding is important in explaining the malaria transmission and provide first incrimination of An. sergenti as the responsible vector of malaria in Siwa-oasis, Egypt.