Isolation of stem cells from the mid gut epithelium of Culex pipiens mosquitoes (Diptera: Culicidae).

Stem cells are undifferentiated cells that remarkable ability to self-renew and produce differentiated cells that support normal development and tissue homeostasis. The authors isolated spherical stem cells from the midgut epithelium of the late third larval instars of Culex pipiens mosquitoes. In vitro, cultivated epithelial stem cells were able to proliferate and differentiate in fresh culture for 48 hr in absence of 20- hydroxyecdysone (20-E). The stem cells were the most common cells in the initial culture. One hundred of epithelial stem cells had been cultured. After 24 hr became 132 cells, 78% was undifferentiated stem cells and 8.3% &13.7% was enterocytes and goblet cells respectively. This ratio slightly decreased after de 48 hr to be 74% undifferentiated stem cells, 4.5% enterocytes and 5.6% goblet cells. After 72 hr the undifferentiated stem cells were not able to proliferate .The most differentiated goblet and enterocytes survived few days then died.

Distinguishing the two forms of Egyptian Aedes (Ochlerotatus) caspius Palias species (Diptera: Culicidae) by ultra structure micrographs of eggs.

Ultrastructure of the two forms autogenous and anautogenous eggs of Aedes (Ochlerotatus) caspius of Egypt are described using Scanning Electron Microscope (SEM). The eggs of the two forms are slightly boat shape with quite difference in width. Chorionic cells of the ventral surface are ultimately different in both forms in shape, width of reticulum, number and size of tubercles. The chorionic cells of the autogenous form's egg are elongate, narrow and almost curved with unusually wide, outer reticulum contain 2 - 13 large tubercles along with a few number in small size. However, the anautogenous form's egg, the chorionic cells of the ventral surface fairly distinct, very regular in outline with thin reticulum and usually hexagonal, each cell contain one or two large tubercles with many small scattered peripheral tubercles. Fine structure micrographic work of eggs of the Egyptian Ae. caspius provides new morphological evidence that both autogenous and unautogenous forms are certainly different and suggests that those forms are two distinct species.

Vectorial competence of Phlebotomus papatasi (Diptera: Psychodidae) to transmit two old world Leishmania species: Leishmania major and L. Tropica.

The vectorial competence of Phlebotomus papatasi for two old world Leishmania species, L. major & L. tropica was investigated. Phlebotomus papatasi originally collected from Suez Governorate, were membrane fed on homogenized hamster's lesion infected with L. major, MHOM/EG/06/RTC-63, and L. tropica, MGER/EG/06/RTC-74 identified from patients with suspected CL in Northern Sinai, Egypt. Fed flies were dissected at different time intervals and examined microscopically to determine the infection rate and parasite intensity. The feeding rate of P. papatasi on L. major (58.69%) was found higher than on L. tropica (45.99%). Infection rate with L. major (60.19%) was significantly higher than that with L. tropica (39.73%). Transmission by bites in case of P. papatasi/L. tropica failed. A characteristic L. major lesion was developed on the foot pads region 120 days post infective bites on healthy hamster. It is therefore concluded that P. papatasi is a much more effective vector for L. major than for L. tropica.

Potential for Culex pipiens to develop resistance against Bacillus sphaericus toxins.

Susceptibility of field Culex pipiens populations to Bacillus sphaericus and the possibility of resistance development in the selected laboratory colony were investigated. 180 populations collected from Giza and Qualyobia over one year show no marked variation at LC50 and LC90 values. Larvae of laboratory colony of Cx pipiens were subjected to selection pressure with a preparation of Bacillus sphaericus strain 2362 at LC80 values for 20 successive generations. The selected laboratory colony began developing resistance at F10 (RR = 1.69) when compared with its unselected counterpart. The magnitude of resistance increased gradually and reached 33 fold by F20. The unselected colony reared without any exposure to the B. sphaericus toxin, did not show any marked change in their susceptibility to this microbial agent.

Development of Wuchereria bancrofti in Culex pipiens L. (Diptera: Culicidae) exposed in the larval instar to sublethal dosages of insecticides and one insect growth regulator and their influence on reproduction of filaria-infected mosquitoes.

The effects of exposure of Culex pipiens larvae to sublethel concentrations of larvicides on uptake, development of Wuchereria bancrofti, survival rate and reproduction of filaria-infected mosquitoes were investigated. Fourth instar larvae of Cx. pipiens were exposed to LC40 of the surfactant Triton X-100, the insect growth regulator DPX alone or combined with LC10 of the surfactant and permethrin alone or combined with LC10 of the surfactant. Adults that survived insecticide treatments and controls were infected by allowing them to feed on microfilaremic volunteers. Significant reduction in the uptake of microfilaria was observed in groups treated with Triton X-100 alone or combined either with permethrin or DPX when compared to control. The overall infection and infective rates were significantly reduced in mosquitoes treated with Triton X-100 either alone or combined with permethrin. Treatment with Triton X-100 and DPX prolonged the extrinsic incubation period (EIP) and retarded the development of filarial larvae, while permethrin either alone or combined with Triton X-100 and DPX combined with Triton X-100 shortened the EIP. All larvicides reduced the number of infective larvae (L3)/mosquito and induced deformities among he different parasite stages, especially in mosquitoes treated with combination of permethrin and Triton X-100 or mixture of DPX and Triton X-100 where 36% and 54.9% respectively of L3S were deformed. In treated mosquitoes, a low percentage of L3S was detected in the head and proboscis region while the majority was trapped in the thoracic region. The survival rates of mosquitoes were reduced in cases treated with permethrin, DPX and Triton X-100 while treatment with mixture of DPX and Triton X-100 induced higher rate of mortalities when compared to control. Egg production of filaria- infected Cx. pipiens was significantly reduced in mosquitoes treated with DPX and Triton X-100. It was observed that the addition of Triton X-100 to DPX or to permethrin significantly reduced egg production. The results suggest that sublethal concentrations of larvicides especially Triton X-100 applied to 4th instar larvae of Cx. pipiens could effectively interfere with the development of W. bancrofti in Cx. pipiens and reduced the survival rate and fecundity of the vector.

Evaluation of arthropod-borne viruses and other infectious disease pathogens as the causes of febrile illnesses in the Khartoum Province of Sudan.

The relative importance of arthropod-borne and other disease pathogens as the cause of an outbreak of febrile illnesses was assessed during August 1988, following severe flooding in Khartoum, Sudan. A total of 200 patients with acute febrile illness and 100 afebrile controls were enrolled in the study during October and November 1988; at the Omdurman Military Hospital, Khartoum, Sudan. Sera were tested for IgM and IgG antibodies to six arthropod-borne viruses by an enzyme-linked immunoabsorbent assay, and for similar antibodies to Lassa fever, Crimean-Congo hemorrhagic fever, and Ebola and Marburg viruses by an indirect fluorescence assay. Thick and thin blood smears were examined microscopically for malaria parasites, and fecal and blood specimens were tested for bacteria by standard culture methods. Among the acute and convalescent sera collected from 67 febrile patients, five cases were caused by sandfly fever Sicilian (SFS), six by sandfly fever Naples (SFN), and 12 by unidentified phleboviruses. Of 233 remaining unpaired, acute-phase sera collected from cases and controls, 49 (21%) had IgM antibodies to SFS or SFN, RVF, West Nile (WN), and Chikungunya (CHIK) viruses. Forty-three (22%) of 192 febrile cases and two of the 100 afebrile controls were positive for Plasmodium falciparum, and bacterial enteropathogens were associated with 25 (13%) cases and four controls. These data indicated that phleboviruses and to a lesser extent, WN, P. falciparum, and enterobacterial pathogens were causes of acute febrile illnesses following the 1988 flood in Khartoum, Sudan.

Identification of endemic foci of filariasis by examination of mosquitoes for microfilariae.

Studies were conducted in the Nile Delta of Egypt to determine the feasibility of detecting Wuchereria bancrofti microfilariae (Mf) in mosquitoes as a primary surveillance method for the identification of filariasis-endemic villages. Initial experimental studies evaluated the ingestion, survival, and migration rates of W. bancrofti Mf in Culex pipiens and Culex antennatus after mosquitoes were fed on infected volunteers. In 2 villages, 1,684 bloodfed mosquitoes were dissected during the night immediately after collections inside houses. In the village of Kafr Tahoria, Mf were found in 27 of 519 Cx. pipiens and in one of 8 Anopheles pharoensis. In Tahoria, Mf were detected in 7 of 799 Cx. pipiens and in one of 302 Cx. antennatus. Identifying filariasis-endemic villages based on the detection of Mf in mosquitoes may be a useful strategy for epidemiologic studies or for filariasis control programs.

The ultrastructure of the foregut and its influence on bancroftian microfilariae ingestion in three Egyptian mosquito species.

Laboratory observations on the uptake of bancroftian microfilariae (mf.) by three Egyptian mosquito species revealed that microfilariae ingested by some tested species were badly damaged during ingestion. The foregut structures in Culex pipiens, Aedes caspius and Anopheles multicolor were investigated by light and scanning microscope techniques. In Ae. caspius which have well developed pharyngeal armatures, and An multicolor which have well developed cibarial armatures, high proportion of microfilariae were scored and damaged. Vice virsa, Cx. pipiens, considered as the main vector of bancroftian filariaris have neither developed pharyngeal nor cibarial pumps, the percentage of damaged mf was very small. The relationship between the injury of mf. in mosquito midgut and the presence of the foregut armatures was discussed.

Comparative exsheathment of microfilariae of Wuchereria bancrofti in certain mosquito species.

The exsheathment of ingested microfilariae (mf) of Wuchereria bancrofti in their vector Culex. (Cx.) pipiens and in a refractory mosquito species Aedes (Ae.) caspius was assessed. No exsheathed mf were encountered in the mid gut of tested mosquitoes, while they were observed in abdomen and thoracic muscles. All exsheathed mf migrated from the mid gut of both tested species. The lowest percentage of ingested mf was recorded in the mid gut of Cx. pipiens and the thoracic muscles of Ae. caspius one day post feeding. On the other hand, 94.2% out of the exsheathed mf reached the thoracic region of Cx. pipiens and one-tenth of this proportion was observed in the thorax of Ae. caspius. Failure of a large percentage of mf to exsheath after being ingested in the Ae. caspius indicates inefficient vector ability to support the filarial development to the infective stage.

Exposure variables in bancroftian filariasis in the Nile Delta.

To demonstrate focality of filariasis within endemic rural areas and to define exposure variables which may influence this phenomenon, the population of an agrarian endemic village, of 12,500 individuals, in the Nile Delta of Egypt was censused. A sequential sample of individuals residing in every fifth house was tested for microfilaremia (239 households with 8.6 +/- 3.5 individuals per household (HHD). Three areas of the village were tested simultaneously and a questionnaire was filled out for each sampled HHD with special emphasis given to the entomological and environmental factors that might affect filarial infection. One area (area A) had a higher intensity of larvae and biting adults of the main filarial vector, Culex pipiens, than the other two areas (areas B and C). Of the 1488 persons who agreed to be tested in the three areas 181 (12.2%) were microfilaremic. Microfilaremia prevalences were the same in males and females and microfilariae were present in all age groups. Filarial infection was most prevalent in area "A" (1.16 +/- 0.14 infected people per HHD) than in area "B" (0.44 +/- 0.11) or "C" (0.72 +/- 0.10) (ANOVA; p = 0.0003). several possible predictor variables were analyzed by logistic regression with the presence of infection as the response variable. Among individuals residing around the main Cx. pipiens development sites, those living in houses facing vacant land are exposed to more mosquito bites and had a greater chance of having filarial infection (relative risk [RR] = 1.5; logistic regression, P = 0.0089). People residing in large households had a reduced chance of having filarial infection (RR = 0.87; logistic regression, p = 0.0015). These data show that the distribution of microfilaremic individuals is uneven within the study village and suggest that small HHD and houses that bordered open areas containing mosquito development sites are potential risk factors for acquiring filarial infection.

Survival estimates for adult Culex pipiens in the Nile Delta.

In an endemic area for Wuchereria bancrofti filariasis in the Nile Delta, survival of adult female Culex pipiens was estimated by parity rate, mosquito infection and infectivity rates. Infection rates and 4th instar larval populations, as well as infection and parity rates, were linearly correlated. Infectivity correlated only with parity rates. These associations corresponded to parallel changes in ambient temperature. Although survival calculated from parity rates measured longevity of both infected and non-infected Cx. pipiens, survival based on infection and infectivity was a more reliable indicator for parasite transmission.

A possible route for the introduction of Rift Valley fever virus into Egypt during 1977.

Rift Valley fever (RVF), which was enzootic in Sudan in 1976 and epidemic in Egypt in 1977-78, may have been introduced into Egypt from Sudan via sheep transported along Lake Nasser. A hypothesis is presented which describes sheep transport from holding areas in north-central Sudan, where RVF was epizootic, to live animal markets in southern Egypt. Travel time from north-central Sudan to the Aswan area was less than 5 days, approximating the incubation period of RVF virus in sheep. Reintroduction of RVF or other diseases from Sudan into Egypt will be facilitated by the construction of new roads linking the two countries.