Does the mosquito Culex pipiens represent a potential vector of hepatitis C virus?

Infection with hepatitis C virus (HCV) is a public health burden in several countries. Although transmission through blood is the most likely potential route of HCV infection, other sources warrant exploration. This study was designed to examine the possibility that the mosquito Culex pipiens (Diptera: Culicidae) might serve as a vector of HCV. A series of laboratory experiments were conducted in female Cx. pipiens that were fed on blood taken from HCV patients and tested for the presence of HCV RNAs using a reverse transcription polymerase chain reaction technique. In addition, the ability of the female mosquito to transmit HCV to human blood through membrane feeding or to its offspring (larvae) was tested. Although positive strand RNA was detected on days 1,7 and 14, negative strand HCV RNA was detected in mosquito body homogenate on days 7 and 14. Positive strands were also detected in the head, alimentary canal and salivary glands of mosquito adults at 1 week post-feeding, as well as in their offspring (larvae). An ex vivo assay demonstrated that HCV-infected mosquitoes were able to transmit the virus RNA into naive human blood samples via a membrane feeder. The present data indicate that the mosquito Cx. pipiens may be a potential vector of HCV.

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.