Studies On The Role Of Mosquitoes-birds-mosquitoes Cycle In The Transmission Of West Nile Virus

West Nile virus (WNV) (family Flaviviridae, genus Flavivirus,) can cause West Nile fever or meningitis/encephalitis, sometimes fatal illnesses in human. Transmission cycle of WNV in nature includes bird to mosquito to bird, human and horses are end hosts. To date, about more 80 mosquitoes species and 300 birds species have been identified infection with WNV in CDC's (Centers for Disease Control and Prevention, USA) reports.The virus was originally isolated in 1937 from a febrile human who resided in the West Nile District of Ugan. Since then, it has been isolated in western and central Asia, the Middle East, southern and eastern Eourope. In 1999, WNV was isolated in New York City for the first time, and spread rapidly across North America subsequently, resulting in human deaths and in the deaths of untold numbers of birds, mammals, and reptiles. During the next four summers it spread with incredible speed to large portions of 46 US states, and to Canada, Mexico, Central America and the Caribbean, this spreading in western hemisphere has become a compelling public health issue in worldwide.CDC has reported about more 332 birds species infected with WNV in America, including Passeriformes birds ( 129 species), Anseriformes (32), Falconiformes(27),Galliformes(22),Caprimulgiformes(20)and Psittaciformes (16) . Among these birds, 77 species are introduced birds, yet 3 species are unknown origin. Birds also become infected with WNV through means other than arhropod transmission. The five most competent species were passerine in experimental condition, i.e.Blue Jay (Cyanocitta cristata), American Crow (Corvus brachyrhynchos), Common Grackle (Quiscalus guiscula), House Finch ( Carpodacus mexicanus) and House Sparrow (Passer domesticus) . Various WNV strains could lead to kinds of viremia and deaths in birds.More than 80 mosquito species are demonstrated infection with WNV in worldwide. Members of the Culex genus account for the majority of the infected mosquitoes and are considered as the primary vectors. But studies indicate that major vectors vary with zones ; the susceptivity and transmission efficacy of different mosquitoes strains to WNV are differences. Seasonal shift of blood-feeding and spatio-temporal distributing of mosquitoes are favor of transmission of WNV between mosquitoes and birds.There are many habitats for wintering of migratory birds in the mainland of China. The primary vectors, host and entironment for transmission and prevalence of WNV are available in our country. It seems unlikely that China would be excluded from epidemic of WNV. There are 4 reasons for this. Firstly, it is possible that WNV enters the country with migrating of the birds. Secondly, the lawful and/or unlawful trade for domestic fowl and birds among nations may lead to the introduction of WNV by seaport. Thirdly, all the members of Cx. pipiens complex distribute extensively in the country, and the Cx. pipiens pal lens , Cx. pipiens quinquefasciatus, Cx. tritaeniorhynchus, Aedes albopictus and Ae. aegypti are identified as potential vectors of WNV in China. Fourthly, the former investigations suggest that WNV antibody exists in the serum of human population and birds in some areas. The above factors increase risks of epidemic of WNV in China.It needs to study native mosquitoes' and birds 'role in the transmission cycle of WNV in China, including host-feeding pattern of preponderant mosquitoes to the potential host of WNV; virus detection of potential host and mosquitoes collected in fields; susceptivity of Leghorn chicken with antibodies of JEV to WNV. Above work were carried out in field and laboratory. The results are as follows:1. Bloodfeeding behavior of mosquitoes based on animal baits in the fields In a town field near to mountain, Cx. pipiens pallens collected by animals baits-traps are more higher significantly than other mosquito species of collected. Attractting efficiency of chicken to mosquito differs significantly from that of rats and sparrow (SE=54. 39, T=0. 002, T=0. 006) . There are insignificantly attractting efficiency between chicken and pigeon (SE=54.39, T=0.057) . In multi-water system rural field, Cx. pipiens pallens collected by chicken baits traps differs significantly from that of rats, pigeon and rabbit baits (F=997. 661, P=0. 000) . The number of same mosquitoes species collected in animals stalls varies from each stall (F=6. 950, P=0. 000). In sheep stall, Cx. pipiens pallens is the most abundant; whereas, Cx. tritaeniorhynchus and An. sinensis are the most abundant in Milch cow stall. Preponderant mosquitoes in milch cow stall, pig stall, pigeon stall, sheep stall and chicken stall are Cx. tritaeniorhynchus and An. sinensis, Cx. tritaeniorhynchus and Cx. pipiens pallens, Cx. pipiens pallens, Cx. pipiens pallens , Cx. tritaeniorhynchusand Cx. pipiens pallens respectively.2. Analysis of blood-meals of engorged mosquitoes collected in fieldsGenomic DNA from blood mosquitoes was extracted and then was used to polymerase chain reaction analysis. Only mammalian Cytb fragment (772bp) was detected in blood-meals of mosquitoes collected in fields. No avian Cytb fragment was detected in engorged mosquitoes collected in fields.3. Virus detection of mosquitoes, avian blood and chicken bloodVirus molecular detection for WNV in mosquitoes, avian blood and chicken blood indicated that no positive viral RNA fragments were detected except 2 individuals of Carpodacus erythrinus in all samples. It implies that WNV nucleic acid fragments detected in 2 individuals of birds originate from Eg101 strain based on bioinformation analysis. Detection of WNV antigen is negative in those two birds. 4. Protection of JEV vaccine from infecting WNV for leghorn chickenEach Leghorn chicken immuned by JEV vaccine (JEV antibodyl: 80) were bited by 5 Aedes albopictus infected with WNV blood-meal, 7 of 32 leghorn chicken were detected positive viral RNA fragment of WNV; 2 of 11 chicken inoculated via hypodermic were detected positive viral RNA fragmentof WNV too. The results implies that Leghorn chickens with JEV antibody can not be completely protected to infection of WNV.