The transmission cycle of WNV involves several species of mosquitoes (primarily Culex
spp) and various species of birds. Mosquitoes become infected with WNV when they feed on a bird carrying the virus in its blood. After 10 to 14 days, the virus can be transmitted to another bird, person, or other animal such as horse, dog, cats that the mosquito bites. During blood feeding the mosquito injects the virus, contained in its saliva, into the bird, animal, or person and may cause illness. Horses and humans, are considered dead-end or incidental hosts for the virus because they do not produce enough virus to reinfect a mosquito and maintain the transmission cycle. However, they are capable of showing clinical symptoms (Bunning et al. 2002
Various test methods can be used for the diagnosis of WNV. Virus isolation can be attempted from cerebrospinal fluid (CSF), blood or tissues in cell cultures such as Vero, RK-13 cells or mosquito cell lines (Ostlund et al. 2001
). Real Time RT PCR methods were designed to specifically detect WNV. This method has demonstrated greater sensitivity than traditional RT-PCR methods and gives advantages over classical virological methods (Porter et al. 1993
, Lanciotti et al. 2000
The presence of WNV has been reported with virological and serological study results in many European countries (Hubalek and Halouzka. 1999
, Zeller et al. 2004
). In Turkey, WNV had been identified only serologically until 2009 (Meco 1977
, Ozkul et al. 2005, Ozer et al. 2007
). Subsequently, Arpaci et al. (2009)
reported the first time virological identification of WNV from graft-versus-host disease patient using RT-PCR in Turkey. However WNV has not been virologically identified from animal and vectors in Turkey.
In this study, WNV-RNA was not detected in screening horses in a Middle Black Sea Region of Turkey. However, the reasons of these negative results can depend on many factors such as the quantity of the virus in the material; region’s environmental features i.e. having cold weather conditions in winter which provides unsuitable circumstances for the presence of mosquitoes all around the year in Northern Turkey.
In conclusion, although obtained result indicated no evidence of WNV–RNA in horses, Black Sea Region of Turkey is one of the suitable places for the WNV infection. For this reason, our research will continue for the determination of the viruses in vectors and susceptible animals such as horses, dogs, e.g.