West Nile virus in Turkey

West Nile infection is caused by a virus transmitted by mosquitoes. Most people infected with West Nile virus don't experience any signs or symptoms, or may experience only minor ones, such as fever and mild headache. However, in less than one per cent of people, a West Nile virus infection can result in more serious illnesses such as meningitis, encephalitis, or polio-like paralysis. Mild signs and symptoms of a West Nile virus infection generally go away on their own. But severe signs and symptoms — such as a very strong headache, fever, disorientation or sudden weakness — require immediate attention.

The virus itself is an arbovirus (viruses that are transmitted by arthropod vectors) belonging to the genus Flavivirus which is normally found in temperate and tropical regions of the world. It was first identified in the West Nile sub-region of Uganda but has spread globally over the last 15 years, all  across the continental United States, north into Canada, and southward into the Caribbean islands and Latin America. It also became established in Europe, beyond the Mediterranean Basin, and a new strain of the virus was identified in Italy in 2012. It is now considered to be an endemic pathogen in Africa, Asia, Australia, the Middle East, Europe and in the United States.

The genus Flavivirus contains a couple of rather nasty fellows such as the dengue virus, the tick-borne encephalitis virus, the yellow fever virus, and several other viruses which may cause encephalitis.

The West Nile virus is transmitted through mosquitoes, which are the prime vectors of the virus.The infected mosquito species vary according to geographical area and usually they prefer birds of the order passeriformes for their blood meal. However, if the number of available birds becomes too low the mosquitoes become less selective and begin feeding more readily on other animal types such as humans and horses which are considered incidental hosts. The infected mosquito species vary according to geographical area and this made large scale screening efforts rather difficult. 

A new study just published in PLoS Neglected Tropical  Diseases shows the results of a study that looked at the frequency and distribution of viral infections in potential vectors and several mammal species in Turkey, where previous data indicated viral circulation. Only limited information was available on West Nile virus epidemiology in Turkey, although the country lies in the endemic zone of the virus. The researchers collected in 11 provinces in Turkey and tested over 2600 mosquito specimens for presence of the West Nile virus. In addition some 1100 sera, obtained from humans, horses, ducks, and sheep were screened for antibodies. The mosquito specimens were identified using DNA Barcoding. 

Our findings indicate virus exposure in humans and various animals in previously unexplored regions as well as a high rate of virus circulation in equine blood samples during the mosquito season. Field-captured mosquito specimens demonstrated the presence of major West Nile virus vectors among 15 species identified. West Nile virus infection was detected in 1.9% of the pooled mosquito specimens. 

DNA Barcoding analysis of the infected pools showed  the presence of very common vector species such as Culex quinquefasciatus and Culex perexiguus, however, Culex quinquefasciatus was previously not known to occur in Turkey. 

In conclusion, our findings from vectors and exposed animals indicate a wider zone of West Nile virus activity in Turkey than previously anticipated, including Eastern Thrace and Mediterranean-Aegean regions as well as Southeastern and Northeastern Anatolia. Ongoing virus circulation with limited genomic diversity was observed in certain regions. West Nile virus must be considered in etiology of human or equine febrile diseases with/without central nervous system involvement in these regions. Zones of priority for surveillance of West Nile virus activity via mosquito and/or sentinel animals must be established.

Accurate identification of mosquito species is of significant importance to reveal and predict West Nile virus emergence, because only certain species in any given area can act effectively as primary and bridge vectors to human or equine populations. Mosquitoes are really not easy to identify using morphology alone and I don't think that there is no other more reliable and more rapid way to provide the accurate identification than DNA Barcoding. This study has confirmed that once more.