Risk assessments need to be updated after a mosquito known to be a carrier of West Nile virus was shown to be thriving on Sheppey, according to a recently published study.

Experts from Public Health England collected samples of the different species of the insect at wetland sites across north Kent, including two on the Island, to monitor potential dangers.

At a barn and a field in Elmley, an average of 27.97 adult mosquitoes were caught each night and an average of 26.17 of them – nearly 94% – were a species called Culex modestus.

The variety is capable of spreading West Nile virus through its bite. The virus can cause flu-like symptoms that last several days, and in serious cases can cause swelling of the brain and spinal cord.

The disease, and the similar Usutu virus, were not detected in any samples taken in the study and so far there have been no reports of it in north west Europe.

“Culex modestus seems to exploit the ditches in the north Kent marshes, and owing to the large number of wild birds and farm animals, there is sufficient blood source to sustain populations" - Dr Jolyon Medlock, Public Health England

However, the scientists behind the study have warned the abundance of the insect at marshes in north Kent highlights the need to look again at it potentially reaching the UK and the importance of being vigilant.

Mosquitoes can transmit the virus between birds and humans in African countries. Although migratory birds, which are also monitored, are known to land on Sheppey after returning from warmer countries, so far none have been known to carry West Nile virus here.

It is not certain how Culex modestus reached the area, and previous surveys between 2001 and 2003 found no reported evidence of it being here.

Its dominance in the region appears to be increasing as a previous study from 2010 reported 75% of adult mosquitoes were Culex modestus.

The latest survey, carried out during the peak months of July to September in 2013, showed the species accounting for 90% of all samples collected on the marshes – however, this could be down to numbers varying from year to year depending on the weather.

Dr Jolyon Medlock, of Public Health England, said: “Culex modestus seems to exploit the ditches in the north Kent marshes, and owing to the large number of wild birds and farm animals, there is sufficient blood source to sustain populations.

“This species is recognised as a potential vector of West Nile virus, and that is why increased survey effort has targeted the region.

“The University of Greenwich currently has a PhD student, supported by Public Health England, investigating this further.

Our scientists have been contributing to the updated national risk assessment on West Nile virus.”