West Nile disease: review of clinical features and risk factors associated with severe disease

West Nile Disease (WND) is an acute viral disease that is transmitted by a mosquito vector. Birds are the virus reservoirs and the natural amplifying hosts for the life cycle of the virus. Mammals, such as horses and humans, are secondary accidental hosts. In human cases the disease can be asymptomatic or show mild systemic symptoms, such as fever, headache, myalgia, fatigue, anorexia and lymphoadenopathy, and a non-pruritic maculo-papular rash can occur. In the elderly and immunocompromised severe clinical manifestations include the West Nile Neuro-invasive Disease (WNND): encephalitises, meningitises, meningo-encephalitises, Guillain-Barre-like syndromes, polyradiculoneuritis and acute flaccid paralyses. In the last 10 years many European countries have experienced outbreaks in animals and in humans (Romania, the Czech Republic, France, Italy). The increasing number of human cases indicates the public health threat of WND and the importance of achieving a better case definition of this disease at international level. The aim of this article is to scrutinise the available literature for the most frequently occurring clinical features of WNND and detect any associations with pre-existing risk factors.