West N ile fever

Public Health Significance of Urban Pests 351 beus in Europe. Typically, An. plumbeusis a tree-hole breeder and usually does not occur at high densities. For some years, however, it has adopted several significant nuisances, using slurry pits, liquid manure pits and the like as breeding sites Schaffner et al., 2001a. Recently, An. plumbeuswas found at high larval densities in rainwater pools in used tyres Schaffner, van Bortel Coosemans, 2004.

11.4. Mosquitoes as vectors of disease

Mosquitoes are important vectors of viruses, parasitic protozoa plasmodia and filarial worms Table 11.1. Species receptive to one or more pathogens have been indigenous to Europe and the United States, but because the pathogens have either been absent or have only rarely become apparent, they mostly have been long neglected. Because of changes in travel and commerce, however, vector species and pathogens may be spread actively or be introduced passively to areas and become established.

11.4.1. West N ile fever

West Nile fever is a viral, sometimes neuroinvasive mosquito-borne disease. Due to its ongoing spread in the western hemisphere, it is becoming increasingly important. While about 80 of human infections with WNV are apparently asymptomatic, about 20 of them result in symptomatic illness, with 1 leading to encephalitis, meningitis or acute flaccid paralysis Mostashari et al., 2001. A substantial portion of people who develop severe neuroinvasive West Nile fever will suffer from long-term disability or else will die as a result of the infection Pepperell et al., 2003; Klee et al., 2004. Since the 1960s, Europe has faced West Nile fever epidemics that involve people and hor- ses Panthier, 1968. However, morbidity and mortality rates were significantly higher during the outbreaks of the last decade – in Romania 19961997, the Russian Federation 1999, France 2000 and Italy 2002 Tsai et al., 1998; Platonov et al., 2001; Murgue et al., 2001; Autorino et al., 2002 – than in earlier times, probably due to the circulation of new virus strains Gratz, 2004. The 19961997 Romanian and 1999 Russian epidemics, for example, which mainly affected human beings, had case fatality rates of nearly 10 Tsai et al., 1998; Platonov et al., 2001. Birds are important reservoir hosts for the virus, and migrating birds play an important role in the epidemiology of West Nile fever, as they regularly transport the virus from endemic areas in sub-Saharan Africa to Europe Lundström, 1999. Certain mechanisms, however, obviously prevent the virus from becoming endemic in Europe. As there is no observed association between bird mortality and WNV infection, European birds, for example, seem to have adapted immunologically to most of the circulating virus variants and may contribute to virus elimination Buckley et al., 2003. WNV activity has been found directly virus isolation or indirectly antibody detection in southern and eastern Europe mainly Hubálek Halouzka, 1999; however little is known about the situation elsewhere, probably because it has been explored inadequately. Mosquitoes 350

11.3. Mosquitoes as a pest nuisance