Dengue haemorrhagic fever and yellow fever

Public Health Significance of Urban Pests Mosquitoes 355 354 et al., 1969a,b; Moore et al., 1974. It is a febrile, but usually not fatal disease transmitted by Aedes spp., especially the subgenera Aedimorphus, Diceromyia and Stegomyia Jupp McIntosh, 1988; Diallo et al., 1999. Recently, epidemics of chikungunya fever have occur- red on several islands in the Indian Ocean, such as the Union of the Comoros, Madagascar, Mayotte, Mauritius, Seychelles and Réunion, as well as in southern Asia India and Malaysia Institut de Veille Sanitaire, 2006; WHO, 2006a. As of 29 March 2006, the Réunion outbreak has affected more than a fourth of the total population and has brought about extraordinarily severe cases, including meningoencephalitis and multi- organ failure, and even 155 deaths associated directly or indirectly with the infection ProMED Mail, 2006. As the virus vector in the Indian Ocean is the Asian tiger mos- quito, which had been introduced at least a century ago Fontenille Rodhain, 1989; Salvan Mouchet, 1994, there is great concern that the virus will be imported by tra- vellers and be transmitted and established in Europe by the Asian tiger mosquito. In fact, 160 cases of chikungunya disease were imported to France between April 2005 and 31 January 2006 Institut de Veille Sanitaire, 2006, and several others were imported to Germany, Italy, Norway and Switzerland WHO, 2006b. As a consequence, the ECDC, together with a group of experts, is at present conducting a risk assessment for Europe.

11.4.5. Malaria

With a high level of morbidity, but moderate mortality, malaria pestered Europe even northern Europe until the middle of the 20th century. The Second World War provided an opportunity to install wide-ranging control programmes and to rehabilitate previously neglected areas. Thus, countries in southern Europe saw a large reduction of the ende- mic disease, which finally disappeared, due to such factors as improvement of sanitary conditions, drainage of swampy areas, effective medical treatment, separation of animal and human dwellings, and the instability of the Plasmodium cycle in temperate climate zones. Malaria was declared eradicated from Europe in the early 1970s Bruce-Chwatt de Zulueta, 1980. In contrast, it has never disappeared from the south-eastern part of Turkey where, although there were considerably fewer cases in the 1970s, malaria increa- sed to the former endemic level after control programmes were largely discontinued Ça˘glar Alten, 2000. In some eastern countries of the WHO European Region, such as Armenia, Azerbaijan and Tajikistan, the number of cases of malaria increased after the dissolution of the Union of Soviet Socialist Republics, owing to the collapse of the infras- tructure and public health services Majori, Sabatinelli Kondrachine, 1999. Unlike the endemic situation in the eastern European countries, there are sporadic cases of autochthonous malaria in central and southern Europe and in the United States. These locally acquired infections result mainly from bites of Anopheles mosquitoes that have become infected by feeding on malarial tourists, immigrants, seasonal workers and other sources. In particular, travellers often return home with a case of malaria when they have underestimated the risk of becoming infected in tropical holiday destinations, have dis- regarded chemical malaria prophylaxis regimens or have been misinformed about the malaria situation at their holiday destination by travel agencies. Moreover, during the Crosse encephalitis viruses. As with WNV, SLEV has been involved in large urban epi- demics, resulting in thousands of human deaths since 1933 CDC, 2001; Day, 2001.

11.4.3. Dengue haemorrhagic fever and yellow fever

Globally, dengue haemorrhagic fever is the most important human viral disease trans- mitted by mosquitoes Aedes spp.. It is endemic in tropical and subtropical regions of Africa, Asia, Australia and South America, but at present only imported cases are found in Europe and the United States. This was not always the case, and the potential for the return of active transmission still exists, as global dengue virus transmission increases rapidly, especially in Central America and South America Malavige et al., 2004. In the United States, dengue epidemics occurred in the 1800s and the first half of the 1900s. While there apparently was no indigenous transmission between the late 1940s and the 1970s, autochthonous cases were again registered between 1980 and 1999 along the bor- der between Texas and Mexico Reiter et al., 2003. During the 19271928 dengue epide- mic in Europe, Greece was badly affected, with about a million people infected and more than 1500 deaths Cardamatis, 1929; Rosen, 1986. Ninety percent of the population of Athens was infected with the virus. However, the appearance of some level of immunity among infected people, combined with vector control programmes that targeted the yel- low fever mosquito Aedes aegypti, successfully eradicated the disease from Europe. A somewhat similar situation occurred with yellow fever, which is endemic in sub- Saharan Africa and South America. Although Europe and the United States had expe- rienced yellow fever epidemics for a while Eager, 1902; Tomlinson Hodgson, 2005, they are only affected by imported cases at present. However, unlike the situation with dengue, an efficient vaccination keeps the number of imported yellow fever cases quite low. Also, few imported cases have been reported. Travellers imported only two cases to Europe during the last four years Bae et al., 2005, and only three imported cases have been reported in the United States since 1996 Hall et al., 2002. Nowadays, the advent of the Asian tiger mosquito an efficient dengue virus vector in yellow fever mosquito-free areas of Europe and North America and the proximity of the United States to the southern dengue endemic countries have evoked a climate of uncer- tainty about the potential return of dengue fever. Preventing the further spread of this mosquito species, by using effective control measures, is now imperative. The classical yel- low fever vector and also the most efficient vector of the dengue virus, the yellow fever mosquito, could never be completely eradicated from the United States and adds to the list of possible viral vectors. Despite occasional reports from Italy Callot Delécolle, 1972 and Turkey B. Alten, Hacettepe University, Ankara, personal communication, 2001, the yellow fever mosquito is supposed to have been eradicated from Europe for decades.

11.4.4. Chikungunya fever