Phong trào rộng rãi của quân đội và người tị nạn trong và sau khi chiến tranh thế giới thứ II giới thiệu vectơ và virus vào nhiều lĩnh vực mới, và xu hướng này vẫn tiếp tục (Calisher năm 2005) với sự phát triển của mạng lưới giao thông toàn cầu (Tatem et al, khối lượng này, trang 293 -343). | 190 . ROGERS ET AL. Siler et al. 1926 . Widespread movements of troops and refugees during and after World War II introduced vectors and viruses into many new areas and this trend has continued Calisher 2005 with the growth of global transport networks Tatem et al. this volume pp. 293-343 . By the end of the 20th century annual epidemics of dengue were occurring in many parts of Central and South America Pinheiro 1989 Rod-riguez-Roche et al. 2005 throughout the Pacific Islands Effler et al. 2005 and South East Asia and with occasional outbreaks in North Australia Doherty et al. 1967 and Africa. . Symptoms Infection with any of the four dengue serotypes may result in a spectrum of clinical manifestations. After an incubation period of around five to six days Siler et al. 1926 Innis et al. 1988 patients develop symptoms including joint pain fever and headaches Halstead 1997 Nisalak et al. 2002 . Dengue fever has unsurprisingly been mistaken for yellow fever as well as other diseases including influenza measles typhoid and malaria Hare 1898 Siler et al. 1926 Lopez-Correa et al. 1979 Holmes et al. 1998 . Although highly uncomfortable dengue fever is rarely fatal and survivors appear to have lifelong immunity to the homologous serotype. Far more serious is dengue haemorrhagic fever DHF where additional symptoms develop including haemorrhaging and shock. The mortality from DHF can exceed 30 if appropriate care is unavailable. The most significant risk factor for DHF is when secondary infection with a different serotype occurs in people who have already had and recovered from a primary dengue infection. It is suggested that virus infection is enhanced by the presence of pre-existing heterotypic antibodies Halstead 1970 1988 Halstead et al. 1980 . Under this antibody-dependent enhancement hypothesis pre-existing antibodies bind to the heterotypic dengue virus particles but fail to neutralise them once cross-reactive antibodies have decayed below a certain level. .
