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West-Nile in the Caribbean

Pagès N., Vachiéry N., Lefrançois T., Giraud-Girard K., Albina E., Pradel J.. 2015. In : Changing viruses in a changing world. Montpellier : CIRAD, p. 151-152. International Congress for Veterinary Virology. 10, 2015-08-31/2015-09-03, Montpellier (France).

Since its discovery in Uganda (1937), West Nile (WN) fever historically remained confined in Africa and Middle East with sporadic incursions in Southern Europe. However, it has expanded in the last decades, and is now one of the most widespread arboviruses in the world. Nowadays WN remains present over six continents. The disease is produced by a virus (WNV, genus Flavivirus) and transmitted by mosquitoes among susceptible hosts, usually birds. The virus can also affect dead-end hosts, like humans and equines. The identification of the drivers for WN emergence and spread is difficult. At local scale, WN transmission cycle can occur through different ecosystems with involvement of different species of vectors and hosts. High viral genetic variation and wide range of vectors and hosts makes WN a complex arthropod-borne disease. Recently, up to nine different WNV lineages have been proposed. WNV has been detected in more than 60 mosquito species in 11 genera. However species in the Culex genus are considered the main WNV vectors worldwide. Major amplifying hosts are birds, with more than 300 species of birds supporting infection. Mammals are generally considered as dead-end hosts as they are not efficient WNV amplifiers. Nevertheless, multiple mammalian species, amphibian and reptiles are susceptible to WNV infection. WNV emerged in the New World in New York, 1999. Since then the virus provoked in the USA the major WNV epidemics ever recorded globally. Disease burden was high, causing significant morbidity and mortality in birds, horses and humans. The disease further spread northward (Canada) and southward. The southern spread of WNV into the Caribbean, Central and South America was apparently silent. In contrast to USA and Canada, WNV has caused no or very limited health impact on animal and human populations in the Caribbean. The apparent absence of bird mortality and clinical manifestations among humans or equines makes difficult to track WNV spread in the region. Thus, evidence for WNV circulation is mostly based on serological evidences in a region with other antigenically cross-reacting viruses potentially co-circulating. In the Caribbean, the disease was recorded for the first time in October 2001 in Cayman Islands, on a patient without previous history of travel. First serological investigations were implemented by 2001/2002 across the Caribbean Sea in Mexico, in the Greater Antilles (Dominican Republic, Jamaica and Puerto Rico) and in the Lesser Antilles (Guadeloupe). Such early wave of activities serologically enabled to detect WNV circulation among birds and equines in the Caribbean. Since then, other serological studies supported evidence for consistent WNV circulation in the Caribbean region, Central and South America, including records of sporadic human and equine cases. The Great Caribbean region is very diverse and heterogeneous. Wide environmental and climatic variation is found along its number of islands but also some continental countries/territories. The Greater and Lesser Antilles are situated at the Carrefour of North and South America, along the ¿Mississippi and the Atlantic migratory flyways¿. The most likely way of WNV introduction in the region is through infected wild birds flying from North to South America. What remains unclear is whether endemic WNV cycles were established or whether detection follows regular introduction by wild birds. Also in some islands (Martinique at least, Guadeloupe's sister island) several serological investigations have been conducted in horses. However these investigations never succeeded in evidencing WNV circulation suggesting heterogeneous distribution of WNV in the region due to (still) undetermined factors. Also, the diversity of climate and environments in the Caribbean (Greater Antilles vs Lesser Antilles) suggests different epidemiological cycles. Unfortunately, information on mosquitoes and hosts is scarce and heterogeneous, and viral isolations have been much...

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