Zdenek Hubálek and Jirí Halouzka ,br> Academy of Sciences, Brno, Czech Republic
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West Nile virus causes sporadic cases and outbreaks of human and equine disease in Europe (western Mediterranean and southern Russia in 1962-64, Belarus and Ukraine in the 1970s and 1980s, Romania in 1996-97, Czechland in 1997, and Italy in 1998). Environmental factors, including human activities, that enhance population densities of vector mosquitoes (heavy rains followed by floods, irrigation, higher than usual temperature, or formation of ecologic niches that enable mass breeding of mosquitoes) could increase the incidence of West Nile fever.
The 1996-97 outbreak of West Nile fever in and near Bucharest, Romania, with more than 500 clinical cases and a case-fatality rate approaching 10% (1-3), was the largest outbreak of arboviral illness in Europe since the Ockelbo-Pogosta-Karelian fever epidemic caused by Sindbis virus in northern Europe in the 1980s. This latest outbreak reaffirmed that mosquito-borne viral diseases may occur on a mass scale, even in temperate climates.
West Nile virus is a member of the Japanese encephalitis antigenic complex of the genus Flavivirus, family Flaviviridae (4). All known members of this complex (Alfuy, Japanese encephalitis, Kokobera, Koutango, Kunjin, Murray Valley encephalitis, St. Louis encephalitis, Stratford, Usutu, and West Nile viruses) are transmissible by mosquitoes and many of them can cause febrile, sometimes fatal, illnesses in humans.
West Nile virus was first isolated from the blood of a febrile woman in the West Nile district of Uganda in 1937 (5) and was subsequently isolated from patients, birds, and mosquitoes in Egypt in the early 1950s (6-7). The virus was soon recognized as the most widespread of the flaviviruses, with geographic distribution including Africa and Eurasia. Outside Europe (Figure), the virus has been reported from Algeria, Asian Russia, Azerbaijan, Botswana, Central African Republic, Côte d'Ivoire, Cyprus, Democratic Republic of Congo (former Zaire), Egypt, Ethiopia, India, Israel, Kazakhstan, Madagascar, Morocco, Mozambique, Nigeria, Pakistan, Senegal, South Africa, Tajikistan, Turkmenia, Uganda, and Uzbekistan. Furthermore, West Nile virus antibodies have been detected in human sera from Armenia, Borneo, China, Georgia, Iraq, Kenya, Lebanon, Malaysia, the Philippines, Sri Lanka, Sudan, Syria, Thailand, Tunisia, and Turkey (8-10). Kunjin virus is closely related to West Nile virus (11,12), representing a counterpart or subtype for Australia and Southeast Asia; some West Nile virus seroreactions in Southeast Asia may, in fact, represent antibodies to Kunjin virus.
Hundreds of West Nile fever cases have been described in Israel and South Africa. The largest African epidemic, with approximately 3,000 clinical cases, occurred in an arid region of the Cape Province after heavy rains in 1974 (23). An outbreak with approximately 50 patients, eight of whom died, was described in Algeria in 1994 (1). Other cases or outbreaks have been observed in Azerbaijan, Central African Republic, Democratic Republic of Congo (former Zaire), Egypt, Ethiopia, India, Madagascar, Nigeria, Pakistan, Senegal, Sudan, and in a few European countries.
Thank you for the information. The Romania case seems to be the most serious outbreak of the West Nile virus in a climate comparable to the U.S. climate. Romania is 91,725 square miles, approximately the size of Oregon. If the West Nile virus had been spread across the entire European continent in three years then our current experience would not be unique, however, it did not.
There is little question that West Nile is a naturally occurring virus. The unproven suggestion is that an enemy may have intentionally spread the West Nile virus in the U.S., since there are no historical precedents for a mosquito-borne virus to completely cover the U.S. in three years. Of course there is a first time for everything.
I am not convinced that established migratory bird patterns support the spread in three years, absent intervention. For example, birds do not migrate from New York to Oregon.
I guess a better example for the moment would be that birds do not migrate from NY to Montana, however,heath officials in Oregon are expecting the virus in their state any day now.