Global Warming Spreads West Nile Virus Further Than Ever

Global warming is pushing the limits of environment, spreading dreadful bugs worldwide into areas never present before.

West Nile Virus is spread by mosquitoes which become infected when they feed on infected birds. Infected mosquitoes then spread WNV to humans and other animals when they bite. The potential threat from human infection is the risk of causing irreversible brain damage or even death through encephalitis or meningitis. The elderly and individuals with weak immune systems are most susceptible.

The virus has circulated in Africa since at least 1937 and has been reported in the Middle East, India, Europe, and more recently in the New World since 1999. The year 2012 was the second worst outbreak of West Nile virus (WNV) cases reported, according to the Centers for Disease Control and Infection (CDC, Atlanta). In 2012, all 48 contiguous states, the District of Columbia, and Puerto Rico reported WNV infections in people, birds, or mosquitoes. A total of 5,674 cases of WNV disease in people, including 286 deaths, were reported to CDC. Of these, 2,873 (51%) were classified as a neuroinvasive disease (such as meningitis or encephalitis) and 2,801 (49%) were classified as a non-neuroinvasive disease.  There is no specific treatment, and intravenous fluids are used as supportive therapy.

The West Nile Virus is now spreading into new regions in Europe and neighboring countries, where the disease wasn't present before, according to a new study by the University of Haifa. Exceptional heat waves and a record-setting sequence of consecutive hot nights during the summer of 2010 in southeastern Europe have contributed to humidity and the spread of the disease, according to a study commissioned by the European Centre for Disease Prevention and Control (ECDC) in Stockholm.

In a study published in PLoS ONE, Shlomit Paz, and colleagues at the University of Haifa, Israel found positive correlations between several WNF cases and temperature, with the northern ("colder") countries displaying strong correlations with a lag of up to four weeks, while the southern ("warmer") countries showed immediate response.

"These results are an additional testament that global warming contributes to the outbreak of mosquito-borne and other temperature-sensitive vector-borne diseases. The indications to this are piling up in different parts around the globe," Dr. Shlomit Paz said.

The research, conducted by a team from the University of Haifa led by Dr. Shlomit Paz, also included Dr. Dan Malkinson and Gil Tzioni from the Department of Geography and Environmental Studies, along with Prof. Manfred Green, the head of the School of Public Health, and in collaboration with Prof. Jan Semenza from the ECDC.  "We used statistical tools and found that as a result of heat waves, a dramatic increase in the number of cases resulted from increased activity of the virus and a growth of the mosquito population," claims Paz.

"Significant temperature deviations during summer months might be considered environmental precursors of WNF outbreaks in humans, particularly at more northern latitudes. These insights can guide vector abatement strategies by health practitioners in areas at risk for persistent transmission cycles," the authors conclude.

Paz and colleagues are now looking into additional factors that influence the spread of the disease, such as the location of mosquito populations or various human conditions.

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