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First human case of West Nile virus in 2017 reported

County typically has one to two cases reported each year

OTTAWA — Although it’s late in the year, a lengthy and warm autumn allowed infected mosquitoes additional time to make their presence known. The LaSalle County Health Department recently confirmed its first human case of West Nile virus for 2017.

The department reported a resident in their 60’s tested positive for the virus in November.

They also reported human cases were previously reported in LaSalle County in 2016 (1), 2014 (1), 2013 (1), 2007 (2), 2006 (1), 2005 (1), 2004 (5), 2003 (1), and 2002 (11) during the late summer and early autumn. Additionally, local mosquitoes and birds also tested positive for the virus during the summer.

“Although we’ve experienced much cooler temperatures over the last few weeks, the confirmation of a human case isn’t surprising due to the prolonged warmer temperatures and late frost we experienced this fall,” Chris Pozzi, LaSalle County’s director of environmental health, said in a press release.

“As we look forward to the spring season and warmer weather in 2018, it’s important to remember the best way to protect yourself against illness is to wear insect repellent and to get rid of any stagnant water around your home to reduce the number of mosquitoes,” Pozzi said.

According to the World Health Organization, West Nile virus was first isolated in a Ugandan woman in 1937. It was later identified in birds in the Nile’s delta region in 1953.

Before 1997, it wasn’t considered pathogenic for birds, but a more virulent strain developed in Israel that caused the death of various bird species presenting signs of encephalitis and paralysis. Human infections have been reported in many countries for more than 50 years. 

In 1999, the virus circulating in Israel and Tunisia was imported to New York and through the subsequent years, it’s spread dramatically across the nation.

The propagation of the virus over the next decade helped highlight that the establishment of pathogens outside their current habitats represents a serious health concern.

The largest outbreaks occurred in Greece, Israel, Romania, Russia and the U.S. and are along the migratory routes of birds. In its original range, West Nile virus was prevalent throughout Africa, parts of Europe, the Middle East, West Asia, and Australia. Since its introduction here in 1999, the virus has now become firmly established from Canada to Venezuela.

In 2016, Illinois had 154 total cases of West Nile virus, according to the Centers for Disease Control. Texas had the most of any state with 370 total cases, and across the nation, there were 2,149 infections.

West Nile virus is transmitted through the bite of a Culex pipiens mosquito, commonly called a house mosquito, which has acquired the virus by feeding on an infected bird. Common symptoms include fever, nausea, headache and muscle aches. Symptoms may last from a few days to a few weeks and 80 percent of those infected won’t show any symptoms.

However, in rare cases, severe illness, including meningitis, encephalitis, or even death, can occur. People older than 50 and immunocompromised individuals are at higher risk for severe illness from the virus.

A complete listing of West Nile virus statistics for LaSalle County is available on its website at A statewide listing is available at the Illinois Department of Public Health’s website at

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