West Nile Virus Was Much Worst In 2003, as 9,862 cases 264 Deaths reported

West Nile virus was first isolated from a febrile adult woman in the West Nile District of Uganda in 1937. the ecology was characterized in Egypt in the 1950s. the virus became recognized as a cause of severe human meningitis or encephalitis (inflammation of the spinal cord and brain) in elderly patients during an outbreak in Israel in 1957. In recent years it has spread beyond its traditional boundaries, causing illness in birds, horses, and humans in Europe and now the United States. It was first discovered in the U.S. in 1999 in New York City. Since that time, WNV has been detected in humans, animals, and mosquitoes in 47 states from coast to coast.

Outbreaks of WNV encephalitis in humans have occurred in Algeria in 1994, Romania in 1996-1997, the Czech Republic in 1997, the Democratic Republic of the Congo in 1998, Russia in 1999, the United States in 1999-2003, and Israel in 2000.  Epizootics of disease in horses occurred in Morocco in 1996, Italy in 1998, the United States in 1999-2001, and France in 2000, and in birds in Israel in 1997-2001 and in the United States in 1999-2002.

In the U.S. since 1999, WNV human, bird, veterinary or mosquito activity have been reported from all states except Hawaii, Alaska, and Oregon.

In response to the threat of WNV to Michigan, in 2000 the WNV Working Group emerged from the Arbovirus Core Group.  In 2001, a toll-free hot line was established for citizens to report dead crows, as monitoring death amongst these birds can be an early indicator of virus activity in an area. Information was collected as to the location and condition of these birds, and appropriate birds were collected for testing. As a result of this effort, WNV was first detected in Michigan in August 2001, in dead crows. There were 65 WNV-positive birds detected in 10 counties including Wayne, Oakland, Macomb, Washtenaw, Jackson, Calhoun, Ingham, Barry, Ottawa, and Muskegon. In addition, 3 WNV positive mosquito pools 3 were detected in Oakland (2) and Macomb (1) counties.

This surveillance system was continued in 2002 and WNV was first detected in a dead crow from Wayne County that was confirmed to be infected with the virus on May 24, 2002. Testing of dead corvids (crows, blue jays, and ravens) was conducted from May-October. Bird testing ended October 31, 2002 with 73 of 83 Michigan counties in both the Upper and Lower Peninsulas having WNV positive birds detected. In addition to birds, there were 341 confirmed cases of WNV in horses in 45 counties in both the Upper and Lower Peninsula of Michigan. WNV is now considered to be endemic to the state.

Limited mosquito surveillance in 2002 revealed 58 positive mosquito pools in 7 of 9 counties surveyed in the Lower Peninsula of Michigan. The counties with positive mosquito pools identified were Wayne, Oakland, Macomb, Ingham, Saginaw, Tuscola, and Midland. The majority of these were Culex species, the most common mosquito in Michigan to be associated with WNV transmission. In addition, a positive Coquillettidia perturbans pool was detected for the first time in the state in 2002. This species may be important as a potential bridge vector as it bites both birds and mammals.

In 2002, Michigan as well as other Great Lakes states experienced the first documented cases of WNV in humans in this region. The first 2 cases in Michigan were reported on August 16, 2002. Although transmission of WNV ended with the first hard frost in mid-October, laboratory testing of samples continued into November and December. The Michigan Department of Community Health Laboratory received over 2900 specimens for WNV testing in 2002. Of these, there were a total of 644 laboratory positive specimens.

For 2003, a system for web-based reporting of dead birds was developed. This has allowed for rapid reporting of dead bird sightings, and has provided a means of collecting appropriate birds for WNV testing.   In 2003 this web reporting form was used over 5,000 times to report death and illness in nearly 7,000 birds and mammals, 1,800 of which were corvid species. On May 5, 2003 the first positive corvid was confirmed from Lenawee county.  A total of 89 corvids, from 75 zip codes, located in 33 counties tested positive.  The first human case occurred in early September and was followed by 18 additional cases in Huron, Ingham, Macomb, Oakland and Wayne counties.

The worst US outbreak occurred in 2003, with 9,862 cases and 264 deaths that year.

More than half of this year’s cases are in Texas, but the disease now has been detected in 47 states, and 38 states have reported cases in humans, with only Alaska, Hawaii and Vermont reporting no cases.

The US is experiencing one of its worst ever outbreaks of the West Nile virus, with the number of cases of the mosquito-borne infection jumping nearly 60 per cent since last week.

The US Centers for Disease Control (CDC) said on Wednesday that 1,221 cases and 43 deaths had been reported across the US so far this year, up from fewer than 700 cases and 26 deaths just one week ago.

“We’re in the midst of one of the largest West Nile virus outbreaks ever seen in the United States,” said Dr Lyle Petersen, director of the CDC’s division of vector-borne infectious diseases.

The number of infections reported through the third week of August is the highest it has been since the virus was first detected in the US in 1999, the CDC said.

The worst US outbreak occurred in 2003, with 9,862 cases and 264 deaths that year.

More than half of this year’s cases are in Texas, but the disease now has been detected in 47 states, and 38 states have reported cases in humans, with only Alaska, Hawaii and Vermont reporting no cases.

More serious type

About 75 per cent of this year’s cases have been in Texas, Mississippi, Louisiana and South Dakota, officials said.

About 56 per cent of cases are of the more serious type that can cause paralysis, meningitis or encephalitis, the CDC said. The remaining 44 per cent are the milder form of West Nile Fever.

Cases usually flare up in the summer because the illness is most often transmitted from infected birds to people by mosquitoes.

Victims may suffer fever and aches that can become severe or even cause death, especially in the elderly, children and other at-risk groups. There is no specific treatment for the infection.

Symptoms are often mild and many people stricken do not see a doctor, meaning cases are likely under-reported.

Experts think the mild winter, early spring and very hot summer helped stimulate mosquito breeding and the spread of the virus.

CDC officials are also looking into the possibility that the virus mutated, but so far have no information showing that happened, Petersen said.

Texas emergency

It is not clear why Texas is experiencing so many cases, but it is alarming.

Dallas, where a health state of emergency was declared this month, is experiencing an unprecedented epidemic, said Petersen.

Latest figures show there have been 640 cases of the disease in Texas. Texas state health officials said 23 people had died, including 15 in north Texas.

“Dallas has been hardest hit,” Dr David Lakey, commissioner of the Texas department of state health services, said.

So far, 11 deaths have been reported in Dallas County this year, compared with 10 in the period between 2003 – when the disease was first detected in Dallas – and 2011.

Officials last week started aerial spraying for mosquitoes in Dallas county. But it is too soon to measure the effect – it takes between three and 14 days for people to develop symptoms after being infected by a mosquito.

The best way to avoid West Nile disease is to avoid mosquito bites.

Recommended strategies

Insect repellents, screens on doors and windows, and wearing long sleeves and pants are some of the recommended strategies.

It peaked in 2002 and 2003, when severe illnesses reached nearly 3,000 and deaths surpassed 260. Last year was mild, with fewer than 700 cases.

Only about 1 in 5 infected people get sick. Early symptoms can include fever, headache and body aches. Some recover in a matter of days.

But one in 150 infected people will develop severe symptoms including neck stiffness, disorientation, coma and paralysis.

Contribution D. Chandler

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