This year has the dubious honor of being the year in which both Philadelphia and Pennsylvania set new records for the number of West Nile Virus cases in the area.
According to the Centers for Disease Control and Prevention, there have been 72 reported cases of West Nile Virus in Pennsylvania so far this year. The city's count for 2003 is at eight, according to the Philadelphia Daily News. There were only 62 cases statewide and six within the city in 2002.
"The biggest issue is the rain," said Laurence Buxbaum, an instructor in the Department of Infectious Disease, of the increase in cases this year. More rain means more mosquitoes, and mosquitoes spread viruses, he explained.
This time of year is a particularly risky time to contract West Nile Virus.
"September is like the main mosquito transmission month," said Emily Blumberg, a professor of Infectious Disease. To prevent infection, both she and Buxbaum recommended using insect repellent that contains DEET, a chemical that Buxbaum said "is one of the few that really work."
Buxbaum also spoke of the relative newness of the disease as a reason for its high rate of infection. According to him, a disease will often spread rapidly in a population until it runs out of candidates for infection -- in other words, until "it plays itself out."
West Nile Virus is part of the Flavi virus family, which also includes yellow fever, St. Louis virus and Hepatitis C, Blumberg said.
Native to Africa, west Nile Virus was first reported in the United States in 1999.
Since then, the number of reported cases has increased each year. Nationwide, a total of 149 cases were reported before 2002. In that year, 4,156 cases were reported, and an additional 4,137 cases have been reported so far this year, according to the CDC Web site.
However, Buxbaum stressed that this is not a particularly high rate when compared to other diseases.
"It's a relatively rare disease," Buxbaum said. "It's not worth hysteria."
There is more good news. Though the number of cases rises annually, the number of people who die from West Nile Virus is decreasing each year.
According to CDC reports, 284 people died from West Nile across the country in 2002, while 80 have died since January. Last year, two of the six people infected in Philadelphia died, the Daily News reported. There have been no fatalities so far this year.
Eighty percent of cases are asymptomatic, Blumberg said. In 20 percent of cases, the virus will cause infection and inflammation, leading to flu-like symptoms such as fever, headaches or swollen lymph nodes.
Only in a very small percentage of cases does the virus go to the brain, causing damage to the brain tissue, she added.
The disease is transmitted mostly through mosquito bites, though there have been a small number of reported transmissions through blood donation, which has led blood banks to screen donors for the disease, Blumberg said.
Despite preventive measures that can be taken, there is no specific medication for those infected with West Nile Virus.
"It's not like you can give an antibiotic," Blumberg said. However, she added, early detection of the disease is key to cutting down transmission, as well as to treating the symptoms, if not the disease.
