LITTLE ROCK, Ark. (AP) — Arkansas has the most cases of West Nile virus since 2007 and the state Health Department said Thursday that the number of people sickened by the mosquito-borne illness is expected to grow.Ten cases have been confirmed so far, and August is ordinarily the most active month for the disease, said Susan Weinstein, state public health veterinarian.The illness is spread from birds to mosquitoes and transmitted to humans. In about 1 percent of cases, people with the virus can develop brain swelling, which can be fatal.About 20 percent of people infected show symptoms that include fever, headache, body aches, joint pains, vomiting, diarrhea, or a rash, Weinstein said. Those symptoms are common among any number of illnesses, so the department has asked doctors to send samples from suspected cases to outside labs for testing.There is a time lag for positive tests to be reported to the Health Department, so most cases from August likely haven't been logged yet.Weinstein said she expects physicians will heed the call to have more patient samples tested."I think when that happens our numbers will likely go up," she said.Weinstein said the drought Arkansas has been experiencing may be responsible for the uptick in cases."One possible explanation could be with water sources drying up, the sources that are where not only mosquitoes are concentrated but also birds are concentrated," Weinstein said. "It puts the vectors in closer contact with one another.""It's not proven, but it makes good sense," she said.The Health Department is urging people to take precautions against being bitten by wearing insect repellent, dumping standing water and wearing protective clothing, particularly around dawn and dusk when mosquitoes are most active.People most at risk for serious illness are those age 50 and older and people with health conditions that include cancer, diabetes, high blood pressure, kidney disease, and organ transplants.West Nile virus first emerged in Arkansas in 2002, when 43 cases were detected, and between 20 and 30 cases were confirmed for several years following. After 20 cases in 2007, cases dropped to nine in 2008, six in 2009, seven in 2010 and one last year.Weinstein noted that surrounding states have seen a greater spike in cases."We are just seeing a little bit of a lag in it," she said.West Nile data from this year from the Centers for Disease Control and Prevention in Atlanta shows that Pulaski County had three cases, with one each in Columbia, Sebastian and Union counties. Not all the confirmed cases have shown up on the CDC's map.Copyright 2012 The Associated Press.