By October 10th almost all areas should have experienced their first frost event, and mosquito activity should be severely suppressed. Case numbers will continue to increase as the year ends, but these are new reports of old cases, not new exposures to the virus. 

Three to eight counties are expected to report cases in the week of Sept. 19th - 25th. Brown County has a 1 in 2 chance of reporting a case, and all other counties are below this level of risk. Killing frosts may start to occur towards the end of this week. 

Four to ten counties are expected to report human cases in the week beginning September 12th. By Sept. 18th, we should be 95% through the WNV season. Estimated risk is definitely declining, but numbers will continue to increase as old cases are reported. Aedes vexans populations are behaving oddly. 

Five to fifteen counties are expected to report human cases in the week beginning September 5th. By Sept. 11th, we should be 9/10 through the WNV season. Estimated risk has begun to decline, but mosquitoes are still infected and their populations are not yet crashing as expected.   

Seven to seventeen counties are expected to report human cases in the week of August 29th - September 4th. By Sept. 4th, we should be 4/5 through the WNV season. Estimated risk has begun to decline due to unexpectedly cool days, and risk will be lower than earlier predicted if it stays cool. 

Seven to seventeen counties are expected to report human cases in the week of August 22nd - 28th. By the end of the week, we should be 3/4 through the WNV season. Risk is beginning to fall, but ever so slowly. Citizens should be encouraged to take reasonable precautions when outdoors. 

Seven to eighteen counties are expected to report human cases in the week of August 15th - 21st. By the end of the week, we should be 2/3 through the WNV season. This is the beginning of the home stretch, but 1/3 of cases are still waiting and control measures are still recommended. 

Seven to eighteen counties are expected to report human cases in the week of August 8th - 14th. By the end of the week, we should be halfway through the WNV season. Vector counts are low, but this is not a good thing - mosquito infection rates are higher than usual. 

Six to fourteen counties are expected to report human cases in the week of August 1st - 7th. Brown County is more likely to report a case than not. Our model continues to suggest that this will likely be an above-average year for human WNV in SD. 

Four to ten counties are expected to report cases in the week of July 25th - August 1st. We continue to see evidence that 2016 will be an above-average year for WNV in SD; specifically, additional human cases and positive mosquitoes have been reported. Other states are observing early cases. 

Four to eight counties are expected to report at least one human case. Due to lower temperatures and rain, some counties in the east have fallen in risk this week, but this is expected to reverse as temperatures again rise above normal. By the 24th, we will be 1/6 of the way through total 2016 cases. 

Brown County is estimated to have a high chance (3 in 5) chance of reporting a case. Three to seven counties are estimated  to report at least one human case. Yearly estimates have been updated, but 2016 is still just a slightly-above-average year. We recommend continuing early spraying efforts. 

There has been a confirmed human case in Minnehaha, and risk is doubling every week. Brown now has a 1 in 2 chance of reporting a human case, and Minnehaha a 1 in 4 chance. We expect two to five counties to report human cases this week. 

Mosquitoes in SD are positive for the virus, and the first report was early this year. There is an increasing chance (1 in 4) that the most populated counties will report cases. Although outdoor activities during the July 4th holiday increase risk, the holiday is not responsible for large spikes in human cases.

After a warm start, the year has settled back down to historical average temperatures. The season has begun and there is a small (1 in 8) chance that our most populated counties will see human cases in this week. There is a larger chance (1 in 6) that we will see cases somewhere. 

We are still too early in the season to see substantial numbers of cases. Temperatures have returned to normal in the past few months, but the state may be warmer than usual over the next weeks. Precipitation is above normal. When the season does begin, we expect that there will be more cases than usual. 

The West Nile Weekly provides up-to-date information about West Nile virus (WNV) in South Dakota. We use records of human cases, information about current mosquito abundance and infection, and recent weather to estimate the risk of human infection across the state