By June 29, West Nile virus (WNV) cases had popped up in areas of the United States, Canada, and Central America. Eleven states had recorded equine cases in 2004, and while horse owners are more educated than ever on WNV prevention, officials expect to see more cases in late summer and fall, when equine and other case counts typically soar.

In the United States, as of June 29 (according to the CDC):

• Eleven states had discovered a total of 42 equine cases this year–Alabama, Arizona, California, Idaho, Missouri, North Carolina, South Dakota, Tennessee, Oklahoma, Texas, and Virginia;
  
• Fifty-seven human cases had appeared in eight states–Arizona, California, Florida, Michigan, Nebraska, New Mexico, South Dakota, and Wyoming;
  
• Twenty-three states had confirmed WNV in a total of 845 birds; and
  
• Eleven states had detected a total of 180 infected mosquito pools: Arizona, California, Illinois, Indiana, Louisiana, Michigan, Missouri, New Jersey, Pennsylvania, Texas, and Virginia.

In Canada, avian WNV has turned up in Manitoba, Ontario, Quebec, and Saskatchewan. No Canadian horse cases have been detected in 2004 so far.

According to a June 20 ProMED-mail report, three equine cases of WNV had been confirmed in Fajardo, Puerto Rico (in the northeastern corner of the island). On June 9, WNV had been detected in two birds in Ceiba (a city in the eastern part of the country), so according to the ProMED moderator, “Evidence of West Nile virus infection of horses represents a significant extension of host range, confirming that WNV is now circulating in Puerto Rico