The University of Illinois is reporting the first West Nile virus death in a dog in the United States. Officials at the school say the eight-year old Irish Setter-golden retriever mix may have had another immunity compromising infection that contributed to his death. The virus primarily attacks birds, but mosquitoes can pass it to humans, horses and other hosts. The only other documented case of West Nile in a dog occured in Botswana in 1978. Dr. Jeff Bender is an assistant professor of veterinary public health at the University of Minnesota. He says pet owners shouldn't worry: