Case Study 8 A healthy 49-year-old man from Manhattan, New York, presented with a fever and malaise three days after returning from a horseback riding trip on the Western slope of the Rocky Mountains. He removed four ticks from his body and reported chills, fever, and severe myalgia. His symptoms resolved, only to recur two days later. He had a fever of 100.6º F (38.1º C), conjunctivitis

A healthy 49-year-old man from Manhattan, New York, presented with a fever and malaise three days after returning from a horseback riding trip on the Western slope of the Rocky Mountains. He removed four ticks from his body and reported chills, fever, and severe myalgia. His symptoms resolved, only to recur two days later. He had a fever of 100.6º F (38.1º C), conjunctivitis, and a sore throat. His WBC count was 2.0 x 10⁹ /mL, and neutralizing antibodies were undetectable in acute serum but were 1:40 in convalescent serum.

Which viral disease is it most likely to be?