A man with chills, fever, and headache is thought to have "atypical" pneumonia. History reveals that he raises chickens, and that approximately 2 weeks ago he lost a large number of them to an undiagnosed disease. Which of the following is the most likely diagnosis of this man's condition?

Ornithosis (psittacosis) is caused by C. psittaci. Humans usually contract the disease from infected birds kept as pets or from infected poultry, including poultry in dressing plants. Although ornithosis may be asymptomatic in humans, severe pneumonia can develop. Fortunately, the disease is cured easily with tetracycline. Bacillus anthracis is a spore-forming, gram-positive bacillus that has a protective capsule made of glutamic acid (amino acid) residues. Humans are infected accidentally by contact with infected animals or their products. Skin lesions, seen most often, are known as wools orter's disease. Leptospira organisms are tightly coiled spirochetes. Human contact is often in water, where the organism enters breaks in the skin. They produce hemorrhage and necrosis in the liver and kidneys and often present as aseptic meningitis. Relapsing fever is caused by Borrelia recurrentis and is transmitted by the body louse or Ornithodoros ticks. An unusual feature of this disease is the selection of new antigenic forms of the organism after host antibody formation. Q fever is caused by a rickettsial organism, C. burnetii.