TULAREMIA

acute infectious disease resembling plague, but much less severe. It was described in 1911 among ground squirrels in Tulare county, Calif. (from which the name is derived), and was first reported in humans in the United States in 1914. The causative agent is the gram-negative bacterium Francisella tularensis. The disease is primarily one of animals; human infections are incidental. It occurs naturally in many types of wildlife. In the United States the rabbit, especially the cottontail, Sylvilagus, is an important source of human infection, but other mammals, birds, and insects also spread the disease. Human cases in Sweden and Norway have been transmitted by hares; in the Soviet Union, by water rats. F. tularensis has been found in some natural water sources, causing incidences of the disease in humans and animals. The disease is mainly acquired by humans from the animal reservoir of infection, either directly by handling the carcasses of infected rabbits or indirectly through an insect carrier, most commonly a deerfly, Chrysops discalis; the human disease is also called deerfly fever. Various ticks of the genera Dermacentor, Haemaphysalis, Rhipicephalus, Amblyomma, and Ixodes may be largely responsible for maintenance of the animal infection. In addition, the infection is transmitted from the adult tick to the egg, and both larvae and nymphs are infectious and form an insect reservoir of infection. No case of human-to-human contamination has been reported. The disease in humans occurs in two forms: the more common glandular, or ulceroglandular, form and the less common typhoidal form. Local lesions occur in the first, usually beginning with a papule at the site of initial infection that breaks down to form an ulcer. The infection then spreads to the lymph glands in the armpits, which become painful and swollen and may break down and discharge purulent material. Infection of the eye is also common, with swelling of related lymph glands. The general symptoms common to both forms of the disease are headache, bodily aches, and fever. The disease persists for two to four weeks. The fatality rate is very low. Up to 300 cases of the disease are reported each year in the United States, and the disease has been encountered in all parts of the country except Hawaii, although it is most common in the Midwest. The tetracyclines are reasonably effective in treating the disease; gentamicin and streptomycin are the most effective antibiotics, and healing usually takes place within 10 days. A live attenuated vaccine has been generally successful in conferring immunity on susceptible hosts, although its use is usually limited to persons at high risk.