TULAREMIA : CLINICAL ASPECTS
After an incubation period of 2 to 5 days, tularemia may follow a number of courses, de-pending on the site of inoculation and extent of spread. All begin with the acute onset of fever, chills, and malaise. In the ulceroglandular form, a local papule at the inoculation site becomes necrotic and ulcerative. Regional lymph nodes become swollen and painful. The oculoglandular form, which follows conjunctival inoculation, is similar except that the lo-cal lesion is a painful purulent conjunctivitis. Ingestion of large numbers of F. tularensis (>108) leads to typhoidal tularemia, with abdominal manifestations and a prolonged febrile course similar to that of typhoid fever. Inhalation of the organisms can result in pneumonic tularemia or a more generalized infection similar to the typhoidal form. Like plague pneu-monia, tularemic pneumonia may also develop through seeding of the lungs by bacteremic spread of one of the other forms. Any form of tularemia may progress to a systemic infec- tion with lesions in multiple organs.
Without treatment, mortality ranges from 5 to 30%, depending on the type of infec- tion. Ulceroglandular tularemia, the most common form, generally carries the lowest risk of a fatal outcome. In the US surveillance study mentioned earlier, the mortality was 2%.
Because tularemia is uncommon and F. tularensis has unique growth requirements, the diagnosis is easily overlooked. Although some strains grow on chocolate agar, laboratories must be alerted to the suspicion of tularemia so that specialized media can be prepared and precautions taken against the considerable risk of laboratory infection. An immunofluorescent reagent is available in reference laboratories for use directly on smears from clinical material. Because of the difficulty and risk of cultural techniques, many cases are diagnosed by serologic tests. Agglutinating antibodies are usually present in titers of 1:40 by the second week of illness, increasing to 1:320 or greater after 3 to 4 weeks. Unless previous exposure is known, single high antibody titers are considered diagnostic.
Streptomycin is the drug of choice in all forms of tularemia, although recent experience indicates that gentamicin may be just as effective. Tetracycline and chloramphenicol have also been effective, but relapses are more common than with streptomycin. Prevention mainly involves the use of rubber gloves and eye protection when handling potentially infected wild mammals. Prompt removal of ticks is also important. A live attenuated vaccine exists, but it is used only in laboratory workers and those individuals who cannot avoid contact with infected animals.