The geographic distribution includes North America, Europe, the former republics of the USSR, Japan, and Spain. Tularemia is present throughout the United States but is most prevalent in Missouri, Arkansas, Oklahoma, Massachusetts, South Dakota, and Kansas. Hunters, game wardens, trappers, and campers are particularly susceptible. In the Southwest United States, tribal populations are overrepresented among tularemia cases. Animals known to have transmitted tularemia include rabbits (most common), foxes, squirrels, skunks, muskrats, beavers, voles, and even fish. Other routes of infectivity include contact with contaminated water or mud and aerosol droplets. Prevalence is greatest from June through August (more tick-related infections) and in the fall (during hunting season).
There are 7 major clinical patterns of tularemia: glandular, ulceroglandular (most common), oculoglandular, typhoidal, pneumonic, oropharyngeal, and septicemic. Any form of tularemia can be complicated by hematogenous spread, resulting in secondary pleuropneumonia, sepsis, or meningitis (rare).
Tularemia has an extremely variable presentation. The incubation period may range from a few hours to 21 days with a mean of 4.5 days. Tularemia typically has an abrupt onset consisting of fever, headache, chills and rigors, myalgia (especially the low back), coryza, and sore throat. In 42% of patients, pulse-temperature dissociation has been observed. Other manifestations depend more on the type of tularemia.
- In glandular tularemia, no primary inoculation site lesion is seen and adenopathy may be generalized.
- In oculoglandular tularemia, a purulent conjunctivitis is apparent, with pain, edema, and possibly ulceration.
- The pneumonic form presents with acute signs of illness such as pharyngitis, bronchiolitis, pleuropneumonitis, and hilar lymphadenitis along with other signs of systemic illness.
- Typhoidal tularemia presents with nonproductive cough, fever and chills, chest discomfort, sore throat, abdominal pain, and diarrhea.
Complications include acute respiratory distress syndrome (ARDS), renal failure, rhabdomyolysis, hepatitis, and disseminated intravascular coagulation. Less common complications include meningitis, osteomyelitis, splenic rupture, encephalitis, and peritonitis. Seeding of internal organs can result in granulomas in the lung, liver, spleen, lymph nodes, and bone marrow.
The Centers for Disease Control and Prevention (CDC) has classified tularemia as a Class A bioterrorism agent due to its ease of dissemination, morbidity, and ability to infect with as few as 10 bacterial organisms. The Soviet Union had developed weaponized antibiotic- and vaccine-resistant strains of F tularensis. Francisella tularensis is so infective that exposure to an open culture plate can cause human infection. Aerosol dissemination of F tularensis has been projected to result in the abrupt onset of large numbers of cases of acute, nonspecific febrile illness with pleuropneumonitis as the predominant finding.
While postexposure prophylaxis is not recommended for natural exposure, it can be used for patients with aerosol exposure who are identified early in the incubation period (due to the short incubation period of inhalational tularemia).