Nonhuman mammals rarely develop the skin lesions seen in people. Subclinical infections are common, and animals often develop specific antibodies to the organism. Fever is moderate or very high, and tularemia bacilli can be isolated from blood cultures at this stage. The face and eyes redden and become inflamed. Inflammation spreads to the lymph nodes, which enlarge and may suppurate (mimicking bubonic plague). Lymph node involvement is accompanied by a high fever. Cause
Tularemia is caused by the bacteria Francisella tularensis which is typically spread by ticks, deer flies, and contact with infected animals. Bacteria
The bacteria can penetrate into the body through damaged skin, mucous membranes, and inhalation. Humans are most often infected by tick/deer fly bite or through handling an infected animal. Ingesting infected water, soil, or food can also cause infection. Hunters are at a higher risk for this disease because of the potential of inhaling the bacteria during the skinning process. It has been contracted from inhaling particles from an infected rabbit ground up in a lawnmower (see below). Tularemia is not spread directly from person to person. Humans can also be infected through bioterrorism attempts.Francisella tularensis can live both within and outside the cells of the animal it infects, meaning it is a facultative intracellular bacterium. It primarily infects macrophages, a type of white blood cell, and thus is able to evade the immune system. The course of disease involves the spread of the organism to multiple organ systems, including the lungs, liver, spleen, and lymphatic system.
Serological tests (detection of antibodies in the serum of the patients) are available and widely used. Cross reactivity with Brucella can confuse interpretation of the results, so diagnosis should not rely only on serology. Molecular methods such as PCR are available in reference laboratories. Prevention
There are no safe, available, approved vaccines against tularemia. However, vaccination research and development continues, with live attenuated vaccines being the most thoroughly researched and most likely candidate for approval. Sub-unit vaccine candidates, such as killed-whole cell vaccines, are also under investigation, however research has not reached a state of public use.Optimal preventative practices include limiting direct exposure when handling potentially infected animals by wearing gloves and face masks (importantly when skinning deceased animals). Treatment
If infection occurs or is suspected, treatment is generally with the antibiotics streptomycin or Gentamicin. Doxycycline was previously used. Gentamicin may be easier to obtain than streptomycin. There is also tentative evidence to support the use of quinolone antibiotics. Prognosis
Since the invention of antibiotics, the rate of death associated with tularemia has decreased from 60% to less than 4%. Epidemiology
Tularemia is most common in the Northern Hemisphere, including North America and parts of Europe and Asia. It occurs between 30º and 71º north latitude.In the United States, although records show that tularemia was never particularly common, incidence rates continued to drop over the course of the 20th century.