Tularemia overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Tularemia is a serious infectious disease caused by the bacterium Francisella tularensis. The disease is endemic in North America, and parts of Europe and Asia. The primary vectors are ticks and deer flies, but the disease can also be spread through other arthropods. Animals such as rabbits, prairie dogs, hares and muskrats serve as reservoir hosts. The disease is named after Tulare County, California.
Historical Perspective
Franciscella tularensis was first discovered by George Walter McCoy in 1911. The organism was originally named Bacterium tularense, after Tulare county where the causative agent was first discovered. Expounding upon McCoy's previous research, Dr. Edward Francis furthered global understanding of tularemia, through the discovery of animal reservoirs, vectors, and clinical manifestations. The ailment soon became frequent with hunters, cooks and agricultural workers.[1] Tularemia was later identified as a potential tool for bio-terrorism.
Classification
Tularemia may be classified according the original mode of transmission. The mode of transmission will ultimately dictate the resulting clinical manifestations associated with tularemia infections. There are five common forms of tularemia, they include ulceroglandular, glandular, oculoglandular, oropharyngeal, and pneumonic.[2]
Pathophysiology
Causes
Francisella tularensis is one of the most infective bacteria known; fewer than ten organisms can cause disease leading to severe illness. The bacteria penetrate into the body through damaged skin and mucous membranes, or through inhalation. Humans are most often infected by tick bite or through handling an infected animal. Ingesting infected water, soil, or food can also cause infection. Tularemia can also be acquired by inhalation; 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.
Francisella tularensis is an intracellular bacterium, meaning that it is able to live as a parasite within host cells. It primarily infects macrophages, a type of white blood cell. It is thus able to evade the immune system. The course of disease involves spread of the organism to multiple organ systems, including the lungs, liver, spleen, and lymphatic system. The course of disease is similar regardless of the route of exposure. Mortality in untreated (pre-antibiotic-era) patients has been as high as 50% in the pneumoniac and typhoidal forms of the disease, which however account for less than 10% of cases.[3] Overall mortality was 7% for untreated cases, and the disease responds well to antibiotics with a fatality rate of about 2%. The exact cause of death is unclear, but it is thought be a combination of multiple organ system failures.
Differential Diagnosis
General symptoms reported within the early stages tularemia often resemble those of other tick-borne diseases. These symptoms include fever, chills, headache, and other non-specific flu like symptoms. Later stages of tularemia may include pneumonic clinical manifestations and ulcers in the epidermal tissue.[2]
Epidemiology and Demographics
Tularemia has long been a silent disease plaguing the worldwide community. However, it is difficult to quantify the total worldwide incidence since tularemia is rarely reported. North America and Eurasia are commonly referred to as endemic areas. The majority of cases in the United States have been reported in the South-central and Western states. Seasonal distribution of tularemia infection shows a higher incidence between June and September. A higher incidence has also been reported in children under the age of 10 years.
Risk Factors
The greatest risk factor for contracting tularemia is the bite of an infected tick. Other risk factors include handling contact with infected animals, contamination of water sources, and potential bioterrorism. Individuals are at a higher risk of infection during the late spring and summer months. Children and males are at a higher risk of infection.
Natural History, Complications & Prognosis
The disease has a very rapid onset, with headache, fatigue, dizziness, muscle pains, loss of appetite and nausea. 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. Death may result.
History and Symptoms
Physical Examination
Laboratory Findings
Other Diagnostic Findings
Treatment
Medical Therapy
Surgery
Prevention
References
- ↑ English Pravda. Tularemia. http://english.pravda.ru/main/18/90/363/14923_tularemia.html
- ↑ 2.0 2.1 Centers for Disease Control and Prevention, Signs and Symptoms of Tularemia. http://www.cdc.gov/tularemia/signssymptoms/index.html Accessed March 1, 2016
- ↑ http://www.cidrap.umn.edu/cidrap/content/bt/tularemia/biofacts/tularemiafactsheet.html#_Overview_1