Tularemia (Rabbit Fever)

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Medical Author:

Mary D. Nettleman, MD, MS, MACP

Mary D. Nettleman, MD, MS, MACP

Mary D. Nettleman, MD, MS, MACP is the Chair of the Department of Medicine at Michigan State University. She is a graduate of Vanderbilt Medical School, and completed her residency in Internal Medicine and a fellowship in Infectious Diseases at Indiana University.

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Medical Editor:

Charles Patrick Davis, MD, PhD

Charles Patrick Davis, MD, PhD

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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Tularemia is an infection caused by the Gram-negative bacteria Francisella tularensis. The organism is named after Edward Francis who, while in Tulare County, Calif., helped discover how the disease was spread and how the organism could be cultured.

Tularemia is usually a disease of animals. Humans can acquire tularemia when they come in contact with infected animals or are bitten by insects that have fed on an infected animal. Ticks, biting flies, and mosquitoes have been shown to transmit tularemia between animals and humans. Tularemia is one of several tick-borne diseases and can be spread by many species of ticks, including Dermacentor variabilis and Amblyomma americana. Among biting flies, the deer fly (Chrysops spp.) is the most widely cited vector. Even small doses of these bacteria (10-50 bacteria) have the potential to cause severe disease. For this reason, F. tularensis has the potential to be used as a bioweapon.

There are four subspecies of F. tularensis, and all are capable of causing disease in humans (F. tularensis, F. holarctica, F. mediasiatica, and F. novicida). The subspecies tularensis and holarctica are the most common causes of tularemia in humans. The type of tularemia depends on which subspecies is involved and how the organism was acquired. Disease caused by the subspecies F. holarctica is often milder than that caused by F. tularensis.

The type of disease is often named for the most prominent symptoms. Thus, ulceroglandular tularemia is usually caused by inoculation of the skin and is associated with open sores and swollen lymph nodes. If there is no sore but swollen lymph nodes are prominent, the disease may be classified as glandular. If the eye or throat is involved, oculoglandular or pharyngeal tularemia is said to be present. Disease involving the lungs is termed pneumonic disease. Tularemia that predominately affects the bloodstream and body organs is referred to as typhoidal tularemia.