Report Immediately by Phone If Bioterrorism Suspected
Potential Bioterrorism Agent: Category A
Also known as: Rabbit Fever, Deer Fly Fever
Lab: Report immediately by phone if bioterrorism suspected, otherwise weekly
Physician: Report immediately by phone if bioterrorism suspected, otherwise weekly
Local Public Health Agency (LPHA): Report immediately by phone if bioterrorism suspected.
Local Public Health Agency (LPHA): Follow-up required: Iowa Department of Public Health will lead the follow-up investigation.
Iowa Department of Public Health
Disease Reporting Hotline: (800) 362-2736
Secure Fax: (515) 281-5698
Francisella tularensis is a gram-negative bacterium. Two types occur in the United States: Type A is biovar tularensis and Type B is biovar palaeoarctica. Type A is more virulent than Type B and has a lower infective dose.
B. Clinical Description
Symptoms: There are at least six types of clinical symptoms, depending on the route of infection and the strain of bacteria present. Nearly all cases have a rapid onset of fever. If bacteremia develops it may last for two weeks in untreated cases. Lesions may contain the bacteria for a month. The most common categories of illness are as follows:
- Ulceroglandular: Patients have large, tender lymph nodes and a non-healing skin ulcer at the site of infection, often with fatigue, chills, and malaise.
- Glandular: Patients have one or more enlarged painful nodes that may be filled with purulent exudate.
- Pneumonic (pulmonary): This may be a primary infection following inhalation of the organisms or secondary to bacteremia; plague-like symptoms that may include a non-productive cough, difficulty breathing and chest pain. Patchy infiltrates may be seen on the chest X-ray.
- Typhoidal: This is a rare form, with enlarged and inflamed mesenteric lymph nodes, septicemia, abdominal pain, diarrhea, vomiting and gastrointestinal bleeding.
- Oropharyngeal: This form results from ingestion of bacteria in food or water leading to painful pharyngitis, abdominal pain, diarrhea, and vomiting.
- Oculoglandular: Patients have painful, purulent conjunctivitis with enlarged lymph nodes of the neck or near the ears and usually accompanied with fever, chills and malaise.
Onset: Most cases have a rapid onset of fever. Symptoms usually appear 3 to 5 days after exposure to the bacteria, but can take as long as 14 days.
Complications: The case fatality of type A tularemia is 5% - 15% if untreated. The case fatality rate in pneumonic or primary septicemia is 30 to 60% if untreated. Pneumonia may complicate all clinical types of tularemia and requires prompt identification and specific treatment to prevent fatal outcomes.
Common reservoirs: Type A infections are acquired from rabbits or Dermacentor ticks, including the common dog tick or wood tick.
Less common reservoirs: Type B infection is associated with a wide variety of mammalian hosts: rabbits, hares, and some rodents such as beavers and muskrats are particularly important. Ticks, mosquitoes, and deer flies may serve as vectors for the disease. Humans, however, do not usually transmit the infection to others.
D. Modes of Transmission
Spread: Tularemia may have the most varied modes of spread of any bacterial agent.
- Direct Contact: This can occur when skinning or dressing game.
- Arthropod Vector: The bacteria may be spread by the bite of tick, either Dermacentor andersoni (wood tick) or D. variabilis (dog tick) or amblyomma americana (lone star tick) or a bite from deer flies or horse flies.
- Ingestion: Through contaminated food such as undercooked rabbit meat or drinking contaminated water.
- Inhalation: Infectious aerosols can be generated when handling animal carcasses or cleaning areas where there may be dried rodent carcasses, running over a rabbit’s nest with the lawn mower, or from the dust generated while moving contaminated hay, grain or soil.
- No direct person-to-person transmission
Survival of Organism: Francisella tularensis can survive for weeks to months in cool water or mud, for up to 3 months in tap water and in dry straw for as long as 6 months. Routine water purification is very effective at killing F. tularensis.
E. Incubation period
The incubation period ranges from 1 - 14 days, but is usually 3 - 5 days.
F. Period of Communicability or Infectious Period
The infectious agent may be found in the blood of untreated patients during the first two weeks of disease and in lesions for a month or more. Flies can remain infective for 14 days after infection and ticks through their lifetime. Rabbit meat frozen at 5° F can remain infective for over three years.
Tularemia is found throughout North America and in many parts of continental Europe, Russia, China and Japan. In the United States, it occurs all months of the year. It is a risk for hunters during the fall and early winter, for lawn care workers in the summer when mowing over rabbits, providing an aerosol, and in spring in summer for children when ticks and flies are most prevalent. Type A tularemia is found only in North America where it is common in rabbits and is transmitted by a tick bite. Type B strains in North America are found in mammals other than rabbits.
H. Bioterrorism Potential
Category A: Francisella tularensis is considered a possible weapon of bioterrorism. If the organism were effectively disseminated it could cause a serious challenge to limit the numbers of casualties and to control other repercussions of an attack.
I. Additional Information
The Council of State and Territorial Epidemiologists (CSTE) surveillance case definitions for Tularemia can be found at: www.cdc.gov/osels/ph_surveillance/nndss/phs/infdis.htm#top
CSTE case definitions should not affect the investigation or reporting of a case that fulfills the criteria in this chapter. (CSTE case definitions are used by the state health department and the CDC to maintain uniform standards for national reporting.)
American Academy of Pediatrics. 2003 Red Book: Report of the Committee on Infectious Diseases, 26th Edition. Illinois, American Academy of Pediatrics, 2003.
CDC website: Tularemia at www.cdc.gov/Tularemia/
Heymann, D.L., ed. Control of Communicable Diseases Manual, 20th Edition. Washington, DC, American Public Health Association, 2015.