Clinical Syndromes and Epidemiology - Francisella tularensis

Clinical Syndromes

F. tularensis causes tularemia in humans

◗ Tularemia

The incubation period varies from 3 to 5 days. The onset of the disease is abrupt with symptoms, such as fever, chills, malaise, and fatigue. Tularemia can manifest in one to six well-recognized clinical forms. These include (a) ulceroglandular tularemia, (b) glandular tularemia, (c) occuloglandular tula-remia, (d) oropharyngeal tularemia, (e) pneumonic tularemia, and ( f ) typhoidal (septicemic) tularemia.

Epidemiology

F. tularensis has a worldwide distribution. The infection is foundin more than 100 species of animals, birds, amphibians, and arthropod hosts. The organism may also be found in mud and water.

◗ Geographical distribution

Tularemia occurs throughout the Northern Hemisphere except the United Kingdom. Cases have been reported in the former Soviet Union, Japan, Canada, Mexico, the United States, and Europe. The condition has not been described in either Africa or South America.

◗ Reservoir, source, and transmission of infection

Rabbits, ticks, and muskrats are the reservoir of infections. Domestic cats are also now increasingly recognized as reser-voirs of tularemia. Ticks and deerflies (Chrysops discalis) are com-mon vectors. Hard ticks (Amblyomma americanum, Dermacentorandersoni, andDermacentor variabilis) are also important vectorsand reservoirs due to the vertical transmission of their progeny.

Contact with infected animals or their carcasses is the primary mode of transmission. The infection is transmitted by (a) ingestion of poorly cooked meats of the infected animals, such as rabbit, (b) ingestion of contaminated water, (c) bite of a tick or deerfly, (d) direct contact with contaminated soil, water, or fomites, and (e) inhalation of water aerosols or dust from soil, grains, or contaminated pelts. However, person-to-person transmission is rare.