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Organisms Borne by Ticks and Other Vectors 245

F. tularensis palaearctica, Type B, occurs mainly History of Tularemia
in water-dwelling rodents such as beavers, otters, and
muskrats in North America. This serotype of Fran- In North America, F. tularensis was first discovered dur-
cisella is also found in hares and small rodents such as ing an outburst of “rabbit fever” in 1911. The organism
mice, voles, and ground squirrels in the northern regions and subsequently the disease received its name from the
of both Asia and Europe. The Type B organism is less area of Tulare Lake in California, after the local popula-
virulent than Type A for humans and rabbits. Primary tion of ground squirrels was decimated by infections
vectors for Francisella are ticks and deer flies, but in ad- with the organism. Scientists at the time determined
dition the disease can be spread somewhat easily by in- that tularemia could be dangerous to humans and that
sects other than ticks and deer flies. In addition to the contact with an infected animal may lead to contraction
vectors, tularemia may be readily spread by the handling of the disease. Soon after this initial outbreak it became
of infected animal carcasses, eating or drinking water and apparent that hunters, cooks, and agricultural work-
food contaminated by the organism, and by breathing ers were quite susceptible to the infective organism. As
the organism. previously mentioned, there is a pneumonic form of the
Tularemia has not been found to be spread from disease that could easily lend itself to bioterrorism with
person to person and those infected with F. tularensis an air burst of a bomb that could disperse the disease to
do not require isolation to prevent the spread of dis- many individuals. This has led to the stockpiling of ef-
ease. Rapid treatment upon exposure and subsequent fective antibiotics in the event such an occurrence comes
infection should be initiated quickly as the disease may to fruition. In addition, there is a possibility that an un-
be fatal if untreated. Again, as with other pathogens, licensed vaccine not controlled and tested by governmen-
those who are pregnant or who have weakened im- tal agencies could be useful in preventing the infections
mune systems may be more susceptible to contracting from occurring as emergency procedures.
the illness. Humans can become infected in many ways,
particularly through exposure due to environmental Epidemiology for Tularemia
activities. Methods of transmission are through bites by
infected arthropods, by the handling of the carcasses of Tularemia occurs throughout the more temperate regions
infectious animals or their body fluids, working with or of the Northern Hemisphere. Besides North America
eating and drinking water or food containing the organ- and continental Europe, the original areas of the former
isms, or from exposure to bodies of water or soil con- Soviet Union, and the Asian countries of China, Korea,
taminated by rodents and the inhalation of infectious and Japan are affected by this disease. All states within
aerosols (Figure 11-20). the North American continent (the exception is Hawaii)
have reported cases of tularemia but some reported only
an occasional rare case. The disease in humans is one
Source: Centers for Disease Control and Prevention (CDC) the first 50 years of the 1900s, tularemia infections in the
required to be reported in the same way as for many
venereal diseases and other infectious diseases. During
United States reached a peak with several thousand cases
but since then the number of cases has declined greatly to
only a little over a hundred per year in the entire country.

Clinical Symptoms and

of Tularemia

Depending on the site of infection, tularemia has six
FIGURE 11-20 Waters from which many muskrats Microbiological Diagnosis
were trapped, infecting a number of Vermont trappers characteristic clinical syndromes. The most common
with tularemia type is that of the ulceroglandular variety that comprises