An Introduction to Medical Entomology
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Tularemia is a plague that infects rodents, especially rabbits and hares. The causative agent is the bacterium Francisella tularensis. It is of common in the Northern Hemisphere, being widespread in the United States. Service (2008) reported that 150-300 human cases are a yearly occurrence. The disease also has been reported from Japan, Russia, Norway, Canada, Sweden, Austria, Germany, Czech Republic, Turkey and Tunesia. The bacterial disease has not been considered for the biological control of feral rabbits in Australia, which were an invaded species. However, the rabbit population was subsequently significantly reduced to much less damaging numbers by the introduction of a myxomytosis virus instead.
There are many reservoir hosts including rodents, deer and beavers, some bird species and carnivores. But the principal reservoir host is the cottontail rabbit, Sylvilagus spp. Handling infected animals, both alive and dead, may spread infection. Matheson (1950) reported that the disease is highly infectious to humans and is transmitted by various arthropods either by their bites, their crushed bodies or their feces or by the tissues or body fluids of infected rodents. He also noted that it is occasionally water-borne and infection can result from drinking or coming into contact with infected water. Although many human infections are traceable to contact with rabbits, certain tick species are of great importance in maintaining the disease among the natural reservoirs (Matheson 1950).
A number of hard tick species spread the disease. In Europe the main vectors are Ixodes ricinus and Dermacentor spp. In North America various hard ticks and other arthropods are vectors such as the tabanid fly, Chrysops discalis. However in North America of primary importance are the ticks Haemaphysalis leporis-palustris, Dermacentor andersoni, D. variabilis.
Avoidance with contaminated sources is of the utmost importance. When infections do occur prompt medical attention is essential.
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