Abstract
Abstract Most, and perhaps all, of the tick-borne infections affecting man are zoonoses, that is, they are maintained to a large degree in natural cycles not involving humans. For the most part, we only become interested in those tick-transmitted zoonoses that affect humans or domestic animals, or that show potential for affecting man. However, if we look beyond disease severity or impact on health, it is apparent that the frequency of human infections caused by these zoonoses, or their epidemiologic potency, can vary considerably. Moreover, the intensity of transmission in natural cycles, or zoonotic potency (frequency of animal infections), may correlate directly, inversely, or not at all with a zoonosis’ epidemiologic potency. Even the same zoonosis, when maintained in a different ecological setting, can vary significantly in the number of infections produced, and so, the degree of infection risk to humans. For instance, in North America, Lyme borreliosis has become perhaps the single most important of these tick-transmitted zoonoses; the number of human infections recorded far outnumbering that of most other tick-borne diseases. However, vectors of this infection are only focally abundant with a relatively limited distribution. Many tick-borne infections, such as those caused by the spotted fever group (SFG) rickettsias, produce far fewer human infections, even in areas where their tick vectors are quite abundant. The vectors of this group of infections are generally more common and have a much broader distribution. Clearly then, transmission factors, and not just tick abundance, play a large part in determining the potency as well as the infection risk of a particular tick-borne zoonosis.
Published Version
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