Geographic Distributions of Tick-Borne Diseases and Their Vectors

Abstract

This chapter reviews information on the geographic distributions of tick-borne diseases and their primary tick vectors. It first addresses tick-borne encephalitis (TBE); Crimean-Congo hemorrhagic fever (CCHF); Colorado tick fever (CTF); tularemia; the tick-borne rickettsioses, including the rickettsial spotted fevers, tick typhuses, and Q fever; human granulocytic anaplasmosis (HGA) (previously called human granulocytic ehrlichiosis), human monocytotropic ehrlichiosis (HME), and ehrlichiosis caused by Ehrlichia ewingii; the tick-borne borrelioses, including Lyme borreliosis (LB) and tick-borne relapsing fever (TBRF); and babesiosis. Causative agents are identified, and principal ecological and epidemiological determinants of the diseases are outlined, providing information on vectors and vertebrate hosts, as well as features of the diseases useful in understanding exposures and spread and in framing case definitions. Modes of transmission other than tick bite are noted. The chapter describes primary tick vectors and their distributions. It specifically addresses 35 ixodid species and 10 argasid species of the 867 recognized species of ticks that commonly bite people. Risk of transmission to humans in foci of tick-borne diseases is determined by such factors as the density of competent vectors and reservoir hosts, infection thresholds of the pathogens, and the behaviors of humans that place them at risk of bites by infective ticks.