zoonoses and communicable diseases common to ... - PAHO/WHO

TICK-BORNE RELAPSING FEVER 273Figure 18. Tick-borne relapsing fever (Ornithodoros spp.).Mode of transmission.Wild animals(rodents, armadillos,skunks, weasels,squirrels, and bats)Tick biteTickOrnithodoros spp.BiteWild animals(rodents, armadillos,skunks, weasels,squirrels, and bats)By bites, uponentering natural fociManSource of Infection and Mode of Transmission (Figure 18): The borreliae thatcause endemic relapsing fever have as their reservoir wild animals and ticks of thegenus Ornithodoros; in addition, the latter are vectors of the infection. These ticksare xerophilic argasids that are long-lived and very resistant to dessication and longperiods of fasting in environments with low humidity and high temperatures.Borreliae survive in the ticks for a long time. Depending on the species ofOrnithodoros,transovarial transmission may vary from less than 1% to 100%. In theWestern Hemisphere, the most important vectors of Borrelia are O. hermsii, O. turicata,O. rudis, and possibly O. talaje. The continuous circulation of borreliae innature is ensured by the ticks’ characteristics and their feeding on infected wild animals.O. hermsii lives at altitudes of over 1,000 meters, feeds on the blood of squirrels,and can be found in rodent burrows and wooden huts. O. turicata attacks sheepand goats, as well as other animals, and infests hides, rodent and snake burrows, andpigsties.Transmission to humans is caused by a bite from an infected tick.Role of Animals in the Epidemiology of the Disease: Several species of wildanimals constitute the reservoir of the etiologic agent. The relative importance ofticks and wild animals as reservoirs is the subject of debate, but both undoubtedlyplay important roles in maintaining the infection in nature. An exception is infectionby B. duttoni in Africa, which has not been found in animals and is transmitteddirectly to man by the tick O. moubata.Diagnosis: Diagnosis is based on demonstrating the presence of the etiologicagent in the patient’s blood during the febrile phase by dark-field microscopy usingfresh smears or films stained by Giemsa or Wright techniques, or by inoculation inmice. The number of borreliae diminishes or disappears at the end of a fever attack;