Borrelia persica transmitted by the argasid tick Ornithodoros tholozani causes human tick-borne relapsing fever in the Middle East and Central Asia. Infection is acquired often when visiting tick-infested caves and reported to be transmitted mainly transovarially between ticks occasionally infecting humans. To study the epidemiology of this infection, ticks were trapped in 24 caves in 12 geographic zones covering all of Israel and identified morphologically. DNA was extracted from larvae, nymphs and adult stages from each location and PCR followed by DNA sequencing was performed to identify Borrelia infection, tick species, and tick blood-meal sources. 51,472 argasid ticks were collected from 16 of 24 caves surveyed. 2,774 O. tholozani were analyzed and 72 (2.6%) from nine caves were PCR-positive for B. persica. Infection rates in male, female and nymphal ticks (4.4%, 3% and 3.2%, respectively) were higher than in larva (p<0.001) with only 3 (0.04%) positive larvae. Presence of blood-meal was associated with B. persica infection in ticks (p=0.003), and blood-meals of golden jackals, red foxes and Cairo spiny mouse were associated with infection (p≤0.043). PCR survey of 402 wild mammals revealed B. persica infection with the highest rate in social voles (22%), red foxes (16%), golden jackals (8%) and Cairo spiny mice (3%). In conclusion, although transovarial tick transmission of B. persica occurs at low levels, ticks apparently acquire infection mainly from wildlife canid and rodents and may eventually transmit relapsing fever borreliosis to humans who enter their habitat.
Importance
Borrelia persica is a spirochete that causes tick-borne relapsing fever in humans in an area that spans from India to the Mediterranean. Until now it was thought that the soft tick vector of this infection, Orhinthodoros tholozani, is also its main reservoir and it transmits B. persica mostly transovarially between tick generations. This study showed that tick infection with B. persica is associated with feeding blood from wild jackals, foxes and rodents, and that transovarial transmission is minimal. Since O. tholozani ticks are found in isolated caves and ruins, it is assumed that wild canids who migrate over long distances have a major role in the transmission of B. persica between remote tick populations, and its then maintained locally also by rodents and eventually transferred to humans during tick bites. Prevention of human infection could be achieved by restricting entrance of canines and humans to habitats with O. tholozani populations.
Transmission of the human relapsing fever spirochete Borrelia persica by the argasid tick Ornithodoros tholozani involves blood meals from wildlife animal reservoirs and mainly transstadial transfer