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Amblyomma aureolatum ticks transmit disease faster than previously thought
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New research shows that Amblyomma aureolatum ticks that had recently fed on another host needed only minutes to transmit Rickettsia rickettsii, the bacterium that causes Rocky Mountain spotted fever.
“The results of our study were surprising, since we demonstrated that a tick that previously fed on a host — namely, a dog — would require only 10 minutes to transmit the bacterium of Rocky Mountain spotted fever (RMSF) to a person,” Marcelo B. Labruna, DVM, PhD, of the Universidade de São Paulo in Brazil, told Infectious Disease News.
Marcelo B. Labruna
Before this study, medical guidelines and textbooks advised that an infected tick required between 2 and 10 hours to transmit R. rickettsia. “Indeed, our results will change some of our current recommendations for the prevention of RMSF in endemic areas,” Labruna said.
RMSF is the most lethal tick-borne disease and is endemic in Brazil. From 2007 to 2013, there were 800 laboratory-confirmed cases reported in Brazil, and nearly 30% of those cases resulted in death, according to Labruna. In the densely populated state of São Paulo, the fatality rate is near 50% — the highest in Brazil.
In this study, the researchers sought to narrow down the 2- to 10-hour feeding time because quicker tick removal reduces the risk of disease acquisition. They infested guinea pigs with unfed A. aerolatum ticks for a period ranging from 2 to 48 hours. In addition, they allowed a group of infected ticks to first feed on rabbits. Those fed ticks were subsequently removed and allowed to feed on guinea pigs.
The results showed that unfed nymphs and unfed adult male A. aerolatum ticks required more than 10 hours of feeding time to transmit R. rickettsia to their hosts. Fed ticks, however, required only about 10 minutes of feeding time.
People residing in RMSF-endemic areas must beware of ticks, especially people who come into contact with dogs, according to Labruna. Previous research has shown that 93% of RMSF cases in São Paulo were associated with direct contact with dogs. “Always keep your dogs free of ticks in RMSF-endemic areas through frequent treatments of the dog with acaricides,” he said.
Disclosure: Labruna reports no relevant financial disclosures.
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