The bacterium Orientia tsutsugamushi causes a disease called scrub typhus or bush typhus, and it spreads to people through the bites of larval mites or chiggers. The mites are only parasitic in the larval stage. Typical symptoms of scrub typhus can be nonspecific, and include body aches, fever, and headache. The infection can be fatal if left untreated. The symptoms of scrub typhus tend to be similar to those caused by Rocky Mountain spotted fever, which is caused by tick bites.
Scrub typhus tends to affect people in living or traveling to rural areas of Southeast Asia, Northern Australia, Indonesia, China, India, and Japan. However, scientists have now detected the bacterium that causes scrub typhus in chiggers in North Carolina. No cases of the disease have been identified in people or animals there yet. The findings have been reported in Emerging Infectious Diseases.
The bacterium was found in many trombiculid mites or chiggers which were mature enough to bite in several North Carolina recreational parks.
Researchers at North Carolina State University (NC State) and UNC-Greensboro wanted to know if local chiggers carried the Orientia microbes. In the past, scientists have not had access to diagnostic tests that can identify the bacteria, said co-corresponding study author Loganathan Ponnusamy, an NC State principal research scholar in entomology.
In this work, the researchers collected chiggers that moved across a black tile set down on the ground in North Carolina parks. Next, they identified all of the microbes in the chiggers. At one park, 90 percent of the chiggers collected carried the bacteria, while at another, the positivity rate was 80 percent. Other parks had rates as low as ten percent.
"Chiggers can spread bacteria to people or rodents when they bite but can also pass bacteria to future generations of mites through their eggs," Longanathan noted.
Right now, scientists don't know whether goods, animals, or people are moving the chiggers that are spreading the disease to new areas.
"We don't know if this is a recent introduction into the state or if the bacterium has been here for years," said study co-author R. Michael Roe, William Neal Reynolds Distinguished Professor of Entomology at NC State. Right now, the researchers are unsure whether the infected chiggers in North Carolina will cause disease if they bite people, and more research will be needed to answer that question.
Now the researchers are taking more chigger samples at park sites to determine whether the data is consistent.
Sources: North Carolina State University, Emerging Infectious Diseases
