By Sarah Carey
University of Florida veterinary researchers say a simple DNA-based test could help identify strains of a debilitating tickborne disease that infects an increasing number of people.
The research marks the first time scientists have demonstrated the ability to distinguish human from animal strains in ticks carrying the organism that causes anaplasmosis, the researchers said. This information could help them pinpoint areas where ticks that carry these strains are present in large numbers.
“With that knowledge, physicians could potentially enhance screening for the disease agent and begin earlier treatment of patients suspected of being infected,” said Dr. Anthony Barbet, a professor of infectious diseases at the UF College of Veterinary Medicine and a co-author of the study. “In addition, blood supplies used for transfusions could be better protected.”
The findings, by Barbet and Dr. Basima Al-Khedery, a scientist with the UF veterinary college, in collaboration with researchers in Minnesota and Norway, appear in two papers published recently in the journal Pathogens.
Anaplasmosis is widespread globally and is caused by the bacterium Anaplasma phagocytophilum. The disease is transmitted to humans by tick bites, primarily from the blacklegged tick and the Western blacklegged tick, according to the Centers for Disease Control and Prevention. These same ticks also transmit Lyme disease and a parasitic disease called babesiosis, both of which have been reported in humans.
The number of anaplasmosis cases reported to the CDC has increased steadily since the disease became reportable, climbing from 348 cases in 2000 to 1,761 cases in 2010, although the mortality rate has remained low, at less than 1 percent.
In humans, the disease can be difficult to diagnose, as its symptoms are similar to those associated with other conditions, such as influenza and Lyme disease. These can range from mild to severe and include rashes, fever and chills, as well as aches and pains.
“The organism causing the disease is present in many domestic animals, wildlife, rodents and ticks worldwide, but not all strains infect humans,” Barbet said. “We have been analyzing the organism’s genome structure to try to work out ways to differentiate the strains that are causing human disease from other strains infecting ruminants, horses and other animals.”
The researchers found that strains that infect humans in the United States were very similar to one another and to the strains infecting U.S. dogs, but differed from strains infecting ruminants and horses. They discovered that these strains could be differentiated by a simple test that checks for a gene deleted in the human strains.
“So far, only a small number of strains have been analyzed, mostly from the U.S., and the test now has to be applied to many more samples and animals globally,” Barbet said.
Barbet and his colleagues have studied anaplasma for years, first focusing on the strain that affects cattle, known as Anaplasma marginale.
“We just really want to understand more about the organisms that cause these diseases,” Barbet said. “Lots of what we worked out with the cattle strain is relevant to these new strains that are now infecting humans. We’re using the same methods to access the genetics of these organisms.”
Although anaplasmosis infects a relatively small number of people compared with, say, malaria, as an emerging infection it is important to understand and control, Barbet said.
“The organism wasn’t even named until 13 years ago,” he said. “Then people realized it was similar to the one causing diseases in ruminants.”
Scientists seeking to better understand the nature of the disease need to ask how the organism is evolving to cause different kinds of infections, Barbet said.
“What’s causing the changes in its genetics and genomic organization to allow infection in people as well as in animals? These are the main questions we ask to learn more about how new diseases emerge,” he said.
The study was supported by a grant from the National Institutes of Health under award number RO1GM081714.