Researchers have found that birds may also play a role in the spread of Lyme disease, taking the spotlight away from the usual culprits like western gray squirrels, wood rats and other small mammals.
According to Erica Newman, a Ph.D. student from the University of California, Berkeley and the lead author for the study published in journal PLOS ONE, the role that birds play in maintaining the bacteria responsible for Lyme disease in California has not been clearly understood. The work Newman and colleagues did for the study represents the most extensive research done yet exploring birds and Lyme disease in western United States. Their group was also the first to consider bird diversity, habitats and behavior in weeding out which bird species were the most important carriers of Lyme disease bacteria.
"Birds are much more capable of carrying diseases long distances than the small-mammal hosts typical of Lyme disease, and so may constitute an underappreciated component of Lyme disease ecology," explained Morgan Tingley, an ecology and evolutionary biology assistant professor at the University of Connecticut. Tingley is not part of Newman's team but he did conduct bird studies in UC Berkeley as a graduate student.
People usually get infected with Lyme disease when bitten by infected ticks. The black-legged deer tick transmits the Borrelia burgdorferi in areas in the eastern and north-central regions of the country while the western black-legged tick is responsible for spreading the bacterium in the western region.
For the study, Newman and colleagues investigated 14 sites inside the UC Hopland Research and Extension Center, including habitats like dense and chaparral woodlands, grasslands and savannas. Blood samples were taken from 623 birds from 53 species. All ticks on the birds where blood samples were collected were also taken and identified, totaling 92 nymphs and 192 larvae. Over 99 percent of the juvenile ticks were of the western black-leg variety.
According to the results of the study, 57 out of 100 tick-carrying birds tested positive for Lyme disease spirochetes. Among the 23 bird species that were infected, dark-eyed junco, oak titmouse and the lesser goldfinch were singled out as harboring the most subtypes of bacteria associated with Lyme disease. Additionally, the golden-crowned sparrow was identified to be the most frequently infected of the bird species. Researchers also discovered a certain spirochete called Borrelia bissettii is in birds in California when the bacterium has been associated with southern and central Europe.
"It is worth watching to see if this spirochete expands in this state," said Robert Lane, a UC Berkeley professor and one of the authors for the study.