Avian Ticks May Increase Lyme Disease Cases In Humans, Researchers Say

Lyme disease may become more widespread with the help of songbirds, a new study revealed. In recent years Lyme disease has been on the rise, which is why people have become quite skilled at scouring their pant legs after a hike through wooded areas or tall grasses to make sure blacklegged ticks (Ixodes scapularis) haven't latched on. But human-biting ticks are not the only concern, which is why researchers from Old Dominion University in Virginia have shifted their focus to another avian-biting species.

Lyme disease-carrying ticks now in the limelight are known as Ixodes affinis, and researchers have found that the tiny buggers are parasitizing five songbird species on which it had not previously been documented, according to a news release that details the recent study titled "New records of Ixodes affinis parasitizing avian hosts in southeastern Virginia."

So why do we care about ticks on birds? Because birds are able to travel long distances and bring their tick hitchhikers with them, researchers explained. Therefore, as I. affinis expands its range northwards and overlaps with I. scapularis researchers expect to see an increased number of Lyme disease cases in humans. This study is particularly prevalent as the numbers of reported Lyme disease cases have reached an all-time high in the U.S., according to the Centers for Disease Control and Prevention.

I. affinis is a hard-bodied tick species distributed throughout much of the southeastern U.S. In order to understand the disease better, it is important to know that it is not only based on the bacterium that causes it (Borrelia burgdorferi), but also the ecology and range of the species that act as the pathogen's vectors and hosts.

In this case, ticks are the vectors that transmit Lyme disease between many animals, including birds, which act as hosts for the bacterium. So when animals are infected, they can transmit the disease to the next, possibly sterile, tick that bites them -- thus spreading the disease further and further.

For their study, researchers collected ticks off birds captured using mist nets set up throughout several locations in southeastern Virginia from 2012 to 2014. Birds captured were banded and examined for ticks around the head, in the ears, under the wings, and around the cloaca, which is where the intestines and genitals open up on a bird. Ticks were removed, placed into vials and preserved for further DNA testing, while the captured birds were immediately released after banding and sample collection.

A total of 1,888 birds were captured, from which 18 immature I. affinis were found on 12 birds. This included six Carolina Wrens (Thyrothorus ludovicianus), two Brown Thrashers (Toxostoma rufum), and one American Robin (Turdus migratorius), Eastern Towhee (Pipilo erythrophthalmus), Northern Cardinal (Cardinalis cardinalis) and White-throated Sparrow (Zonotrichia albicollis). As a result, researchers noted migrating birds that move northwards through Virginia in the spring likely encounter I. affinis, and White-throated Sparrows in particular may extend the range of I. affinis because they fly all the way to Canada to breed in the spring and only winter in Virginia.

Their study, recently published in the Journal of Medical Entomology, sheds light on new avian species that may play a role in the dispersal of tick species. Ultimately, this will help researchers better asses the public health risk of contracting Lyme disease. 

Aside from a bull's-eye rash that generally develops within a week of being bitten, humans infected with B. burgdorferi may experience fever, chills, headache, fatigue, swollen lymph nodes, or muscle and joint aches. More long-term side effects include heart palpitations, episodes of dizziness, nerve pain, and even short-term memory loss.  

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