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Migratory birds can bring along dangerous stowaways – ticks – on their epic journeys. These blood-sucking arachnids can carry serious pathogens, including Lyme disease, anaplasmosis, and Powassan virus infection. Now, the ticks that hitchhike on birds may be able to spread more easily and establish themselves in newer locations due to climate change. The findings are detailed in a study published Nov. 18 in the journal Frontiers in cellular and infection microbiology.
“As conditions become more hospitable for tropical tick species to establish in areas where they previously would not have been successful, they may bring new diseases with them,” study co-author and biologist Shahid Karim of the University of South Mississippi. said in a statement.
Unwanted traveling companions
Ticks are among the most effective on earth disease vectors. They can link people and pets to diseases that typically only occur in the wild, such as Lyme disease. Ticks can also bite birds, especially migratory birds that travel thousands of miles. This hitchhiking allows the ticks to travel over great distances.
[Related: You’re less likely to get a tick bite if you steer clear of these spots.]
Rises in global temperatures due to climate change are now making it easier for some tick species to live as invasive species. This can also happen very quickly. For example the Asian long-horned tick (Haemaphysalis longicornis) was first discovered in the state of New Jersey in 2017 and can now be found in 14 additional states.
“The geographic distribution of many tick species is changing very rapidly,” study co-author and biologist Lorenza Beati of Georgia Southern University said in a statement. “For some migrating exotic ticks, global warming may create conditions at their northern destination[s] that are comparable to their usual range. If warmer climatic conditions are combined with the presence of suitable vertebrate hosts for all life stages of ticks, the likelihood of establishment will increase.”
Bird watching
In the new studythe team investigated the spread of ticks via migratory birds. The team set up nets at six locations where birds typically stop to rest along the northern Gulf of Mexico. Each of the birds was fitted with a numbered identification band, measured, subjected to a physical examination and combed for ticks. If and when ticks were found, the arachnids were saved for later DNA analysis to confirm the species and identify what pathogens they carried.
Then the team divided the birds into three categories–residents, short-distance migrants and long-distance migrants. They also mapped the geographic distribution of each bird species to understand where they might have picked up ticks. These maps showed how far ticks could be transmitted. Average dispersal distances were up to 3,100 miles (5,000 kilometers)
However, the number of ticks turned out to be quite low. Nearly 15,000 birds were sampled – almost 2,000 of them more than once – yet only 421 ticks were collected from 164 birds. While 18 different species of ticks were identifiedjust four species were responsible for 81 percent of the ticks identified by the scientists. The short-distance migrants carried more ticks than the long-distance migrants, and several of the tick samples were neotropical species not found in the United States.
Under the microscope
The team then analyzed the bacteria the ticks carried. Francisella bacteria were the most common. These endosymbionts of bacteria help the ticks function, but some species can cause a disease called tick ticks tularemia. Higher levels of Francisella bacteria in a tick have been linked to lower levels of two other bacteria:Rickettsia or Cutibacterium.
Rickettsia species were the second most common bacteria. These bacteria cause fever or rash depending on the species. This could indicate that they have a symbiotic relationship with ticks that was previously unknown to scientists. Sucking the blood of migratory birds over long distances requires: significant amount of the tick’s energy remain attached.
It is possible that the Rickettsia species can help the ticks cope with the energy loss during travel. Some species Rickettsia can cause human illness, including spotted fever. However, scientists do not yet know whether invasive tick species are likely to transmit these diseases to humans
According to the teamMore research is needed to better understand the impact of bird-assisted tick dispersal. Future studies could investigate whether birds act as reservoirs by carrying tick-borne diseases when not harboring ticks.
“Not only could these ticks carry new pathogens, but if they succeed in establishing themselves in the U.S., they could become additional vectors of pathogens already present in this country, or maintain pathogens in wildlife reservoirs , which can then become sources of infection,” says Karim. .
The best ways to protect yourself from tick-borne diseases are to wear long sleeves outdoors, use good insect repellent, and perform tick checks after being outdoors or spending time in tick-infested areas.