By Stephen Beech via SWNS
Ticks could spread new diseases around the world by hitching a lift on migrating birds, warns new research.
The parasitic bugs have always traveled with birds – but rising temperatures due to global warming mean they may now survive at their destination along with the diseases they carry, say scientists.
Some journeys can take ticks thousands of miles from their usual geographic range but, historically, they haven’t been able to establish themselves, due to unsuitable climate conditions at their final destination.
Now, a new study suggests that it’s getting easier for ticks to survive and spread thanks to climate change, potentially bringing new diseases with them.
Study lead author Professor Shahid Karim, of the University of Southern Mississippi, said: “If conditions become more hospitable for tropical tick species to establish themselves in areas where they would previously have been unsuccessful, then there is a chance they could bring new diseases with them.”
Karim says that ticks are “very effective” disease vectors, connecting humans and domestic animals to diseases carried in wild reservoirs such as Lyme disease, and birds – particularly migratory birds – allow them to travel very long distances.
The changes to global temperatures caused by climate change are now making it easier for some ticks to establish themselves as invasive species.
Karim says establishment can be very rapid: for example, the Asian long-horned tick was first detected in New Jersey in 2017 and has since been found in 14 other US states.
Study co-author Dr. Lorenza Beati, of Georgia Southern University, said: “Geographic distribution is changing very rapidly in many tick species.
“For some migrating exotic ticks, global warming may create conditions at their northern destination that are similar to their usual range.
“If warmer climatic conditions are combined with the presence of suitable vertebrate hosts for all tick life stages, the chance of establishment is going to increase.”
To investigate tick dispersal through migrating birds, the research team set up nets at six locations where birds stop to rest along the northern Gulf of Mexico.
Each bird was ringed with a band carrying an identification number, measured, and examined to check its physical condition and look for ticks.
When ticks were found, these were removed and preserved for later DNA analysis to confirm the species and identify the micro-organisms they carried.
The scientists divided the birds into three categories – residents, short-distance migrants, and long-distance migrants – and mapped out the different species’ geographic distributions to understand where they could have picked up ticks.
That highlighted just how far ticks could be carried: mean dispersal distances rose as high as 5,000 km (3,100 miles).
Nearly 15,000 birds were sampled, almost 2,000 of them more than once, but only 421 ticks were collected from 164 birds.
Although 18 different species of tick were identified – including several neotropical species not established in the US – just four species accounted for 81% of the ticks found by the scientists.
Short-distance migrants carried more ticks than long-distance migrants.
The scientists then analyzed the bacteria carried by the ticks.
Their findings, published in the journal Frontiers in Cellular and Infection Microbiology, showed that the most common bacteria were Francisella bacteria, which are endosymbionts that help ticks function.
Higher levels of Francisella bacteria in a tick have previously been associated with lower levels of Rickettsia or Cutibacterium.
The second most abundant bacteria were Rickettsia species, which the research team said could indicate that they have a “symbiotic” relationship with ticks which is currently unknown to science.
The research team explained that parasitizing migrating birds, which travel long distances, demands “significant” energy expenditure from the ticks attached to the birds.
They say it may be that the Rickettsia species somehow help them cope.
Some species of Rickettsia can cause diseases in humans, including spotted fevers, but it’s not known if invasive species of ticks are likely to transmit the diseases to humans.
To understand the full impact of bird-assisted tick dispersal, the team says more research is needed, particularly to find out whether birds act as “reservoirs” by carrying tick-borne diseases when they aren’t hosting ticks.
Karim added: “Not only could these ticks bring new pathogens, but if they manage to establish themselves in the US, 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.”
He recommended that people protect themselves with insect repellent and check themselves for bugs after walking in tick-infested areas.
