Study finds ticks choose humans over dogs when temperature rises.

Experiment put a human in one box, a dog in another and saw which the ticks preferred.

Confining a young researcher in one box and a dog in another and unleashing blood-sucking ticks to scamper between the boxes sounds like a stunt from I’m A Celebrity.

But the stomach-churning scientific experiment has revealed that ticks carrying the deadly Rocky Mountain spotted fever (RMSF) disease are more than twice as likely to shift their feeding preference from dogs to humans when temperatures rise.

The study, presented at the annual meeting of the American Society of Tropical Medicine and Hygiene (ASTMH), observed whether the ticks, which use smell to seek out a host upon whose blood to feed, scuttled along a plastic tube towards the dog or the human.

When the temperature in the laboratory was raised from 23.3C to 37.8C, one type of “brown dog” tick, known as the tropical lineage tick, was particularly prone to shifting its preference from the box containing the dog to the box containing the person.

“Our work indicates that when the weather gets hot, we should be much more vigilant for infections of RMSF in humans,” said Laura Backus, who led the study at the University of California, Davis School of Veterinary Medicine. “We found that when temperatures rose from about 74F (23.3C) to 100F (37.8C), brown dog ticks that carry the disease were 2.5 times more likely to prefer humans over dogs.”

There is growing concern over the increase in tick-borne diseases. Cases of Lyme disease, a potentially debilitating condition primarily transmitted by black-legged ticks, have doubled over the past two decades to about 30,000 cases a year in the US.

Cases of RMSF and other related diseases, known as spotted fever rickettsiosis, have risen dramatically over the last two decades. The disease is treatable with antibiotics if detected in the first week of infection but, if left untreated, the fatality rate can exceed one in five.

Tropical lineage brown dog ticks are currently found across southern US states such as Arizona, Florida and southern California. Their range is expected to move northward as climate change causes average temperatures to rise.

With hot days also arriving more frequently due to the climate crisis, Backus said it was important to identify conditions that could increase the risk of infection, particularly because the early phase of RMSF is easily mistaken for more common ailments, with symptoms including headache, fever and muscle aches.

“The findings from the use of this simple but effective laboratory experiment to gauge how rising temperatures might lead to more human infections with a very dangerous tick-borne pathogen adds to the growing evidence of the increasing connection between climate change and its impact on health,” said Joel Breman, the president of ASTMH.

“Climate change is moving so quickly that it is critical to keep pace with the many ways it may alter and intensify the risk of a wide range of infectious diseases so we are better prepared to diagnose, treat and prevent them.”

16 November 2020

The Guardian