Scientists have discovered that arthritis caused by mosquito-borne viruses is worse in the limbs than the rest of the body because of their usually cooler temperature.
Researchers from QIMR Berghofer Medical Research Institute made the discovery while looking into how the immune system combats arthritic joint inflammation caused by Ross River virus and chikungunya virus.
QIMR Berghofer Inflammation Biology group leader Professor Andreas Suhrbier said arthritis from mosquito-borne viruses usually affected joints in the limbs, such as the arms, wrists, legs, ankles and feet.
He said the arthritis was debilitating and painful, lasting from weeks to many months.
“We’ve now worked out why these joints are so badly affected by inflammation,” Professor Suhrbier said.
“The bizarrely simple answer is because these joints in the limbs are usually a few degrees cooler than the rest of the body.”
He said the first line of defence used by the body to fight off a viral infection were cell proteins called type 1 interferons.
“What we have discovered is that interferons work optimally at 37C, which is the body’s normal temperature,” Professor Suhrbier said.
“However, we found that when the temperature is a few degrees cooler, this defence system works very poorly.”
Professor Suhrbier said when the limb temperature in mice was warmer, the anti-viral defence system was more effective at fighting off the virus.
He said the mice housed at 30C also had less severe arthritis than the mice housed at the standard 22C.
“This is the first time that ambient temperature has been shown to have such a dramatic effect on viral infections in warm-blooded animals,” Professor Suhrbier said.
“In the 1930s, an Australian nurse called Elizabeth Kenny pioneered a highly controversial limb-warming therapy for children suffering from polio, which became known as the ‘Kenny method’.
“Our findings would appear to vindicate the Kenny method. They also beg the question: Can the Kenny method of warming the limbs also potentially treat arthritis caused by Ross River virus and chikungunya virus?”
Professor Suhrbier said heat treatment would need to be started very early in the infection and how this related to humans would need to be established in future clinical investigations.
He said the findings also raised other questions.
“Older people, aged over 75 years, are the most at risk of death from chikungunya virus. Could this be because the body temperature in the elderly is often slightly lower?” he said.
“Do these findings also suggest that these viral diseases should be less severe in people who live in hot, tropical climates, like Far North Queensland?
“Unfortunately, a number of confounding factors such as the use of air-conditioning and better access to anti-inflammatory medications make this difficult to unravel.”
Professor Suhrbier said mosquito-borne viruses that caused outbreaks of rheumatic disease occurred across the world.
“The recent large global epidemic of chikungunya virus has so far only affected Australian travellers, but it has caused millions of cases across Africa, Asia and the Americas,” he said.
“Between 4000 and 5000 Australians get Ross River virus each year.”
The study involved collaborators from the University of Queensland, Griffith University, the National Institute of Infectious Diseases in Japan, the School of Pharmaceutical Sciences in Brazil, and the University of Pittsburgh in the United States.
The research was supported by the National Health and Medical Research Council, and the first author, QIMR Berghofer researcher Dr Natalie Prow, was awarded an Advance Queensland Research Fellowship.