While not the first to link infection to raised risk of brain damage following a stroke, a new UK study also suggests an inflammatory response by the immune system may be the reason. The University of Manchester team reports the findings in the Annals of Neurology.
Speaking about the implications of their work, joint senior investigator Stuart Allan, a professor in the Faculty of Life Sciences at Manchester, says:
"The results of this new study strongly suggest that patients with stroke, especially if they have preceding infections, could benefit substantially from anti-inflammatory therapies."
Previous studies have already shown that bacterial infection can worsen the damage caused by a stroke, which is where the blood supply to a part of the brain is cut off. In the most severe cases, strokes can be fatal or cause long-term disability.
In developed countries, stroke is the third most common cause of death and the leading cause of adult disability. The most common cause of stroke is a blockage to an artery in the brain (ischemia).
Streptococcus pneumoniae is the most common infection in patients at risk of stroke. Yet, while infection with this pneumonia is a major cause of prolonged hospitalization and death of stroke patients, we know little about how it affects the chances of brain damage from stroke, say the researchers.
So, for their study, they compared stroke outcomes in mice and rats infected with S. pneumoniae to those of non-infected animals. They found the infected rodents fared worse than the non-infected ones.
Blood platelets and interleukin-1 exacerbate brain damage when infection is present
Streptococcus pneumoniae is the most common infection in patients at risk of stroke.
Plus, they also discovered why this might be so. Blood platelets that normally do a good job to stop bleeding after injury by forming clots, together with interleukin-1 - a molecule that the immune system launches as part of its inflammation response to fight infection - worked together in a way to worsen the damage that a stroke inflicts on brain blood vessels.
They noted that ischemic brain injury following strokes in mice and rats infected with S. pneumoniae was between 50% and 90% worse than that of uninfected rodents. Also, the older the animals, the worse the injury, particularly if they also had atherosclerosis (hardening of the arteries).
In previous experimental work, the team had already shown that the anti-inflammatory drug interleukin-1 receptor antagonist can dramatically limit the amount of brain damage caused by a stroke. This led to the drug being tested in stroke patients.
Anti-inflammatory 'fully reversed' infection-induced exacerbation of stroke injury
In this study, they found that giving the anti-inflammatory to the pneumonia-infected rodents soon after they suffered strokes "fully reversed infection-induced exacerbation of brain injury and functional impairment," so they were no worse off than the uninfected animals who suffered strokes.
Prof. Allan says their findings add to existing evidence that interleukin-1 receptor antagonist may be beneficial for stroke patients, even those who might already have had an infection before the stroke.
"A clinical trial of interleukin-1 receptor antagonist is soon to complete in patients with bleeding in the brain and is starting soon in stroke," he adds.
Medical News Today recently learned that insomniacs have a higher risk of stroke. This was the conclusion of a large Taiwanese study that compared health records of over 21,000 people with insomnia to those of 64,000 individuals without the disorder.
Written by Catharine Paddock PhD