Indigenous populations have stronger immunity to a serious bacterial infection than non-Indigenous populations, regardless of whether they live in an area where the infection is common or uncommon, according to a study published online today in PLOS ONE.
Haemophilus influenzae type A (Hia) is a bacterial infection that can lead to serious illnesses including pneumonia, meningitis, sepsis and epiglottitis, all of which can result in permanent disability or death.
The study compared naturally-acquired immunity to Hia infection in Indigenous adults living in Ojibwa First Nations communities in Northwestern Ontario to that of non-Indigenous people living in Northwestern Ontario and across the country, as well as Indigenous adults living in Ojibwa First Nations communities in Southern Ontario.
The researchers examined serum bactericidal antibodies—antibodies occurring naturally in the blood that kill bacteria—in 110 Indigenous and 76 non-Indigenous adults. Of the 186 people studied, bactericidal antibodies against Hia were detected at higher rates in Indigenous compared to non-Indigenous adults: 80 per cent of Indigenous adults in Northwestern Ontario and 96 per cent of Indigenous adults in Southern Ontario had these antibodies, compared to only 64 per cent of non-Indigenous Canadian adults from across the country.
Northwestern Ontario has one of the highest rates of invasive Hia infections in Canada, second only to Nunavut, according to Dr. Marina Ulanova, a faculty member in the Medical Sciences division at the Northern Ontario School of Medicine (NOSM) and lead author of the study published today.
The infection occurs most commonly in young children, the elderly and adults with chronic diseases or other health issues that affect their immune system, according to the authors, and is more common in Indigenous versus non-Indigenous populations.
Previous research by Ulanova’s team has found that Indigenous adults in Thunder Bay have a higher immunity against Hia compared with non-Indigenous people living there. She says the results of today’s study are surprising because Indigenous adults from both the Northwestern and Southern Ontario communities both had high rates of immunity, despite Hia infection being very uncommon in Southern Ontario.
“One of the ways you develop natural immunity to bacteria is through exposure,” she says. “So it makes sense that adults who live in an area where the infection is common have a higher immunity to it. But because Hia is not common in Southern Ontario, the higher rate of immunity in Indigenous populations living there suggests there are other factors at play here.”
While the study did not directly answer the question of why Indigenous adults have higher immunity to Hia than non-Indigenous adults, Ulanova says she thinks immunity may be influenced by changes to gene expression over time as the result of stress and intergenerational trauma.
“Indigenous populations have been exposed to a number of highly unfavorable environmental factors that could cause epigenetic changes in the body–changes in the expression of genes in charge of immune responses,” she says. “This may increase the production of natural antibodies, and could explain why healthy adults do not normally develop serious Hia infections despite the fact that Hia widely circulates in Indigenous communities in Northwestern Ontario.”
However, very young children or people with a weakened immune system as a result of aging or chronic diseases still experience very serious Hia infections at a higher rate in Indigenous versus non-Indigenous communities, says Ulanova, and this study emphasizes the need to further address the role of the social determinants of health in the formation of immune defenses as well as in susceptibility to infectious diseases.
