H7N9 in men is associated with testosterone level
In early 2013, human infections with avian influenza A (H7N9) virus were first reported in China. Since then, H7N9 caused five epidemic waves from 2013 to 2017, making it one of the major zoonoses in the current decade. Exposure to live poultry markets is considered a major risk factor for human infections with the H7N9 virus. An initial epidemiological study revealed that 71% of all H7N9 cases were males in the first wave. A high degree of infection in men was consistently observed, with similar proportions (68–71%) throughout the entire five H7N9 epidemic waves. Currently, very little is known regarding the complex interplay of biological sex and gender-specific behaviour as contributors to influenza disease outcomes.
The World Health Organization (WHO) first proposed that gender-associated practices and norms, such as more frequent exposure of men to birds, may pose one of the reasons for sex-specific H7N9 incidence. However, a follow-up study suggested that increased risk in older men is not due to higher exposure time in the live poultry market. Thus, the impact of biological sex on H7N9 influenza outcome remains unknown. There is increasing evidence from small animal models that sex hormones play an important role in influenza virus pathogenesis. However, the role of sex hormones in infectious diseases in humans remains to be elucidated.
A new study shows that low testosterone levels are linked to the development of severe or even fatal disease. The researchers found that testosterone levels are negatively associated with the expression of key cytokines involved in antiviral immune responses. The study suggests that reduced testosterone levels upon H7N9 infection represent a poor prognostic marker in critically ill patients.
