An international team of researchers has shown that
natural infection by influenza viruses in pigs causes important changes in the
lung microbiota, increasing the presence of potentially pathogenic bacteria and
the diversity of bacterial genera compared to healthy animals. The work,
published in the journal Frontiers in Cellular and Infection Microbiology,
has been led by the Virology and Innate Immunity (VII) group at CEU San
Pablo University and warns about the risks of secondary bacterial
complications beyond the most common bacteria that cause respiratory pneumonias
associated with flu infections by analysing the lung microbiota in pigs. This
animal model is especially relevant because it presents an influenza disease
similar to humans.
Key points
- The lungs of pigs infected with influenza viruses
have a higher load and diversity of bacteria compared to healthy animals.
- In respiratory infections caused by influenza
viruses, a significant increase in associated bacterial genera was
detected, such as Glaesserella (present in 60% of cases), Pasteurella,
Staphylococcus, Mycoplasma and Fusobacterium among others.
- The bacterial profiles associated with the viral
infection allow the identification of different bacterial signatures,
which opens new perspectives for differential diagnosis in both pigs and
humans.
Pigs are considered an important reservoir and
'genetic mixer' of influenza viruses with pandemic potential, as evidenced in
the 2009 H1N1 pandemic. However, until now little was known about how the flu
directly affects the lung bacterial ecosystem. Understanding these alterations
is key to understanding and helping to prevent secondary bacterial infections.
The research, carried out with samples of necropsies
from the lungs of pigs from different Spanish regions and third-generation
sequencing technology of nanopores, provides a fast and practical method to
diagnose modifications in the respiratory microbiota. In addition, it confirms
that the appearance of opportunistic pathogens after viral infection would
complicate the clinical course and recovery.
The team developed advanced bioinformatics tools to
compare the lung microbiota of 53 infected pigs and 39 healthy pigs. The
analysis included metrics of richness and diversity, as well as predictive
models of species clustering. In addition to CEU group VII, the following
groups have participated in the study: Gustavo del Real (INIA), María
Montoya (CIB), Adolfo García-Sastre (Icahn School of Medicine at
Mount Sinai), César Bernardo Gutiérrez Marín (University of León), Juergen
Richt (Kansas State University), Eric Bortz (University of Alaska), Jordi
Cano Ochando (ISCIII) and Juan Luis Tejerina del Valle (Salamanca).
The study is part of the work of the CRIPT Center for Influenza Research
of the CEIRR program funded by the National Institutes of Health of
the United States.
"Our work helps to understand the complexity of
the microbiota in the evolution of influenza-associated respiratory infections.
Currently, microbiological diagnosis and treatment of infections focuses on
finding the virus that causes the flu infection and, in the case of subsequent
bacterial pneumonia, the bacteria responsible for the complication," says Javier
Arranz-Herrero, first author of the study.
The bacteria that cause pneumonia do not only come
from outside, "our respiratory system is colonised by a multitude of
bacteria that live with us. Some of them take advantage of the flu infection to
replicate and complicate the clinical picture of infection," says Sara
Izpura de Luis, co-author of the study. "In this study we look at the
most common opportunistic bacteria in these infections in pigs, but also how
they are not alone. There is a great bacterial diversity that accompanies those
that are commonly diagnosed," he points out.
"At the moment, the role of this bacterial
diversity is not known, as well as how it can determine the development of the
disease both in viral infections where subsequent bacterial pneumonia does not
develop, and in those where it does occur and antibiotic treatment does not
solve the problem," says Estanislao Nistal Villán, co-author and
head of the research.
This methodology and its results open the door to
similar studies in humans and to possible diagnostic and therapeutic
applications, allowing us to anticipate complications associated with influenza
and other respiratory diseases caused by viruses.
Note: This release is based on the study 'Swine
Influenza-Modified Pulmonary Microbiota', data for which are available
through the doi: 10.3389/fcimb.2025.1634469
The research described in this press release was
supported by Ministerio de Ciencia e Innovación Project
PID2023-150116OB-I00 and by the National Institute of Allergy and Infectious
Diseases of the National Institutes of Health under contract number 75N93021C00014.