Viral infections continue to cause considerable morbidity and mortality around the world. Its risk has dramatically increased due to changes in human ecology such as global warming and an increased geographical movement of people and goods.
When fighting against pathogens, a healthy immune system is one of the most important weapons that our human body owns. A proper nutritional status is essential for the correct immune system function and the prevention and management of viral infections.
Viral Respiratory Tract Infections
Community-acquired respiratory viruses are pathogens such as influenza, respiratory syncytial virus, adenovirus, parainfluenza virus, human metapneumovirus, rhinovirus and enterovirus. They cause millions of deaths and hospitalizations around all over the world every year.
Emerging viruses, especially the RNA viruses like coronavirus, are more pathogenic since most people have no herd immunity. The RNA viruses can adapt to the rapidly changing global and local environment due to the high error rate of their polymerases that replicate their genomes.
Coronavirus disease 2019 (COVID-19) is determined as an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which was first identified in 2019 in Wuhan (China) .
Immunity and the Microbiome
Since around 70% of our immune system resides in our gastrointestinal tract, paying attention to digestive function has been relevant in viral respiratory infections, including COVID-19.
Recent research suggests that the composition of the human microbiome, in various niches, is relevant to viral pathogenesis and play a key role in the host response.
The interplay between bacteria, viruses and host physiology is complex, and we still have much to learn. Despite this, an amounting body of evidence is beginning to reveal the fascinating contribution of both commensal and probiotic organisms to host defence against viral pathogens.
When viruses are exposed to mucosal surfaces (e.g. respiratory or gastrointestinal) they have three broad lines of defence to overcome: the mucus layer, innate immune defences and adaptive immune defences.
Evidence suggests that various commensal and probiotic bacteria influence each of these lines of defence with important relevance to a range of viral infections.
Then, the gut microbiome appears to operate as a signalling hub that is capable to affect host metabolism, immunity, and response to infection.
COVID-19 disease presents with a spectrum of disease severity causing the symptoms ranging from mild and non-specific flu like symptoms, to pneumonia, and life-threatening complications such as acute respiratory distress syndrome (ARDS) and multiple organ failure, and in severe cases requires ventilatory support.
Most symptomatic patients typically display mild to moderate symptoms, including dry cough, fever, shortness of breath, body aches, headache, fatigue, diarrhoea, nausea, anosmia and ageusia. Older people, especially those with existing morbidities like diabetes, obesity, cardiovascular disease, respiratory disease and hypertension, are particularly susceptible to severe symptoms and mortality, as they are individuals with compromised immune function.
Targeting intestinal microbiota has been proposed as a potential strategy against SARS-CoV-2