Both bacterial and viral infections can contribute to the development and worsening of asthma symptoms, research has shown. Sinusitis, rhinitis, pharyngitis, laryngitis, and bronchitis are some of the most common respiratory infections, and they can be of variable origin. The appropriate assessment of these patients is required in order to reach the correct diagnosis and apply the necessary treatment.
Who is at risk of respiratory infections?
Respiratory infections are the most common acute diseases in the human population. The frequency of these infections peaks during childhood, although they affect people of all ages. It has been noted that childhood-onset asthma is more prevalent in males, but when it comes to asthma induced by infection, there are no gender-related differences.
The appearance of asthma induced by infection follows the seasonal pattern of respiratory infections. Therefore, spring and autumn come with the highest risk of this type of asthma. Scientists have found that there are several genes which contribute to the intensity of the body's response to infections. People with a higher immunological response are at a higher risk of developing infection-induced asthma. Socioeconomic conditions and climate are also important factors that affect the frequency of respiratory infections.
Viral infections and asthma
Rhinoviruses and the respiratory syncytial virus (RSV) are the most common types of viruses which cause upper respiratory tract infections, both in adults and in children. Viruses are intracellular microorganisms, which means that they cannot live for a long time or reproduce outside of the living cell. This is why the adaptive T-cell mediated immune response is activated when a virus infects a cell. As a result, cytokines are created, which attract other mediators and intensify the inflammation.
On the other side, there are cells called CD8+ T lymphocytes, which are able to kill the infected cells in order to stop spreading the infection. These mechanisms are important because the nature of asthma is also inflammatory, and this is the way in which viral infections initiate inflammation and potentially trigger the onset of asthma.
Bacterial infections and asthma
Unlike viruses, bacteria are extracellular microorganisms, which means that they reside end reproduce in the spaces between the cells (interstitial spaces) and in bodily fluids. They invoke a so-called humoral response mediated by B-lymphocytes which produce antibodies. The result of this complex mechanism is also inflammation, which can be localized or systemic.
There are exceptions, such as Chlamydia, Mycoplasma, etc, which live inside the cells and the organism fights them using the defense mechanisms similar to that for defense from viruses. Those are atypical bacterial infections, and scientists have found that Mycoplasma Pneumoniae and Chlamydia pneumoniae can worsen the symptoms of existing asthma.
Asthma triggered by an infection: Clinical characteristics
Viral infections with rhinoviruses and RSV can go with or without symptoms. If they are symptomatic, they usually present with typical local symptoms of a viral respiratory infection — nasal discharge, sore throat, and sometimes systemic symptoms, such as fever and a general feeling of illness.
Asthma triggered by a viral infection usually strikes on the first or second day from the appearance of the first symptoms. It starts with wheezing, and by using spirometry, decreased expiratory volumes can be detected. Within one to two weeks of infection, the symptoms usually subside.
Children with existing asthma experience worsening of the symptoms for different reasons, but in about 80 per cent of cases, the cause is an acute respiratory infection. In adults, this rate is lower, but still significant – about 50 per cent.
Treatment of infection induced asthma
For bacterial infections, doctors prescribe the appropriate antibiotics, which can be taken orally, intramuscularly, or in severe cases intravenously. For the treatment of viral infections, there are antiviral drugs, but their efficacy is often limited. Supportive therapy is the main principle in the treatment of viral infections.
There are also the cases of more severe, longer-lasting infections, such as tuberculosis. Patients with asthma and tuberculosis need special attention and intensive antibacterial and support therapy.