The cause of a cold is viruses. In particular, the following pathogens are among them: After the cause of the transmission by direct contact with a sick person or by droplet or smear infection, the viruses nest in the cells of the body (host) and cause the typical symptoms of a cold. The cold (hypothermia, freezing), which is often discussed as the cause of a cold, probably contributes to the development of a cold by weakening the immune system. This weakening of the immune system makes the body as a whole more susceptible to disease, so that the viruses can more easily unfold their pathogenic effect and a cold develops as a result.
- Rhinoviruses
- Corona viruses
- Adenoviruses
- Parainfluenza viruses
- Respiratory Syncytial Virus (RSV)
Pathogen
The pathogens that cause a cold are all viruses that can be divided into different virus families. The names of the virus families can be recognized by the suffix “Viridae” (viruses). Rhinoviruses belong to the family Picornaviridae, influenza viruses to the Orthomyxoviridae and parainfluenza viruses to the Paramyxoviridae.
In the case of corona viruses and adenoviruses, the family is called like the viruses themselves: Coronaviridae and Adenoviridae. The Respiratoy syncytial virus belongs to the Pneumoviridae. Human rhinoviruses as the cause of the common cold comprise more than 100 subtypes, which can be divided into two groups (major group, minor group) according to their mechanism of cell invasion.
Rhinoviruses are transmitted from person to person by droplet or smear infection. The time to the appearance of the symptoms of rhinitis (incubation period) is one to four days and the rhinitis lasts about seven days. An accumulation of infection with rhinoviruses occurs in spring and autumn; in principle, however, infection with rhinitis is possible throughout the year.
The environmental resistance of these viruses is not particularly high, which is why these rhinovirus pathogens cannot survive for long outside the host (target cells of the infection). The name of the corona viruses is derived from their electron microscopic image, since their envelope is like a “halo” (corona). Several different subtypes of this rhinitis-causing virus are also known, although in all probability not all of them are known.
The transmission/cause of the rhinitis is done by droplet infection and can be asymptomatic. Already in children the infection is high, which means that many infections with this virus occur at a young age. Adenoviruses as further pathogens of a cold show a high environmental resistance and comprise about 50 subgroups.
In addition to rhinitis, they cause other clinical pictures such as conjunctivitis or gastroenteritis. In addition, asymptomatic courses (without symptoms) are also possible. They are transmitted by droplet or smear infection, and even infants and toddlers are affected by this virus, with a correspondingly high rate of infection.
The incubation period is between several and ten days. Parainfluenza viruses that cause a cold contain four subtypes. The transmission takes place via direct contact or by droplet infection.
First symptoms appear after three to five days incubation. Infants and toddlers are also frequently infected with parainfluenza viruses, which is why the infection rate in children is between 50% and 90%. The respiratory syncytial virus, which also belongs to the rhinitis pathogens, is divided into two groups (A and B).
The name derives from the fact that when cells are infected, they fuse with neighbouring non-infected cells and form syncytia called “giant cells”. These viruses are transmitted via droplet and smear infection and mainly infect infants and small children, so that even two-year-olds show a high rate of infection. More serious diseases also affect older people and those with weakened immune systems (immunocompromised persons).
Acute rhinitis is in most cases a classic symptom in the context of a simple cold or similar infection, such as influenza. One speaks then of an infectious rhinitis acuta. Triggers are almost always (cold) viruses that are transmitted by droplet or smear infection, of which more than 200 different types are known.
Most common are rhinoviruses (from the family of Picornaviridae), which in turn have over 100 different subtypes.In addition, respiratory syncytial, corona, parainfluenza and adenoviruses, and in summertime especially coxsackie, entero- and echo viruses are possible. The fact that of these mostly also a multiplicity of different subtypes exists, explains why such a frequent illness is possible without developing a general immunity. A nasal mucosa that is attacked by dry room air or that is poorly supplied with blood due to hypothermia makes it easier for the viruses to settle.
Other favourable factors include a weakened immune system (e.g. due to stress, lack of sleep, cold, other diseases), irritation by chemical substances or cigarette smoke, systemic diseases (e.g. cystic fibrosis) or a narrowing of the nasal cavity (due to polyps or a crooked nasal septum). Likewise, a cold can be caused by an infection with the influenza virus, which is the trigger for the “real” flu, which is much more severe than a common cold and starts very suddenly.
Viral infectious diseases such as measles or chickenpox or the initial infection with a herpes simplex virus can also be responsible for a cold. Bacteria, on the other hand, are only rarely the cause of a cold and if they are, then usually only in the context of a bacterial super-infection: through the nasal mucous membrane damaged by a viral infection or through the i. The nasal mucous membrane damaged by a viral infection or by the generally weakened immune system promotes an additional infection with bacteria, especially staphylo-, strepto- and pneumococci.
Sometimes, however, bacterial infectious diseases such as scarlet fever, whooping cough, legionellosis, typhoid, tuberculosis, even syphilis or gonorrhea are accompanied by rhinitis, whereby the nasal secretion is yellowish to green in contrast to viral infections. Rhinitis pseudomembranacea is a special case here as a possible, rare manifestation of diphtheria, in which the nasal mucous membrane is damaged by the formation of a pseudomembrane, resulting in a bloody and fluid rhinitis. Apart from this, the consumption of spicy food can also lead to a short-term cold or a “runny nose“. In addition, a fracture of the base of the skull can cause cerebrospinal fluid (liquor) to leak into the nasal cavities (rhinoliquorrhea), so that it may appear to be a cold.
