Types of Cold and Flu

Cold and Flu Virus

The appearance of these two typical winter diseases is a reason for frequent consultations. Although both have a similar symptomatology, cold and flu types should not be confused. While in the cold, the symptoms are benign and usually disappear after a few days, the flu is potentially serious. Since it may present complications, a medical consultation is advisable.

The flu and the cold are diseases of viral origin, and give rise to various clinical conditions. For example, rhinitis, pharyngitis, bronchitis, bronchiolitis and pneumonia.

*Cold Virus*

Although more than 120 different strains of virus have been isolated. The most common causative agents of the common cold are rhinoviruses (with more than 100 serotypes) and coronaviruses. The seasonal period determines the predominance of one type or another. The severity of the infection will depend on the incubation period, which can vary from 1 to 10 days, being the most typical 24-72 h.

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Rhinoviruses are the most common viral infectious agents in humans and are the predominant cause of the common cold. Rhinovirus infection proliferates in temperatures between 91–95 °F(33–35 °C), the temperatures found in the nose.
There are 99 recognized types of human rhinoviruses that differ according to their surface proteins (serotypes). They are lytic in nature(causes the destruction of infected cells) and are among the smallest viruses, with diameters of about 30 nanometers.

The primary route of entry for human rhinoviruses is the upper respiratory tract (mouth and nose). As the virus replicates and spreads, infected cells release distress signals known as chemokines and cytokines (which in turn activate inflammatory mediators).

Infection occurs rapidly, with the virus adhering to surface receptors within 15 minutes of entering the respiratory tract. High risk individuals includes children and the elderly. Just over 50% of individuals will experience symptoms within 2 days of infection. Only about 5% of cases will have an incubation period of less than 20 hours, and, at the other extreme, it is expected that 5% of cases would have an incubation period of greater than four and a half days. Types of cold and flu
Human rhinoviruses preferably grow at 89.6 ° F (32 ° C) instead of 98.6 ° F (37 ° C), thus infecting the upper respiratory tract where the flow of respiratory air is in continuous contact with the outside environment (colder).


Coronaviruses are a group of viruses known to cause the common cold. They have a halo or crown appearance (crown) when viewed under an electron microscope.










Coronaviruses primarily infect the upper respiratory and gastrointestinal tract of mammals and birds. Six different currently known strains of coronaviruses infect humans. The much publicized human coronavirus, SARS-CoV which causes SARS, has a unique pathogenesis because it causes both upper and lower respiratory tract infections.

Coronaviruses are believed to cause a significant percentage of all common colds in human adults. Coronaviruses cause colds in humans primarily in the winter and early spring seasons. The significance and economic impact of coronaviruses as causative agents of the common cold are hard to assess because, unlike rhinoviruses (another common cold virus), human coronaviruses are difficult to grow in the laboratory. Coronaviruses can cause pneumonia, either direct viral pneumonia or a secondary bacterial pneumonia, and bronchitis, either direct viral bronchitis or a secondary bacterial bronchitis.

Human Respiratory Syncytial Virus:

respiratory syncytial virus












Human respiratory syncytial virus (RSV) is a virus that causes respiratory tract infections. It is an important cause of lower respiratory tract infections and hospital visits during infancy and childhood. A prophylactic medication, Palivizumab, can be used to prevent RSV in premature babies (under 35 weeks of gestation), babies with certain congenital heart defects (CHD) or bronchopulmonary dysplasia (BPD), and babies with congenital airway malformations . Treatment is limited to supportive care (for example, C-PAP), including oxygen therapy.

1- In temperate climates there is an annual epidemic during the winter months. In tropical climates, infection is most common during the rainy season.

2- In the United States, 60% of infants are infected during their first RSV season, and nearly all children will have been infected with the virus by 2–3 years of age. Of those infected with RSV, 2–3% will develop bronchiolitis, necessitating hospitalization.

See also: “Common Cold and Flu Diagnosis

Flu (Influenza Virus)

The etiologic agent of influenza is the influenza virus, which is characterized by having a high capacity for mutation, and those that affect the human race are those of type A, B and C.

Influenza A Virus:

Influenzzavirus A











  • Influenza A, virus causes influenza in birds and some mammals, and is the only species of influenza virus A.
  • Strains of all subtypes of influenza A virus have been isolated from wild birds, although the disease is rare. Some influenza A virus isolates, cause serious diseases, both in domestic birds and in humans. Occasionally, viruses are transmitted from wild waterfowl to domestic birds, and this can cause an outbreak or lead to pandemics of human influenza.

Influenza A viruses are negative-sense, single-stranded, segmented RNA viruses.

The several subtypes are labeled according to an:

H number (for the type of hemagglutinin)

N number (for the type of neuraminidase).

There are 18 different known H antigens (H1 to H18) and 11 different known N antigens (N1 to N11).

H17 was isolated from fruit bats in 2012. While, H18N11 was discovered in a Peruvian bat in 2013. (Types of cold and flu)

Influenza B Virus

Influenza B virus











This genus has one species, influenza B virus. Influenza B almost exclusively infects humans and is less common than influenza A. This type of influenza mutates at a rate 2–3 times slower than type A and consequently is less genetically diverse, with only one influenza B serotype. As a result of this lack of antigenic diversity, a degree of immunity to influenza B is usually acquired at an early age. However, influenza B mutates enough that lasting immunity is not possible. This reduced rate of antigenic change, combined with its limited host range (inhibiting cross species antigenic shift), ensures that pandemics of influenza B do not occur.

Influenza C Virus

Influenzzavirus C










Influenza viruses A, B and C represent the three antigenic types of influenza viruses. Of the three antigenic types, influenza virus A is the most severe, influenza virus B is less severe but can still cause outbreaks, and influenza virus C is usually only associated with minor symptoms.

Influenza viris A can infect a variety of animals as well as humans and its natural host or reservoir is birds whereas influenza viruses B and C do not have animal reservoirs. Influenza virus C is not as easily isolated so less information is known of this type, but studies show that it occurs worldwide.

See also: “Coronavirus: Know the symptoms and what care to take for this pandemic

This virus (Types of cold and flu) may be spread from person to person through respiratory droplets or by fomites (non-living material) due to its ability to survive on surfaces for short durations. Influenza viruses have a relatively short incubation period (lapse of time from exposure to pathogen to the appearance of symptoms) of 18–72 hours and infect the epithelial cells of the respiratory tract. Influenza virus C tends to cause mild upper respiratory infections. Cold-like symptoms are associated with the virus including fever (100.4-104ᵒF), dry cough, rhinorrhea (nasal discharge), headache and muscle pain. The virus may lead to more severe infections such as bronchitis and pneumonia.

As with all influenza viruses, type C affects individuals of all ages. But is most severe in young children, the elderly and individuals with underlying health problems. Young children have less prior exposure and have not developed the antibodies and the elderly have less effective immune systems. Influenza virus infections have one of the highest preventable mortalities in many countries of the world.

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