What is it
Infection is when microorganisms, such as bacteria, fungi or viruses, penetrate and multiply in the body.
If the infection is kept under control by the immune system and does not cause obvious damage, it is called a latent infection.
Causes
To generate an infection, the microorganism must:
- overcome the body’s external barriers (skin or mucous membranes)
- be pathogenic (i.e. capable of causing damage to the body)
- be present in sufficient quantity to overcome the natural organic defenses.
The microorganism that causes the infection can enter the body through different routes, and transmission can be direct or indirect.
| Direct transmission | Infection passes from one individual to another, for example through the air breathed (as is the case for exanthematous diseases childhood) or by contact (as in venereal diseases) |
| Indirect transmission | There is an intermediate passage through water, food or objects, or through an animal (mosquitoes, fleas, etc.), which is called a vector |
The type of transmission depends on the specific microorganism and its ability to survive in the external environment.
The different types of infection
Depending on the nature of the infectious agent, infections are divided into two macro categories: viral infections and bacterial infections. Then there are fungal infections, due to a fungus, and parasitic infections, when the responsible agent is a parasite.
Viruses are not able to reproduce themselves; To do this they must attack a living cell (host cell) by penetrating inside it, where they release their own genetic material by infecting it. The cell thus loses the ability to perform its functions and dies, after releasing new viruses that will infect other cells, triggering the progress of the infection.
However, the infected cell does not always die. Some viruses, in fact, limit themselves to altering their functions, depositing their genetic material inside them and remaining quiescent. However, it may happen that, even after years, the virus begins to replicate causing the disease again.
Viral infections
The most frequent viral infections affect the respiratory tract and involve the nose, throat, upper airways and lungs. The common cold is also a respiratory tract infection. Hundreds of viruses are responsible: the most common are adenovirus and rhinovirus.
Other viral infections can affect the gastrointestinal tract and are caused by norovirus and rotavirus, which are manifested by vomiting and diarrhea. In all these cases, the infection occurs by air. A sneeze or a cough is enough to convey in the air, by means of micro droplets of saliva, a myriad of microorganisms.
The liver is the target organ of hepatitis viruses, classified in A, B, C. Hepatitis C can be cured in some cases thanks to the availability of specific drugs directed against the virus, while for hepatitis B there is a vaccine. Hepatitis A, unlike B and C that contract through contact with infected blood, is transmitted through contaminated food and water and tends to resolve spontaneously.
Other viral forms affect the skin. This happens for example with the herpesvirus family, of which there are eight different types. In addition to herpes simplex virus, very common is shingles, which causes chickenpox. This virus has the characteristic of remaining in the body in a quiescent state and “awakening”, giving rise to other manifestations such as the fire of St. Anthony, even after years and repeatedly, in moments in which there is a lowering of the immune defenses.
Cytomegalovirus also belongs to the herpes virus family. In most cases it causes asymptomatic infections because the immune system is able to keep them under control. In immunosuppressed subjects it can instead cause potentially dangerous infections and if it is contracted by the future mother and transmitted to the fetus during gestation, it can also have serious and permanent repercussions on the unborn child.
It is not uncommon to observe the appearance, typically on hands and feet, of warts. It is in this case a manifestation of the human papilloma virus. There are numerous strains of this virus, some of which are responsible for the onset of cervical cancer.
Bacterial infections
Bacteria are single-celled organisms. They can be found in any environment and are equipped with an extraordinary capacity for resistance and self-protection, to guarantee their survival.
They can live in the soil as in water or in the body of humans and animals, in the presence or absence of oxygen. They also reproduce outside the cells.
Not all bacteria are pathogenic. Some, in fact, belong to the normal resident flora and can be found on the skin and inside the airways, mouth and digestive, reproductive and urinary systems, where they live without causing damage.
Some bacteria are useful for the digestive process or to prevent other harmful bacteria from taking over. The number of bacteria present in the human body, belonging to hundreds of different species, is greater than the number of cells to the extent of 10 to 1.
However, it may happen that the same normally resident bacteria cause diseases, for example in the event that the mucous membranes are damaged and allow the passage to areas and tissues that normally do not contain them and which are therefore defenseless. From the mucous membranes of the mouth, throat, intestine for example they can infect the ear, lungs, sinuses, kidneys and urinary tract.
Infections: common symptoms
Each infection causes an increase in the levels in the blood of lymphocytes, cells belonging to the category of white blood cells that have the task of fighting germs and foreign substances.
The symptom that characterizes all infections is fever, often accompanied by fatigue, malaise, muscle and bone pain. The other symptoms are variable and depend on both the microorganism and the characteristics of the affected person. Symptoms may also include skin lesions, itching, accelerated heart rate, anxiety and confusion.
Some microorganisms cause a local reaction (such as sore throat) at the point of entry into the body, others spread throughout the body or reach a particular organ. Still others produce toxins that give symptoms in different organs. Often the infection is accompanied by an inflammatory reaction. For this reason, depending on whether they affect only one part of the body or the whole organism, infections are divided into local (such as urinary tract infections) and systemic (such as sepsis).
Some microorganisms that are not normally pathogenic can cause an infection in people whose immune system is weakened due to acute or chronic diseases (AIDS), immunosuppressive therapies (transplants), anticancer or prolonged antibiotics, severe malnutrition, surgery.
Diagnosis and treatment
Diagnosis of common viral infections can be based on observation of symptoms. For other diseases, such as hepatitis and AIDS, a blood test is needed to search for antibodies and determine viral load. Finally, papilloma virus infections of the cervix require tissue sampling and subsequent cytological examination.
With regard to the treatment of viral diseases, the generic supportive therapy useful in all types of infection – represented by the administration of antipyretics, anti-inflammatories and good hydration – it is possible in some cases to resort to specific drugs (antiviral drugs) for the particular microorganism that supports the infection.
Most antiviral drugs can be administered orally: they can act by interfering with the replication of the virus, as in the case of drugs used against HIV or hepatitis C, or by strengthening the immune response against viral infection. Most antivirals are directed against only one virus.
Antibiotics have no effect on viral infections, but can be administered in order to prevent further bacterial infection, the onset of which can be facilitated by the weakening of the defenses caused by the viral infection. The choice to take antibiotics is in any case up to the doctor.
For some infectious diseases (such as measles, mumps, rubella) it is possible to resort to prophylaxis through vaccination, serotherapy or chemoprophylaxis.
In bacterial infections, specific antibiotics and chemotherapy are used, which can be identified through a special laboratory test, the antibiogram. Antibiotics must for this reason necessarily be prescribed by a doctor. Fungal infections are also treated with specific chemotherapeutics.
In selected cases (such as following surgery), antibiotics are prescribed in healthy individuals for prophylactic purposes, that is, to prevent possible infections.
Prevention is generally a factor of great importance for infection control, which must be achieved with the elimination, when possible, of the “reservoirs” of the infection (for example mosquitoes), the isolation of contagious patients, the disinfection and sterilization of contaminated objects.
Washing hands is also a simple, but very effective, way to prevent the direct transmission of infectious microorganisms and reduce the spread of diseases.
Complications
The type and severity of complications that may occur also depend on the specific microorganism and the general condition of the person. More at risk are young children, the elderly and severely debilitated people.
When to consult your doctor
In the face of any infection that is not obviously trivial, such as a cold, it is advisable to consult a doctor.
Joycelyn Elders is the author and creator of EmpowerEssence, a health and wellness blog. Elders is a respected public health advocate and pediatrician dedicated to promoting general health and well-being.
The blog covers a wide range of topics related to health and wellness, with articles organized into several categories.