Introduction to infectious diseases

2021-04-15 04:09 PM

Infectious diseases have the ability to spread from sick to healthy people, many diseases develop into epidemics


Infectious disease also called contagious disease - A common disease in all continents but especially in hot and humid climates (tropical). The cause of infectious diseases caused by microorganisms is called pathogens, which are capable of transmitting in the community by many different ways and sometimes become epidemics with a very large number of people. The disease usually progresses in stages.

Research history

Infectious diseases are known since ancient times. In the Hypocrat period, infectious disease was known as the "Plague" to denote the severe and widespread nature of the disease. At that time, it was thought that the disease was related to "Toxic gas". In the sixteenth century, the theory of "Ray" was born instead of the concept "Toxic gas". The theory of disease-to-human transmission was proposed by DSSamoilovitra in 1784, with this hypothesis the author believes that the cause of infectious diseases including the plague is a very small living organism. However, it was not until the beginning of the nineteenth century that with the advent of microscopes, the scientific bases of infectious diseases were proven by the discovery of a number of bacteria whose contributions belonged to scientists. Head like L. Pasteur, R. Koch, I. Mechnhicop, G. Minx, D. Ivanôpski… The microbiological achievements of the second half of the nineteenth century are the basis for separating infectious disease from general medical pathology by its own scientific principles. The proliferation and detection of more and more pathogenic microorganisms makes infectious diseases more and more plentiful. Today the number of infectious diseases studied is in the hundreds and as progresses more new diseases will be added to the list of infectious diseases.

Position and importance of the subject

In the past, infectious diseases were classified as medical diseases. From the first half of the nineteenth century, it was split into an independent specialty.

Infectious diseases are mostly common diseases in all countries of the world. Depending on geographical regions, climates, and depending on the educational level and living conditions of each region, the morbidity rate and disease structure vary (tropical and subtropical regions, regions with socio-economic conditions. Poor backwardness, morbidity rate is high and there are more infectious diseases).

Infectious diseases have the ability to spread from sick to healthy people, many diseases develop into epidemics (even pandemic). Therefore, the number of infectious patients is very large and the number of deaths is also large.

Today, thanks to the development of science in general and medicine in particular, many infectious diseases have been repelled, some diseases have been permanently eliminated (such as smallpox). However, some infectious diseases are still rampant and also a threat to humanity such as malaria, viral hepatitis, dengue haemorrhagic fever, Ebola haemorrhagic fever, HIV / AIDS ...

Vietnam is a tropical country with low living conditions and backward living habits. Therefore, infectious diseases account for a very high rate, many outbreaks occur all year round (such as dengue haemorrhage, malaria, meningococcal infections, cholera, plague ...).

Features of infectious disease

General characteristics

Infectious diseases are diseases caused by microorganisms, called pathogens. Each infectious disease is caused by a single pathogen.

Infectious diseases can be transmitted from sick to healthy people by many different ways. Many diseases have one transmission route, a few diseases have 2 to 3 transmission routes.

The disease develops often in a cycle that clinically calls successive stages of the disease: incubation, onset, full recovery, recovery and recovery.

After contracting infectious diseases, the human body has a humoral immune response and a cell-mediated immune response. That process is called immunomodulation. Depending on the disease and depending on the human body, the immunity is formed with different levels, the duration of the protective immunity is also different.

The receptivity is different depending on the type of disease and the patient's body: there are diseases when the body is infected with the pathogen, it will become 100% sick; But there are also pathogens that, when the body is infected with the pathogen, it is not necessary to get the disease in all cases.

Progressive characteristics of the disease

The infectious disease takes place through the following periods (also known as "stages"):

Incubation period

From the moment the pathogen enters the human body until before the first symptoms appear. During this period, the patient does not feel any symptoms. The incubation period is long or short depending on the type of disease, the number and toxicity of the pathogen, the resistance of the body. This period can be very short (hourly) but can be very long (monthly). There are many cases of infected people carrying a prolonged pathogen (latent or benign human form carries bacteria).

Onset period

It is the first symptoms of the disease to appear, but not the time when the disease is most severe and most obvious. Infectious diseases usually start in two ways: slowly and suddenly. Fever is present in most infectious diseases, and one of the first symptoms of the onset is also a fever.

Full-blown period

 Is the time when the disease develops the most loudly and manifests the fullest symptoms, at the same time the disease is the worst. Complications are also common during this period. Can manifest many symptoms at the same time in many different organs.

Recovery period

Due to the good resistance of the patient's body, on the other hand, due to the effects of treatment, the pathogens and their toxins are gradually eliminated from the body. The sick person will feel better gradually. Symptoms of the disease at the full stage also gradually disappeared. Without early and effective intervention, some diseases develop long and recur with serious complications and consequences.

Recovery period (rejuvenation)

 After the pathogens and their toxins are eliminated from the patient's body, the damaged organs gradually recover and return to almost normal function, leaving only minor disturbances. The patient can be discharged from the hospital to rest or can continue to work, fight depending on the ability to recover.

Classification of infectious diseases

There are many ways to classify infectious diseases according to different conceptions and purposes. In clinical, people often apply the classification of diseases by transmission route including 5 groups to facilitate isolation, management and also convenient for care and treatment. The 5 groups of diseases are:

The disease is transmitted in the gastrointestinal tract.

The disease is transmitted by the respiratory tract.

The disease spreads through the bloodstream.

The disease is transmitted by the skin and mucous membranes.

Infectious diseases can be spread by many different ways.

A few other notions

Mixed infections

Usually, an infectious disease is caused by only one pathogen, but sometimes two or more pathogens work together to cause the disease at the same time. This is called a mixed infection or co-infection.

Secondary infection

While the disease is progressing, not yet recovered, there are other pathogens that, thanks to such favourable conditions, cause more serious illness, called secondary infection (or superinfection).

Occur again periodically

When the disease has not completely cured, due to a certain favourable condition, the symptoms of the disease can return.


Being infected again, by re-infection with the germ (which was previously infected) again.

Diagnosis bases and treatment directions

Basis of diagnosis

Diagnosis of infectious diseases is usually based on the following:


Exploit those living together who have had anyone with a similar illness; especially contact with patients with a diagnosed illness.

There is nothing special about animals in the habitat (because there are diseases spread from animals to humans such as anthrax, plague ...).

What epidemic outbreaks are present in the living or working area (malaria, plague, cholera ...); sick season.

The epidemiological factor is only a reference factor, suggesting a diagnostic direction.


Based on the outstanding clinical symptoms and specific for each disease. This is a ground of scientific significance and in clinical practice is sometimes decisive.


Nonspecific tests: blood count, blood sedimentation rate, urine test and related functional tests.

Specific test: Is the determining factor in diagnosis. Identify the pathogen or pathogen markers (antigens, antibodies ...).

Treatments for infectious diseases

Specific treatment

Kill pathogens (bacteria, viruses, rickettsia, parasites, fungi ...). Pathogens are usually antibiotics and chemical or herbal chemicals. Specific treatment is decisive to cure the disease completely.

Treatment according to the pathogenetic mechanism

Effects on pathogenesis to prevent or correct pathological disorders. The current pathogenetic mechanism is the only way to help patients get rid of viral diseases because there are currently no drugs that can actually kill the virus.

Symptomatic treatment

 In order to reduce the symptoms to make the patient more comfortable and is considered a very necessary supportive treatment.


Infectious diseases are very common. Infectious diseases have common characteristics, the disease progresses as a rule over time. The division of infectious diseases as well as diagnosis and treatment follow a unified concept and principle.