Infectious diseases

We all know it: winter is approaching, the temperatures drop abruptly, the days become shorter and the infection rate increases. Fever, colds and sore throats accompany all of us from time to time throughout the year, but most often in winter. We feel sluggish, tired and drained.

Triggered by viruses, fungi or bacteria, however, infectious diseases can be treated well with the appropriate medications and annoying symptoms can be controlled.

How to recognize an infectious disease as soon as possible and treat it effectively, you will learn in this article.

infectious diseases

What is an infectious disease?

One speaks of an infectious disease when an organism has been infected by a pathogen that causes illness and subsequently shows symptoms. In this process, the pathogen – bacterium, virus, fungus or parasite – penetrates the organism of the host, multiplies and spreads there.

Direct contact in the form of coughing or sneezing can lead to infection, but so can indirect contact, such as shaking hands or eating food. The duration of an infectious disease and the severity of symptoms depend on the type of infection, the characteristics of the pathogen, the physical condition of the host, and the host’s immune response.

Infections can be localized (e.g., wound infections) or affect the entire organism (e.g., measles). However, under no circumstances is an infection to be equated with an infectious disease, as one only speaks of an infectious disease when the affected person also shows symptoms of illness.

This need not always be the case with an infection. Thus, people who carry an infection can infect others without developing symptoms of the disease themselves.

Common infectious diseases

Infectious diseases usually occur in bundles in epidemics, in which many people of a distribution area become infected at the same time. That is why you certainly often have the feeling that many people from your environment always get sick at a certain time. You often hear similar phrases, such as, “At the moment, everyone is getting sick again.” or “At the moment, the flu is going around again.”

Certain infectious diseases are characteristic of different age groups, such as measles, rubella, or chickenpox for children. However, these infectious diseases can also be dangerous for older people with a weakened immune system.

To prevent infections, compliance with necessary hygiene measures or taking antibiotics serves. As a rule, many infectious diseases in Germany are harmless, such as the flu or diarrheal diseases. However, the number of deaths is also increasing here, as more and more people are resistant to drugs used to fight these infections. The reason for this is, on the one hand, the improper use of antibiotics and, on the other hand, the inconsistent adherence to necessary hygiene measures.

Infectious diseases can be divided into eye infections, ear infections, respiratory tract infections, gastrointestinal infections, skin infections and infections of the urinary and genital organs:

Eye infections

  • Conjunctivitis
  • Inflammation of the eyelids
  • Barley grains

Ear infections

  • Middle ear and ear canal infections

Respiratory infections

  • Flu (Influenza)
  • Tonsillitis
  • Whooping cough
  • Tuberculosis

Gastrointestinal infections

  • Campylobacter enteritis
  • Salmonellosis
  • EHEC
  • Norovirus gastroenteritis
  • Rotavirus gastroenteritis

Skin infections

  • Chickenpox
  • Wound infections
  • Shingles
  • Herpes
  • Fungal diseases (e.g. athlete’s foot)

Infections of the urinary and genital organs

  • Renal pelvic inflammation
  • Cystitis
  • Urethritis
  • Vaginal fungus
  • Penile fungus
  • Various venereal diseases

The RKI regularly records the most common infectious diseases of the year and highlighted the following infectious diseases for 2020:

  • COVID-19
  • Flu
  • Gastrointestinal infection
  • Chickenpox

What are the different pathogens?

Infectious diseases can usually be caused by four different pathogens: Viruses, bacteria, fungi and parasites.

1. Viruses

Viruses are very small and do not consist of their own cells, but of one or more molecules containing the genetic material (DNA or RNA). Viruses are surrounded by a protein envelope. In general, viruses are not considered to be living organisms, since they do not have their own metabolism and do not have their own energy production, nor do they have a possibility for protein synthesis. Viruses can occur in many different forms.

Not all viruses make you sick. However, they can invade human, animal and plant cells, where they dock onto host cells. If they fail to do so, they die.


After viruses enter the organism, they begin to multiply. To do this, they dock onto host cells and make them produce the building blocks they need. Once this happens, the host cells die and thousands of new viruses are released, which in turn dock onto more host cells.


Antibiotics are ineffective against viruses. However, there are some antiviral drugs, but they are effective only against certain types of viruses. If our immune system was able to successfully fight the viruses for the first time, we are usually immune to them.

Possible infectious diseases

  • Cold
  • Labial herpes
  • Gastrointestinal infections
  • Chickenpox
  • Measles

2. Bacteria

Bacteria are much larger than viruses and come in a variety of forms. As unicellular organisms, they are capable of self-sufficiency. They possess their own genetic material and have their own metabolism. They are found in the air, water and food.

Not all bacteria make you sick. In fact, many bacteria are important to our bodies and occur naturally in our intestines, skin and oral cavity. Only one percent of bacteria are pathogenic for the human organism. Once such a bacterium has penetrated the organism, it produces metabolic products which cause the corresponding disease symptoms.


Bacteria multiply by cell division.


If you suffer from an infectious disease caused by bacteria, you can easily treat it with appropriate antibiotics.

Possible infectious diseases

  • Salmonellosis
  • Abscesses
  • Sepsis
  • Whooping cough
  • Urinary tract infections

3. Mushrooms

Mushrooms are very versatile. They occur as porcini mushrooms in the forest, as truffles underground, and naturally in the human body or on the skin as skin fungi. Only a few fungi, including individual skin fungi, yeasts and molds, make people really sick. They love habitats where it is very humid. For example, fungi like to spread in damp bathrooms, basements or wet forest floors. The yeast fungus, however, belongs to the natural skin flora and lives in our skin scales, where it feeds on dead tissue particles. Fungi penetrate the human organism only when the immune system is weakened.


Fungi can reproduce by simple division or by the formation of spores.


Infectious diseases caused by fungi are called mycoses. For their treatment there are certain antifungal drugs, called antifungals.

Possible infectious diseases

  • Mycoses on the skin, nails, mucous membranes

Rarely internal organs are affected


4. Parasites

Head lice, tapeworms, ticks, and fleas are well-known examples of so-called parasites, i.e. creatures that feed on the blood of the host they infest. However, not all parasites make you sick. Lice, for example, only causes an unpleasant itch in the affected area and can be easily controlled by chemical means.

Tick bites, on the other hand, may well pose a greater danger. This is because there is a possibility that pathogens can enter our blood and cause inflammation of the brain or meninges.

Some fleas can also transmit plague bacteria, among other things.

However, plasmodia are particularly dangerous. These can be transmitted by the bite of the Anopheles mosquito and cause the infectious disease malaria.

You can be infected by parasites by eating infested food, intensive contact with animals – pets are often used as a way station by parasites to then infect the human organism – or by simply walking in the woods without appropriate clothing.


Parasites reproduce by laying eggs.


You can protect yourself from parasites by wearing appropriately long, thick clothing when outdoors, washing your hands thoroughly on a regular basis, and, if you have a pet, deworming it regularly and treating it with flea and tick preventatives.

Possible infectious diseases

  • TBE
  • Lyme disease

Toxoplasmosis (especially dangerous for unborn babies during pregnancy)

How dangerous are infectious diseases?

In Germany, the vast majority of infectious diseases do not pose a major threat to those affected, since medical care here is of a high standard and the country has a diverse repertoire of effective medicines. Infectious diseases can therefore be treated well here and dangerous courses of the disease can usually be avoided.

However, there are also some infectious diseases that pose a greater risk to humans than others. This includes:

  • Inflammation of the heart muscle (myocarditis)
  • Inflammation of the brain (encephalitis)
  • Inflammation of the meninges (meningitis)
  • Blood poisoning (sepsis)

The ever-increasing number of people resistant to antibiotics and other drugs has already been addressed. However, just as humans can develop resistance, bacteria can also become resistant to multiple antibiotics. This is referred to as multi-resistant germs.

A well-known example of this are nosocomial infections, so-called “hospital germs”. These are infections that a person contracted during their hospital stay. Generally, an infection 48 hours after admission is referred to as a nosocomial infection.

However, if we turn our gaze to other countries in the world, it is striking that infectious diseases are still considered the most common cause of death everywhere in the world. The reason for this fact has in…

  • … scarce medical care
  • … poor hygienic conditions
  • … lack of nutrition

Moreover, the same pathogens do not occur everywhere in the world. In different climatic zones, there are other pathogens that can cause infectious diseases that are much more dangerous than those we are familiar with in Germany.

In general, the risk of infectious disease depends on many different factors. As already mentioned, children, for example, are much more susceptible to certain infectious diseases, such as measles or chickenpox, than people of an older age. Your own immune system, diet, physical fitness, and pre-existing immune protection affect how dangerous an infectious disease is to you.

Other factors on which the risk of an infectious disease depends are:

  • Photogenicity and virulence of the pathogen (how harmful is the invader and how resistant is the pathogen?)
  • Transmission and contagion (How easy is it to get infected with the pathogen?)
  • Medical care (How well developed is the medical care in the country? Are there effective drugs against the respective pathogen?)
  • Condition of the patient (How strong is the patient’s immune system? Does the affected person have special immune protection, such as a vaccination? Does the affected person already suffer from underlying diseases?)

Routes of infection: How do you get infected?

Surely you know this: your whole circle of friends is sick, except you. You have to take care of a sick child at home, yet you don’t get infected. The next day you are on the train and suddenly feel miserable in the evening.

You can get infected in many different ways. Not all germs are equally contagious, which means you can be out and about in a large crowd for days and be fit, but suddenly be sick after a visit to the daycare center.

Basically, there are six different routes of infection:


Droplet infection

In droplet infection, pathogens from the throat or respiratory tract are released into the air through saliva droplets by sneezing, coughing, or talking. These are then either inhaled by other people and thus absorbed through the mucous membranes, or absorbed through direct contact, such as a kiss.

The size of the saliva droplets is decisive for their range. Droplets larger than 5 µm in diameter descend quickly in the air and are therefore only transmitted over a distance of one meter. So here enough distance is enough to protect against infection.

However, saliva droplets, which have a smaller diameter than 5 µm, float in the air for a long time thanks to their low weight and can thus be transmitted over longer distances.

Viruses are often transmitted via droplet infection. Flu infections or even the real flu are thus passed on from person to person. However, bacterial infections such as scarlet fever or meningococcal infections are also transmitted by droplet infection.


Smear infection

Smear infection occurs through touch. It can be from person to person or from an object to a person. For example, if a person sneezes into the palm of his or her hand and then passes that hand to another person, the viruses are passed on. If the second person now puts their hand to their mouth or nose, the pathogens can enter the organism through the mucous membranes.

If the first-mentioned person operates a door handle after sneezing, for example, the germs adhere to it. If the second person then also operates this door handle, the germs are on his or her palm and can again be absorbed by the mucous membranes via a touch of the mouth or nose.

Diarrheal diseases are often passed on via this route. This is where noro or rotaviruses are passed from one organism to another. However, conjunctivitis can also occur in this way if, for example, adenoviruses have been transmitted.


Food infection

Pathogens can also be ingested through food because some pathogens, such as viruses and bacteria, can stick to food. Other pathogens, such as salmonella, are also found directly in foods such as raw eggs, raw sausages and raw meat, among others. To be on the safe side here, you should always fry such foods well before eating them.

But germs in food are not easy to detect because you can’t see, smell or taste them. Some bacteria that produce toxins can only be detected a few hours after consumption, when they manifest themselves in the form of vomiting and diarrhea. In such cases, the term food poisoning is often used. The toxins here affect the digestive tract of the affected person and usually lead to vomiting diarrhea.

This symptom can be triggered by pathogens such as salmonella, E.coli, campylobacter, listten, noro and rotaviruses as well as individual parasites.


Infection via water

Many people prefer still water from the tap, carbonated water. But unfortunately, you can also contract an infection by consuming drinking water. Bathing in contaminated water and drinking untreated water can also lead to infection.

Pathogens are found in particularly large quantities in swimming pools. They enter the water through feces and are passed on via oral-focal infection. However, the fine spray that is mostly found in water slides or in the form of waterfalls also contains pathogens that can easily be inhaled. In most cases, these are pathogens such as Salmonella, Campylobacter or EHEC.

Because of the high risk of infection, the Infection Protection Act and the Drinking Water Ordinance always control the quality of water during its treatment.


Infection through exchange of body fluids

Infections can also be transmitted from person to person through body fluids. This can happen through kissing, sexual intercourse, blood shots, or needle stick injuries.


Infection through animals

As mentioned earlier, animals can also play a significant role in the spread of pathogens. However, in addition to parasites, animals can also infect humans through bites or stings.

Pathogens can enter the human organism through many different ports of entry:

  • Eye conjunctiva: Smear infections can be picked up via the conjunctiva when the hand to which pathogens are attached is brought to the eye.
  • Nasal mucosa
  • Oral mucosa
  • Bloodstream
  • lower respiratory tract: Saliva droplets can be absorbed from the air through the respiratory tract.
  • Maggot Intestinal Tract: Foodborne infection may occur if toxins contained in food are consumed.
  • Skin injuries/wounds
  • Genital mucous membranes: If pathogens enter the genital mucous membranes, infections of the urinary and genital organs may occur.

People as hosts

In a few places in this article, the term “host” has already come up. Thus, viruses seek a host to replicate and spread. Parasites use their host as a food source and a place to live. However, humans also represent a host in some situations.

The host organism serves to transport the pathogen. Here it develops, through him it multiplies and spreads. Pathogens are passed from host to host in a chain of infection. However, carriers of a pathogen do not have to fall ill. Often they serve only for transport and transmission and are then also called vectors.

Endogenous infectious diseases

The infectious diseases highlighted so far are exogenous. In each case, the pathogens originated from outside and only entered the organism of the affected person. However, endogenous infectious diseases represent a special feature.

Here, the pathogen originates from the patient’s own organism. As mentioned in some sections before, in humans there are many bacteria and fungi that are very peculiar to the body and enrich it in a natural way. However, if these pathogens reach another location in the organism, for example as a result of an accident, a surgical intervention or other effects, the germ of the patient’s own body becomes a pathogen.

What symptoms do infectious diseases bring?

The symptoms of an infectious disease depend on the nature of the pathogen and the body structure it attacks. Depending on the type of infection, you can usually expect the following symptoms:

Eye infection

  • Pain
  • Swellings
  • Redness
  • Light sensitivity
  • Secretion
  • Corneal opacities
  • Visual impairments

Ear infection

  • Stabbing, throbbing pain
  • Purulent ear discharge
  • Fatigue
  • Fever
  • Hearing impairments

Respiratory infection

  • Cough
  • Sore throat
  • Common cold
  • High fever
  • Muscle, back, head and limb pain
  • Respiratory impairment

Gastrointestinal infection

  • Nausea
  • Abdominal pain
  • Diarrhea
  • Vomiting

Skin infection

  • Redness
  • Itching
  • Swellings
  • Bubbles
  • Lichens
  • Boils
  • Ulcers
  • Pain

Infection of the urinary and genital organs

  • Burning pain during urination
  • Frequent urination
  • Intense smell of urine
  • Dark/cloudy urine color
  • Traces of blood in urine
  • Small amount of urine

In addition to the symptoms typical of each infectious disease, there are also general symptoms that can usually accompany you with any type of infection:

  • Tiredness, fatigue
  • Lack of strength, rapid exhaustion
  • Chills, fever
  • Headache and pain in the limbs
  • Loss of appetite
  • Malaise

What is the course of an infectious disease?

The course of an infectious disease depends on the type of infection. There are generally three types: florid infections, chronic infections, and latent infections. From person to person, each course of the disease shows itself individually. Basically, however, the course can be divided into five different stages:

Common infectious diseases

1st invasion stage:

In the first stage of the disease process, the pathogens enter the organism. Symptoms do not yet appear at this time.

2nd incubation stage:

The second stage describes the period from the first infection to the outbreak of the disease, i.e. until the development of the first symptoms. At this stage, the pathogens multiply.

3. acute stage:

The acute stage represents the peak of the disease process. Here, all the typical symptoms show up.

4th convalescence stage:

In the fourth stage, the immune system begins to fight against the pathogens. If it manages to do so, the symptoms decrease again and the organism recovers.

5th convalescence stage:

The affected person is completely healed again.

A florid infection is when the immune system fails to fight the pathogens quickly. As a result, the symptoms can develop further and the acute stage lasts longer.

If the immune system then manages to fight the pathogens in a renewed attempt, the convalescence stage follows and the organism can slowly recover. However, if the immune system does not succeed in this, so that it has to repeatedly fight the pathogens, it is a chronic infection.

Finally, in a latent infection, the immune system manages to hold back the pathogens so that no symptoms develop. However, the pathogens are still present in the organism, so that the infection can already show itself again at the next weakness of the immune system.

Successfully prevent infections

Now you are an expert in infectious diseases and their control. To protect yourself from infection, it is important to carefully maintain your health at all times. To successfully prevent infections, you need a strong immune system, you should always follow hygiene measures, as well as provide for certain immune protection – for example, in the form of vaccinations.

To strengthen your defenses, you should …

  • … eat a balanced and healthy diet
  • … integrate enough exercise into your everyday life
  • … allow yourself enough sleep every night
  • … ensure a healthy work-life balance
  • … abstain from the consumption of alcohol and other drugs

To further protect yourself, you should also follow essential hygiene measures. These include:

  • Regular thorough hand washing
  • Compliance with cough and sneeze labels
  • Regular airing
  • Household hygiene
  • Hygiene in the preparation of food
  • Wearing appropriate “protective” clothing


Infectious diseases accompany us throughout our lives and occur more frequently during the colder seasons. They are triggered by viruses, fungi, parasites or bacteria and become noticeable through various symptoms. Fortunately, infectious diseases can be treated well with the appropriate medications. People can also resort to numerous preventive measures to prevent infections and prevent them from breaking out in the first place.

Illustration - Tests Possible - EN

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