Infectiology

Infectiology (from Latin infectio, “the infection”) is an interdisciplinary field that combines the fields of microbiology and medicine. It deals with the appearance, course and consequences of disease patterns caused by microorganisms such as bacteria, viruses, fungi, parasites and prions, which can affect all kinds of organs or the entire body system. The task of medical infectiology is to develop and apply measures for the prevention, containment, diagnosis and treatment of infectious diseases in addition to research into infectiological diseases.

Classification of infectiology

Infectiological diseases can be roughly divided into: In addition, a further classification is useful in:

  • Bacterial diseases
  • Viral diseases
  • Fungal diseases
  • Parasitic diseases
  • Prion diseases
  • Infectious diarrhoea
  • Sexually transmitted diseases
  • Infectious childhood diseases
  • Nosocomial infections
  • Multi-resistant hospital germs
  • Blood poisoning (sepsis)

Bacterial diseases or infections in humans are caused by the invasion of bacteria into the organism, their multiplication within the host and the body’s reaction to them. Bacteria (lat. bacterium “rod, stick”) are unicellular, seedless microorganisms (prokaryotes).

They can be distinguished and categorized in many characteristics, such as staining in the Gram stain, shape, arrangement or disease-causing factors. Not every bacterium triggers a disease or infection. In humans, there are also benign (apathogenic) bacteria that do not trigger an infection and permanently colonize the skin and mucous membranes (“normal flora”), thus protecting them from infection-causing bacteria or, for example, on the intestinal mucosa, taking over important degradation processes in the course of digestion.

On the other hand, there are also disease-causing (pathogenic) bacteria whose contact with the body leads to disease. But even benign bacteria can cause a so-called opportunistic disease when the immune system is weakened. The typical therapy of bacterial diseases is represented by various antibiotics.

See Infectious diarrheaSalmonella gastroenteritis. See Infectious diarrheal diseases – Campylobacter enteritis. See Infectious diarrheal diseases – E. coli enteritis.

See Infectious diarrheal diseases – Pseudomembranous colitis. See Infectious diarrheal diseases – Cholera. See under Infectious childhood diseases – Pertussis.

See Infectious childhood diseasesEpiglottitis (laryngitis). See Infectious childhood diseasesdiphtheria (real croup). See Infectious childhood diseases – scarlet fever,Tuberculosis, one of the most common infectious diseases worldwide, is caused by the bacterium Mycobacterium tuberculosis.

In most cases, it is transmitted via air via droplet infection and initially settles in the lungs of infected persons. There, the infection either proceeds without symptoms or a B-symptom (weight loss, slight fever, night sweat) or a persistent cough with sputum is observed. This condition is called primary tuberculosis or initial infection.

A secondary infection occurs when the immune system is weakened for any reason and the bacterium can infect other organs. The tuberculosis pathogen spreads via the blood system and can theoretically colonize any organ. The diagnosis consists of many modalities.

These include a laboratory examination, an X-ray of the lungs and direct detection of the pathogen using various methods. Since the bacterium has various protective mechanisms, antibiotic therapy must be carried out over a long period of time. The standard schedule includes four different antibiotics that must be taken over two months.

Then two of these antibiotics are taken for another four months. The vaccination against tuberculosis is no longer recommended. Brucellosis is caused by the bacterium Brucella melitensis.

Different subtypes are distinguished, depending on the room or bacterial carrier. The most common carrier to humans are infected farm animals such as cattle, pigs, goats, dogs, camels and others.Especially the consumption of contaminated food such as unpasteurized milk carries the risk of infection. Brucellosis is rather rare in Germany.

As a rule, the disease progresses subclinically (mildly aging), with individual symptoms. The main symptoms are fever, night sweats, chills and nausea. Standard therapy is the use of antibiotics.

Viruses are infectious particles consisting of a DNA or RNA strand and a protein envelope. As a cellular parasite, they are dependent on a host cell for reproduction and can cause diseases in the human body. Many viral infections can also be asymptomatic without being noticed by the person affected.

In addition, some viral infections can remain in the body for a lifetime (persistence), such as herpes infections, and only break out under certain conditions, such as an immune deficiency. Transmission is also possible in the asymptomatic stage, so that some viral diseases have a high prevalence in the population (e.g. herpes virus, EBV, HPV). The containment of these diseases is difficult due to the lack of specific therapies.

See Infectious childhood diseases – measles. See Infectious childhood diseases – Mumps. See Infectious Childhood Diseases – Rubella.

See Infectious Childhood Diseases – Rubella. See under Infectious Childhood Diseases – Three Day Fever. See Infectious Childhood Diseases – Hand-Mouth-Foot Disease.

See Infectious Childhood Diseases – Chickenpox (varicella). and Whistling Glandular Fever. The so-called real flu is caused by the influenza virus.

They are transmitted both by direct contact and by droplets in the air. If the virus is subsequently absorbed by the mucous membrane of the respiratory tract, the incubation period ranges from a few hours to several days. In three quarters of the cases, the infection with the influenza virus is mild and can also proceed without symptoms.

In the remaining cases the following typical symptoms occur. Suddenly occurring high fever with chills. In addition, headache and aching limbs.

The patients feel weakened and a distinct feeling of illness is present. In the course of the disease, a dry cough can develop, which is caused by an inflammation of the bronchial tubes. In addition, a lowered blood pressure and a slower pulse rate can occur.

Influenza flu is diagnosed on the basis of the symptoms and a blood test. First, a quick test is performed so that, if necessary, a therapy can be initiated as soon as possible. In addition, a special test can be used to detect the genetic material of the virus and thus ensure the diagnosis.

In addition to fluid intake and antipyretic measures, the therapy consists of drugs that are directly directed against the virus and are used especially in severe cases. There is a seasonal vaccination against the influenza virus, which is especially recommended for people with risk factors. See Infectious childhood diseases – Pseudocroup.

The human immunodeficiency virus triggers a disease in humans that damages a central part of the immune system, resulting in immunodeficiency. The virus can be transmitted, among other things, during sexual contact, when using the same needles while taking drugs or during the birth process. There are three stages in the course of the disease.

In stage A there is progressive physical weakness and swelling of the lymph nodes. In stage B further infections develop, which are caused by various viruses or fungi. If defined, serious infections or malignant diseases occur due to the immune deficiency, this is referred to as stage C or AIDS (acquired immunodeficiency syndrome).

These infections would not cause disease in healthy people and only break out due to the immunodeficiency in HIV patients. The diagnosis is made in the laboratory and at the same time the so-called viral load is determined, which is decisive for the type of therapy and the time of onset. The therapy consists of a combination of three drugs directed against the virus.

If the patient takes these regularly, a normal life expectancy can be expected. Hepatitis C is caused by the virus of the same name. The disease is transmitted via contaminated needles, for example when using drugs or tattooing.

However, it can also be passed from mother to her unborn child.The virus particularly damages the liver and in untreated cases leads to a chronic disease of the liver (liver cirrhosis). Since this process takes decades, patients initially notice unspecific symptoms such as fatigue, fever, abdominal pain and in some cases jaundice. Liver cirrhosis, on the other hand, manifests itself with the manifold symptoms of a weakness in liver function (hepatic insufficiency).

The diagnosis is made by means of various laboratory medical examinations of the blood. Among other things, the genetic material of the virus is detected in the blood. In acute hepatitis C infection, the drug interferon-alpha is given as therapy.

This shows a very good effect, but has serious side effects. The therapy of chronic hepatitis C with the drug interferon-alpha has been largely abandoned nowadays due to the side effects, so that inferon-free therapy regimens (sofosbuvir with ledi-pasvir or velpatasvir) with good chances of success are the treatment of choice. See Infectious diarrhoea – Norovirus infection.

See Infectious diarrhea – rotavirus gastroenteritis. See Infectious Childhood Diseases – Poliomyelitis. Dell’s warts (mollusca contagiosa, molluscs) are harmless changes of the skin, which belong to the group of warts and have a dent in the middle.

The trigger for mollusc warts is a specific virus from the smallpox group, namely the DNA virus Molluscum contagiosum. The warts are highly contagious and are mostly found in children and adolescents, and are mainly found on the eyelids, trunk and genitals. Fungal diseases (mycoses) are infectious diseases caused by fungi.

Healthy individuals with a functioning immune system usually only have localized infections, which can be treated with local antifungal drugs. If the immune system is weakened, e.g. in HIV infection or cancer, the fungi are able to enter the blood and cause severe infections (e.g. sepsis or meningitis).

Fungi, which can cause diseases in humans, can be classified as follows:

  • Dermatophytes (filamentous fungi, e.g. trichophyton)
  • Yeast fungi (shoot fungi, e.g. Candida albicans)
  • Molds (for example Aspergillus fumigatus)

. This term is a collective term for infectious diseases caused by fungi of the genus Candida.

If only skin and mucous membranes are affected, one speaks also of the so-called thrush, whereby also here further diffenrections can be met. Infectious fungal species are usually not able to overcome the immune system of a healthy person or even belong to our “normal” flora. With immunosuppression, however, whether congenital or acquired, our immune system is no longer able to keep all pathogens in check and thus various infections, even with organ involvement, can occur.

Parasites are living creatures in various manifestations that depend on a host, so that the host is the basis of life and reproduction. The distribution of benefits is on the side of the parasite, while the host is damaged to a certain degree. A rough distinction is made between

  • Protozoa (unicellular parasites, such as plasmodia (malaria pathogens), toxoplasmas, trypanosomes or amoebae)
  • Helminths (multicellular parasites, such as various worms)
  • Athropods (ectoparasites, such as ticks, mites, fleas or lice)

See Infectious diarrhea – amoebic dysentery (amoebiasis).

See under Infectious diarrheal diseases – Giardiasis (Lambliasis)… Scabies describes a parasitic skin disease caused by scabies mites. It is a very infectious disease, which is mainly transmitted through direct physical contact from person to person or through shared textiles. The itch mite nests in the upper layer of skin, leaving eggs and excrement bales to which a reaction follows.

Affected persons complain of itching (especially at night) and skin rashes with small red comma-shaped skin changes (especially in the spaces between the fingers and toes). The scabies can be treated very well with medication (so-called anti-scabies preparations).It is particularly important to clean up textiles and to avoid prolonged skin contact with the affected persons until the treatment is completed… Prions are infectious misfolded proteins, which are able to transform normally folded proteins into a misfolded structure, causing the death of nerve cells and triggering the disease. An example of this very rare prion disease is Creutzfeldt-Jakob disease (human spongiform encephalopathy).

The nerve cell death leads to early mental abnormalities, dementia, impaired vision and movement disorders, and later to severe inhibition of drive with dumbness. There is no cure and the disease is quickly fatal after the onset. Diarrhea (diarrhoea, from Greek: “diárrhoia”) describes the frequent defecation (more than 3/day) of watery stool or an increased amount of stool.

It can be a symptom of many diseases, but most often it is caused by an infection with pathogens. Often an acute diarrheal disease progresses easily and heals independently without the need for medication. As a rule, a symptom-related therapy with a sufficient supply of fluid and electolytes is sufficient to compensate for the losses.

Infectious diarrhea, especially those caused by bacteria or viruses, is at risk of infection and spread within the population. Consequently, measures to protect the surrounding area are necessary. For many diarrhoea pathogens, there is also an obligation to register in Germany.

Salmonellae are bacteria that can be found in food, such as poultry, eggs or milk. Due to insufficient heating of these foods, Salmonella can be absorbed into the body with food intake. However, only a very high number of ingested Salmonella leads to an actual infection.

Small doses are fended off by the immune system without causing symptoms. The typical symptom of Salmonella gastroenteritis is massive diarrhea with vomiting. The diarrhea is watery to bloody.

Only in people with a limited immune system can such an infection be life-threatening. This patient group is treated with antibiotics. All other patients with an intact immune system should not receive antibiotics, as otherwise the risk of developing new resistances is too high.

Campylobacter jejuni is a bacterium that is found in contaminated food, e.g. in poultry or drinking water. If food is not heated sufficiently, the bacterium survives and can be absorbed into the body and even a few bacteria lead to the outbreak of an infection. The incubation period, i.e. the time between infection and the appearance of the first symptoms, is about 2-6 days.

The first symptoms can resemble those of influenza. They present themselves with headaches and aching limbs, fatigue and fever. Afterwards, watery diarrhea may develop, which may also be “explosive”.

This diarrhoea can be accompanied by abdominal cramps and in some cases can be mixed with blood. In many cases, a symptomatic therapy that focuses on the replacement of fluid and electrolytes is sufficient. In severe cases antibiotics can be used.

The complications of Campylobacter enteritis can be reactive arthritis, which is an inflammatory disease of the joints, or Guillain-Barré syndrome. This syndrome is accompanied by inflammatory damage to the nervous system, which leads to progressive paralysis. Pseudomembranous colitis is a severe inflammation of the colon mucosa caused by the bacterium Clostridium difficile and usually occurs as a result of antibiotic therapy.

The main symptom of this disease is massive watery, foul-smelling diarrhea, which can contain blood. Cholera is a severe infectious disease that mainly causes severe diarrhea, which is described as rice water-like. The main danger is the large loss of fluid during 20-30 watery bowel movements per day.

The disease is triggered by Vibrio cholerae. In humans, the norovirus triggers an infection with severe diarrhoea and vomiting. The virus has a very high infectious power and is transmitted faecal-orally or via nebulized pathogens in the air.

Fecal-oral transmission usually occurs via hands contaminated with vomit or stool. If the hand that is thus contaminated comes into contact with the oral mucosa (e.g. when eating with the hands), the virus can trigger an infection.The symptoms of an infection classically present themselves with nausea and gushing vomiting in combination with watery diarrhea. In addition, abdominal pain, headaches and a feeling of sickness may occur.

Fever is rather untypical. The symptoms subside within 12 to 48 hours. In old people, newborns and small children the high fluid loss is a serious risk.

Infection with the norovirus is diagnosed by the typical symptoms. Further examinations, such as examination of the stool, are not advisable, as this does not result in any consequences for the therapy. The therapy aims solely at the symptoms, a direct control of the virus is not possible.

The most important pillar of therapy is the administration of fluid and electrolytes. If necessary, medication against the nausea can be taken. The inflammation of the gastrointestinal tract caused by the rotavirus is particularly dangerous for small children.

It is transmitted via direct contact with infected stool or vomit or via contaminated food. Just a few particles of the virus are enough to trigger an infection. The symptoms begin suddenly with watery to slimy diarrhea and vomiting.

Abdominal pain and fever are also typical, as are respiratory symptoms in half of all cases. The greatest danger in this infection is the large loss of fluid, which can quickly become life-threatening, especially for small children and the elderly. The diagnosis is made on the basis of clinical appearance.

Further diagnostics, such as stool samples, are only consulted when an epidemic is being processed. The therapy is focused exclusively on the symptoms. Sufficient replacement of fluid and electrolytes is the most important therapeutic measure.

In addition, drugs against vomiting can be given, but these should be dosed carefully. An oral vaccination is available for infants. This consists of three doses of vaccine and should be completed before 6 months of age.

Amoeba dysentery is a serious diarrhea disease that occurs mainly in tropical and subtropical regions. This disease is caused exclusively by the amoeba genus Entamoeba histolytica. Giardiasis or also Lambliasis is an infectious disease caused by the unicellular parasite Giardia lamblia.

It is more common in the tropics and subtropics, where it spreads via contaminated drinking water, for example. In Europe it is often diagnosed after traveling. The disease can either be asymptomatic or cause fatty, foaming diarrhea.

In addition, flu-like symptoms can occur and there is a risk of the disease becoming chronic. In the diagnostic work-up, the consultation with the doctor plays an important role, since the information from a trip abroad can be used to specifically search for the parasite in the stool, whereas this would not be a common diagnostic measure for diarrheal diseases without a trip abroad. The therapy consists of the substitution of fluid and electrolytes and an antibiotic therapy with the active substance metronidazole.

Whooping cough is caused by a bacterium called Bordetella pertussis. It is transmitted via droplets in the air. The disease progresses in three stages, which cannot always be separated from each other.

The first stage is an unspecific cold symptom and possibly conjunctivitis. In the second stage the eponymous cough attacks occur, followed by deep inhalation phases. The tongue is stretched forward and mucus is choked or even vomited.

Bleeding of the conjunctiva of the eye is also possible. In the third stage the symptoms subside, but the cough can persist for many weeks. Since the symptoms are very typical for this clinical picture, the diagnosis can be made on the basis of a consultation with a doctor.

In unclear cases the pathogen can be detected in the laboratory. The therapy consists of measures to widen the respiratory tract and antibiotic therapy. There is a vaccination against whooping cough in four doses, which in combination with the tetanus and diphtheria vaccination should be completed before the age of one year.

Epiglottitis (inflammation of the epiglottis) is an acute, life-threatening disease, mostly caused by the bacterium Haemophilus influenza type B (Hib). However, other bacteria can also be a possible cause of epiglottitis.The age peak is in children between 2 and 7 years, although seniors and unvaccinated adults are also at risk of developing epiglottitis. Due to the infection, the epiglottis can swell considerably as a result of the inflammation, so that in the worst case, breathing is impaired to such an extent that intensive medical care is necessary.

Epiglottitis must therefore always be treated as an emergency. Since the introduction of the vaccination against Hib, the disease has become rarer… Chickenpox results from an infection with the Varicella zoster virus. They occur more frequently in childhood and the viruses are transmitted by droplets in the air.

Therefore, chickenpox is highly contagious. Before the typical skin symptoms appear, the patients show unspecific symptoms such as fatigue or slight fever. In the initial phase, blisters filled with liquid (vesicles and papules) appear on the reddened skin.

As the fluid becomes cloudy, scabs and crusts form. It is typical that the different manifestations of the rash are seen side by side. The hairy skin is also involved and there is severe itching.

In patients with a normal immune system, the blisters heal within a week. In immunocompromised persons, an infection with chickenpox can take a complicated course. The diagnosis is usually based on the symptoms.

The therapy consists of skin care and possibly medication against itching. An antiviral drug can only be used in high-risk cases, for example in newborns or people with an immunodeficiency. There is a live vaccination against the virus with two vaccine doses, which is recommended in early childhood.

Polio (poliomyelitis, “polio”) is caused by poliovirus. In the past, polio was considered a dreaded disease in childhood due to irreversible paralysis. In the meantime, the disease has become very rare thanks to worldwide vaccinations.

The reason for the paralysis symptoms is the virus infestation of muscle controlling nerve cells of the spinal cord. The clinical picture can vary greatly: from mild or asymptomatic symptoms to pronounced flaccid paralysis, especially of the legs. In the worst case, the muscular swallowing apparatus or the respiratory musculature is affected by the paralysis with fatal consequences.

There is no specific therapy. However, the paralysis can partially regress. Sexually transmitted diseases (STD) is a collective term for infectious diseases caused by viruses, bacteria, fungi or parasites, which are mainly transmitted through sexual contact.

Symptoms are usually discharge from the vagina or urethra, pain in the genitals or lower abdomen. However, a course with few or no symptoms is also common, which favors rapid proliferation if contraception with a condom is not used. Among the most common sexually transmitted diseases are You can find an overview of the most common sexually transmitted diseases on our main page on venereal diseases.

  • Mycoses (e.g. vaginal mycosis)
  • Genital herpes
  • Genital warts (condylomas, HPV)
  • Chlamydia infection
  • Gonorrhea
  • Syphilis (syphilis, hard chancre, ulcer durum)
  • HIV
  • Hepatitis B
  • Trichomad colpitis
  • Crabs
  • Soft chancre (Ulcus molle)
  • Lympogranuloma inguinale