How Infectious Diseases Spread

What are the sources of infection? The intake of virulent microorganisms can lead to infection. This is where the biological confrontation of the host organism with the pathogen begins. Infected is the term used for humans and animals that have taken up or are carrying pathogens. Contaminated is the term used for substances and objects that came into contact with pathogens. The source of infection is the infected person or a pathogen carrier. These can include people in incubation, manifestly or abortive ly ill people, contact pathogen carriers who are not themselves ill, convalescent patients, permanent carriers after recovery and immunized pathogen carriers (people who have been vaccinated against a disease).

Can animals also be vector s? Animals also play a major role as vectors or intermediate hosts. When pathogens are transmitted between animals and humans, we speak of “zoonoses”. They can be caused by viruses, bacteria, fungi, parasites or prions (examples of zoonoses are plague , rabies , tuberculosis, malaria or salmonellosis). Anthropozoonoses occur when transmission happens from humans to animals. In zooanthroponoses transmission occurs from animals to humans. In individual cases, the primary pathogen reservoir neither humans nor animals (e.g., Pseudomonas aeruginosa at water taps or spout s, tetanus pathogens in soil and dust that enter the body via wounds).

Which routes of transmission are there? Direct transmission is when the infection occurs by contact ( droplet infection ) from human to human or from animal to human. Indirect transmission occurs via dust particles, contaminated food or utensils. Vertical transmission occurs by diaplacental transmission from the mother to the fetus. Finally, iatrogenic transmission is infections caused by medical personnel or medical procedures (non-sterile instruments, reused needles, blood transfusions); this is also referred as nosocomial infection, which will be presented in a separate article.

What does the pathogenicity of a pathogen stand for? Pathogenicity is the ability of an influencing factor to cause a disease. In microbiology, a differentiation is also made between obligate and facultative pathogen s. The level of pathogenicity is also referred to as virulence. In addition to pathogenicity, other major factors are spread , environmental resistance, and host adaptation. Together with the pathogenicity factors, they define the communicability of an infectious disease, the localization of the ports of entry , the spread of the pathogens in the host organism, and their excretion .

Are there resistant host organisms? What happens now when the host organism comes into contact with an infectious pathogen? The first thing to mention here is natural immunity and acquired immunity . There are non-specific (natural) defense mechanisms (anatomical barriers, cellular factors such as granulocytes and macrophages) and specific (acquired) defense mechanisms. All these factors play an important role in the dissemination and prevention of infectious diseases.

In addition to the change in pathogen characteristics, there is also the extent of acquired immunity in a population, whether by surviving a “ silent infection ,“ a disease, or due to specific immune prophylaxis (active vaccination).

In addition, the genetic determination of specific infections in certain population groups, and age (e.g., meningitis in infants) play a major role in the development of diseases.

What other factors play a role (e.g. environmental factors)? About 70 percent of all infectious diseases are caused by pathogens that originated in the animal world. It is not yet clear under which conditions viruses cross the species border. This risk has increased due to our modern way of life. Factors such as the destruction of nature, mobility, population growth, travel, global networking and the exchange of goods are important risk factors. In areas with low socioeconomic conditions, humans and animals often live in close contact due to poverty, and here the risk that animal pathogens may infect humans increases.

EXERCISE:

1. Indirect transmission is when the infection occurs by contact (droplet infection) from human to human or from animal to human. A. True B. False

2. Which factors might play a role when viruses cross the species border? A. Destruction of nature B. Mobility C. Population growth D. Global networking E. Travel

3. Zoonoses are when pathogens are transmitted between animals and humans. A. True B. False

You’ll find the answer below.

BIBLIOGRAPHY 1. www.cdc.gov 2. http://dict.leo.org 3. www.dict.cc 4. Groß U: Kurzlehrbuch Medizinische Mikrobiologie und Infektiologie, Thieme Verlag, 2013 5. www.rki.de 6. www.webster-dictionary.org

CARMEN LOBITZ Carmen Lobitz ist freie Trainerin, Lehrerin und MTA. Sie gründete 1998 in Berlin lobitz seminare, die unter anderem Englischseminare für Health Professionals anbieten. Kontakt: mail@lobitz-seminare.de www.lobitz-seminare.de

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Lösung für Exercise:

1. B)

2. A)–E)

3. A)

How Infectious Diseases Spread

What are the sources of infection?

Can animals also be vectors?

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How Infectious Diseases Spread

What are the sources of infection?

Can animals also be vectors?

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