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Defense against infections

Last update 1-11-2008

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This website presents the culmination of a life time of scientific research by Dirk van der Waaij.
He started in the field of 'defense against infections' in 1955 under the guidance of Prof. van Tiel by studying Toxoplasmosis infections for a master thesis in 1959.
After finishing his physicians exam in 1961 he moved on to the Radiobiological Institute of the Health Organization of TNO where he studied "Understanding of the functioning of the normal defense to opportunistic infections". He realized that to reach the ultimate goal "prevention and treatment of such infections in subjects with a decreased resistance" this was necessary foundation work.
A key finding was colonization resistance, that focuses on the importance of the intestinal micro flora for the normal defense to (opportunistic) infections. Once this was understood, it soon became apparent that keeping the beneficial bacteria alive during treatment with antibiotics is important, specially for patients with a compromised defense against infections. This approach to using certain antibiotics is called 'selective decontamination' and was proven more effective than the often used sledgehammer approach of 'total decontamination'.

In 1975 he moved to a professorship at the medical faculty of the University of Groningen where he was able to expand the research to human diseases and their treatment besides continuing working with test animals.

After retiring in 1992 he moved from in-depth studies to a focus on developing a synthesis of the available knowledge around the central theme "defense against infections".
As part of that effort he co-founded the International Study Group on New Antimicrobial Strategies (ISGNAS) and was its chairman until 2006.

In an attempt to make his broad knowledge and insights available to whoever is interested, he decided to develop this web-site.
Part of what is presented here is scientific fact. Other parts are hypothesis that require study to confirm or disprove them. Where possible hypothesis are presented as such. Please see the legenda on the home page.

More information about Dick's scientific career can be found at

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This site is developed and maintained by Dick and Michiel van der Waaij as part of a hobby.
Dick uses it, with Michiel's help, to write about his ideas on the evolution and systematics of the defense against infections.

As is stated below each page we claim full copyright on all text and all pictures and videos (except where indicated someone else has the copyright).
We do not mind if someone else uses our text or our own pictures, PROVIDED:

  1. An acknowledgement is given ("Picture thanks to D. van der Waaij" for example)
  2. A link is provided to this site.

We are always open for questions and remarks.