The term infectivity describes the ability of an organism to enter, survive and multiply in the host. As mentioned by World Health Organization (WHO); infectious diseases are caused by pathogenic microorganisms such as bacteria, viruses, parasites and fungus. These diseases may be transmitted from person to person directly or indirectly. In addition to this, transmission of infectious diseases from animals to humans is another form of infectious disease (zoonotic diseases).
Infectious diseases are also known as communicable diseases or contagious diseases. Presence and growth of pathogenic biological agents in an individual host organism may result in a disease. Transmission of pathogenic agent may occur in various ways including physical contact, contaminated food and body fluids or through vector organisms.
Although there are many microorganisms, only a limited number of these are capable of causing diseases. Infectious diseases appear as a result of the interaction of infected host with this limited number of pathogens. Appearance and severity of a disease depends on the damage caused by a pathogen and the resistance of the host to the pathogen. The microorganism that can cause infection despite the host immune system is called primer or opportunistic pathogen.
Primer pathogens cause the disease directly by their existence or activities as they enter a healthy organism. Primer pathogens that infect humans are generally acquired from the environment or from other non-human hosts. On the other hand, opportunistic pathogens do not cause disease as soon as they enter the host; they may cause disease when the immune system of the host weakens.
Just as in other diseases, there are several diagnostic methods for infectious diseases including biochemical methods, serological methods, cell culture methods and methods of nucleic acid amplification (Real Time PCR). The methods concerning the amplification of nucleic acids are being preferred by a dramatically increasing number of labs throughout the world and Turkey because of their higher speed, effectiveness and the guidance that they provide for clinicians. In addition, besides the other tests that are employed, DNA/RNA based tests may also be applied as confirmation tests to help the clinicians to monitor the therapy process.
- Glossary of Notifiable Conditions". Washington State Department of Health. Retrieved 2010-02-03.
- Medical Microbiology Fourth Edition: Chapter 8 (1996) . Baron, Samuel MD. The University of Texas Medical Branch at Galveston
- Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0-8385-8529-9.
- Clinical Microbiology and Infectious Diseases, I. M. Mackay, 2004, Real-time PCR in the microbiology laboratory, Volume 10, Issue 3, pages 190– 212,