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Learning objectives

  • Describe the different types of disease reservoirs
  • Compare contact, vector, and vehicle modes of transmission
  • Identify important disease vectors
  • Explain the prevalence of nosocomial infections

Understanding how infectious pathogens spread is critical to preventing infectious disease. Many pathogens require a living host to survive, while others may be able to persist in a dormant state outside of a living host. But having infected one host, all pathogens must also have a mechanism of transfer from one host to another or they will die when their host dies. Pathogens often have elaborate adaptations to exploit host biology, behavior, and ecology to live in and move between hosts. Hosts have evolved defenses against pathogens, but because their rates of evolution are typically slower than their pathogens (because their generation times are longer), hosts are usually at an evolutionary disadvantage. This section will explore where pathogens survive—both inside and outside hosts—and some of the many ways they move from one host to another.

Reservoirs and carriers

For pathogens to persist over long periods of time they require reservoir s where they normally reside. Reservoirs can be living organisms or nonliving sites. Nonliving reservoirs can include soil and water in the environment. These may naturally harbor the organism because it may grow in that environment. These environments may also become contaminated with pathogens in human feces, pathogens shed by intermediate hosts, or pathogens contained in the remains of intermediate hosts.

Pathogens may have mechanisms of dormancy or resilience that allow them to survive (but typically not to reproduce) for varying periods of time in nonliving environments. For example, Clostridium tetani survives in the soil and in the presence of oxygen as a resistant endospore. Although many viruses are soon destroyed once in contact with air, water, or other non-physiological conditions, certain types are capable of persisting outside of a living cell for varying amounts of time. For example, a study that looked at the ability of influenza viruses to infect a cell culture after varying amounts of time on a banknote showed survival times from 48 hours to 17 days, depending on how they were deposited on the banknote. Yves Thomas, Guido Vogel, Werner Wunderli, Patricia Suter, Mark Witschi, Daniel Koch, Caroline Tapparel, and Laurent Kaiser. “Survival of Influenza Virus on Banknotes.” Applied and Environmental Microbiology 74, no. 10 (2008): 3002–3007. On the other hand, cold-causing rhinoviruses are somewhat fragile, typically surviving less than a day outside of physiological fluids.

A human acting as a reservoir of a pathogen may or may not be capable of transmitting the pathogen, depending on the stage of infection and the pathogen. To help prevent the spread of disease among school children, the CDC has developed guidelines based on the risk of transmission during the course of the disease. For example, children with chickenpox are considered contagious for five days from the start of the rash, whereas children with most gastrointestinal illnesses should be kept home for 24 hours after the symptoms disappear.

Questions & Answers

please which procedure can I use in growing salmonella
Shimi Reply
Classification of fungi
Rabbiyatou Reply
chemical properties of solid
Khadija Reply
describe anatomy of bacterial cell
Okweka Reply
bacteria has rigid cell wall which maintain it's shape (rod , coccus, spiral)
ayesha
lichen rocella source of
JAMADAR Reply
what does that mean
Maryam
lichen rocella source of please explain
Khalil
what is microorganisms
Khalil Reply
organism which cannot be seen with naked eye they need microscopes to be viewed.They are found everywhere from extreme cold places to hot springs.Some are boon to humans while some are bane.
Khushi
what does CD4 cells mean?
Oyong Reply
cell is the basic and structure functional unit of the body
Khalil
CD4 is a receptor that recognises antigens on the surface of a virus infected cell and secretes lymphokins that stimulate B cells and killer T cells.
Simon
Define microbiology
Simon
microbiology is the study of microorganisms that are too small to be seen with naked eye
Khushi
State the types of nutrients
Simon
What is carbohydrates
Simon
What is Name given to body building food?
Simon
carbohydrates is large group of organic compounds found in food and living tissues.Eg. starch ,cellulose,sugars
Khushi
body building food- proteins
Khushi
Define microbiology The bronch of science which deals the study microorganisms and their effect on other living organisms.
Khalil
types of nutrients macronutrients and micronutrients
Khushi
I really appreciate that my dear thanks
Simon
you're welcome
Khushi
Microbiology is the study of all living organisms that are too small to be visible with the naked eye. This includes bacteria, archaea, viruses, fungi, prions, protozoa and algae, collectively known as 'microbes'. These microbes play key roles in nutrient cyclin
mustafe
I want to join this group
Anastasia
In what way do carriers influence epidemics?
Crizzabarquero Reply
causes of occult blood
Acuc Reply
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Martha Reply
need to be sign in online to highlight
Martha
what do you mean
Zahreen
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Judy
what is anatomy
Suleiman Reply
human anatomy is the study of the structure of the human body
Roja
in Gram staining what is primary stain
Obed Reply
crystal violet
Mounika
Gentian violet
fiftrate
The initial infection with human cytomegalovirus most commonly occurs: A. during early childhood, by exchange of body fluids. B. in utero, by transplacental transmission from a latently infected pregnant woman. C. by transfer of saliva between young adults. D. by sexual intercourse. E. as a result of blood transfusion or organ transplantation.
Zahraa Reply
The initial infection with human cytomegalovirus most commonly occurs: A. during early childhood, by exchange of body fluids. B. in utero, by transplacental transmission from a latently infected pregnant woman. C. by transfer of saliva between young adults. D. by sexual intercourse. E. as a result o
Zahraa
define the most serious disease affects the human affects reproductive organs?
nuur
e. coli is one of the most common infectors of the urinary tract. it can attach to epithelial cell in the urethra and resist the pressure of voiding through____
Simeon Reply
adhesins and pili
Mounika
the product obtained by simplest conventional microbial process is
shridhan Reply
the product obtained by simplest conventional microbial fermentation process is
shridhan
curd
Mounika
beer cheese
Khushi

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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