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An individual capable of transmitting a pathogen without displaying symptoms is referred to as a carrier. A passive carrier is contaminated with the pathogen and can mechanically transmit it to another host; however, a passive carrier is not infected. For example, a health-care professional who fails to wash his hands after seeing a patient harboring an infectious agent could become a passive carrier, transmitting the pathogen to another patient who becomes infected.

By contrast, an active carrier is an infected individual who can transmit the disease to others. An active carrier may or may not exhibit signs or symptoms of infection. For example, active carriers may transmit the disease during the incubation period (before they show signs and symptoms) or the period of convalescence (after symptoms have subsided). Active carriers who do not present signs or symptoms of disease despite infection are called asymptomatic carrier s . Pathogens such as hepatitis B virus , herpes simplex virus , and HIV are frequently transmitted by asymptomatic carriers. Mary Mallon , better known as Typhoid Mary , is a famous historical example of an asymptomatic carrier. An Irish immigrant, Mallon worked as a cook for households in and around New York City between 1900 and 1915. In each household, the residents developed typhoid fever (caused by Salmonella typhi ) a few weeks after Mallon started working. Later investigations determined that Mallon was responsible for at least 122 cases of typhoid fever, five of which were fatal. Filio Marineli, Gregory Tsoucalas, Marianna Karamanou, and George Androutsos. “Mary Mallon (1869–1938) and the History of Typhoid Fever.” Annals of Gastroenterology 26 (2013): 132–134. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3959940/pdf/AnnGastroenterol-26-132.pdf. See Eye on Ethics: Typhoid Mary for more about the Mallon case.

A pathogen may have more than one living reservoir. In zoonotic diseases, animals act as reservoirs of human disease and transmit the infectious agent to humans through direct or indirect contact. In some cases, the disease also affects the animal, but in other cases the animal is asymptomatic.

In parasitic infections, the parasite’s preferred host is called the definitive host . In parasites with complex life cycles, the definitive host is the host in which the parasite reaches sexual maturity. Some parasites may also infect one or more intermediate host s in which the parasite goes through several immature life cycle stages or reproduces asexually.

  • List some nonliving reservoirs for pathogens.
  • Explain the difference between a passive carrier and an active carrier.

Transmission

Regardless of the reservoir, transmission must occur for an infection to spread. First, transmission from the reservoir to the individual must occur. Then, the individual must transmit the infectious agent to other susceptible individuals, either directly or indirectly. Pathogenic microorganisms employ diverse transmission mechanisms.

Questions & Answers

what is microbiology
Carol Reply
de study of small living microorganism
Lubinda
what are the benefits microbiologist derive from the follow areas: 1. medicine 2. Environmental science 3. Food and drink production 4. Fundamental research 5. Agriculture 6. pharmaceutical industry 7. Genetic engineering
Narh
microbial genetics mcqs
kajal Reply
hii
Happy
what is the importance of learning microbiology in nursing?
Grace Reply
привет
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it's about child-care?
__
the way of common children disease? hmm 🤔🤔
__
how do you mean child care?
Grace
Was ist die Wichtigkeit beim Lernen von Mikrtobiologie in der Pflege? Es ist notwendig dass die Schwestern allgemein und auch die Kinderschwestern eine Ausbildung in der Mikrobiologie erfahren. Sie sind in ihrem Beruf gefo
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you need to know the truth about diseases. the microbes are have immunity to some pharmacy.
__
is base pairing rule states that adenine pair with thymine cytosine pair with guannie what will be the complementry strand to acggt
KooL Reply
tgcca
Tanaya
yes
Swetha
introduction to microbiology
Shweta Reply
Study the life of microorganisms present in the environment their survivals etc..
ayesha
Microscopic organisms, commonly known as microorganisms or microbes, are found all around us and even inside our bodies. The category 'Microbes' includes a massive range of organisms including bacteria, fungi, viruses, algae, archaea and protozoa.
Amre
fermented foods likely benefited ancestors to preserve foods and make other foods like milk, cheese, and bread using microbes.
Zinnia Reply
the evidence that I would support the statement regarding ancient people ideas that disease was transmitted by things they could not see is by the discoveries under a microscope. Many microbiologists have discovered certain diseases caused by microbes.
Zinnia
plz give the information about glyoxylate cycle
kamini Reply
what type of information?
Sapiens
I need medical microbiology mcqs books for Mbbs
Kisota
for pakistani mbbs or other?
Sapiens
what is microbial soup?
Osborn Reply
😃😂funny question isn't it?!!! sorry for inconvenience 😊
ayesha
most bacterial pathogens that cause disease in humans are classified in terms if their preferable ph as
Beesan Reply
what is micro
Kabul Reply
extremely small in size
Swetha
almost invisible to the naked eye
Peter
thanks
Sadiq
uwc
Peter
invisible sized objects
Sivasri
invisible sized object or specimens.which is used to see in only the microscope that specimens or objective called the micro
Sivasri
small organism that can be seen by use of Microbes
Manyang
why do you need to study microorganisms
Sala
what is microbiology?
Green Reply
microbiology is a branch of biology .it deals with the study of microorganisms life cycle , uses, disadvantages,and it impact in any other fields .which is used to view in microscope .
Sivasri
Microbiology is the study of microorganisms, those being unicellular, multicellular, or acellular. Microbiology encompasses numerous sub-disciplines including virology, bacteriology, protistology, mycology, immunology and parasitology. 
Raj
In short , it is the study of micro organisms and types , characteristics.
Kaviya
can you explain the structure of rna in detail
Dhanalakshmi Reply
RNA is of many types....like mRNA,tRNA,rRNA,snRNA,guideRNA..etc .
Swetha
but generally RNA is single stranded
Swetha
It contains adenine guanine cytosine , instead of thymine it contains uracil.
Swetha
ribonucleic acid present in RNA.. where as in DNA it is deoxyribonucleic acid...and ribonucleotide is present in RNA
Swetha
RNA is a blue print of DNA. it has the information from DNA....and we can predict the base panirs in DNA if we have the RNA....copy of that DNA
Swetha
can either have positive or negative polarity
Ernestine
Diatoms need..... With the help of which they can construct their beautiful cell wall
Prathmesh Reply
Microbial growth curve shows a.... Curve.
Shambhuraj Reply
diminishing curve
Oluwapamilerin
It represents the decreasing growth of an organism.
Swetha
what is meant by reverse isolation in tuberculosis treatment?
Swetha Reply

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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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