What are infectious dieases
A disease - any condition that interferes with the
proper functioning of body and mind
* Characterized by identifiable group of
symptoms
* Infectious diseases = these are diseases caused
by infectious agents (bacteria, virus, protozoa,
fungi)
Infection terms
Infection: an infection occurs when infectious agent enters the
body and begin to reproduce
* Pathogen is the infectious agent that causes the disease
* Host is the organism that is infected with a pathogenic
organism
* Vector is an agent (e.g. animal or microorganism) that carries and transmits an infectious pathogen from one host to another
E.g. Disease: Malaria vector: mosquito
Examples/groups of infectious agents
- Bacteria dieases such as pneuomina, TB, chlorea
- Viruses like COVID-19 measles, AIDS, flu, these are not cell based rather smaller and simple than cells, viruses containng the ability to infect any organism such as bacteria/plant–> Oncoviruses ( cancer cause)
- Protoza: Giardiasis in animals/mammals, malaira spread by mosquitos, eukaryotic single cells , some cause diease
- Fungi- single celled/multi cell such as athletes foot, may also be fungal infection refered to as mycosis– majority being benefical
Bacteria
Prokaryotic single-celled organisms
* Cells do not contain a nucleus
* most varied and the most numerous group of
organisms on Earth
* Only a small percentage of bacterial species are
pathogenic (disease-causing): e.g. Cholera, Typhoid,
Pneumonia, Tuberculosis etc.
* Many types of bacteria are beneficial to humans
E.g., We share our bodies with bacteria and some bacteria
are actually beneficial to us
* Bacteria on skin (normal flora): help defend against
pathogenic bacteria
* Bacteria in colon (digestive system): help us to obtain
nutrients from our food and help defend us from pathogenic bacteria – probiotics allow the gut bactertia to feed , help nourish gut bacteria.
Importance of location
The Location is important” - When our normal flora bacteria are located where they are meant to be, they are beneficial to us; however, when those same bacteria are introduced elsewhere, the
effect can be devastating.
If they are not where they are supposed to be (an ectopic infection).
Example: harmless bacteria on the skin can cause septicemia
(blood poisoning) in the blood.
Bacterial growth and replication
Whereas half life ( amount of time to decay and reduce .5 origanl amount)
Doubling time ( amount of time needed for quanitity to double inital amount) Q= Q(inital) (2) time/Time of 1/2 life
Q= Qo (2) t/T
Discovery of chlorea being transmitted
John Snow (a physician) was the first to apply scientific
thinking to determine how cholera was transmitted
* He is considered as the “father of epidemiology.”
Twenty years before the development of the
microscope, Snow conducted studies about cholera
outbreaks both to discover that:
* cholera is a waterborne disease
* How to prevent its recurrence.
* Epidemiology is the study of the spread of disease and
factors that influence its spread
Discovery behind microbes
- Antoni Van Leeuwenhoek was the dutch microscopicst that was pinoeer in obsveration of bacteria/protoazoa.
- Single cell algae obsevrations, discovred bacteria inside sperm RBC, changed science with discovery
-Although John Snow discovered that cholera is a
waterborne disease however, he was not able to figure
out how contaminated water causes the disease. - This only happened in 1883 when Robert Koch
discovered the bacterium which causes cholera: Vibrio
cholerae
Robert Koch
- Isolating types of bacteria, idenified TB bacteria via articulating the steps needed in finding the agents of diease.
- Koch’s Postulates
- Although John Snow discovered that cholera is a
waterborne disease however, he was not able to figure
out how contaminated water causes the disease. - This only happened in 1883 when Robert Koch
discovered the bacterium which causes cholera: Vibrio
cholera
Koch Postulates
The steps that are necessary in identifying an infectious
agent of a disease
Purpose: to establish a causal (cause and effect)
relationship between a pathogen and a disease
1. The suspected pathogen must be present in every case
of disease individuals and be absent in healthy
individuals
2. Suspected pathogen must be isolated and must be
grown in pure culture (grown outside the body)
3. Show that cultured pathogen causes the same disease
in a healthy individual
4. The suspected pathogen must be re-isolated from the
experimental subject/individual and shown to be the
same as the original.
Challenges to Koch postulates
1) postulate 2: most pathogens are difficult to grow
in culture media (outside the body)
2) Postulate 3 and 4: cannot introduce the pathogen to humans
Prevention of dieases
The best means of prevention and treatment of a
specific disease depends on the infectious agent
and how it is transmitted
1 ) Natural perservation to stay healthy immunity
2) antibiotic/viral meds
3) hygine
4) vaccines
Antibiotics
Antibiotics are called: “miracle drugs”
* Antibiotics are effective only against bacteria
* Approximately 50% of all human diseases are caused
by bacterial infections
* How do antibiotics work?
* Antibiotic is a selective “poison”: Antibiotics kill only
bacterial cells not the cells in our body. Hence, our body
cells are unharmed. work to fight bacteria–> work to target bacteria, is filtered out by kidneys at steady rate
* e.g.: The first antibiotic Penicillin was discovered in 1928 by Scientist named Alexander Fleming
Antibiotic resistance (superbug organism)
Some strains of bacteria are no longer killed by
antibiotics that used to kill them: these are known as
antibiotic resistant strains (common name: “superbugs”)
* This means that certain antibiotic treatments that used to work, may not work anymore.
e.g. antibiotic resistance can be seen with Penicillin
* some bacteria can produce an enzyme called Penicillinase which breaks down Penicillin before it can take effect
How can resistance occur ?
Due to mutations in the DNA of the bacteria
* DNA/RNA carry information that is required for an organism to
function
What is a mutation?
* Genetic material = DNA
* Sequence (or order) of DNA nucleotides determines what
types of proteins are made
* A mutation is caused by a change in the nucleotide
sequence of DNA
The orignail bacteria DNA can change , become resistant
How quick can mutations occur
More bacterial resistance strains occur with 3 years of new antibiotic getting FDA approved, overuse and misued antibiotics speeds how bacterial populations to become resistant
Vaccinations
A vaccine produces immunity to a specific disease.
* Vaccines are made using several different methods.
One example:
* in this method, the vaccine contains a dead or disabled microbe
( or pathogen) that will be introduced into the body
* Every microbe carries its own unique set of antigens
1 ) Dead/inactive virus enters body–> body creates antibodies to attach pathogen antigen–> if certain antige enters body, antibodies will recognize and kill antigen on virus
What are viruses
Viruses are not cell-based (not considered as organisms)
* much smaller and even smaller than bacteria
* Viruses have either RNA or DNA as their genetic material
* viruses could infect any type of organism, including animals, plants, need host for replication
and bacteria
* E.g., a bacteriophage (also known informally as a phage) is a virus that infects and replicates within bacteria. The word “bacteriophage” literally means “bacteria eater,” because bacteriophages destroy their
host cells.
* Viruses can only replicate (reproduce) themselves by infecting a host cell and therefore cannot reproduce on their own.
Life cycles of viruses
1) Lytic lifecycle: the cell’s ribosomes, which synthesize
proteins, are “tricked” into replicating the viral
genes and proteins. These components are
assembled into new viruses that “burst” out of
the cell, destroying the host upon their exit.
–> Others don’t burst out, they take part of membrane , clocks making it harder to be dettected in next host cell as a virus
Bactereophage ( infect bacteria)-> inject DNA into bacteria from virus-> cell divides copy more viruses-> viruses become liced form cell ( copies created split membrane open after being copied to infect other cells)
2) Lysogenic cycle: Second part–Reproduce in nuclei, viruses act by inserting their mutated DNA into host cell recomination, each time DNA is replicated so does the virus DNA–> copies DNA of virus (copies genetic code only) –> virus DNA becomes part of cell’s genetic code and replicates
- These lysogenic viruses remain dorminant in host DNA for period, allow cell to replicate their DNA, may switch to lytic cycle and infect cells , released viruses to attack cells due to cues ( viruses switch and released to infect other cells)
Microbiology
study of microbe life
- Many microbes can be helpful
- Microbes ( normal existing)
- Virus ( requires cell to replicate and function , noncellular)
- Bacteria ( single celled organisums, replicate easily)
- Fungi ( naturally occuring)
Cancer causing cells
- Hep B, cervical cancer due to infectious viruses known as oncoviruses –> genes encoded within single cell stop and lysogenic cycle insterts DNA into host mutation of cells
Antiviral medications
- Viral infections are not cell based, these meds target genes to distrupt virus life cycle.
- Antiviral medications prevent the virus from gaining cell entry
Vaccinations
- Immune system mobilizes defence response, acquired immunity is due to past infection, antigens that produce antibodies as a response
- These antibodies are proteins that attach to antigens and immobilize virus
- Vaccine can be a weak form, surface antigens of virus are present, allows for drop in illness, mortality rates
Why do we evaluate information
- Article, media reports we need to determine how reliable, valid effective of the study and data reported
- Make informed decison about valdiity of argument, hypothesis, evaluate experimental methodlogy of study
