Microbial Diseases Flashcards
What means Phathogenic?
Disease causing
What is phathogenicity?
Ability of bacterium to cause diseases
What is 2 ways pathogens cause diseases?
Damaging host tissues - By reproducing
Toxins
What are main factor affecting pathogenicity?
Features of cell wall and capsule that affects attachment and entry to host cells
Types of toxin(exo or endo)
Infectivity - measure of number bacteria required to cause infection
Invasiveness - ability to spread within host
What use bacteria to attach to protein receptor of host cell?
Ligands and Glycocalyx on cell wall with specific tertiary structure
What is ways bacteria enter host cell?
Attaching to cell membrane receptor
Production of enzymes damaging cell membrane
Endocytosis - bacteria are engulfed by host cell
What is 2 main type of toxin?
Exotoxins - proteins secreated from bacteria, cayses many symptoms of a disease e.g. tetanus and food poisoning
Endotoxins - Lipopolysaccharides present in cell walls, they can be released when cell wall of bacterium breaks up after death
What is Infectivity?
Number of bacteria required to cause infection
Varies between spicies
What is invasiveness?
Ability of the bacteria to spread
Usually in hosts blood and lymph system as its where it enters other places
It has to be able to avoid body immunity and get through fibers, connective tissues and intercellular cement
Toxins can also spread through the body and cause damage to unrelated tissues
Give 2 examples of invasive diseases?
Bubonic plague and anthrax
Give method of trasmission of diseases?
Airborne/droplets
Food-borne
Water-borne
Contact
Sexual intercourse
Vector-borne
How does cholera spread?
Water-borne
Transmission by ingesting water or sometimes food contaminated by faecal material having bacteria
This can happens as:
-Drinking water is not properly purified
-Untreated sewage leaks into water courses
-Food is eated which is contaminated by those preparing or serving
Name bacteria causing cholera?
Vibrio cholerae
What is cholera bacterium structure?
Common prokaryotic structure
Flagellum
Plasmid
Capsule
How is cholera caused by bacteria?
Endotoxin bind to specifically complementary receptors on small intestine epithelial cells
This causes change in cell permeability as ion channel open
Chloride ion diffuse into lumen from cell
This lowers water potential in lumen and increase water potential in cell
So water diffuse via osmosis into lumen from cell
This causes diarrhea and dehydration as blood and cell lose water
What is sympthoms of chloera?
Diarrhoea
Dehydration
Other including stomach cramps, vomiting and fever
What is treatment for chloera?
Restoring water and ions lost through oral rehydration solution(ORS)
Bacteria don’t affect co-transport in epithlial cells
So sodium ions and glucose are taken up as normal
Water potential of epithelial cell is reduced and is lower than the water potential of lume
Water taken by ORS movens from lumen into cell as normal
So water would move into blood, rehydrating patients
What does ORS contain?
Water, sodium ions, chloride ions and glucose
What is ineffective and effective ORS and how it was discovered?
ORS production is long process done using scientific experiments
Mixture with more glucose caused lower water potential in lumen causing more dehydration
Using instead starch was is good
Starch is insoluble so osmotically inactive
But it hydrolyse into maltase and then glucose
As this is slow, its same rate as co-transport taking it up
So can’t affect water potential in lumen
What is ideal scientific trial?
Large number of subjects
Subjects randomly split into 2 groups
One group treated, another group is control
What is real scientific trial condition of ORS testing?
Subjects with dehydration and diarrhoea required
Frequently thse subjects are children in danger of deth
So ideal scientifc trial cannot be conducted as ethically unacceptable
What is virus?
Intracellular parasites reproducing inside their living host cwlla
How does virus cause diseases?
Damage to host cells following entry and replication of viruses
Toxin produced in the process of replication
What structure does virus usually have?
Either DNA or RNA
Enzymes
Outer protein coat or capsid made of capsomeres
Some has lipid envelope which helps entry
Some had glycoprotein spikes on capsid or envelope for attachment, it is also antigens
How does virus usually reproduce?
Viral nucleic acid is replicated
new capsid and other structures are produced and assambled
They are released when cell burst during lytic cycle and these virus particles would infect other cells
What is type of viruses?
Polyhedral(Adenovirus)
Spherical(Influenza)
Helical(Tabacco mosaic virus)
Complex(Bacteriophage)
What virus cause influenza and explain them?
Influenza virus
Contains RNA and RNA polymerase
There are 3 types, A, B and C
Only A causes serious epidemics
Rapid mutation therefore various strains can occur and this antigenic can lead to re-inffection
Influenza is endemic, regularly epidemic and sometimes pandemic
What is influenza viral replication?
Virus enter epithelial cells of nose, throat and sometimes bronchi
Molecules in the outer coat of the virus bind to receptor molecules in the cell membrane of epithelial cells
Inside the cell the viral coat is removed releasing the viral RNA and the enzyme RNA polymerase
Viral RNA enters the host nucleus and controls protein synthesis in the cell
RNA polymerase is activated and sythesises viral mRNA strands
Viral proteins and lipids are formed in the cytoplasm and are assembled into viral coats
Viral RNA and viral coats are assembled into new virus particles
Lysis of the cell occurs and the released virus particles infect other cells
How does influenza transmission happen?
Trasmitted via droplet infection during coughing and sneezing
Overcrouding and poor ventilation enchnce spreading
What is influenza symptoms?
Incubation peridod of 2 days
Headache, sore throat, backache and joint pain, fever, shivering, sweating and dry cough
Usually last up to 7 days
Coughing may continue due too epithelial damage to trachea and bronchi
Depression may presist for some time
Rarely longer than 6 days
The virus attach is usually localised, but can allow secondary invasion of bacteria due to tissue damage on respiratory leading to bronchitis and pneumonia
What is treatment for influenza?
Viruses are intracellular infections
So very difficult to treat since drugs may not penetrate cells, and if they do, they are as likely to damage the host cells as the virus
For the most part we must rely on the body’s own defences
Rest, aspirin to reduce temperature and plenty of fluids, can relieve the symptoms and help the body recover
As with all viral diseases antibiotics are ineffective, however they may be given to treat or prevent secondary infections
What is way of reducing influenza?
Vaccines are available from variety of strains of the virus, annually given to maintain antibody level
However only about 70% effective as antigenic variation in new strains
Vaccination helps to protect particularly susceptible to reduce reseirvoir of infection
Nasal sprays containing a live weakened strain for 2 to 7 years old and 2 to 17 years old at high risk
Affected people should stay isolated to prevent spreading
Also tissues should be used to cut the spread of droplets
Ventilation and less overcrowding help also
What is coronavirus?
Large family of virus with crown-like glycoprotein spikes
They contain RNA and cause respiratory tract infection in mammals and birds
Common diseases caused is usual cold, SARS, MERS and Covid-19
How is coronavirus transmitted?
Coronaviruses are zoonotic(spread between animals with different spicies)
Coronaviruses spread through close contact with people who have the virus through droplets
You can catch these viruses if you breathe in these droplets or touch surfaces covered with droplets
The risk of transmission is highest indoors and in crowded places
How does virus replicate in humans?
It attaches to epithelial cells of respiratory tract using complementary glycoproteins on cell receptor
Once attached it releases RNA genome into host cell cytoplasm
Coronavirus RNA genome allows it to act like a mRNA and be translated by cells ribosome to generate new viral particles
Then viral particles are released from host cell by exocytosis through secretory vesicles and go to infect other cells
What is symptoms of coronavirus in respiratory tract?
Continuous cough
High temperature, fever or chills
Loss of or change in, your normal sense of taste or smell
Shortness of breath
Unexplained tiredness, lack of energy
Muscle aches or pains that are not due to exercise
Not wanting to eat or not feeling hungry
Headache that is unusual or longer lasting than usual
Sore throat, stuffy or runny nose
Diarrhoea
Feeling sick or being sick
What is called when no symptoms exhibited?
Assymptomatic
What is CFR?
Measure of severity of disease
What is equation of CFR?
CFR = Number of deaths from diseases/ Number of deaths from disease + Number of recovered from disease * 100
What is treatment for coronavirus?
Vaccinations
Antiviral medicines
Neutralising monoclonal (nMAb) treatment
Treatment of symptoms by using rehydration treatments and painkillers to tackle dehydratation, pain and fever
What is AIDS?
Disease caused by HIV
HIV is a retrovirus containing RNA and enzyme reverse transcriptase
RNA and enzymes are surrounded by inner protein coat and outer protein capsid forming nucleocapsid
Nucleocapsid is surrounded by a lipid envelope which contains glycoprotein spikes
This enables them to attach on Helper T cells using gp120(glycoprotein)
How is HIV transmitted?
Secual transmission
Blood products/transfusion
Sharing of needles
Mother to baby via placenta, labor, breast milk
How is HIV replicated in body?
Virus attaches to CD4 in helper T cells by gp120 on receptor site
Viral RNA and the reverse transcriptase are released into helper T cell
In helper T cell viral DNA is formed using reverse trancriptase using viral RNA as template
Viral DNA enters the nucleus and attaches to host DNA
Viral DNA gets replicated with host DNA
Viral DNA may remain inactive for up to 10 years
When activaated viral DNA controls synthesis of viral protein and RNA
HIV particles are assembled and helper T cell is destroyed as particles is released
Virus infects other helper T cell
So helper T cell decrease
Immune system breaks and opportunistic infection or tumours that leads to death
Common diseases are kaposi’s sacroma and pneumonia
What is symptoms of HIV infection?
During first phase after infection, body produces HIV antibodies and short flu-like ilness, skin rash and swollen glands
The second phase(antibody-positive phase/HIV positive phase) where no symptoms shown, may last from few weeks to 13 or more years
The third phase is AIDS-related complex, variety of opportunistic diseases appear, not life threating, loss of weight and reduction of T helper cell occurs
The fourth phase involves opportunistic infection organs and development of cancer and HIV wasting symptoms(dramatic weight loss)
Most AIDS patients eventually die from pneumonia as immune system collapses
What is treatment for HIV?
Antiretroviral therapy(ART) is used to treat
HIV positive individuals on ART take a combination of HIV medicines every day
ART cannot cure HIV but reduce the level of HIV in blood allowing immune system to repair to prevent HIV related diseases
This will increase chances for long and healthier life
Also these reduce risk of HIV trasmission as level kept low in blood
HIV medicines prevents HIV from multiplying reduing amount of HIV
What is ART?
Can be classified in 4 ways:
- Reverse transcription inhibitors
-Protein inhibitors
-Fusion and entry inhibitors
-Integrase inhibitors
Taking 2 or more ART is called combination therapy
Combination of three or more anti-HIV drug is called Highly active antiretroviral therapy(HAART)
Choice of drug to take depends on a number of factors including availability and price of drug, no of pills, side effects and other medical condition
Most people living with HIV in developing world still have very limited access to drug and gets treated for opportunistic diseases and not effective for long term
How can be HIV infection be prevented?
Reduce promiscuity and safe sex by using condoms
Blood screening
Tissue screening
Provision of clean needles for drug users to prevent sharing
Caesarean section
Blottle feed of babies instead of breast feed
What is post-exprosure prophylaxis(PEP)?
Anti-HIV medication that can be taken if individual think they have been exposed to HIV
For effectiveness, it should be started within 72 hours, it is only recommended to be taken if high risk explosure
The quicker PEP is started the better
PEP is a month-long treatment with serious side effects and not guaranteed to work
This also involves taking same drugs prescribed to people who have tested positive
What is pre-exprosure prophylaxis(PrEP)?
Course of HIV drugs for HIV negative indivuals at risk of being infecter
Drugs are taken before sex to reduce the risk of getting HIV
Results form trials are promising reducing risk of becoming positive without major side effects
Available on US since 2012 and by NHS since 2016
How is ebola transmitted?
By giving care and thouching victim body or fluid
Handling unsterilised needles or medical equipment used
Having sex with infected victims
How does ebola replicate in host cell?
The glycoproteins on the Ebola virus bind to receptors on a host cell membrane
Virus then enters the cell by endocytosis
On entry into the cell, the protein coat is removed and the viral RNA and RNA polymerase is released
The viral RNA is replicated, transcribed and translated to produce viral RNA and proteins
These are assembled to form new viruses and bud out of the cell to go on to infect other cells
What is symptoms of ebola?
Fever, headache, jont and muscle pain, sore throat and intense muscle weakness between 2 to 21 days after infected first
Then diarrhoea, vomitting, rash, stomach pain and impared kidney and liver
Bleeding internally, and maybe from ears, eyes, nose or mouth
Fatal in 50 to 90 pecent of cases depending on quality of care
What cell gets infected by ebola?
Liver cells, immune system cells, endothelial cell in blood vessels
How is ebola diagnosed?
Difficult to know in early stages as conventional symptoms
If ebola is considered, bodily fluid would be sent to lab to be tested
Suspect would be isolated to minimise contact and spreading
If test is positive, patients are sent to hospital high-level isolation unit
If negative, doctors will test for disease such as malaria, typhoid fever or cholera
What is treatment for ebola?
Vaccines
Intravenous fluids and balancing electrolytes
Maintenance of oxygen status and blood pressure
Treatment of other infections if happens
If one cases confirmed, area should be quarantined
What method use virulent phages?
Lytic pathway resulting in lysis of prokaryotic cells
What methods use temperate phages?
Enter lysogeny
Here, viral DNA is incorporated into host DNA and remain dormant as not expressed
Viral genome is replicated everytime host cell divides
This virus is referred as provious as inactive and host cell is said to be lysogenic and capable of lysis when become active
What happens in lytic cycle?
Host DNA gets digested
Using nucleotides from host DNA, viral DNA formed and increase in number
Host cell synthesise viral phage protein from viral DNA
New phages is assembled and phage enzymes causes lysis
What is life cycle of malaria?
Mosquito gets plasmodium from infected humans
Virus reproduce in gut of female mosquito that would move into salivary glands
When this feeds on humans, it would be passed into blood with anticoagulant
This would multiply in liver cells
They then gest into red blood cells where multiply again
This causes burst releasing more
What is symptoms of malaria?
Fever, headache, nausea, sweating, vomiting, diarrhoea, general aches and pains
Complications can occur such as severe anaemia
In some cases (more severe species) the malarial parasite can accumulate in the blood vessels of the kidney causing kidney failure, or in the brain causing seizures, brain damage and coma
What is prevention and treatment of malaria?
Vaccination
Avoid being bitten by covering arms and legs, using insect repellent and mosquito nets
Use of insecticides (spraying mosquito breeding sites and also in the production of insecticide treated bed nets)
Use of antimalarial drugs, prior to and after travel, such as Atovaquone plus proguanil mefloquine (Larium) and Doxycycline
How can eradication of malaria be done?
This is difficult due to an increase in numbers of Plasmodium resistant to drugs (e.g. chloroquine) and an increase in numbers of mosquitoes that are resistant to insecticides
Previously it was difficult to produce a vaccine due to the plasmodium occupying the liver and red blood cells
However, first malaria vaccine was licensed in 2021 and second roll out in 2023
The larval stages of the mosquito live in stagnant water, so draining can remove breeding sites
How can eradication of malaria be done?
This is difficult due to an increase in numbers of Plasmodium resistant to drugs (e.g. chloroquine) and an increase in numbers of mosquitoes that are resistant to insecticides
Previously it was difficult to produce a vaccine due to the plasmodium occupying the liver and red blood cells
However, first malaria vaccine was licensed in 2021 and second roll out in 2023
The larval stages of the mosquito live in stagnant water, so draining can remove breeding sites
What is parasite?
Feeds on another organism and causes harm
Why is malaria not detected by immune system?
Lives inside host cells so avoids attack by host
Antigens not exposed
So production of antibodies slowed
Rapidly changing surface antigens
So antibodies no longer effective
Hides. in red blood cells/liver
So antigens cannot be detected
