10. Infectious diseases Flashcards
Why do human bodies make ideal hosts?
- Warm environment
- Constant temperature
- Near neutral pH
- Ready supply of nutrients
- Consistent waste removal
Parasite
an organism that benefits by living in or on a host organism, while causing that host harm
Note:
Not all microorganisms are harmful.
Note:
viruses can be termed infectious agents or microorganisms
Pathogen
disease-causing organism
What are the four types of pathogens?
- Disease-causing bacteria
- Disease-causing fungi
- Viruses
- Microscopic disease-causing protoctists
What causes cholera?
- Vibrio cholerae
- Bacterium
- Prokaryote
What causes HIV/AIDS?
- Human immunodeficiency virus
- Virus
- Akaryotic (not a living cell)
What causes TB?
- Mycobacterium bovis
- Mycobacterium tuberculosis
- Bacteria
- Prokaryotes
What causes malaria?
- Plasmodium falciparum
- Plasmodium malariae
- Plasmodium ovale
- Plasmodium vivax
- Protocists
- Eukaryotic
Transmissible disease
Diseases where pathogen is transferred from an infected individual to an uninfected individual (can sometimes be transmitted from an animal)
Carrier
a person who is infected by a pathogen but does not feel ill or have any symptoms of disease. E.g., someone with immunity from previous infection.
Which cells does HIV affect?
- T lymphocytes
- Immune system cells
What does HIV stand for?
Human immunodeficiency virus
What does AIDS stand for?
Acquired immune deficiency syndrome
How does one get AIDS?
HIV becomes AIDS as a result of HIV + opportunistic infections. TB is the most common opportunistic infection. AIDS = collective of infections including HIV.
HIV is a retrovirus. What does this mean?
An enzyme (reverse transcriptase) synthesises DNA from HIV RNA. In this way, DNA integrates into the host genome.
What are the parts of HIV virus in terms of structure?
- Enzyme reverse transcriptase
- Capscid protein coat made of capsomeres
- Glycoproteins
- Envelope
- Outer protein layer (matrix)
- RNA nucleic acid core
What are the two types of HIV?
- HIV-1 (most common)
- HIV-2
How does HIV spread?
- Through bodily fluids
- Vaginal fluid
- Blood
- Semen
So usually:
1) Through sexual contact
2) Transfer of contaminated blood (blood transfusion or drug abuse)
3) Mother to child (uncommonly crosses the placenta during birth, commonly through breastfeeding)
How long does HIV last?
Its life long
Can HIV spread through urine, faeces, sweat, saliva or tears?
No, the concentrations are too low.
What is the economic impact of HIV/AIDS?
- Most prevalent in developing countries so impacts developing countries, worsening the already struggling economy
- Mostly affects 20–40-year-olds (most economically productive population group)
- Scarce financial resources have to be spent on prevention and control measures, as well as expensive medicine and medical treatment
How can HIV be prevented and controlled?
- ART (antiretroviral therapy)
- Vaccine is not possible. It is too risky to develop because weakened HIV could still lead to the virus replicating in cells.
- No cure for HIV/AIDS (any progress made has been hindered by the rapid rate of mutation.
- Various preventative measures can be taken however:
- Advising mothers with HIV/AIDS to avoid breastfeeding
- Contact tracing
- Needle-exchange schemes
- Screening of blood from donors
- HIV testing (detection of antibodies)
- Sexual barriers (e.g. condoms)
- Education
What is ART?
- Antiretroviral therapy
- Treatment for people living with HIV
- Take a combination of drugs. Each has a different action against the virus.
- More effective if taken ASAP after infection.
- If virus is undetectable in HIV tests as a result of ART it does not mean they are cured, it means they have a low risk of transmission.
- ART has been successful in:
- Reducing transmission of HIV to uninfected people
- Reducing mother to child transmission during birth and breast feeding
- Reducing the number of people develop AIDS due to opportunistic illnesses
- Increasing the lifespan of HIV sufferers
- Reducing mortalities
What is the cause of TB?
- Mycobacterium tuberculosis
- Mycobacterium bovis
- Both bacteria
Where is TB usually found?
- Usually found in lungs cuz spreads there first but can affect any part of your body
What are symptoms of TB?
- Coughing
- Shortness of breath
- Tiredness
- Loss of weight
- Loss of appetite
- Fever
- Sweating
What does TB being an endemic disease mean?
It is always present in a population.
How is TB transmitted?
- Transmitted through droplet infection (aerosol)
- Transmitted faster in crowded / poorly ventilated conditions
- Close contact over a long period of time is needed for transmission
- Mycobacterium bovis can be spread through cows to humans, for example, through milk (or subsequent dairy products) and meat from infected cattle.
Who is most at risk of contracting TB?
- People in close contact with TB sufferers (family members, slums)
- HIV/AIDS sufferers that have weakened immune/are susceptible to opportunistic infections
- medical conditions that lower immunity
- those undergoing treatment with immune-suppressant drugs (e.g., after getting an organ transplant)
- malnourished people
- those working in long-term care facilities
- alcoholics and drug users
- regions with infected cattle
What are the two ways that TB can affect people?
- Latent TB
* 90-95% of people who get infected get infected this way
* Don’t show symptoms
* Don’t transfer the disease.
* The bacteria is dormant in the person’s body BUT if immune system is weakened enough the TB may activate - Primary Active TB
* 5-10% of people who get infected are infected this way
* Can transmit the pathogen
* Young developing children and people with a weakened immune system are most at risk
What do all prevention measures for TB aim to do?
Break transmission cycle of disease
What is the result of poorly managed TB treatment?
Drug resistant TB strains (which then “reproduce” via horizontal or vertical gene transmission) and then spread to other uninflected individuals.
TB vaccinations:
- Don’t vaccinate those who already have immunity – that is dangerous
- BCG vaccine exists – gives a weakened form of M. bovis
What is treatment for TB?
- Antibiotics
- Take for 6-9 months
- First 2 months isoniazid, rifampicin and two other drugs taken daily
- Afterwards just I and R until 6 months
- If mycobacterium is resistant taking a combo will help to destroy all bacteria
How is M.bovis spread prevented?
- Pasteurisation
- Cattle herds regularly checked by veterinary surgeons
What is the end TB strategy?
It is a government scheme for:
* Testing for presence of mycobacterium and screening for early diagnosis
* Providing treatment and giving support
* Monitoring and recording each patients treatment
* Giving antibiotics to those with TB
* Vaccination programmes
* Better nutrition to ensure immune system strengthened
What is the economic impact of TB?
- Reduced workforce = decreased productivity = reduced government income through tax = less money for control and prevention schemes
What is the cause of cholera?
Bacterium, vibrio cholerae
What is virulence and why is cholera so virulent?
Virulence – extent to which a pathogen is able to cause disease/damage
Cholera is so virulent because of its flagellum, which makes the bacteria very motile and able to penetrate the mucus barrier of the intestinal wall, where is reaches the epithelial cells it affects
How does vibrio cholerae harm the body?
- Releases toxin (choleragen) which damages the host epithelial cells
- H2O and mineral ions move to the gut lumen from cells as a result of osmotic water potential differences, and are not reabsorbed
- Results in watery diarrhoea faeces
- Can be fatal due to dehydration
- It’s an intestinal disease so difficult for the body to act on
How to treat cholera?
- ORS (oral rehydration solution) containing glucose and salts
- Prevention of faecal matter containing V. cholerae from contaminating food and water (hygiene, education, antibiotics)
- ORT (oral rehydration therapy)
- OCV (oral cholera vaccines, last 3-5 years, 2 doses)
How does a country benefit economically from the eradication of cholera?
- Tourism increases
- Exports increase
- Workforce increases
Why is cholera worsened during natural disasters and war?
- Feeing refugees retransmit disease
- Residents are made homeless
- Health services are overstretched
- Public services (water supply, sewage disposal) disrupted (by e.g., power cuts. Damaged infrastructure)
What % of those infected with cholera are carriers?
75%
How is V. cholerae transmitted?
- Via the faecal-oral route
- Unpurified drinking water
- Untreated and contaminated sewage leaking into water source
- Food washed in contaminated water
- Flies
- Organisms like shellfish
Which pathogens cause malaria?
- P. vivax
- P. faciparum (most widespread and dangerous)
- P. ovale
- P.malariae
P = plasmodium
Protoctist, eukaryotic
Where does pathogen stay in mosquitoes vs in humans?
Mosquitoes – in the gut, in salivary glands
Humans – in red blood cells, liver cells, blood plasma
How is malaria confined to the sub-tropics and tropics?
- Tropical climates are best breeding and living conditions for anopheles mosquitoes
- Plasmodium needs temperatures higher than 20 degrees celsius to complete a life cycle within a mosquito
- Mosquito life cycle requires still bodies of water, which are more common in wetter tropics
What 3 living organisms are involved in the spread of malaria?
- Humans – mobile
- Mosquitoes – mobile as adults
- Plasmodium – developed resistance to drugs, adapts genetically
Hosts vs vectors?
Hosts – organism in which pathogen lives, uses their cells
Vector – organism through pathogen is transported to primary host (not harmed)
What is malaria vector?
Anopheles mosquitos
How is malaria transmitted?
- Infected person bitten by a female anopheles mosquito because human blood good source of protein for development of egg of the insect
- During blood meal insect sucks up plasmodium
- Pathogen migrates from mosquito gut to salivary glands
- When mosquito takes another blood meal (from an uninfected person) plasmodium is injected into that person with an anticoagulant from salivary glands
Note: anticoagulant prevents human blood from clotting
How can malaria be controlled?
- Control of humans (How to avoid being bitten)
• Keeping doors and windows closed
• Insect repellent
• Clothing
• Insecticide-treated bed nets
• Indoor residual spraying - Control of plasmodium
• For P. falciparum WHO recommends ACT (artemisinin-based combination therapy; Use a combination of drugs with different effects)
• Taking protective and preventative (prophylactic) drugs, should be taken before and after exposure. E.g., chloroquine, doxycycline… - Control of mosquitoes (How to reduce their populations)
• Draining marshes and still bodies of water – eggs and larvae develop
• Measures of biological control:
- Introducing fish as predators
- Spraying freshwater areas with parasites that kill mosquito larvae
• Measures of chemical control:
- Spraying freshwater areas with insecticides (can accumulate in food chains though)
- Spraying with oil
Why is the prevention and control of malaria really difficult?
• Poor education results in not following preventative measures correctly
• War, natural disasters and political unrest
• Migrants
• Ease of mobility
• Poverty – no resources for treatment and medication
• Insecticide resistance and drug resistance
• Lack of vaccine
• Global warming
Why has the development of a malaria vaccine been prevented?
Note: RTS,S vaccine is the only one to have shown some effect
• Plasmodium is a eukaryotic pathogen, therefore it has many genes which can code for a wide variety of surface antigens
• There are many stages in life cycles within humans and each stage has a different surface antigen
• Lives inside RBC and liver cells. Because plasmodium is surrounded by membrane of host cells, it does not trigger an immune response. This is known as antigenic concealment.
• Plasmodium species has very specific antigens
Antibiotics
substances produced by microorganisms that destroy other microorganisms or inhibit their growth
Why do antibiotics not affect viruses?
• Viruses aren’t living and don’t have a metabolism
• Viruses are simple and do not contain many of the organelles that antibiotics target
• Viruses have a protein coat not a murein cell wall
• No sites for antibiotics like penicillin to work on
• Viruses live inside host cells, out of reach of antibiotics
What are the three types of antibiotics?
- Organic
- Semi-synthetic (chemical modification of natural antibiotics)
- Synthetic
Who first discovered antibiotics and when?
Alexander Fleming. 1928. Penicillin.
How does penicillin work?
- Prevents bacteria from making cell walls
• Cell wall is made out of peptidoglycan (murein)
• This is a polymer (mixture of animo acids and sugars) that is held together by short peptide molecules that form cross-linkages between them
• Autolysins (enzymes) are secreted as the bacterium cell wall grows. They form tiny holes to allow the wall to stretch, then later they are filled in as cross-linkages form - Penicillin inhibits transpeptidases (enzymes that are required for peptide cross-linkages)
• Penicillin is a permanent inhibitor
• Prevents formation of cross-linkages
• Walls cannot withstand osmotic pressure, burst due to lysis
Note: Penicillin is only effective while bacteria are growing
Mutation
change in the sequence of nucleotides in DNA, results in new allele/form of that gene
How did penicillin resistance work?
• Someone doesn’t take full course of antibiotics – leaves reservoir of bacteria in the body
• Mutation in one of those bacteria left in body = results in enzyme penicillinase = breaks down penicillin = renders penicillin ineffective
What is vertical gene transmission?
• Antibiotic resistance is passed from one generation to the next.
• Penicillin will kill all bacteria except the one that underwent the chance mutation and now can produce penicillinase
• Means that sole survivor will be mutated bacteria, and thus all future offspring wil be of the resistant/mutated type
What is horizontal gene transmission?
When the allele for antibiotic resistance is carried on plasmids which are transferred to A) bacteria of the same species that do not have the allele or B) bacteria of a different species
What can horizontal gene transmission lead to?
Leads to certain bacteria accumulating DNA that gives them resistance to a range of antibiotics – creation of “superbugs”
What is the difference between narrow and broad-spectrum antibiotics?
Broad-spectrum – work against a wide range of suspected bacterial infections
Narrow-spectrum – work against specific bacteria
How to reduce the impact of antibiotic resistance?
• Only give antibiotic treatments where strictly necessary
• Education on following the whole course of antibiotics
• Quarantine people who have drug resistant infections
• Improve vaccination programmes
Can antibiotic resistance affect humans only?
No, also animals.
