Infectious Diseases Flashcards
What is a disease?
A disease IMPAIRS normal functioning of an organism, leading to poor health
What is an INFECTIOUS disease
A disease that is caused by pathogens and can be passed on between individuals
What is a non infectious disease
A disease that is not caused by pathogens and cannot be passed between people
What is an infectious disease key phrases
Transmissible
Passed on from infected organism to uninfected organism
Caused by pathogen (eg HIV causes AIDS, Mycobacterium tuberculosis causes TB)
Caused by virus, bacterium, fungus, protoctist
Examples of non infectious disease
Sickle cell anaemia
Coronary heart disease (CHD)
Emphysema
What type of pathogen causes Cholera
Bacterium
What bacterium causes Cholera
Vibrio Cholerae
How is cholera transmitted
FECAL-ORAL route
1. Enters body in contaminated food and water
2. Bacteria breeds in SMALL INTESTINE and secretes CHOLERAGEN (choleragen enters by endocytosis)
3. Choleragen reduces the ability of the epithelium of the intestine to absorb salts and water in the blood —> increased conc of salts in blood —> higher water potential gradient
4. These are lost in the faeces causing diarrhoea, if not treated loss of fluid can be fatal
Treatment of cholera
Oral rehydration therapy (ORT) - solution of salts and glucose to hydrate the body
Make sure FLUID INTAKE = FLUID LOSSES in the urine and faeces to maintain OSMOTIC balance of blood and tissue fluids
Take ANTIBIOTICS
Prevention and control of cholera
Transmission most likely to occur in CROWDED and IMPOVERISHED condition —> REFUGEE CAMPS
Improper access to proper sanitation, a clean water supply and uncontaminated food
Best controlled by treating sewage effectively, providing a clean water supply and maintaining good hygiene in food preparation
No fully effective vaccine against cholera —> intestinal cells ANTIGENIC CONCEALMENT, antibodies cannot reach intestines
Mode of action of cholera
Bacteria bypasses stomach and enters lumen of small intestine
Enters intestinal cells by endocystosis, choleragen released
Choleragen inhibits protein channels, salts/ions canot enter bloodstream
High conc of ions —> low water potential in intestine
Water enters by osmosis —> diarrhoea
Global distribution of cholera
West and East Africa, Afghanistan
Unknown in MEDC’s due to sewage treatment and cleaned piped water
Transmission cycle broken
Explain how it is possible to reduce the number of deaths during a cholera epidemic
Provide boiled water to kill bacteria
Provide ORT containing electrolytes and salts
Absorption of salts helps absorbs glucose
Absorption of salts increases water uptake by osmosis
Deaths usually caused by rapid dehydration
Rapid provision of medical supplies
For severe cases antibiotics should be taken
Safe sewage disposal
Explain why cholera is unlikely to be transmitted in developed countries
Transmission cycle broken
Sewage treatment plans, mains drainage
Human faeces does not come in contact with drinking water supply
Water treatment plants
Drinking water is piped to homes
Explain why cholera is likely to be transmitted in underdeveloped countries
Greater exposure to contaminated water and food supply
No safe drinking water sources
Lack of hygiene
Faeces and sewage mixed with drinking water
Insufficient access to oral cholera vaccines
Lack of education
Differences in effectiveness of surveillance and reporting
Refugee camps
Increase in antibiotic resistance
Lack of health services
Inadequate access to healthcare and medicine
Explain how cholera bacteria are transmitted from one person to another
Fecal oral route
Bacteria leaves infected person in faeces
Bacteria enters water supply
Bacteria ingested by uninfected person
Discuss the problems involved in preventing the spread of cholera
Poor sanitation, no treatment of faecal waste
Contaminated of drinking water supply
Poverty, poor living conditions
Poor hygiene
Lack of education about transmission and health
Refugee camps
Lack of water purification
No rehydration therapy available
No effective vaccine
What type of pathogen cause Malaria
Protoctist
What protoctist causes malaria
Plasmodium
What are the 4 species of plasmodium
Plasmodium FALCIPARUM
Plasmodium MALARIAE
Plasmodium OVALE
Plasmodium VIVAX
How is malaria transmitted
Mosquito acts as a VECTOR for malaria
Female anopheles mosquito containing plasmodium in salvia feeds on human blood
When a mosquito bites an infected person, plasmodium is taken up into the mosquitos body and eventually reaches its salivary glands
How can malaria be prevented?
Reducing the population of mosquitos: removing sources of water in which the can be, releasing large numbers of sterile males
Preventing mosquito bites: mosquito nets, dark clothing, long sleeved clothes, repellent
Prophylactic drugs- drugs that prevent pathogens from breeding (quinine and chloroquine, mefloquine, proguanil)
Where is malaria prevalent?
Topical and subtropical regions- where humidity is high
Reasons for worldwide concern over the spread of malaria
Increase in drug resistant forms of plasmodium
Difficulties in developing a vaccine
Change in climate and environmental changes that favour the spread of mosquitos
Migration of people
What is the relevance of anticoagulants in malaria?
Anticoagulant in saliva is passed when mosquito feeds/takes a blood meal
anticoagulant prevents blood clotting when the mosquito sucks blood
Discuss the factors that determine the distribution of malaria worldwide
Tropics, subtropic
Areas: Africa, Central America, South America, South Asia
Countries: India, Sri Lanka, china, Vietnam, Naya
Areas where both parasite and anopheles are present
Anopheles survive in hot humid areas
Parasite needs to reproduce within he mosquito
Poor health facilities
Mosquitoes resistant to repellent
Parasite resistant to prophylactic drugs
High population density —> lots of mosquitos
Human activity —> breeding sites for anopheles
Describe how malaria is passed from an infected person to an uninfected person
Female anopheles mosquito takes BLOOD MEAL from an infected person and feeds on uninfected person
Plasmodium transmitted in mosquitos saliva
Blood transfusion
Unlike malaria, TB is found across the whole world, explain the distribution pattern
Anopheles mosquito survives within the tropics
Plasmodium needs to reproduce within the mosquito
Eradicated in some countries outside the tropics
LEDCs do not have mosquito control programmes
Mosquitos resistant to insecticides or repellents
Plasmodium resistant to prophylactic drugs eg chloroquine
TB is airborne and is transmitted through water droplets
Does not require a vector
Describe one method of controlling the spread of malaria by targeting its vector and explain its effect
Elimination of free standing water
Removes mosquito breeding sites
Use insecticides
Kills adult mosquitos
Explain why it has been difficult to develop an effective vaccine for malaria
Plasmodium has many antigens
Many different stages of life cycle
More than one plasmodium species
Different stages of life cycle
Mutation changes antigens due to antigenic shift/drift
Parasite only vulnerable at certain stages of life cycle
Antigenic concealment
Type of pathogen that causes TB
Bacterium
What is the bacterium that causes TB called?
Mycobacterium tuberculosis, mycobacterium bovis (rarely)
How is TB transmitted?
M.tuberculosis can enter lungs in airborne droplets of liquid that are breathed in
M.bovis is the causative form of TB in cattle
Prevention and control of TB
Chest x ray and sputum test
Increasing standards of living
BCG vaccine
Treatment of HIV by drug therapy reduces the risk that an HIV positive person will get TB
Drugs- isoniazid and rifampicin
TB cannot always be cured with antibiotics because
Many strains of M.tuberculosis bacterium that have evolved resistance to most of the antibiotics that are used
The bacteria reproduce inside body cells, where it is difficult for drugs to reach them
Drugs need to be taken over a long period
Describe the global distribution of TB
Both high income and low income countries
Poor housing in inner cities in the developed world and rising homelessness
Breakdown of TB control programs
Increased migration
Refugee camps
Suggest why fatality ratios of TB are higher in some of countries than in others
Overcrowded housing
Not diagnosed early enough
DOTS- direct observation treatment short course
Lack of vaccination
Antibacterial drugs not available
Medical services not available
TB lined to HIV/AIDS
Not completing antibiotic treatment course
No facilities for isolating people
Discuss the problem to be faced in the eradication of TB
Tb found worldwide
High incidence in developing countries (LEDCs)
Problem with vaccine (BCG) —> does not work well for all ethnic groups etc
Difficult to identify infected people
Difficulty with contact tracing
Difficult to diagnose
Explain why the antibiotics used to treat TB are taken in combination over a long period of time
Bacteria likely to be resistant to at least one antibiotic
Less likely to be resistant to all
Antibiotics used is very small
Change/mutation in DNA
Bacteria are inside cells, protected from antibiotics
Mycobacteria divide slowly
Ensures all bacteria killed
Bacteria remains
Prevents development of antibiotic resistance
What type of pathogen causes AIDS
Virus
What is the name of the virus that causes AIDS
HIV- human immunodeficiency virus
What is HIV, what is its structure?
Retrovirus, contains RNA
Protein core contains 2 RNA molecules
Retrovirus- uses RNA to produce a single strand of DNA inside the host cell, using reverse transcriptase
How is HIV transmitted
Infected blood from one person entering another (sharing hypodermic needles)
Exchange of fluids from penis, vagina or anus —> sexual contact
Transmission across placenta from mother to foetus or in breast milk
Promiscuous sex
Mode of action of HIV
HIV attaches to receptors on T-helper cells
Viral RNA fuses with T-helper cell
Viral RNA acts as a template to male a single strand of DNA (cDNA) by using reverse transcriptase
Viral DNA formed
Viral DNA inserts itself into chromosomal DNA of the host cell —> provirus
Viral DNA transcribed into mRNA
New viruses are made from the protein and RNA
Infected T cell bursts open to release new viruses, destroying it which infects other host cells
Role of T-helper cells is eventually reduced or not carried out
Macrophages and T killer cells are not activated
B cells not activated, fewer antibodies produced
Cytokines not released
Immune system weakened and compromised
When is HIV considered AIDS
When CD4 cell count is below 200
How can HIV be prevented and controlled?
Blood transfusions screened
Hypodermic needles should be sterile and only used once, disposed safely
Contact tracing, sexual contact traced
Contraception
Less promiscuous sex
Education programs
Why is there no vaccine available for HIV/AIDS
Virus mutates rapidly- antigens on viral coat keep changing
Harder for immune system to recognise the virus
What is the global distribution of HIV/AIDS
Global, increasing worldwide
Most prevalent in sub Saharan Africa (Gambia think Geo)
Medicine available for HIV/AIDS
No treatments, virus mutates rapidly so antigens on viral coat keeps changing
Drugs available to help with symptoms and prolong life
Zidovudine, similar to nucleotide thymine —> binds to reverse transcriptase blocks it’s action
Suggest how HIV infection may have led to an increase in malarial infections
HIV infects T cells
Both contracted through blood transfusion
List two factors in the prevention and control of HIV/AIDS that would help improve average life expectancy in African countries
Education to prevent transmission
Anti HIV drug therapy
Access to contraception
Avoid promiscuity
HIV positive mothers avoid breast feeding
Screening before blood transfusion
Needle exchange schemes
What type of pathogen causes small pox
Virus
What virus causes small pox
Variola virus
How is small pox transmitted
Airborne- inhalation of droplets of moisture containing the virus
Prevention and control of small pox
Eradicated by vaccine programme coordinated by WHO
What kind of pathogen causes measles
Virus
What virus causes measles
Morbillivirus
How is measles transmitted
Airborne- inhalation of droplets of moisture donating the virus
How can measles be prevented and controlled?
Vaccination, two doses
If infected, prevent close contact —> isolation
What is an antibiotic
Substance that kills bacteria without harming human cells
What is the mode of action of penicillin
When new bacterial cells grow it secretes autolysins which create small holes in cell wall —> allows cell wall to stretch and create cross links
Penicillin inhibits glycoprotein peptidase enzymes by blocking or altering the shape of the active site
This prevents the synthesis of links between peptidoglycan molecules in bacterial cell walls, cross links cannot form
Bacteria takes up water by osmosis which causes cell lysis
How do antibiotics work
By interfering with the growth or metabolism of the target bacterium
Eg. Synthesis of bacterial cell walls, activity of proteins in bacterial cell surface membranes, bacterial enzyme action, bacterial DNA synthesis
Why do antibiotics not affect viruses?
No cell wall
When a virus replicates, it uses the host cell’s mechanisms for transcription and translation —> antibiotics cannot bind to host cell proteins
Why are some antibiotics ineffective against bacteria
Thick cell wall rescues permeability
Some enzymes break down penicillin
Development of resistance to penicillin
Natural selection
Use of penicillin produces SELECTIVE PRESSURE against bacteria causing mutations to occur
Causes bacteria to have GENETIC VARIATION —> new alleles of genes
Gene produced is resistant to penicillin and is found in plasmids of bacteria
Penicillin resistant gene codes for production of b lactamase, enzyme which breaks down penicillin
Survive and reproduce
Pass on their advantages allele to next generation
Higher proportion of bacteria is resistant
How can antibiotic resistance be reduced?
Use antibiotics only when necessary, not for viral infections
Course needs to be complete
Change the type of antibiotic prescribed
Avoid wide spectrum antibiotics
Minimise use in agriculture
What is vertical transmission
Bacteria reproduce asexually by binary fission
One bacterium contains mutant gene, proving antibiotic resistance to other generations
Horizontal transmission
Plasmids contain antibiotic resistant genes
Plasmids transferred between bacteria
Conjugation occurs- thin tube forms between two bacteria to allow exchange of DNA
Why does antibiotic resistance occur?
Overuse of antibiotics
Incorrect use of antibiotics
Eg- treatment for non serious infection
What is a consequence of antibiotic resistance?
Reduced effectiveness of antibiotics
Increase in incidence of antibiotic resistance
Suggest two ways streptomycin acts as ribosomes to inhibit protein synthesis
Binding of tRNA prevented
No anticodon, codon bringing
Peptide bond not formed
mRNA attachment prevented
Inhibition of enzymes involved in translation
Ribosome movement along mRNA hindered
Inhibits association of large and small subunits
Suggest why streptomycin does not harm mammalian cells
Cell surface membrane impermeable
Degraded before entry into cell
Broken down m enzymes
Eukaryotic, 80S ribosomes- different ribosome structure
