AS Level Biology - 10/11) Infectious Diseases and Immunity
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Transcript of AS Level Biology - 10/11) Infectious Diseases and Immunity
Infectious DiseasesAnd Antibiotics
Infectious Diseases
Diseases caused by pathogensSome disease affect us for short periods of
time – common cold measles, influenzaOthers are more chronic – TB, AIDs Infectious diseases are not like COPD or
coronary heart diseases which are degenerative and are not caused by pathogens
Infectious Diseases
Some diseases may even be transmitted without the person contracting it – such person is called carrier
Pathogens pass from one host to another in a transmission cycle
The 5 major diseases required in this syllabus include: Cholera, Malaria, HIV-AIDs, Measles, TB
More definitions
Endemic: Describing a disease that is always present in a population
Incidence: The number of people diagnosed with a disease over a period of time
Prevalence: The number of people with the disease at any one time
Pandemic: An increase in number of cases throughout a continent or across the world
Cholera
Cholera
Caused by Vibrio cholerae
Food-borne, Water-borneDistribution: Asia, Africa, Latin America Incubation period: 2 hours – 5 daysSite of action: Small intestineDiagnosis: Microscopic examination of feces
Cholera Causes
Vibrio Cholerae inhibits the cell in the small intestine – release choleragen
Disrupting the osmotic balance, causing the cell to release large quantity of water due to lost of salt
Transmitted in water – uncontaminated food, feces, in cooking utensils, vegetable irrigated with infected water
Hence the disease is endemic in areas with poor sanitation
Cholera Symptoms
Loss of fluidLoss of saltDehydrationWeaknessSevere diarrhea (rice water)
Treatment/ Prevention
Rehydration – could be through Oral Rehydration Therapy (ORT)
Uses glucose is effective – it is taken right into the blood
Prevention include development of sewage system Provision of clean water No inadequate cooking Always tracing cholera epidemic Vaccines are short term and not very effective
Different Strains
O1 – original strainsEL TOR – transmitted by ship sewage and into
sea food1992: new strain O139 – replaces El Tor very
quickly – may be more virulent
Malaria
Malaria
Caused by protoctist – Plasmodium Insect vector – female anopheles mosquitoesDistribution: The tropicsSite of action: Liver, Red Blood Cells, Brain Incubation: A week to a yearDiagnosis: Microscopial examination of blood.
Dip stick test
Malaria transmissions Anopheles feeds on human blood that is infected Pathogen gametes taken up – fuses in the mosquito’s gut –
enters the salivary gland When it bites another person, it is released with the
anticoagulant the mosquito uses to prevent blood clot Malaria can be transmitted through placenta Also, by blood transfusion Plasmodium multiplies in both human and mosquito People can become immune from malaria – nut only as
long as they are constantly in contact with the disease
Treatment Anti-malarial/ prophylactic (preventive) drug: Quinine,
Mefloquine Chloroguine (inhibits protein synthesis) Proguanil (inhibits sexual reproduction) Strains of drug resistant plasmodium have developed (one
resisting mefloquine appear in Thailand-Laos border) Some doctors can misdiagnose initial malaria symptom as
influenza Some people do not realize they lose immunity when they
re-enter their home country after years of being away
Prevention
Reduce number of mosquitoes- Destroy its habitat, release males with no gamete, use of insecticidesAvoid being bitten- nets, insect repellantsDrugs- Chloroquine
AIDsAcquired Immuno Deficiency Virus
AIDs
A syndrome caused by a retrovirusRetrovirus: Those with RNAHuman immunodeficiency virus
HIV
Infects and destroy T-helper cells of the immune system
Immune systems therefore do not respond effectively
The body is made vulnerable to other diseases – common cold and TB
AIDs – is a conglomeration of opportunistic diseases
HIV Transmission
HIV is transmitted by sexual intercourses – bodily fluid exchange
Transmitted in blood transfusionAcross placenta from mother to childNeedle sharing If someone is discovered to have HIV – they
are asked to contact sexual partner immediately
HIV Transmission
Pregnant woman are advised not to breastfeed their children
Viral particles can be found in breast milkHIV positive woman use antiretroviral drug
before delivery
Treatment
Cannot be curedSpreads of AIDs can be slowed downUsing variety of drugs – problems here are
side effects and costZidovudine – binds to/ block action of reverse
transcriptase – stopping replication Increasing life expectancy
Prevention
Controls of HIV include contact tracingPrograms to exchange used needles for
better onesMore care/ control into working on blood
transfusionAnte-natal care
TBTuberculosis
Tuberculosis
Pathogens: Mycobacterium Tuberculosis, Mycobacterium Bovis
Transmissions: Airborne droplets, undercooked meat, unpasteurized milk
Distribution: Worldwide Incubation: Weeks – years Site of action: primary infection in lungs, secondary
in lymph nodes, bones, guts Diagnosis: microscopic examination of sputum,
chest X-ray
Tuberculosis Symptoms
Coughing blood Coughs Chest pain Shortness of breath Fever Sweating Weight Loss
Transmission
Airborne disease – in aerosol droplets Infect the malnutritioned Those living in overcrowded conditions – at risk Opportunistic infection of AIDs TB transmission can come from cattle milk/ meat 1940s: introduction of Streptomycin 1950s: Introduction of Vaccines The disease was thought to have been eradicated, now
it’s on the rise
Treatment Tuberculosis
When diagnosed – the patient should be isolated
Treatment: Uses several drugs to ensure death to the bacteria
6 – 9 months longThe bacteria – slow growing and not sensitive
to drugsThe patient MUST complete the whole course
of drug or risk the bacteria becoming resistant
Drug ResistanceSome bacteria survive the treatment, mutate
and become drug resistanceDOTS (Direct Observational Treatment
Program) used to ensure complete process in the course of treatment
Isoniazid/ Rifampicin used
Drug ResistanceMDR-TB (Multiple-Drug-Resistant) are on the
riseThey are now resistant to Isoniazid and
Rifampicin
Tuberculosis prevention
BCG VaccineProtects 70-80% of people receiving itEffectiveness of vaccine reduces with age
unless exposed to TBTB can still be transmitted between cattle and
human – cattle are tested on routines, milk is always pasteurized
Contact tracing is very important
Measles
Measles Cause
Virus enters the body and infects respiratory tract
Rash appears, runny nose, cough, watery eyes, white spots inside the cheek
PneumoniaSinus infectionBrain damage Are all symptoms
Measles transmission
One of the most contagious diseaseSneezing/ Coughin can release droplets with
millions of viruses Initial immunity provided for infant from
antibodiesMay infect those deficient of vitamin A
Antibiotics
Antibiotic
Selective toxinsKill or disable pathogen without harming the
hostOnly work on bacteria and some on virusThey are derived from living organismsBacteriostatic: Stop/ prevent bacterial growthBactericidal: Kills Bacteria
PenicillinWhen bacteria grow – they punch holes into
their walls with enzyme autolysin – then they use peptidoglycan to form crosslinks within those holes to strengthen the cell wall
Penicillin prevents Peptidoglycan from forming – hence the cell wall of the bacteria continues to find new holes until they take up too much water and burst
Antibiotic Resistance
Tuberculosis has impermeable wall and has an enzyme that can break down penicillin
Bacterial membranes can sometimes pump out antibiotics
Eg. Enzyme beta-lactamase can be found in soil bacteria which grow in unfavorable condition – this enzyme can break down penicillin – it is transmitted via horizontal and vertical transmission to other bacteria
Antibiotic Resistance
Pathogens can develop resistance to antibiotics
Developing enzymes for destroying penicillinCan develop if people misuse antibioticThere are two ways by which resistance can
be transmitted – vertical and horizontal
Effectively Using Antibiotic
Widespread use of antibiotic can lead to bacteria developing multiple resistance (one plasmid carrying resistance for many antibiotics)
Should be used sparinglyOnly use against bacteria and not virus
ImmunityAnd Vaccines/ Monoclonal Antibodies
External Defences
Defenses that act as the first line of defense for our body
The external defenses of our body include:Our skinOur respiratory tract’s goblet cells and nasal
hairOur stomach acid
Internal Defences
Phagocytes
Phagocytes
White blood cells produced in bone marrowsWhen pathogens attack a cell – the cell
releases histamine In the process of chemotaxis – the cell uses
histamine, in combination with bacterial chemical to call for phagocytes
The phagocytes connect with the antigen – engulfing them in phagocytosis and destroying them
Neutrophils
Produced in the bone marrow
Travel throughout the body
Usually conduct phagocytosis on antigens
Short lived cellsPatrol tissues
Macrophages
Larger More like bodyguard – found in specific parts
of the body – spleen, kidney etc.Travels in blood as monocyte until reaching
the place of guardianThey cut up pathogens to be displayed to T-
Cells
Lymphocytes
Lymphocytes
Smaller than phagocytesHave large nucleus that fill most of the cellB-LymphocytesT-LymphocytesOnly mature lymphocytes can carry out
immune responsesEach lymphocyte specialized to respond to
specific antigens
T-Cells
Have specific receptors – specific to one antigen
Activated when antigen is in contact with cells or presented to them by macrophages
Release cytokines – stimulate B-cells to divide – stimulates Cytotoxic T-cells to differentiate
B-Cells
B-cells produce antibodiesThey can only produce for one type of
pathogenWhen received messages from T-cells the B-
cells begin the process of clonal selection
Clonal Selection
B-cells specific to the antigen begins to divideSome differentiate into memory cellsOthers into plasma cells
Clonal Expansion
Plasma cells divide and release antibodiesMemory cells divide and remain in the body If the pathogen returns, they respond pretty
much immediately
Primary Responses
Macrophage will attackB-cells will go through clonal selection and
expansion It will take more time for antibodies to be
produced and invaders to be suppresses
Secondary Responses
The memory cells recognize the pathogens Immediate attackingThe invaders are immediately suppressesMemories are over a lifetimeExcept for common cold and influenza that
mutate all the time
Antibodies
Globular glycoproteinsUsed to identify and neutralize foreign objectsThey can protect the cells by neutralizing
toxins, kill the bacteria by causing bursting, top the pathogen by sticking to it, attaching to its flagella
Antibodies
ImmunityActive, passive, Artificial, Natural
Active Immunity
Immunity that are derived from real infectionsCan be artificial: In the form of vaccinationCan be natural: in the form of actual infection
Passive Immunity
Immunity that is given and is usually temporary
Artificial: Usually by injections of anti toxinsNatural: Antibodies passed on the children in
breast milk (in colostrum – has IgA)
Vaccines
Vaccines as an Artificial immunity
A prepared antigen used to stimulate an immune response artificially
May use dead pathogensOr those that attenuated
Problem: Poor Responses
Sometimes there is poor responseThe person may have a lack lusting immune
systemMay be malnutritioned – cannot produce
antibodiesMay require buffer
Problem: Live Virus/ Herd immunity
Sometimes virus can continue to infect other people
Herd immunity is required to protect the entire community
This means the entire or most of the population are vaccinated sot he virus cannot survive
Problem: Antigenic Variation
Virus may mutate into many forms and strains
For example, Cholera has mutated several times over the past decades
Tuberculosis mutated to resist drug treatments in the forms of MDR-TB (Multiple-Drug Resistant Tuberculosis)
Problem: Antigenic Concealment
Virus may hide itselfFor example, Cholera can conceal itself in the
small intestine
Autoimmune Disease
Autoimmune Disease
Usually when T-cells are produced that are somehow meant to attack self-antigen they are destroyed in early stages
But in rare circumstances, they escaped detection
These T-cells proceed to order the attack of the human it was create to protect
Myasthenia Gravis
This is caused by a complex process where certain inhibition by antibodies caused by the deformed T-Cells stop transmission of electrical impulse between nerve cells and muscle cells
This causes muscle weakness
Multiple Sclerosis
Destruction of the myelin sheath on the nerve cells
Nerve impulses not transmittedLost of work in the CNS (Central Nervous System)
MRI scan can detect the plaque/ degenerative area
Symptoms: Muscle weakness, loss of sensory input, poor vision, mental problems
Rheumatoid Arthritis
Attack the joints and spread to the rest of the body
Start in fingers, hands then spread to the rest of the body
Tendons inflames, muscle spasm and pain
Type 1 Diabetes
Inhibition of the islets of LangerhansStop the production of insulinHence leads to high blood sugar content
Monoclonal Antibodies
Monoclonal Antibodies
Antibodies that are produced by human over and over again for uses that we want
Important because it can be use for diagnosis and treatment
Normal antibodies are hard to replicate because B-cells that divide do not produce antibodies and plasma cells that produce antibodies, do not divide.
Making such Antibodies
Inject an animal with an antigen that would induce an immune response that would produce the kind of plasma cell we want
Extract the plasma cell from the spleen of the animal
Fuses the plasma cell with cancer cellThe cell will begin to divide
Diagnosis with Mabs
Mabs are marked by radioactive markersThey are sent into the blood (sometimes to
detect blood clot)When they reach the ‘destination’ – the
doctors can detect the clot
Treatment with Mabs
Can pose problems because they have to be administered more than once
Because the Mabs are from animals – they are still non-self, so our immune response will soon detect that too
We can still modify the sugar chains of the antibodies to make them look like ours
Or change the gene that code for those chains… same result
Trastuzumab
Treat breast cancerBinds to cells that multiply in abnormal
quantityMarks for destruction for immune response
Ipilumab
Treat for Melanoma – a skin cancerBlocks the actions of the proteins that stop
the production of T-cellsHence sustain the immune response
Infliximab
Treat Rheumatoid ArthritisBinds to the proteins secreted by T-cells that
damage the jointsUsually takes up to 2 months to treat Important that these antibodies are
humanized
Rituximab
Binds to the surface membrane of B-cellsCause the death of the cell eventuallyUsed to treat diseases where there are over
production of B-cells – leukemia (cancer of the bone marrow – causing deformed cells to be created)
May be used against Rheumatoid arthritis, Multiple Sclerosis and Myasthenia Gravis