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