diseases Flashcards
HEALTH
A state of mental, physical and social wellbeing
DISEASE
Poor state of mental, physical and social well-being or an abnormal
condition affecting an organism that reduces the effectiveness or function of that organism
INFECTIOUS DISEASES [communicable diseases]
A disease caused by a pathogen
that spreads from one person to another. E.g., HIV, cholera, common cold
PATHOGEN
an organism that causes disease
Transmission
the transfer of a pathogen from a person infected with
that pathogen to an uninfected person; transmission may occur by direct contact, through the air or water, or by animal vectors, such as insect
DISEASE CARRIER / CARRIER
a person infected with a pathogen who shows no
symptoms, but can be the source of infection in other people [not carrier of inherited diseases]
TRANSMISSION CYCLE
the passage of a pathogen from one host to another is
continually repeated as the pathogen infects new hosts
disease eradication
the complete breakage of the transmission cycle of a
pathogen so that there are no cases of the disease caused by the pathogen anywhere in the world
ENDEMIC DISEASES
a disease that is always in a population [e.g. TB,
malaria
. INCIDENCE
the incidence of a disease is the number of people who are
diagnosed over a certain period of time, usually a week, month or a year
PREVALENCE
the prevalence of a disease is the number of people who have
that disease at any one time
EPIDEMIC
an epidemic occurs when there is a sudden increase in the
number of people with a disease
PANDEMIC
a pandemic occurs when there is an increase in the number
of cases throughout a continent or across the world
MORTALITY RATE
the number of deaths over a particular length of
time (usually a year) is the mortality rate [usually shown as “per 100,000
people”]
NATALITY
birth rate
NON-INFECTIOUS DISEASE
Not caused by a pathogen. Does not spread from one person to another. E.g., sickle cell anemia and cancer
ACUTE
comes out suddenly and rapidly and lasts for a short time.
CHRONIC
progressive disease that lasts for a long tim
INCUBATION PERIOD
The incubation period is the time taken for an
infection to develop after a person has been exposed to a disease-causing organism (such as bacteria, viruses, or fungi). The incubation period ends when the first signs or symptoms of the disease appear
cholera name of pathogen
Vibrio cholerae
cholera type of pathogen
Bacterium
[prokaryote]
malaria pathogen
Four species of plasmodium:
1. Plasmodium falciparum
2. Plasmodium malariae
3. Plasmodium ovale
4. Plasmodium vivax
malaria type of pathogen
Protoctist [eukaryote]
HIV/ AIDS pathogen
Human immunodeficiency virus
HIV/AIDS types of pathogen
Virus
TB pathogen
- Mycobacterium tuberculosis
- Mycobacterium bovis
TB types of pathogen
Bacterium
[prokaryote]
cholera methods of transmission
food-borne, water-borne
Global distrbution of cholera
Asia, Africa, Latin America
cholera incubation period
two hours to five days
site of action of pathogens for cholera
wall of small intestine
clinical features of cholera
severe diarrhoea (‘rice water’), loss of water and
salts, dehydration, weakness
method of diagnosis cholera
dipstick test rectal swabs; identification of
V.cholerae in faecal samples using microscopy
To reach the site of infection [wall of small intestine
the bacteria have to pass through the stomach. If the contents are sufficiently acidic [pH less than 4.5], the bacteria are unlikely to survive
ACTION IN THE SMALL INTESTINE
- after reaching small intestine, they multiply and secrete the toxin [named choleragen]
- this toxin disrupts the functions of the epithelium lining, so that salts water leave the blood
- the loss of salts and water causes severe diarrhoea
- loss of fluid can be fatal if not treated within 24 hours
As Vibrio cholerae reaches the small intestine lumen
it releases a toxin named choleragen / enterotoxin. It is a quaternary protein made up of 6 polypeptide chains. It has 2 subunits, subunit A [1 polypeptide] and subunit B [5 polypeptide]Choleragen makes a complementary binding with ganglioside receptor/GM1 in the
small intestine epithelial cell [hydrogen or ionic bond] [NOTE: subunit B makes complementary binding with GM1]
* membrane pinches in or invaginates to form endocytotic vacuole - ENDOCYTOSIS
* choleragen gets transported to the ER
* altered Subunit A is released from ER
* A subunit activates the G-protein and enzyme adenylate cyclase that leads to an increase in the concentration of cAMP [cyclic adenosine monophosphate], a second messenger which initiates a cascade of chemical reactions within the cell
* As a response, Clchannels open and leads to the efflux of ions into the lumen decreasing the water potential, so water comes out of cells to the lumen by osmosis
* This leads to severe diarrhoea
Oral rehydration therapy
- Water for rehydration
- Glucose to provide energy for active uptake of ions
- Na+ ions to replace lost ions, lowers water potential of epithelial cells
- K+ ions to replace lost ions and stimulate appetite
- Other electrolyte to prevent electrolyte imbalance
Problems involved in preventing the spread of cholera
- Poor sanitation / no treatment of faecal matter
- Contamination of drinking water supply
- Poverty / poor living condition
- Poor hygiene
- Contamination of vegetable plots with faecal matter
- Poor/ lack of health education about transmission
- Natural disaster, refuges, no effective vaccine
- Lack of water purification equipment or bottled water
- No rehydration therapy at time when needed
- Bacteria live in gut where immune system is not very
effective. [antigenic concealment]
Why is cholera not common in developed countries?
- Transmission cycle is broken
- Better sewage treatment plant
- Human faeces don’t come in contact with drinking water supply.
- Water is treated with chlorine to kill bacteria
- Drinking water clean piped at home
- Good sewage dispersal
- Good health services
- No residents are homeless
Why cholera is more common after a natural disaster?
Increased number of people / lack of infrastructure
Problem in providing safe drinking water
Faeces / sewage mixed with drinking water
Poor sanitation
Unable to practice good hygiene
Infected people share same latrines with uninfected
Lack of proper medical care/ drugs/ antibiotics/ skilled person/ ORT
Unable to supply sufficient vaccine
Lack of food/ poor diet so vaccine is not effective
Cholera vaccine is used for
active immunization against cholera
Use of cholera vaccine does not prevent
transmission of infection.
Reasons why vaccination has not eradicated cholera
1 transmission cycle is difficult to break;
2 difficulty in administering e.g. refugee camp, displaced, disaster;
3 poor diet, lowered immune response;
4 more than one strain (needs more than one type of vaccine);
5 vaccine, only gives short-term protection / requiring boosters;
6 antigenic concealment - live beyond the reach of antibodies
malaria pathogen
Plasmodium falciparum, P. vivax, P. ovale, P. malariae
malaria methods of transmission
Insect vector: female Anopheles mosquito [about 30 different
species]
malaria global distribution
throughout the tropics and sub-tropics (endemic in 106 countries)
malaria incubation period
from a week to a year
malaria site of action of pathogen
liver, red blood cells, brain
malaria clinical features
fever, anaemia, nausea, headaches, muscle pain, shivering,
sweating, enlarged spleen
malaria methods of diagnosis
microscopical examination of blood; dip stick test for malaria
antigens in blood
Why only female Anopheles feed on human blood?
Female Anopheles mosquitoes feed on human blood
to obtain the protein they need to develop their
eggs.
Gametocyte:
a cell (as of a protozoan causing malaria) that
divides to produce gametes.
SPOROZOITES
the infective mature stage of plasmodium seen in the gut and salivary glands
The life cycle of Plasmodium
- The parasite has two hosts: the sexual stage occurs in
mosquitoes, the asexual stage in humans - The time between infection and appearance of parasites inside red blood cells is 7–30 days in P. falciparum; longer in other species.
All cases of suspected malaria should be confirmed by
using microscopical examination of blood before treatment is started [result available in 30 minutes]
Treating malaria
- Anti-malarial drugs like quinine [an extract from cinchona tree]and chloroquinine are used to treat infected people
- Newer drug - Mefloquine –has side effects like dizziness, vomiting [The antimalarial Mefloquine targets the Plasmodium falciparum 80S ribosome to inhibit protein synthesis.]
- Mefloquine resistance seen in S. E. Asia
- Artemisinin based combination therapy [ACT]- Artimisia plant extract + mefloquine is the best treatment at present [Artemisinin enhances efficacy and has the potential of lowering the rate at which resistance emerges and spreads.]
Prophylactic drugs [preventive drugs] are
❑ Chloroquine – inhibits protein synthesis thus prevents spreading with in the body
❑ Proguanil – prevents sexual reproduction of plasmodium within mosquitoes
* Prophylactic drugs has to be taken before going to countries endemic to malaria
Where anti-malarial drugs have been used widely,
drug-resistant Plasmodium are also seen
* Chloroquine resistance widespread in parts of S. America, Africa and S. E. Asia
Preventing Malaria
ABCD method
A- Awareness
B- Bite control
C- Control of mosquitoes
D- Diagnosis and drugs
B- Bite control
use of repellent creams, sprays, mosquito coil, using mosquito nets, mesh on windows and doors, covering body from head to toes
C- Control of mosquitoes
- by adding oil on the surface of still water to break the oxygen supply.
Spray insecticides, drain water from unused things like trees, pots etc. - biological control method - use the normal predators of mosquitoes:
❑ stocking ponds, irrigation and drainage ditches and other permanent
bodies of water with fish which feed on mosquito larvae
❑ spraying a preparation containing the bacterium Bacillus thuringiensis which kills mosquito larvae but is not toxic to other forms of life
D- Diagnosis and drug
- Diagnosis by blood test.
- Quinine is the drug used against malaria extracted from the bark of
cinchona. - The whole genome of Plasmodium has been sequenced, and this is leading to the
development of new treatments and vaccines. - RTS,S / AS01(RTS,S) – also known as Mosquirix – is an injectable vaccine that provides
partial protection against malaria in young children
Describe the factors that may lead to improvements in the control of malaria?
- Use of modern techniques in gene sequencing and drug design
- Development of vaccines targeted against different stages of the parasite’s life cycle
- A renewed international will to remove the burden of malaria from the poorest parts of the world, allied to generous donations from wealthy individuals and foundations
Reason behind worldwide spread of malaria
- Migration of people/ tourism promotes spreading
- Drug resistance in plasmodium
- Mosquito resistance to insecticides
- No vaccine available because of antigenic variability and antigenic concealment [some pathogens evade/escape attack by the immune system by living or hiding inside cells]
- Lack of awareness
- Global warming- suitable condition for plasmodium
- Poverty in affected area
- War and political unrest – preventing implementation of antimalarial programme
Explain why it has been difficult to develop an effective vaccine for malaria
- Plasmodium, has many genes as they are eukaryotes, so, many types of antigens.
- It has many different stages of life cycle within human so antigens change in different stages and also antibodies cannot work against stages within cells [e.g. trophozoites]
- More than one Plasmodium species;
- Variation generated during meiosis
- Parasite only vulnerable at certain stages of life cycle / when free in plasma - antigenic concealment.
Describe how malaria is passed from an infected person to an
uninfected person
female, Anopheles (mosquito) ; takes blood (meal) from an (infected) person, feeds on an
(uninfected) person ;
Plasmodium / parasite, transmitted in (mosquito’s) saliva ;
blood transfusion / shared needles / across placenta / at birth ;
Why malaria is restricted to the tropics
1 Anopheles mosquito / vector, survives / breeds / lives, within the tropics / in hot andhumid areas ;
2 Plasmodium / pathogen / parasite, needs to reproduce within the mosquito (at temperatures above 20°C) ;
Mosquitoes need area of still water to complete its life cycle [High rainfall]
3. eradicated in areas outside tropics. E.g., North America
HIV/AIDS methods of transmission
- in semen and vaginal fluids during sexual intercourse
- infected blood or blood products
- contaminated hypodermic syringes
- mother to fetus across placenta and at birth
- mother to infant in breast milk
HIV/AIDS global distrbution
worldwide, especially in sub-Saharan Africa and South-East Asia
HIV/AIDS incubation period
Initial incubation – a few weeks
But upto ten years or more before symptoms of AIDS may develop
HIV/AIDS site of action of pathogen
T helper lymphocytes, macrophages, brain cells
HIV/AIDS clinical features
HIV infection – flu-like symptoms and then symptomless
AIDS – opportunistic infections including pneumonia, TB and
cancers; weight loss, diarrhoea, fever, sweating, dementia[loss of cognitive functioning — thinking, remembering, and reasoning]
HIV/AIDS methods of diagnosis
testing blood, saliva or urine for the presence of antibodies produced
against HIV
What is HIV?
- H – Human – This particular virus can only infect human beings.
- I – Immunodeficiency – HIV weakens your immune system by destroying important cells that fight disease and infection [helper T cells]. A “deficient” immune system can’t protect you.
- V – Virus – A virus can only reproduce itself by taking over a cell in the body of its host
Disease: AIDS – ACQUIRED IMMUNO DEFICIENCY SYNDROME
- A – Acquired – AIDS is not something you inherit from your parents like eye color.
You acquire AIDS. - I – Immuno – Your body’s immune system includes all the organs and cells that work to fight off infection or disease.
- D – Deficiency – You get AIDS when your immune system is “deficient,” or isn’t working the way
it should. - S – Syndrome – A syndrome is a collection of symptoms and signs of disease. AIDS is a syndrome, rather than a single disease. It is a complex illness with a wide range of symptoms.
Human immunodeficiency virus (HIV) structure
- The outer lipid membrane forms the envelope, which also has two
glycoproteins: gp120 and gp41 - The protein core contains genetic material (RNA) and has enzymes:
protease, integrase and reverse transcriptase. - Reverse transcriptase uses the RNA as a template to produce DNA once the virus is inside a host cell
- Integrase enzyme helps to integrate viral DNA with human nuclear DNA
VHIV is a retrovirus
Its genetic material is RNA, not DNA. Once inside the host cell [helper T cell / macrophage], the viral RNA is converted back to DNA [hence called ‘retro’]
- HIV binds to CD4 receptors on T-helper cells using glycoprotein gp120
- Genetic material [RNA] and enzymes present in virus enter the cell
- RNA gets converted to double stranded DNA. It undergoes reverse transcription inside the host cell with the help of reverse transcriptase enzyme [present inside the HIV]. It takes nucleotides from the cytoplasm of host cells. – many errors occur during this process
leading to formation of new antigens - Viral DNA enters nucleus through nuclear pore.
- It attaches to the DNA [in host cell nucleus] with the help of the enzyme integrase.
- It undergoes transcription and a viral RNA is formed.
- It undergoes translation to produce gp120, reverse transcriptase, integrase, protease and RNA molecules.
- All this comes to the surface of T-helper cells and buds off as an active HIV
- HIV infected T helper cells trigger self destruction mechanism
- Reverse transcriptase makes mistakes during reverse transcription [develops resistance to drugs and hard to develop vaccine
Problems controlling spread of HIV
- No cure / no vaccine;
- Drugs are expensive.
- Problems with symptomless carriers (spreading the virus);
- Problems with testing people for HIV status;
- Problems with providing, condoms/femidoms;
- Problems with educating about risks;
- Problems with tracing contacts (of infected people);
- Problems with screening blood donations;
- Problems with treating blood to kill HIV;
Combat against HIV
- testing people for HIV status;
- providing, condoms/femidoms;
- educating about risks;
- tracing contacts (of infected people);
- screening blood donations and treating blood to kill hiv
High risk groups for AIDS
- Male homosexuals
- Prostitutes
- People with multiple partners
- Injected drug users
- Haemophiliacs, who are injected with Factor 8 [essential blood-clotting protein] from the blood of several donors
Treating HIV/AIDS
- No vaccine or cure, but drugs can slow down its action:
- zidovudine binds to reverse transcriptase and blocks its action
- Combinations of drugs can significantly aid the slowing of AIDS but is expensive and has side effects.
Tb pathogen
Mycobacterium tuberculosis; Mycobacterium bovis
Tb methods of transmission
airborne droplets (M. tuberculosis); via undercooked meat and unpasteurized milk (M. bovis)
Tb global distrbution
worldwide
Tb incubation period
few weeks or up to several years
Tb site of action of pathogen
primary infection in lungs; secondary infections in lymph
nodes, bones and gut
Tb clinical features
wracking cough, coughing blood, chest pain, shortness of breath, fever,
sweating, weight loss
Tb methods of diagnosis
Rapid molecular test detecting presence of DNA from M.tuberculosis;
microscopical examination of sputum for bacteria; chest X-ray; long-term culture of bacteria (up to 12 weeks)
TRANSMISSION OF TUBERCULOSIS [TB]
- inhalation of mycobacteria present in aerosol droplets
- bacteria meet with alveolar macrophages
- bacteria ingested by the macrophages, but they manage to survive inside
- an inflammatory response gets triggered bringing other defensive cells to the area, forming a mass of tissue, called a granuloma [core of infected macrophages enclosed by other cells of the immune
system] - macrophages loaded with bacteria are killed, resulting in the formation of the caseous center of the granuloma
latent tuberculosis
bacteria become dormant and remain alive for decades without symptoms
active pulmonary tuberculosis
infection stops in healthy people at this stage, but if the immune system is compromised by immunosuppressive drugs, HIV infections, malnutrition, aging, or other factors, the bacteria can be reactivated, replicate, escape from the granuloma and spread to other parts of the lungs causing, This reactivation may occur after months or even years after the initial infection
In some cases, the bacteria may also spread to other organs of the body via the
lymphatic system or the bloodstream. This widespread form of TB disease, called disseminated TB or miliary TB, occurs most commonly in the very young, the very old and those with HIV infections.
Tuberculosis is generally treatable with antibiotics
Several antibiotics are usually prescribed for many
months due to the slow growth rate of the bacteria. It’s very important that the patients complete the course of the treatment to prevent development of drug-resistant bacteria and re-occurrence of the
disease.
TB transmission
An infection is initiated following inhalation of mycobacteria present in aerosol droplets discharged into the atmosphere by a person with an active infection.
* The transmission process is very efficient as these droplets can persist in the atmosphere for several hours and the infectious dose is very low – less than 10 bacilli are needed to start the infection.
* Once in the lung, the bacteria meet with the body’s first-line defense - the alveolar macrophages. The bacteria are ingested by the macrophages but manage to survive inside. Internalization of the bacilli triggers an inflammatory response that brings other defensive cells to the area. Together, these cells form a mass of tissue, called a granuloma, characteristic of the disease.
TB early stages
- In its early stage, the granuloma has a core of infected macrophages enclosed by other cells of the immune system. As cellular immunity develops, macrophages loaded with bacteria are killed, resulting in the formation of the caseous center of the granuloma.
- The bacteria become dormant but may remain alive for decades. This enclosed infection is referred to as latent tuberculosis and may persist throughout a person’s life without causing any symptoms. The strength of the body’s immune response determines whether an infection is arrested here or progresses to the next stage. In healthy people, the infection may be stopped permanently at this point. The granulomas subsequently heal, leaving small calcified lesions.
- On the other hand, if the immune system is compromised by immunosuppressive drugs, HIV infections, malnutrition, aging, or other factors, the bacteria can be re-activated, replicate, escape from the granuloma and spread to other parts of the lungs causing active pulmonary tuberculosis. This reactivation may occur months or even years after the initial infection.
In some cases, the bacteria may also spread to other organs of the body via the lymphatic system or the bloodstream
This widespread form of TB disease, called disseminated TB or
miliary TB, occurs most commonly in the very young, the very old and those with HIV infections.
Tuberculosis is generally treatable with antibiotics. Several antibiotics are usually prescribed for many months due to the slow growth rate of the bacteria.
It’s very important that the patients complete the course of the treatment to prevent development of drug-resistant bacteria and re-occurrence of the disease.
TB diagnosis
- Rapid molecular test detecting presence of DNA
- Microscopical examination of sputum for bacteria
- Chest X-ray
- Long term culture of bacteria [up to 12 weeks]
- Skin test- [purified protein derivative/ tuberculin skin test] inject PPT into the skin which is prepared from dead TB bacteria. If a swelling appears at the injection site after 48-72 hours, then it is positive for TB.
TB vaccine and treatment
BCG- [Bacillus Calmette–Guérin vaccine]- a weak attenuated [made harmless] form. One dose at the time of birth
* DOTS – [Direct Observable Treatment, short course] health worker or family member make sure that medicines are taken regularly for six to eight months.
* The drug widely used are isoniazid, rifampicin [in combination with other drugs like INH and pyrazinamide to avoid antibiotic resistance], ethambutol [in combination with other drugs like INH and rifampin to minimize resistance], pyrazinamide, etc
* Streptomycin was the first antibiotic to be discovered that was effective against the pathogen that causes tuberculosis. Streptomycin causes the death of the pathogen by binding to ribosomes and inhibiting protein synthesis
Drug-resistant TB
Drug-resistant TB can occur when the drugs used to treat TB are misused or mismanaged.
Examples of misuse or mismanagement include:
People do not complete a full course of TB treatment
Health care providers prescribe the wrong treatment (the wrong dose or length of time)
Drugs for proper treatment are not available
Drugs are of poor quality
Drug-resistant TB is more common in people who
Do not take their TB drugs regularly
Do not take all of their TB drugs
Develop TB disease again, after being treated for TB disease in the past
Come from areas of the world where drug-resistant TB is common
Have spent time with someone known to have drug-resistant TB disease
Mutation is a
random event and occurs with a frequency of about one in every thousand bacteria.
People who do not complete a course of treatment are
highly likely to infect others with drug-resistant forms of TB
DOTS (direct observation treatment
short course) involves health workers or responsible
family members making sure that patients take their medicine regularly for six to eight months.
Multiple-drug-resistant
forms of TB (MDR-TB) now exist. These strains are resistant to at least
the two main drugs used to treat TB – isoniazid and rifampicin – which are known as first-line drugs.
Extensively (or extremely) drug-resistant TB (XDR-TB)
has also emerged as a very serious threat to health, especially for those people who are HIV-positive . XDR-TB strains are resistant to first-line drugs and to the drugs used to treat MDR-TB.
Why antibiotic is necessary for TB
Bacteria that causes TB enter cells in lungs and hide from immune system. So antibiotics are given to kill / destroy / reduce the growth of bacteria.
To make sure that all bacteria are killed
To prevent the bacteria leaving the reservoir of infection [NOTE: Reservoir of infection: Any person, animal, plant, soil or substance in which an infectious agent normally lives and multiplies]
To prevent death
Inhibit protein synthesis
Does not affect human cells
Why TB has not been eradicated even though a vaccine has
existed since 1921?
*Vaccine [BCG] does not always give lasting protection or effectiveness decreases with years unless exposure to TB
*No worldwide vaccination programs like the one we had for smallpox
*Many are symptomless carriers
*Bacteria remain in the body for a long time and become active anytime
*Bacteria or parasite lives inside the cells or intracellular
*Lack of protein in the diet so less antibodies are produced
*Difficult to produce herd immunity
Why TB has a greater impact on the health of people in some regions rather than others?
- TB is the disease of the poverty that means people living in overcrowding conditions prone to get the disease
- TB is also an opportunistic disease i.e., disease that occur more often or are more severe in people with weakened immune systems than in people with healthy immune systems. HIV weakens the immune system.
- Vaccination programs for TB are better in some countries/ region than others
Suggest how this drug resistance may have arisen in TB
Patient does not complete course or takes inadequate dose or stop taking when feels better, so not all bacteria are killed. Remaining bacteria develop resistance to the antibiotics. These resistant strains survive, and multiply.
Drug resistance can also occurs as a result of mutation in the bacterial DNA.
May be continuous supply of antibiotic is not available
Drug resistance might increase if only one type of antibiotic is used
Changes in bacteria and host cells membrane structure also increases the chances of drug resistance in bacteria
Treatment with four different antibiotics for TB
increases chances of, killing all bacteria ;
if bacteria are resistant to one antibiotic, then still susceptible to other antibiotics
reduces chance of mutations arising / (if bacteria susceptible) mutations unlikely to occur against all antibiotics ;
Antibiotic can be stopped because of side effects
idea that more effective because different antibiotics will work on different targets (in the bacteria)
random mutations in dna allow
some bacteria to be resistant (antibiotics dont
CAUSE mutations in bacterial dna)
antibiotic usage + resistance
a narrow spectrum antibiotic shud be when u confirm know what
bacteria causes that disease
a broad spectrum is used when ydk what pathogen causes the disease
if you use one for the other’s purpose, it leads to antibiotic resistance
ans to this question is A
not all mutations lead to
resistance
the proportion of antibiotic-resistant bacteria in a population only increases if
the antibiotic is used!
malaria cannot be passed from
human to human !
Disease
- ill-health / absence of well-being / abnormal condition / AW, (affecting an organism) ;
- reduced effectiveness of, functions / named function ; AW
- (illness with a set of) symptoms ; AW A signs
- poor / AW, physical, mental or social, well-being ; A two out of the three
Describe how TB is transmitted from infected to uninfected people.
- (infected) person, sneezes/coughs/sputum/spitting/breathes out;
- aerosol/droplets, in the air/moist air, inhaled/breathed in by (uninfected person);
Non-infectious disease
- not transmissible from one person to another / AW ;
- not caused by a pathogen ; R bacterium / virus / fungus / AW / ‘worm’
Reason for increase in the cases of TB in developed countries now:
- development of antibiotic resistance (by organism) ; A drug resistance R immunity
- ref. impact of HIV infection ;
- higher rate of immigration from countries with high incidence / AW ;
- increase in tourism to countries with high incidence ;
- reduced surveillance leading to undetected cases (and hence spread) ;
- (detected cases, MDR) unwillingness / AW, to maintain drug regimen / AW ;
- ref. to vaccination programmes no longer taking place ;
- ref. to poor / overcrowded, housing (in cities) / AW ; must be in context of developed countries
Discuss the biological and social factors which make TB a difficult disease to control
7 factors
- TRANSMISSION
-HIV/IMMUNODEFICIENCY
-DIAGNOSIS IS DIFFICULT
-TREATMENT - ACQUIRED RESISTANCE
-VACCINATION
-EDUCATION
transmission of TB
Eg. aerosol, droplet infection
overcrowded, housing / living conditions / AW
migration / travel, from areas with high rates of TB
reservoir of infection in people not, diagnosed / not treated
HIV / immunodeficiency of TB
e.g. infection with HIV may activate (dormant) TB (pathogen)
immunodeficiency / AW, makes people more susceptible to TB
intravenous drug taking increases risk of, immunodeficiency / HIV
diagnosis is difficult of TB
e.g. TB (pathogen) remains dormant / symptomless carriers
limited access to health care for diagnosis / AW
idea that contact tracing is difficult
treatment of TB
e.g. treatment is long term / treatment may not start early enough
people may not finish the course of treatment
limited access to health care for treatment
acquired resistance of TB
e.g. bacterium / TB (pathogen), develops resistance to, antibiotic(s) / drug(s)
multi-drug resistance / MDR-TB / XDR-TB
vaccination of TB
e.g. vaccine may not always be effective in providing protection
difficult to achieve herd immunity
concerns / misconceptions, about vaccination
limited access to vaccination (programmes)
poor (immune) response in people who are malnourished
poor thermostability of vaccine
educationof TB
e.g. limited education / low awareness, about prevention for general population
limited education / low awareness, for health care professionals
Transmission of HIV:
- Sexual intercourse;
- Infected, blood/blood products;
- Sharing/re-using, hypodermic needles;
- Across placenta/from mother to foetus;
- Breast milk;
Explain why cholera remains a significant infectious disease in some parts of the world.
- poor sanitation / no treatment of faecal waste;
- contamination of (drinking) water supply;
- poverty / poor living conditions / poor hygiene / poor (health) education;
- ref to natural disasters; e.g. assistance / aid / medical help / AW, cannot arrive in time
- no rehydration therapy available (at time when needed);
- no (effective) vaccine;
- further detail; (bacteria live in gut, where immune system is not effective)
Describe the methods of prevention of cholera.
ref. to treat drinking water ; A clean / sterilised / chlorinated / safe / bottled / boiled A ref. to water treatment plants
provide sewage treatment plants ; A treat waste water / containment of sewage / provide latrines (in temporary camps) ;
ref. to keeping sewage and (drinking) water sources separate ; A examples e.g. avoid swimming downstream of sewage outlets avoid defecating near rivers used for washing water treatment plants upstream of sewage disposal bury faeces
ref. to vaccination / providing vaccines ;
ref. to education in ways to prevent spread ;
ref. to (encourage) hand washing ;
ref. to food hygiene ; e.g. use of clean cooking utensils / covering food to prevent flies landing / washing food in treated water / cook food thoroughly / peel fruit and vegetable washed in (suspected) contaminated water
discourage use of human faeces for fertiliser / use fertiliser other than human faeces / do not irrigate plant food with contaminated water;
control breeding of, vectors / flies ;
rapid diagnosis ;
rapid treatment (for earlier recovery to minimise risk of spreading) ;
ref. to oral rehydration, salts / therapy ;
use of antibiotics ;
ref. to isolation / quarantine ;
Explain why it is recommended that antibiotics should not be given as a preventative to cholera or to treat mild cases of cholera
Oral rehydration therapy is effective to treat cholera
ORS is a solution of glucose and salts which help rehydrate the body
Antibiotics can act as a selection pressure
Ref. to antibiotic resistance developed
Transmission of resistance by [vertical or horizontal transmission] (not in 2022 syllabus) AVP. through plasmid or through binary fission of bacteria
Antibiotics will become less effective
And so should only be used as a last resort
Ref. to cost
Antibiotics will also kill gut bacteria
Idea that it will disrupt the gut function
AVP. antibiotics can cause mutations etc.
Explain why vaccination programs have not be able to eradicate malaria
pathogen
(because) four / several, different, causative species / AW, (with different antigens) ;
(pathogen has) many antigens as it is eukaryotic / many genes coding for antigens ;
ref. to mutation changing antigens ;
pathogen has different stages of life cycle (within human) with different antigens ;
I ref. to antigenic shift
antigenic concealment / pathogen spends part of life cycle within host cells / AW ;
A short time in blood plasma
vaccine
ref. to more than one type of vaccine needed ;
suggestion that antigens used have not given the strongest immune response ;
vaccination programme
ref. to only trial programmes ;
A programmes not global
ref. to not achieving herd immunity / not enough people (successfully) vaccinated ;
detail ;
e.g. lack of willingness to be vaccinated
lack of trained people to give vaccines
poor nutrition and poor immune response
Discuss the reasons why vaccination has not eradicated cholera and sickle cell anaemia.
cholera up to max 4
cholera up to max 4
1 transmission cycle is difficult to break; A described with example(s)
2 ref. difficulty in administering e.g. refugee camp, displaced, disaster ;
3 poor diet, lowered immune response ;
4 more than one strain (needs more than one type of vaccine) ; A more than one
type (that causes cholera) R constantly mutating
5 vaccine, only gives short-term protection / requiring boosters ;
6 antigenic concealment ;
7 qualified ; e.g. organism in intestines, difficult for antibodies to reach
8 ref. (older or newer oral) vaccine, not successful for everyone / variable (60–65% up
to 90% depending on population group) protection ;
9 no requirement by health authorities (for vaccine) / vaccine not used by health
authorities ; AW
sickle cell
1 no vaccine available ; A cannot vaccinate against sickle cell
2 not caused by pathogen / non-infectious / non-transmissible / non-communicable ;
3 genetic / inherited, disease / AW ; A caused by a mutation
4 affects all red blood cells so vaccine would lead to their destruction ;
Outline how a vaccine can protect against xyz
Vaccine contains antigens
Primary immune response occurs
B-lymphocytes undergo clonal selection. Only specific B cells with receptors complementary to antigen will be activated
These cells divide by mitosis (clonal expansion) to develop into plasma cells
which secrete antibodies
Production of memory cells
T-helper cells secrete cytokines
Cytokines stimulate specific B-cells/ macrophages/ killer T-cells / increases humoral response
Secondary immune response is much faster
Higher level antibodies are produced during reinfection
This gives artificial active immunity
Explain how resistance to drugs such as rifampicin develops
Overuse of antibiotics or misuse of antibiotics eg. taking antibiotics for viral infections, overprescribing for bacterial infections
not completing an antibiotic course
Reservoir of bacteria remains
Ref to mutation (i wrote, antibiotic acts as a selection pressure and induces a mutation in bacteria which makes it resistant)
Any detail of mutation eg. protein produced as a changed binding site
Bacteria with resistance survive or only bacteria sensitive to antibiotic are killed A antibiotic acts as a selection pressure
Bacteria reproduce and pass on gene/allele for resistance to offspring or [vertical transmission] (not in 2022 syllabus)
Frequency of resistance alleles/gene increase in bacterial population
