Infectious Diseases Flashcards
Define a disease.
Ill health/Sickness
Cause reduced effectiveness of functions.
Illness with a set of of symptoms and signs.
Poor physical,mental and social well being.
What is an infectious disease?
Diseases caused by pathogens.
Cause harm to health of host
Can be passed from one organism to another i.e. communicable/transmissable.
For example through;
Direct contact
Exchange of fluids
Contamination
Airborne
Vector
What is a pathogen?
Pathogens are parasitic disease-causing microorganisms.
pathogens can be prokaryotes/eukaryotes
For example Bacteria (prokaryote), Virus (Not living), proctoctists (eukaryotes), fungi (eukaryotes).
What is a transmission cycle?
The passage of a pathogen from one host to another is continually repeated as the pathogen infects new hosts. The way in which a pathogen passes from one host to another is called the transmission cycle.
pathogens:
1. Gain entry to host
2.Colonise host tissue (multiply)
3.Damage host’s tissues
4.Resist host defenses
How can we kill pathogen?
We need to break the disease transmission cycle to prevent disease from spreading. Control methods attempt to break transmission cycles by removing the conditions that favor the spread of the pathogen.
What is a protoctist?
A protist or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus.
Describe viruses.
Non-cellular structure
No plasma membrane, cytoplasm, ribosomes.
Only
1.DNA or RNA
2.Protein coat=capsid
-protective coat
-may have one or two coats
3. Many viruses also have a lipid envelope.
4. Some proteins may be present for e.g. heamagglutin,neuramindiase.
Describe how viruses reproduce.
Viruses are all parasitic
Can only reproduce by infecting living cells
Uses protein synthesizing machinery of host cells to replicate.
They:
Virus bind to cell
Incorporate viral DNA/RNA into cell
use host cell’s ribosomes, ER,Golgi to produce viral proteins.
Produce more viruses.
What features are not present in all bacteria?
Non-mebrane bound organelles
No nucleus
DNA lies free in cytoplasm in the nuceloid region and is not associated with histone proteins.
What features are present in all bacteria?
plasma membrane
cytoplasm
Peptidoglycan cell wall
→ made of chains crossed linked by amino acids
70s ribosomes
Circular DNA
DNA is naked
Not associated with histones
What are the different types of pathogens?
Disease → Type of causative agent →Name of causative agent
1.Cholera → Bacteria → Vibrio Cholerae
2. Malaria →Proctoctist →Plasmodium falciparum/P.malariae/P.Vivax/P.ovale
3. HIV/AIDS → (Retro)virus → Human Immunodeficiency virus.
4. Tuberculosis →Bacteria →Mycobacterium tuberculosis/M. bovis
5. Smallpox → Virus →Variola Virus.
Define a disease carrier?
A disease carrier (or just a carrier) is a person infected with a pathogen who shows no symptoms, but can be a source of infection in other people (not carrier of an inherited disease). It can be very difficult to trace them as a source of infection.
Give an example of a control measure for infectious diseases.
Vaccination is a major control measure for many infectious diseases. Vaccinations work by making us immune to specific pathogens so that they do not live and reproduce within us and do not spread to others, so breaking the transmission cycle.
Define disease eradication?
The complete breakage of the transmission cycle of a pathogen so that they are no more cases of the disease caused by the pathogen anywhere in the world.
Give examples of two diseases that have been eradicated.
in 1980 WHO declared that small pox had been eradicated and in 2011 rinderpest a severe disease in livestock was eradicated.
Define endemic.
A disease that is always in a population.
For example tuberculosis is a disease endemic in the whole human population and Malaria is endemic in tropical and sub-tropical regions such as Africa.
Define epidemic.
An epidemic is when there is a sudden increase in the number of people with a disease. For example SARS epidemic in Malaysia.
Define pandemic.
A pandemic occurs when there is an increase in the number of cases throughout the continent or across the world . For example covid 19 and HIV/AIDS.
Define incidence.
The incidence is the number of people who are diagnosed over a certain period of time, usually a week, month or a year.
Define prevalence.
The prevalence of a disease is the number of people who have that disease at any one time.
Define mortality rate.
The number of deaths over a particular length of time, usually a year is the mortality rate.
Describe the structure of the causative agent cholera?
The causative agent is a bacterium called vibrio cholera. Vibrio cholera is comma shaped, has flagella and is motile.
Describe how cholera is transmitted.
Large numbers of vibrio cholera are found in faeces of infected people. Infected person’s faeces/ sewage contaminates food/water.
Houseflies land on faeces and contaminate food/water.
Uninfected person eats contaminated food/water.
Due to absence of proper sanitation-no treatment of faecal waste→poor hygiene and poor living conditions.
Lack of education about transmission.
What is the faecal-oral route?
Cholera is transmitted by the faecal-oral route. The faecal-oral route comprises both of water and food borne transmission.
What are the symptoms and effects of cholera?
- if bacteria is not killed by stomach acid, bacteria reaches the small intestine.
- Bacteria secretes choleragen toxin.
- Toxin binds to complementary receptor on intestinal epithelial cell and enters via endocytosis.
- Disrupts function of intestine epithelium lining.
- Loss of chloride and sodium ions (salts) from epithelium cell into intestine.
- water potential of intestine decreases, water moves out from blood, down water potential gradient by osmosis through partially permeable membrane.
- causes severe diarrhoea + dehydration which can lead to death if not treated.
What are some more symptoms are cholera?
Diarrhoea
severe dehydration
Loss of water and salts
Weakness and fatigue
Low Blood Pressure
Weight Loss
Vomitting
How can we diagnose cholera?
Dipstick tests of rectal swabs
Identification of vibrio cholera in faecal samples using microscopy.
How can we treat cholera?
If people can drink they are given oral rehydration therapy. This involves the use of oral rehydration solution (ORS) that has glucose/salts. We need to ensure that fluid intake=fluid losses in urine and faeces. This helps maintain osmotic balance of blood and tissue fluids. If a person cannot drink they are given the solution intravenously to rehydrate the body.
Almost all treated patients survive.
How can cholera be prevented?
Proper sewage treatment to break the transmission cycle.
Chlorinate water to kill bacteria before drinking.
Drink bottled water.
Vaccination only offers short term protection and is no longer recommended.
Describe the global distribution of cholera.
Endemic in developing countries for example west and east Africa, Afghanistan, latin America and parts of Asia.
Outbreaks also follow natural disasters or war. For example cholera epidemic during 2010 earthquake in Haiti, 2014-2016 outbreak in Yemen.
Why is it hard to vaccinate against cholera?
There are many different strains of vibrio cholera. Each strain that caused a bacteria is more virulent than the last. Adults can be reinfected and have cholera again. This is why it is hard to vaccinate against cholera.
What is the causative organism of malaria in humans?
In humans, malaria is caused by plasmodium falciparum (75%), Plasmodium Malariae, Plasmodium Ovale and Plasmodium Vivax (20%).
Describe the structure of the causative agent of malaria.
The causative agent is plasmodium- a protoctist (eukaryote), parasite. The appearance changes depending on life cycle stages.
Plasmodium is most motile during initial effective stages.
Define a disease vector.
An organism which carries a pathogen from one person to another or from an animal to a human.
What is the disease vector of malaria?
Insect Vector=Female Anopheles mosquitoes
Only Female take blood meals to supply eggs with nutrients.
Although blood transfusions, use of unsterile needles, and can pass across placenta from mother can also transmit malaria.
How does the disease vector transmit malaria from infected to uninfected person.
Female anopheles mosquito takes a blood meal from infected person and then takes a blood meal from uninfected person.
Describe the life cycle of plasmodium.
1.Plasmodium’s gametes fuse, multiplies in and form infective stages in mosquitoes.
2. When mos takes a blood meal, parasite enters host with mos’s anticoagulant and saliva.
3. Infective stages of parasite enter bloodstream and then liver cells.
4. Parasite matures in liver cells, then leaves liver to enter RBC.
5. Parasite multiply in RBCs, causing RBC’s to lyse. (break)
6. Parasites are released and infect other RBC’s.
7. Parasites picked up by another mos in a blood meal.
Remember first: Blood stream, liver than red blood cells.
Describe the symptoms of Malaria.
Fever
Anaemia
Nausea
Headaches
Muscle Pain
Shivering
Sweating
Enlarged Spleen
How can we diagnose malaria?
Micrscopical analysis of Blood
Dip Stick test for malaria antigens in blood.
When is transmission of malaria most intense?
Transmission is more intense in places where the mosquito lifespan is longer (so that the mosquito has time to complete its devolopment inside the mosquito) and where its prefer to bite humans rather than other animals. The long lifespan and strong human biting habit pf the species of anopheles is found in Africa are the main reasons why about 90% of cases are found in africa.
What does transmission of malaria depend upon?
Transmission also depends upon climatic conditions that may affect the number and survival of mosquitoes, such as rainfall patterns, temperature and humidity. Transmission may be seasonal with the peak occuring during and just after rainy season.
