10.0 Infectious diseases Flashcards
What is a disease
- poor health
- reduced effectiveness of functions
- illness with a set of symptoms
- poor physical, mental, social well being
whats makes a disease infectious
- caused by a pathogen
- causes harm to health of host
- transmissible: can be passed from one organism to another
Cholera
RESPECITIVE PATHOGEN:
- Bacterium
- Vibrio Cholerae
- has flagella, motile
TRANSMISSION PROCESS:
-** faecal-oral route: food-borne, water borne**
- large number of Vibrio Cholerae found in faeces of infected people
- infected faeces contaminates sewage food or water
- houseflies land on faeces and contaminates food and water
- uninfected person ingests contaminated food or water
SYMPTOMS & EFFECTS:
➤ Diarrhea
➤ Severe dehydration
➤ Loss of water and slats
➤ Weakness and fatigue
➤ Low blood pressure
➤ Weight Loss
➤ Vomitting
- If bacteria are not killed by stomach acid, bacteria reaches the small
intestine - Bacteria secrete choleragen toxin
- Toxin binds to complementary receptor on intestinal epithelial cell
and enters via endocytosis - Disrupts function of intestine epithelium lining
- Loss of chloride ions and sodium ions from epithelial cells
- Water potential decreases, water moves out from blood down water
potential gradient by osmosis through partially permeable membrane - Causes severe diarrhore + dehydration
TREATMENT:
- oral rehydration therapy
- use ORAL REHYDRATION THERAPY (ORT) contains glucose and salts
- ensures fluid intake = makes up for fluid loss in urine and faeces
- maintains osmotic balance of blood and tissue fluid
PREVENTION:
- proper sewage treatment to break transmission cycle
- Chlorinate water to kill bacteria before drinking
- drink bottled water
- vaccination only offeres short-term protection
INFLUENCING FACTORS:
➤ Due to absence of proper sanitation - no treatment of faecal waste ➡ water supply
contaminated
➤ Poor hygiene and poor living conditions
➤ Lack of education about transmission
➤ Adults can be reinfected and have cholera again
➤ This is also why it is hard to vaccinate against cholera
Malaria
RESPECITIVE PATHOGEN:
- protoctist
- Plasmodium Malariae
TRANSMISSION PROCESS:
➤VECTOR:
- organism that carries a disease from a person to another / from an animal to a human
- femal Anopheles mosquitoes
- only female take blood meals to supply eggs with nutrients
- also through blood transfusions, use of unsterile needles and passing across placenta from mother to child
➤* Life cycle of plasmodium*:
1. Plasmodium’s gametes fuse, multiplies in and form infective stages in mosquitoes
2. When mosquito takes blood meal, parasite enters host with mosquito’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 RBCs
5. Parasites multiply in RBCs, causing RBCs to lyse
6. Parasites are released and infect other RBCs
7. Parasites picked up by another mosquito in a blood meal
SYMPTOMS AND EFFECTS:
➤ Fever
➤ Anaemia
➤ Nausea
➤ Headaches
➤ Muscle pain
➤ Shivering
➤ Sweating
➤ Enlarged spleen
TREATMENT:
Diagnosis:
➤ Microscopical analysis of blood
➤ Dip stick test for malaria antigens in blood
Treatment:
➤ Anti-malarial drugs
➤ E.g. quinine, chloroquine, artemisin
➤ Chloroquine inhibits protein synthesis and prevents parasite from spreading
within the body
➤ Proguanil inhibits sexual reproduction of plasmodium in the mosquito
➤ Combined therapy = where multiple drugs are used at the same time
➤ Used to prevent drug-resistance
PREVENTION:
➤ No vaccine for malaria
➤ 1. Use prophylactic / preventive drugs (e.g. chloroquine)
➤ 2. Reduce No. Of mosquitoes
➤ E.g. spray insecticides, spread oil over water surface to prevent mosquito
breeding, breed fish that feeds on larva, spray Bacillus thuringiensis bacteria to
kill mosquito larvae etc.
➤ 3. Prevention of bites (best method)
➤ e.g. use mosquito nets, soak mosquito nets in insecticide, most repellent, don’t
expose skin when mosquitoes are active at dusk etc.
INFLUENCING FACTORS:
Global distribution:
➤ Malaria is endemic in …
➤ Tropical areas
➤ Sub-tropical areas
Why:
➤ The vector, the Anopheles mosquito, survives and breeds in hot and humid areas
➤ Needs still / stagnant water to reproduce
➤ Plasmodium reproduces within the mosquito at >20 。C
➤ Eradicated outside tropics
Other problems:
➤ Drug-resistant plasmodium (e.g. chloroquine)
➤ Insecticide-resistant mosquitoes (e.g. DDT)
➤ DDT is the most common insecticide
➤ Insecticides used also killed other organisms
➤ Reduction in mosquito also caused lost in immunity to malaria in local
community, making them more vulnerable when the disease return
➤ Global warming has resulted in spread of mosquitoes
➤ More warm areas for mosquito to breed and survive
HIV/AIDS
RESPECITIVE PATHOGEN:
- virus
- human immunodeficiency virus (HIV)
structure:
➤ It is a RNA virus / retrovirus
➤ Contains single-stranded RNA as genetic material
➤ Has protein coat/capsid made of capsomeres
➤ Has outer viral envelope made of a lipid
➤ Bilayer and proteins (mostly derived from host)
➤ Has viral glycoproteins on the outer envelope
➤ Has 2 enzymes:
1. Reverse transcriptase uses RNA as template to produce
DNA in host cell
2. Protease: cleave/process new viral proteins
TRANSMISSION PROCESS:
1. The viral RNA and reverse transcriptase
(RT) enters T helper lymphocytes
2. RT converts RNA into DNA
3. The viral DNA is incorporated into the
host DNA
4. The cell’s machinery is used to express
viral proteins (through transcription and
translation)
5. Viral proteins are assembled into many
new viruses
- use of non-sterile syringe and medical tools
- pregnancy breastfeeding
- blood transfusion
- organ transplant
- unprotected sexual intercourse
SYMPTOMS AND EFFECTS:
* Acute infection: Flu-like symptoms (fever, sore throat, rash, swollen lymph nodes).
* Chronic infection: May be asymptomatic but gradually leads to immune system weakening.
* Symptomatic stage: Fever, fatigue, weight loss, recurrent infections, and diarrhea.
* AIDS: Severe immune suppression with opportunistic infections and cancers, extreme weight loss, and chronic illness.
Tuberculosis
RESPECITIVE PATHOGEN:
- bacteria
- Mycobacterium tuberculosis
TRANSMISSION PROCESS:
➤ Airborne droplets (M. Tuberculosis)
➤ The pathogens may survive for many months in the air and the dust of homes, due to the lipid-rich cell walls of the bacteria
➤ Undercooked meat and unpasteurized milk (M. Bovis)
➤ Fist infection site in human: lungs
➤ Can spread throughout the body and even the bone tissues
SYMPTOMS AND EFFECTS:
- A persistent cough, producing sputum (phlegm), with fatigue, loss of appetite, weight loss and fever
- Confirmation by a skin test, a chest X-ray and bacteriological test of sputum
- For patients with HIV/AIDS, TB is likely to be the cause of death
TREATMENT:
- A combination of antibiotics, particularly isoniazid and rifampicin, for at least 6 months
PREVENTION:
- BCG vaccination often protects younger people and is typically given to children and young adults at risk
Penicillin
In the absence of penicillin:
➤ Bacterial celll wall is made of peptidoglycan
➤ When bacterial cells grow, it secretes
autolysins
➤ Autolysins make tiny holes to allow the cell
wall to stretch
➤ New peptidoglycan formed
➤ Peptidase enzyme form cross-links between
peptidoglycan chains
➤ To form cell wall
In the presence of penicillin:
➤ Penicillin inhibits peptidase enzyme
➤ Stops formation of cross-links between peptidoglycan polymers in the cell wall
➤ Autolysins make tiny holes to allow the cell wall to stretch
➤ New peptidoglycan formed but cannot link up
➤ Cell wall is weaker
➤ Cell wall is unable to withstand turgor pressure
➤ When water moves in by osmosis, bacteria lyses and dies
➤ Penicillin is only effective when bacteria is growing
Antibiotics
➤ Antibiotics are drugs used
➤ Usually derived from microorganisms
➤ To kill / inhibit growth of bacteria
➤ Without harming the infected organism
➤ Bactericidal antibiotics - kill bacteria
➤ Bacteriostatic antibiotics - inhibit bacterial growth
➤ Prevent spread of bacteria within body
➤ Harmless to human cells
➤ Have NO effect on viruses
FUNCTION:
➤ Inhibit bacterial cell wall synthesis
➤ Inhibit activity of specific membrane protein /
glycoprotein ➡ block binding to cells
➤ Block specific enzyme action
➤ Inhibit protein synthesis and nucleic acid synthesis
➤ Target enzymes that bacteria have, but humans don’t
➤ Note: many different antibiotics each have different mechanisms
Antibiotic resistance
➤ When antibiotics are no longer effective against bacteria
➤ Antibiotic resistance can be spread from bacteria to bacteria
E.g.
➤ Many bacteria have penicillinase enzymes can break down penicillin
➤ Become resistant to penicillin
Caused by:
➤ Spontaneous / random mutation in bacteria
➤ Mutation cause change in protein / production of new protein that cannot targeted by antibiotics
➤ Natural selection enables resistance
genes to spread
➤ Antibiotic is the selection pressure
➤ Antibiotics only kill bacteria that are
non-resistant
➤ Resistant bacteria survive and
reproduce
➤ Antibiotic resistance gene is spread to
next generation and other bacteria
- *Antibiotic resistance genes are usually found in plasmids ! *
Bacteria can spread antibiotic resistance genes using:
➤ Vertical transmission
➤ Pass plasmids down to daughter cells by binary
fission
➤ Horizontal transmission
➤ Pass plasmids to other bacteria by conjugation
Causes:
➤ Due to patients not completing the
course of antibiotics given
➤ Treatment may not be completed so
some susceptible bacteria survives
➤ Bacteria replicates and have
increased chance of mutation /
becoming resistant
Solution:
➤ We need to discover more new antibiotics
➤ We can slightly alter / modify chemical
structure of known antibiotics to produce
new antibiotic
➤ BUT discovery takes time !
➤ The best solution is PREVENTION !
➤ Only use antibiotics when prescribed
➤ Always finish the course of antibiotics
Antibiotics against viruses
➤ Viruses do not have peptidoglycan cell wall, have protein
coat
➤ Viruses do not have their own metabolism, rely on host cells
➤ Viruses have no cell structure / very few organelles
➤ Very few sites for antibiotic to act on
➤ Viruses live inside host cells, out of reach of antibiotics
➤ Antivirals exist
➤ Usually target viral glycoproteins on viral envelope
➤ Prevent binding of virus to host cells
➤ Inhibit specific viral enzymes
