CHAPTER 6: DISEASE CHALLENGES AND STRATEGIES Flashcards
what are infectious diseases
transmitted from person to person through the transfer of a pathogen such as bacteria, viruses, fungi or parasites
what are emerging diseases
a disease caused by a newly identified or previously unknown agent
what are re-emerging diseases
- a disease that reappears after a significant decline in its incidence
- re-emerging diseases were once controlled but have increased to a level that causes significant health issues
epidemic
- the widespread of an infectious disease in an area at a particular time
- cholera in Haiti (2010-present)
- ebola in west Africa (2013-2016)
pandemic
- the global outbreak of a disease
- widespread outbreak of a disease over a large geographical area
- an epidemic has become a pandemic once there are community-level outbreaks in at least two WHO regions
- eg COVID-19 6.28 million deaths → 0.08% of population
why living in a ‘globally connected world’ increases the likelihood of pandemics
- transport (planes)
- interact with more people from different communities
impact of European arrival on Indigenous Australians
- Australia is geographically isolated
- prior to European arrival, there was little interaction between Indigenous peoples and Europeans
- after settlement, they brought various new diseases and pathogens
- Major epidemic diseases were introduced
- smallpox, chicken pox, syphilis, tuberculosis, influenza
- indigenous populations had no immunity against them
- large numbers of susceptible individuals and low herd immunity
- the rapid spread of new infectious diseases and significant fatalities
what is in a vaccine
- vaccines are substances that cause an immune response without inducing the disease
- active, artificial immunity
- they can be pathogens that are:
- live attenuated - strain of pathogen that doesn’t cause the disease
- inactivated
- toxoid
- subunits
- they work because your body makes antibodies and memory cells
3 vaccines that are on the Australian vaccination schedule and the age at which they are given
- meningococcal ACWY - 12 months and 14-16yrs
- measles - 12 and 18 months
- HPV - 12-13 years
how vaccines provide long-term immunity
- Stimulate the immune system to produce memory cells
- These memory cells remain in lymphatic system and can initiate a stronger and more rapid immune response upon reinfection with the same specific antigen
why are boosters needed for some vaccines
- to retain a memory of the pathogen and maintain the concentration of antibodies
- killed/inactivated vaccines produce a weaker immune response than live attenuated vaccines so immunity lasts for a shorter period
- need booster for killed/inactivated vaccines to maintain immunity
- BOOSTER SHOTS HELP CREATE LONG TERM MEMORY BECAUSE IT INCREASES THE NUMBER OF MEMORY B CELLS
- This is because memory cells are short lived
why diseases such as Influenza need new vaccines each year
- the virus changes each year
- to keep up with the different strains of the virus
- target the antigens of the specific strain
- any previous vaccinations wouldn’t be effective against the new strains of virus because antigens are different
herd immunity
- indirect protection of populations from infection
- protection is created by the presence of immune individuals
- protection is received by unvaccinated individuals
- those who cannot be vaccinated (old, young, sick and immunocompromised)
- no vaccination - contagious disease spreads
- high vaccination - contagious disease contained (reducing the number of hosts that continue to transmit the pathogen) decreases the spread
- vaccines protect those who can’t be vaccinated
- reduces the number of incidences
95%
the percentage of a population that must be exposed to a disease or a vaccine to achieve herd immunity varies widely for different diseases.
reasons that prevent some people from being vaccinated
- they are immunocompromised
- access to hospitals/medical facitilities
- lack of education
- lack of accessibility to vaccines due to cost
- lack of medical staff who can deliver and administer vaccines
- lack of mandatory vaccination laws
identifying bacteria
- phenotypic methods:
- cell size/shape
- gram -/+
- aerobic/anaerobic
- immunological methods
- MAB
- ELISA
- immunofluorescence
- genotypic/molecular method
- sequence
- probes
identifying viruses
- physical methods
- X-ray crystallography
- electron microscopy
- immunological
- ELISA
- molecular
- probes
- fingerprinting
what is ELISA
- enzyme-linked immunosorbent assay
- wells are coated with an antigen specific to the disease being tested
- antibodies present in the sample bind to the antigen in the well
- the wells are then washed to remove any unbound antibodies
- new different conjugated antibodies are added to each well → the antibody also has an associated enzyme indicator
- the substrate for the enzyme is added leading to colour change if an antigen-antibody complex is formed → indicates a positive test
identify the host and mode of transmission
- the reservoir of a pathogen is the habitat in which it lives, grows and multiplies
- host - an organism that can get the disease
- zoonotic diseases are infectious diseases that are transmitted from animals to humans
- pathogens can spread via
- direct contact - touch, air, droplets, swapping fluids
- indirect contact - aerosol, surfaces, food/water, host animals
- vectors
control measures to prevent spread of disease
- prevention: clean water, wash hands, safe sex
- vaccination: reduce the number of hosts, long-term immunity
- medication: treat people to reduce transmission
- surveillance: monitor outbreaks
- modification of environment: drain ponds, mosquito nets (vector control)
- improving infection control standards: sterilisation of surfaces/objects, mask, quarantine
antibiotics
- antibiotics treat bacterial infection
- role: inhibit the growth of or kill bacteria
- action
- penicillin inhibits cell wall synthesis in bacteria and so targets actively reproducing bacteria. Since human cells do not have cell walls, penicillin does not attack human cells and so has low toxicity
- chloramphenicol, erythromycin, tetracyclines and streptomycin inhibit protein synthesis by acting on the ribosomes of prokaryotic cells.
- sulfanilamide acts as an antimetabolite by competitively inhibiting enzyme activity in bacteria.
- rifampin and quinolones inhibit nucleic acid synthesis.
- injury to plasma membrane
action of viruses
viruses need to be able to :
- find and attach to host cells
- get through plasma membrane
- take over host DNA and replicate by getting into nucleus, insert their DNA
- get out
antivirals
- act only on viruses actively replicating
- mode of action
- block entry of the virus into host cells
- block fusion of the virus with host cell
- block uncoating
- prevent replication of the viral genome
- prevent the release of new viruses
- stimulate the host immune system
sensitivity test
carried out to determine the antibiotic that would be most effective to treat a bacterial infection
why are antibiotics not effective in treating viral infections
antibiotics are a useful treatment against bacterial diseases because:
- antibiotics inhibit the reproduction of bacteria/cell wall synthesis/protein synthesis
- but viruses do not have cellular structures as they are not cellular
- and viruses are reproduced by a host cell
immunotherapy
- designed to target specific cells + allow the immune system to target the specific cells/components of the body that are causing disease
- the use of monoclonal antibodies for the treatment of autoimmune diseases and cancer
monoclonal antibodies (MAbs)
- artificially produced antibodies that bind to ONE SPECIFIC type of antigen
- produced in the laboratory by stimulating the production of B lymphocytes in mice injected w/ a specific type of antigen
monoclonal antibodies may stimulate, suppress or have no effect on the immune response.
how are monoclonal antibodies made
- a mouse is injected with an antigen
- this activates the production of its B cells, which produce antibodies against the antigen
- the spleen of the mouse is removed, placed in a culture medium and its cells are separated.
- B cells fuse with tumour cells to form new cells called hybridomas
- hybridoma cells divide repeatedly and multiple identical copies of each individual hybridoma cell are produced.
- clones are screened for the presence of the required antibody so that clones of cells that produce antibodies against antigen X are identified.
- required antibodies against the antigen can be harvested
PLASMA CELLS ARE SHORT LIVED WHILE MYELOMA CELLS (TUMOUR CELLS) ARE IMMORTAL
what is cancer
- uncontrollable growth (passes the checkpoints)
- use blood vessels to provide blood w nutrients and O2
- can spread (metastasis)
action of MAbs
- blocks the growth of blood vessels to a tumour
- attach to the cancer cell to stimulate its destruction by immune cells
- block signals for cell reproduction/growth
- take chemicals (w/ chemotherapy or for drugs) directly to cancer
how does MAbs stop the growth of new blood vessels to cancers
- cancer cell needs nutrients and oxygen
- without a direct blood supply → cannot grow beyond 2mm
- cancer cells release hormones to trigger the growth of new vessels
- vessels allow cancer to grow and spread
- MAb binds to the hormone released by the cancer cell → stops growth of new vessels
how does MAbs block signals for cell division
- when growth factors bind to receptors on cancer cells → produces a signal for the cancer cell to divide
- healthy tissue has normal cell replacement
- some cancer cells have receptors that are overexpressed
- increased signalling that directs cancer cells to divide uncontrollably
- MAb (Herceptin) binds to these receptors, blocking them from receiving signals from growth factors
- slow/no growth of cancer cells
how does MAbs deliver anticancer/radioisotopes
- MAb join with a chemotherapy drug and deliver the cancer-killing drug directly to the target antigen on particular cancer cells
- MAb binds to the radioisotope particle and delivers it to cancer cells
- antibody and antigen link cause the radioisotope to emit radiation destroying the cancer cells
how does MAbs signal immune cells to attack cancers
- some MAbs bind to antigens on cancer cells
- act as markers that attract immune cells to attack cancer cells
- eg. Campath → treatment of leukaemia white blood cell cancer
what is an autoimmune disease
- when the body’s immune system attacks its own cells
- produces autoantibodies
- these attack own cells
- T and/or B cells are inappropriately activated
- eg. type 1 diabetes, multiple sclerosis
how monoclonal antibodies can be used to treat autoimmune diseases
- as autoimmune diseases are caused by the immune system overreacting, MABs aim to reduce the immune response
- attach to cytokines to prevent cell signalling and activation
- attach to T cells, stopping them from getting into the brain/spinal cord and attacking the myelin sheath
- bind to IgE to prevent allergies
- directing antibodies against major histocompatibility antigens (MHC markers) to prevent them from triggering an autoimmune response
- can possibly stop autoimmunity by using monoclonal antibodies to block certain MHC II antigens
why identifying host and resovoir is important for controlling spread of disease
- transmission occurs when a pathogen leaves its reservoir (habitat) or host (organism that can be infected) and enters a susceptible host
- by identifying these areas, preventative measures can be placed to control the spread
advantages/disadvantages of herd immunity
Advantages
- protects vulnerable individuals who cannot be vaccinated
- reduces the spread of diseases
Disadvantages
- relies on very high vaccination rates (difficult for poor countries to achieve)
advantages/disadvantages of mAbs
Advantages
- highly specific (only binds to specific antigens and does not affect healthy cells)
- can be standardised world-wide
- high consistency among experiments
Disadvantages
- high cost of production
- limited availability
- potential side effects
scientific vs social strategies
- scientific strategies act to reduce or stop transmission of an infection and to develop treatments to control or eliminate the pathogen.
- social strategies are strategies that support the scientific effort to reduce and control the spread of a pathogen in a population.
virulent
virulent: the severity of the disease caused by the pathogen
why is correct identification of viral pathogen important in the control of a disease
- help identify medication effective in treating pathogen
- help identify methods of transmission so preventative measures can be put in place
- help development of a vaccine (antigen can be isolated)
