Infectious disease Epidemics Flashcards
how do you define infection
Infection is the infiltration of body tissue by micro- organisms (or microbes) that may cause disease, followed by the multiplication of these micro-organisms
How do you define microorganism
A micro-organism that can cause disease is called a pathogen
How do you define contagious
- derived from the word contact and describes infections that are transmissible person to person and thus this can also be termed communicable
Whats another word for contagious
- Communicable
virtually all viral diseases are
virtually all viral diseases are caused by viruses that are communicable
How can you prevent trachoma
clean water and sanitation
What is the commonest cause of blindness
Trachoma
name the types of pathogens
- viruses
- bacteria
- fungi, protozoa, worms
What are the two types of pathogens
- opportunistic pathogens
- obligate pathogens
What is an opportunistic pathogen
Micro-organisms found in healthy host animals that may cause disease in certain circumstances, they take advantage of an “opportunity” not normally available
give examples of opportunistic pathogens
Commensals (staphylococcus, streptococcus)
describe opportunistic pathogens
- Cannot infect healthy people (nor do they need to)
- do so only when illness or injury introduces them to normally sterile parts of the body
- do not make infected people infectious to other healthy people
- do not cause epidemics
describe obligate pathogens
- have no reservoir
- must cause disease to be transmitted from one host to another
- organisms with no environmental reservoir
- do infect healthy people - they need to for their own survival
- make infected people infectious to others - need to for their survival
- introduced into a susceptible population and will spread from person to person and cause an epidemic
Name the animal sources of human pathogens
- measles
- smallpox
- coronavirus
- influenza
- tuberculosis
- herpes
- hepaitits B
- HIV
- ebola
- measles = dogs, cattle
- smallpox = cattle (cowpox)
- coronavirus = cattle, poultry
- influenza = chickens, swine
- tuberculosis = cattle (bovine TB)
- herpes = Monkeys
- hepaitits B = monkeys
- HIV = chimpanzees
- ebola = fruit bats
name some human pathogens that have derived from other human pathogens
- syphilis from bejel
- leprosy from TB
What has caused the pathogens to spread around the world
- human migration carried the organisms around the world
for organisms to survive in the short term what must it do
- cause mild symptoms that will propagate the organism to other humans
- not to kill humans or make them very ill
Why is it in the interests of the human to develop the symptoms (coughing & sneezing or diarrhoea?)
- To dump live organisms from the body (help out the immune system)
describe examples of conditions that spread by respiratory means
- Measles
- TB
- Influenza
What casues respriatory illnesses to spread
- sneezing
- coughing
- over-crowding
what illnesses spread by faecal-oral transmission
- polio
- H pylori
- rotavirus
- cholera
what casues spread of faecal oral transmission
- Poor sanitation
what illnesses spread by sexual transmission
- HPV
- Chlamydia
What casues illnesses to sprad by sexual tranmsission
- mutiple partners
- failure to use a condom
what illnesses spread by insect vector
- Malaria
- yellow fever
- lyme disease
What casues illnesses to spread by insect vector
- bare skin
what strategies do organisms use to survive in the long term
- continue to infect one susceptible person after another
- reinfect the same humans by changing its surface antigens so the IgG fails to recognise it
- find a safe haven in our body - area not accessed by the immune system
List organsims that find a safe haven
- Varicella
- Tubercle
- Helicobacter pylori
- typhoid fever
hygiene prevents
spread of the virus
What poeple get post-primary TB
Immunocompromised
- alcoholics
- homeless
- old men
what diseases are protective of malaria
- sickle cell disease
- thalassaemia
- cystic firbosis
What is the differnet between the epidemics and endemics
Epidemics
- goes through the community
- but after a few waves everyone has been infected and it will die out
Endemics
- infects people slow
- goes on for longer peroids of time
- matches the birth rate
organisms with no environemental reservoir must…
Organisms with no environmental reservoir must infect healthy people, and characteristically do so in epidemics rather than sporadically
What are the determinants of the risk of an outbreak in a community
- Susceptible population
- induction of organsims into community
- spread fo organisms in the community
Name the cholera statistics
- 4 million cases
- 100,000 deaths
What are the principles of management of cholera outbreaks
- Clean water - boiled, bottled or chlorinated
- beware of food washed in water
- safe disposal of faeces
what can increase the severity of the epidemic
- major epidemics of severe illness are generally caused by organisms that are new to the community
- age
- nutritional status
- infecting dose
List the major influenza outbreaks
- 1847 - H1N1
- 1889-90 - H2N2
- 1899-1900 - Russian - H3N2
- 1918-20 - Spanish - H1N1 - 40 million dead
- 1957-60 - Asian - H2N2
- 1968-72 - Hong Kong - H3N2
What is the survival rate of ebola
- 70% with good supportive care (especially IV fluids) but much lower in malnourished people wihtout good care
What organism called the bubonic plague
- Yersinia Pestis
- humans contract it from the bites of infected fleas, the fleas live in the fur of the rats
describe how EBV is differnet in children and adults
- commonly asymptomatic in children
- can be debilitating in teenagers and young adults (glandular fever)
- Contracting the infection in teenage/young adult years may lead to multiple sclerosis
the symtpoms that follow an infection…
The symptoms that follow an infection are often caused not directly by the organism but by the host response
- e.g. cytokines (host derived peptides released in response to a wide variety of stimuli)
Why is case severity greater on average during an epidemic that from sporadic cases
- because during an epidemic a person is oftne infected by two or more people so the infecting dose is greater
What cancers can HPV cause
- cervical cancer,
- anal cancer
What cancers can EBV cause
- nasopharyngeal cancer, - Burkitt’s lymphoma
- Hodgkin’s lymphoma
What cancer can HTLV cause
- T cell leukaemia
What cancer can cause Kaposi’s sarcoma virus and associated herpes virus
Kaposi’s sarcoma
What cancer can cause Helicobacter pylori
Stomach cancer
what cancer can schistosomiasis cause
- Bladder cancer
What cancer can hepatitis B and C cause
- Liver cancer
Why is there a higher incidence in developing countries of epidemics
- Poor sanitation
- Overcrowding
- Parasites (and mosquitoes) thrive in tropical climates
- Limited vaccination
Why is the case severity worse in developing countries
- Malnutrition
- overcrowding - high infection dose
- communal life style - infants under 1 year infected
- genetic factors in some areas
