Pathogens and Disease Flashcards
Disease
Any condition (other than a disability) in which the normal structure or function of the body are damaged or impaired
Infectious disease
It occurs when the above damage is the result of an infection by disease-causing micro organisms
Infection
Successful colonisation of a host by a M or parasite
-infections lead to disease when there is a deviation from the normal structure or functioning of the host as a result of the colonisation
Pathogens
M that can cause disease
-May be cellular (bacteria, parasites, fungi) or acellular (virus, viroids and prions)
Pathogenicity
The ability of a pathogen (P) to inflict damage on the host
Horizontal transmission
If a disease is communicable and spreads from one individual to another
contagiousness
The ease by which a pathogen spreads
-Largely directed by mode of transmission
E. Contagious
Measles or whooping cough (Bordetella pertussis) are transmitted via the respiratory route (via inhalation) and are therefore highly contagious whereas gonorrhoea is not as contagious as measle because it spreads via sexual transmission
surfaces of body that can be infected
Nose and Mouth
-Respiratory tract
-Alimentary tract (contaminated food)
-Urogenital tract
-Anus
-skin
-Capillary
-scratch/injury
-Conjuctiva
Respiratory tract transmission
Aerosols- tiny droplets of liquid containing the virus expelled by an infected individual by coughing, sneezing, etc- are inhaled by individual
Respiratory tract protection
Mucous blanket and cillary cells that line the nasal cavity and most of lower respiratory tract
Respiratory tract mechanism of defence against virus
Inhaled viral particles, deposited on this surface are trapped in mucus and carried by cillary action from the nasal cavity and airways to the pharynx and then swallowed
-Particles inhaled directly into the lungs may also be killed by alveolar macrophages
E. pathogens of respiratory tract
Mycobacterium tuberculosis
Streptococcus pneumonia
-pathogens may stay within the tract or move to other sites within the body
E. Conjunctival route
Ebola virus
Staphyloccus
Chlamydia trachomatis (via flies or human contact)
E. Oral/Faecal route
Vibrio cholera
Shigella
Salmonella
(both Eu and Pro use this route)
Route through skin
Pathogens can replicate in the skin to produce local lesions, after entry through minor abrasions or burns
-An efficient way pathogens are introduced through the skin is by the bite of an anthropod vector such as mosquito, tick or sandfly
E. Skin
HPV
Staphylococcus aureus
Pseudomonas aeruginosa
E. anthropod vector to skin
Yellow fever virus (mosquito)
Leishmaniasis (sand fly)
Lyme disease (tics)
Mechanical route
Injection of virus via dirty syringe, contaminated medical equipment (iatrogenic infections), puncture wounds from dirty objects
E. Sexually transmitted
HIV-1, HSV-2, Neisseria gonorrhoea, Syphilis
E. Urine
Lassa fever
-Haemorrhagic fever spread through human exposure to rat urine and droppings
Zoonosis
Animals to humans such as rabies
-You can still get vaccinated for rabbies after you are bitten because of the slow rate of establishment of virus
Plague
Infection cycle-Rabies
Inoculation by bite
Uptake into peripheral nerves
Spread to central nervous system
Massive viral repliaction in brain
-Spread to salivary glands, virus replication and excretion in saliva, clinical signs and death (infectious period)
Nosocomial diseases
-Diseases aquired in hospital settings
-P are spread via contaminated hospital equipment, bed sheets, poor hygiene
-often easily infect patients with poor immune systems or wounds from surgical procedures
-often antibiotic resistant
E. Nosocomial
Acinetobacter baumanii
Vertical transmission
transfer of a virus from mother to baby/foetus
-includes HIV-1, german measles (rubella) and syphilis
Noncommunicable infectious diseases
Not spread from person to person but diseases is rather contracted from infectious agent
E. Noncommunicable
tetanus by Clostridium tetani (spores)
Legionnaires disease caused by Legionella pneumophila
-The bacterium maintains a symbiotic relationship with amoeba in water sources (including water cooling systems like air conditioners) and it is contracted by inhaling the aerosol
Types of infections
Acute
Subclinical
persistent/chronic
latent
Slowly progressive
Acute infections
A sudden or rapid onset of disease which can be quickly resolved by robust innate immune responese by the host or may kill the host
-Influenza (kills old but not young)
-scarlet fever
Subclinical infection
An infection resultin in no detectable signs of disease, no symptoms, although infected individuals can be infectious
-HIV-1, Syphilis, Typhoid
Typhoid mechanism
Typhoid colonises gut and has high mortality rate (20%)
-In certain people (2%-5%), they carry the virus even after they have recovered and can spread it.
-Typhoid Mary had poor hygiene which caused her to infect others
Persistant/chronic infection
It is not cleared by host and remains active with hosts immune system
immune system keeps P in control
HCV and leprosy
Latent
A dormant or inactive viral infection that may become productive under appropriate conditions
-Varicella Zoster
-HSV 1,2
HIV-1
-Syphilis
Slowly progressive infection
A disease that ultimately causes irreversible damage to host
-HIV-1, syphilis or Lyme disease
Primary P
Causes disease in host, regardless of immune or health status
-Vibrio cholera
Opportunistic P
Causes disease in compromised host, where protective barriers, immune function or normal flora are sub-optimal or lacking
-Situations that compromise the host defences
-Clostridum difficile
Virulence
The degree to which an organism is pathogenic (how effective it is at causing disease)
-It is a continuuk ranging from harmless and only under exceptional conditions (lactobacillus) to almost always cause infection (Yersinia pestis)
-It also determines severity of disease as increased virulence results in greater disease severity and mortality
ID50
Median infectious dose
-It is the number of pathogen cells or virions required to cause active infection in 50% of inoculated animals
LD50
Median lethal dose
-It is the number of pathogen cells, virions or toxin required to kill in 50% of infected animals
LD50 and virulence
Highly virulent pathogens show little difference in number of cells needed to kill 100% to 50% as they are very successful at infecting and killing
-Moderate virulence leads to lineard trend of mortality rate
Attenuation
-The decrease or loss of virulence
-When P are kept in a lab culture rather than isolated from diseased animals, their virulence decreases or is lost as it does not need them to grow
-Attenuated strains are often used to make vaccines especially before RNA vaccines like Edmonston strain of measles or Sabin polio vaccine
Attenuation procedure
-Isolate virus from diseased patient
-Mulitple passages of virus are grown in non human host (primates)
-multiple passages of virus in mouse embryos
-multiple passages of virus in chicken embryos
-Final preperation of attenuated vaccine in fertilised chicken eggs
-Administration of vaccine to susceptible individual to elicit immune response without disease symptoms
Virulence steps
-Contact
-Adhesion
-Invasion
-Infection
The pathogen must gain entry to host, travel to loaction to establish an infection, evade or overcome host’s immune response and cause damage to host
-The cycle is completed when pathogen exists host and transmitted to new host
Virulence factors
Molecular tools that allow virulence to be successful
