TOPIC 7 – INFECTIOUS DISEASES
VOCABULARY
infectious disease: a disease in which pathogens invade a susceptible host and carry out at least
part of their life cycle in the host
infection: the growth of microorganisms in the body
pathology: the scientific study of disease, concerned with etiology (cause), pathogenesis (how a
disease develops), and structural changes caused by disease
epidemiology: study of when and where diseases occur, and how they are transmitted
communicable: spread from person to person (ex. Ebola)
contagious: easily spread (ex. Flu)
sporadic: occurs occasionally in a population (ex. tetanus)
endemic: always present in a certain population (ex. chicken pox)
epidemic: acquired by many people in a given area in a short time period (ex. measles)
pandemic: world-wide epidemic (ex. Coronavirus)
DISEASES CAN BE
acute: develops rapidly; lasts a short time (ex. appendicitis)
chronic: develops slowly; lasts a long time (ex. diabetes)
primary infection: acute infection causing initial illness (ex. viruses)
secondary infection: a second infection that occurs when host’s defences weakened (ex. yeast
infection after taking antibiotics)
TRANSMISSION OF DISEASES
1.
-
contract transmission
direct: person-to-person transmission
indirect: fomites, objects
droplet transmission
2.
3.
-
vehicle transmission
water, air, food
vectors
compromised host, microorganisms, invasive procedures, antibiotics and resistance
THE STAGES OF A DISEASE
1. incubation period – the time period between actual infection and first appearance of
signs and symptoms
2. prodromal period – time following incubation period when first signs and symptoms
appear
3. period of illness – disease most severe, overt signs and symptoms
4. period of decline
5. period of convalescence
BACTERIA
-
classified into 2 large groups depending on the cell wall structure
gram-positive and gram-negative
colour bacteria appear under microscope after the gram staining procedure that uses a
purple then a pink stain
used for identification and susceptibility to antibiotics
gram-positives look purple under the microscope after gram staining (thicker
peptidoglycan and penicillin)
gram-negatives pink under microscope after gram staining (outer membrane has
lipopolysaccharide and endotoxin)
virulence: how likely it is that a pathogen will make a person seriously ill
1.
2.
3.
4.
5.
pathogens have special properties that allow them to cause disease
there are 5 steps in microbial disease production
get inside the human body
attach
evade defences
multiply
damage
STEPS IN DISEASE PRODUCTION
1. getting inside
- portals of entry (mucous membranes, respiratory tract, gastrointestinal tract,
genitourinary tract, and conjunctiva)
- parenteral route (ex. bites, injections, wounds)
2.
-
attachment or adherence
pathogens have surface projections adhesions, that enable attachment/adherence
adhere to receptors (ex. fimbriae, spikes)
pathogens have a preference for cells in particular areas of the body (ex. gonorrhea
causing bacteria: urogenital epithelia)
3. evading host defences
- some bacteria have capsules to evade phagocytosis
- some bacteria can survive phagocytosis
- some produce enzymes (ex. IgA proteases)
- change surface antigens
- viruses grow inside cells
4. multiply
- once inside the body
- bacteria find nutrients and can reproduce
- may remain localized or spread to lymph vessels or blood and then to other parts of the
body
- viruses enter cells and reproduce
5. damage
- some bacteria produce toxins
- exotoxins (proteins, many are enzymes): damage host cells membranes, interfere with
protein synthesis, some produce neurotoxins, some produce enterotoxins that disrupt
cell fluid and electrolyte balance
- endotoxins lipid A of LPS (gram-negatives) cause: fever and shock
- infection of a host cell by a virus usually kills the host cell
DISEASES
BOTULINUM
-
clostridium botulinum produces an aextremely potent toxin
causes flaccid paralysis (muscles cannot contract)
death can occur from respiratory failure
the most potent biological toxins known
TETANUS
-
clostridium tetani
neurotoxin but blocks muscle relaxation (lockjaw)
clean wound, passive immunity, active immunization
STREP THROAT
-
streptococcal pharyngitis caused by streptococcus pyogenes
gram positive cocci
-
group A strep
transmitted by respiratory secretions
pharyngitis: local inflammation, red, sore throat, fever
lymph nodes swollen
pus-containing abscesses on tonsils
antibiotics
PNEUMONIA
-
the lungs become inflamed because of an infection
many cases caused by streptococcus pneumoniae
gram positive cocci
circular bacteria in pairs and capsule protects it from phagocytosis
bacteria infect bronchi and alveoli, alveoli fill with RBCs, leukocytes, and fluid
impairing exchange of oxygen and carbon dioxide
signs/symptoms include high fever, chills, breathing difficulty, chest pain, cough, blood in
sputum
treated with antibiotics
BACTERIAL MENINGITIS
-
inflammation of the meninges
3 membranes that cover and protect the CNS (brain and spinal cord)
between pia and arachnoid membranes is the subarachnoid space that contains
cerebrospinal fluid
if CSF becomes infected, meninges become inflamed
caused by several bacteria including Neisseria meningitidis
also called meningococcus
a gram-negative coccus that has a capsule to evade phagocytosis
bacteria spread by respiratory droplets and colonizes the nasopharynx
starts as a throat infection, blood invaded, and then CSF
signs are sore throat, fever, headache, stiff neck, sensitivity to light, nausea, rash
spinal tap
treated with antibiotics
GONORRHEA
-
STD caused by bacteria called Neisseria gonorrhoeae
gonococcus, gram negative, small
attaches to columnar epithelium and invades spaces between epithelial cells
inflammation, leukocytes move in, pus formation
males experience painful urination and discharge of pus from the urethra
females experience burning during urination and vaginal discharge
50% of women are asymptomatic as gonococci cannot attach to vaginal cells
-
can cause pelvic inflammatory disease which can lead to scarring of the uterine tubes,
ectopic pregnancies, and sterility
treated with antibiotics but, many strains are not antibiotic-resistant
LYME DISEASE
-
caused by spirochete bacterium called borrelia burgdorferi
mice, birds are reservoir
spread by bite of infected ticks
in the first phase some people have an expanding rash at the bite site
causes fever, chills, fatigue, headache, muscle, joint pains
second phase causes irregular heartbeat, facial paralysis, meningitis, encephalitis,
extreme fatigue, and memory loss
third phase is months or year later and causes arthritis
diagnosis includes signs and symptoms
treatment is antibiotics
VIRUSES
1.
2.
3.
4.
5.
-
attachment
entry and uncoating
synthesis
assembly
release
avoid host immune system by growing inside cells
cause cell damage and cell death
THE COMMON COLD
-
the common cold and “the flu” are different diseases caused by different viruses
over 200 viruses cause colds (no vaccine)
aerosols, coughing, sneezing, formites, hand-to-hand contact, touching the mucous
membranes of the nostrils and eyes
remain infective for hours
attach to cells in nasal mucosa and replicate, then kill cells
infected cells lose ciliary action and slough off
inflammation blocks nasal cavities, resulting in congestion
hand washing is probably the most effective means of prevention
antihistamines, decongestants, pain relivers, fluids, rest, relieve symptoms,, and allow
body to mount an immune response
INFLUENZA (FLU)
-
caused by influenza virus
-
8 pieces of RNA
protein capsid
envelope with HA and NA spikes, HA help with attachment (hemagglutinin), NA spikes
help viruses exit (neuraminidase)
enters body via respiratory tract and infects epithelial cells of lungs
replicates
causes chills, fever, headache, general muscular aches, coughing
susceptible to secondary bacterial infections
HA and NA spikes are glycoproteins and viral strains are identified by antigenic
differences in NA and NA spikes (ex. H1, N2, H3, N1, N2)
we make antibodies to Ha and NA but RNA viruses are prone to mutating
viruses undergo minor changes in genes (antigenic drift), so need new vaccines every
year
can get major genetic recombination between strands (antigenic shift)
CORONA VIRUSES
-
can cause the “common cold”
2003: SARS-CoV (severe acute respiratory syndrome corona virus)
fever, headache, malaise, muscle aches, cough, difficulty breathing
2012: MERS-CoV (arabian peninsula)
both zoonotic viruses where viruses mutate and spread to humans
2019: SARS-CoV-2 (COVID-19)
enveloped RNA virus, spike S protein promotes attachment
transmitted by respiratory droplets from coughs, sneeze
incubation period usually 4-5 days, but can be 2-14
signs and symptoms include respiratory symptoms, fever, cough, difficulty breathing,
shortness of breath, pneumonia
PROTECTING OURSELVES
-
wash hands frequently or use alcohol-based hand gel
avoid touching nose, mouth, eyes
practice respiratory hygiene
avoid casual contact (shaking hands, kissing as greeting)
social distancing
arriving from outside Canada? isolate for 14 days
if fever develops, cough, or difficulty breathing seek medical attention and call 811
HUMAN PAPILLOMAVIRUSES (HPV)
-
causes papillomas, benign growths of epithelium of skin and mucous membranes
commonly known as warts
100 types and 40 types are transmitted through sexual activity
-
incubation period of weeks or months
warts in genital area, some smooth or flat, some large
connection to certain cancers
most cancers attributed to HPV types 16 and 18
cancers: cervix, penis, anus, mouth, and throat
3 vaccines in Canada
2-valent (Cervarix) females
4-valent (Gardasil) males and females
9-valent (Gardasil 9) males and females