8.3 Spreading It

Diseases 8.3

8.3 Spreading It

Learning Outcomes:
6. Describe how infectious diseases spread.
For today: Watch the 5 min video Cholera: domesticating disease
http://www.pbs.org/wgbh/evolution/library/10/4/l_104_01.html

Readings for next week: Chapter 5: 109-130, Reading Quiz due Monday Nov 2

Antibiotics
Natural antibiotics are produced by different strains of fungi against certain bacteria. Fungi
secrete a chemical which targets a structure or process unique to bacterial cells. In this way
bacteria are killed but not fungi. Man-made antibiotics also exist, which target processes or cell
structures found in the pathogen but not shared by the host.

QUESTION: Although there are some antibiotics
against protists like Giardia lamblia and Trichomonas
vaginalis, it is generally harder to find antibiotics
against protists and there is often a greater chance
that some of these antibiotics may make people sick.
Considering what you know about protist cells
why might this be
Giardia lamblia Trichomonas vaginalis
http://www.biotech- http://www.uthscsa.edu/missio
weblog.com/50226711/giardia_l n/spring00/std.htm
amblia_genome_sequenced.php
Some strains of pathogenic bacteria are able to “fight back” by producing toxins.
These toxins can be found attached on the outside of the pathogen and act locally at the sight
of the bacterial infection or some strains secrete toxins which travel through the blood stream
of the host and can target cells far from the site of the initial bacterial infection.
How do toxins make the host sick? Like antibiotics they target processes or cellular structures
found in the host but absent from the pathogen. Examples:
diphtheria toxin –stops protein synthesis in Eukaryotes, killing cells
cholera toxin – specific to cells lining the intestine, it causes these cells to keep their chloride
ion channels open so that intestinal cells secrete chloride ions and water into the lumen of the
intestine causing dehydration and diarrhea.
tetanus toxin –prevents some nerve cells from transmitting signals to muscles resulting in a
type of spastic paralysis.
QUESTION: What natural toxin produced by dinoflagellates have we discussed before? What
does it target that will have no effect on dinoflagellates?

Neurotoxin – paralysis. (dinofagellates cause red tide)

Diseases 8.3

Influenza – a deadly disease
During World War I a new strain of
flu virus infected troops in the
trenches of the battle fields.

These individuals were quickly
moved into hospitals where most
patients had weak or compromised
immune systems.

The flu spread quickly through
hospitals into battle fields and into
the general public.

The pathogen was transmitted across the oceans as troops returned home. In the UK 280,000 died
while in the US 600,000 died. Over 40 million died world wide (8 million in Spain alone, hence the
frequent reference to this outbreak as the Spanish flu). Since that time the flu has been one of the most
well studied diseases in the world.
How do you know if you have H1N1?
a. You have a runny nose and are sneezing
b. You have a fever and your body aches
c. Your feel very tired and lethargic
d. You have a runny nose, sneezing, a sore throat but no fever
e. You have a fever, body aches and feel tired and lethargic

How do you know your condition is not a cold?
Cold causing adenoviruses are specialized to attach to the epithelial cells of the respiratory tract.
The symptoms differ from H1N1 in that….
No fever, runny nose, headache, possible coughing

Epidemiology is the study of the transmission, frequency or prevalence of a disease through
a population. Epidemiology is the foundation of public health where officials are charged with
identifying outbreaks and occurrences of diseases and enforcing containment of contagious
diseases by quarantine. They investigate and identify the agents of transfer and either remove
or limit the effectiveness of the agents.

Epidemics are higher than normal incidence of the disease and may be localized where as
pandemics are worldwide e.g., the Flu pandemic of 1918.

Undetected transmission of pathogens
Airborne pathogens such as droplets from the nose and mouth are transmitted by coughing and
sneezing. Alternately the pathogen may be transmitted through direct or close contact (< 1 m)
or transferred from surfaces (your hands pick up pathogens from door knobs etc.)

Diseases 8.3

Evaluate your behaviour: Do you sneeze or cough into your sleeve or shoulder? Vs. Sneezing into
your hand (used to touch other surfaces) When you sniff do you wipe your nose with a tissue? Do you
reuse the tissue? Where do you dispose of it? OR Do you rub your hand under your nose?
How often do you wash your hands? After you get off of transit where you held onto poles and straps
held by others? After you come in from outside when handling door handles? Do you wash your hands
thoroughly when you go to the bathroom?
SURVEY: How many times a day do you wash your hands?
a. 0-3 times
b. 4-8 times
c. 9-12 times
d. Only 3 or 4 hand washes, but plenty of sanitizer
e. other

Following transmission the pathogen must pass through the skin or lining of respiratory system
to infect bodily tissues where they begin to grow and reproduce. The incubation period
where the individual is infected but shows no symptoms varies among pathogens and the
vigor of the host’s immune system. (~24 hours for H1N1) The symptoms of the disease may be
caused directly by the pathogens (effect of toxins) or by your body’s response to the pathogens.
An individual may not show symptoms until such time as the pathogen has increased sufficiently
to illicit an effect on the immune system. The infected individuals can be carriers and capable
of infecting others that they contact.

A fine balance: Pathogens have a special interaction with the host. They depend on the
host for survival and reproduction, but if they kill the host then their ability to spread decreases.
How likely are pathogens of different levels of virulence to be transmitted, to spread?

from: http://evolution.berkeley.edu/evolibrary/news/071201_adenovirus

Virulence is the FYI: The H1N1 virus can survive on hard surfaces (eg door knobs)
extent of microorganisms for 24-48 hrs., on soft surfaces (eg towel) for 15 min. and on
to cause disease or the hands for 5 min. Dried secretions on hands can be transmitted to
severity of a pathogen the eyes, nose and mouth (How often do you touch your face?)
e.g., Imagine Influenza A is highly virulent while type C is mild.

Diseases 8.3
A highly virulent strain or type of flu (Flu A) will be quick to infect, with a short incubation period and
therefore the host immune system has little time to respond. These infections are often fatal.

An infection of medium virulence (Flu B) may develop over 3 to 10 days before the symptoms become
apparent. The immune system is actively combating the pathogen.

A pathogen with low virulence (Flu C) induces mild symptoms or they many not be noticeable. The
pathogen has a slow rate of production and is a feasible strategy for infecting long-lived hosts.

Is there an "optimal virulence”? Watch the 5 min video with Dr. Paul Ewald.
http://www.pbs.org/wgbh/evolution/library/10/4/l_104_01.html

QUESTION: After watching the video and considering how influenza is transmitted, how
‘optimal’ is the virulence of H1N1?

Why do we keep getting colds and influenzas?
The genetic material from different strains of viruses can recombine to produce new strains. The new
combination of genetic information results in the production of new surface proteins that the human
immune system has never encountered and doesn’t recognize. This can occur where humans live closely
with other animals such as ducks, pigs and chicken that harbour strains of viruses (antigenic variation
occurs between different species). Humans have no immediate antibody protection to these new strains
and depending on the virulence of the pathogen this can lead to epidemics (e.g., SARS and H1N1).

For influenza (H_N_) the various strains are named depending on what variant they have of the
hemaggluttinin protein (H_) and what variant they have of the neuraminadase protein (N_)
Different strains are adapted to attach to receptors on cells of the respiratory tract of specific animals.
Pigs happen to have both the human type receptors and the avian (bird) type receptors. This means
that in a pig, viruses from swine (pigs), birds and humans can all recombine into a new form, which is
what happened for H1N1. It is a triply recombined virus made from two different swine viruses, one bird
virus and one human virus. Fortunately since it appeared last spring it has not seemed to have
undergone much further mutation. This is good news because the form of the H1N1 virus for the vaccine
was chosen in June. It takes 4-5 months to grow the virus inside fertilized chicken eggs and 3 more
months to test it. During this time it is possible for the virus to mutate so that vaccine is not as effective.
This has not happened.

Diseases 8.3

For Your Information: For Your Information: Adjuvants
Plain formulations of vaccine are only moderately effective against seasonal flu viruses
(60-70% effective). For H1N1 there was concern that individuals would require two doses of
this regular formulation for it to be effective and we would not be able to produce enough.
Adjuvants are immune boosters that cause a faster stronger response while allowing less
antigen (dead virus particles) to be used. Different types of adjuvants have been used for
many vaccines in the past such as all the shots you had in childhood. In order for people to
only need one dose of the H1N1 vaccine it was decide to add adjuvants. The type of
adjuvant added to the H1N1 vaccine in Canada has already been used for the last 10 years
in Europe on over 25 million people. This particular adjuvant contains:
-squalene, a natural component of human blood cell membranes and a precursor of
cholesterol and vitamin D
-alpha tocopherol (vitamin E) 1/3rd of your daily recommended intake
-polysorbate, a detergent which emulsifies oils
When mixed together this adjuvant makes oil droplets which, when injected, cause a local
tissue reaction. They cause macrophages to gather up the viral antigens, travel to the lymph
nodes and present the antigens to the B and T cells to allow them to respond. The response
caused by the adjuvant at the site of injection is short-lived because the oil droplets dissolve.
However, by causing the macrophages to bring the antigens to the immune cells the
antibody production is fast and strong. Occasionally there is a little redness and swelling at
the site of injection for 1-2 days. There has never been any auto-immune response
observed.
In the Canada adjuvanted vaccine is being distributed to all people except to pregnant
women in their last trimester. Those women are getting unadjuvanted vaccine because
although the adjuvant is believed to be safe based on a large dataset, there is even more
data (25 years worth) that unadjuvanted vaccine has never harmed pregnant women.
In the US, unadjuvanted vaccine is being distributed (60-70% effective remember). Doctors
believe the Canadian adjuvanted vaccine will be more effective.

Diseases 8.3

National Institute of Allergy and Infectious Diseases

The Center for Disease Control and Prevention (CDC) the World Health Organization (WHO)
track contagious diseases such as the influenza virus. With systematic surveillance and
reporting of local outbreaks they develop models of disease transmission and virulence. They
promote means of containing the disease and make recommendations for specific vaccine
components. The small changes in the regular flu viruses from year to year are called
antigenic drift (eg small changes in last year’s virus H3N2). When we get a large change
(whole new strain like H1N1) where very few have immunity it is called an antigenic shift.

When no one has immunity to a new strain, epidemiologists expect at least 50% of the
population to become infected. Depending on the virulence of the strain between one third to
two thirds of those infected will become sick. A conservative estimate of approximately 25% of
the whole population will become ill, most of which would require hospitalization. The most

Diseases 8.3
susceptible to the strain would be individuals that have chronic conditions, the very young, the
very old and those with weak immune systems. The seasonal flu kills 700 to 2500 people per
year in Canada. The greatest cause of seasonal flu-related deaths is due to pneumonia. The
bacterium invades after the flu depletes and weakens the body’s defense mechanism and
significantly decreases the chances of patient survival.

Epidemiologists have closely examined the data on who got H1N1 in Australia and New Zealand,
which have just finished their winter flu season and had no vaccine. They saw that more males
were hospitalized. The largest number of cases by far were in 0-4 year olds. There were also
twice as many cases as usual in 18-30 yr olds and 30-50 year olds. The normal seasonal flu
usually most strongly affects small children and the elderly. Because a variety of H1N1 existed
before 1957, people born before that time that had the flu are protected against H1N1. Based
on the data in the southern hemisphere we expect 8-10 deaths in BC, 130 hospitalizations (with
the largest group being children under 5) and we expect 5-6 patients in the ICU per week.

Question: Researchers predict a lower number of deaths from the flu this year compared to
the regular seasonal flu. Why?
The most susceptible to becoming very sick (the elderly) have some degree of immunity.

Question (asked by one of Wed. nights H1N1 seminar attendee’s): “Why should a healthy 55
year old woman who never gets the seasonal flu vaccine and never gets sick with seasonal flu
bother getting the H1N1 vaccine?” If you were the doctor what would you say?

Create your own pandemic at this website: http://www.awfulgames.com/games/pandemic/

How do we stop epidemics?
Preventative measures include: Washing hands frequently
Ensuring clean water supply
Ensuring proper food preparation

Medical treatments include: Vaccines (for some viruses)
Antiviral drugs (Tamaflu and Relenza)
Antibiotics, will kill bacterial pathogens only

Non-pharmaceutical treatments: Washing hands, masks
Social distancing – avoid close person to person contact
(ban public gatherings, shut down mass transit, close schools)
Contain and quarantine all outbreaks of contagious diseases

Question: Will you get vaccinated against H1N1? Why or why not?

Question: What is the most likely reason we get sick when the virus mutates?
a. We do not have a large pool 78 of memory cells and antibodies which
recognize the new shapes

Diseases 8.3
b. The new shape of the hemagluttinin allows the virus to bind more easily to cells of our
respitory tract
c. The new shape of the hemagluttinin allows it to more easily transfer it’s genetic material
into cells

8.3 Spreading It

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