Aleena Zaidi & Jessica Wong
Notes for Thursday, October 27th
Readings: P.W. Ewald, Evolution of Infection Disease – Chapter 6 & 7
Speaker: Professor John Ebersole – Biology Dept.
Chapter Six – Attendant Born Transmission





Attendants (doctors and nurses) in hospitals as cultural vectors  carry pathogens from
patients to patients, without getting infected themselves
o Ex. Diarrheal disease in neonatal nurseries  newborns lack acquired immunity, highly
susceptible to infection
Pathogens present on the hands of doctors/nurses, but remain there even after hand-washing
 Bacteria evolve to becoming resistant to anti-bacterial disinfectants and even drugs!
o Ex. “Three-week preventative treatment of newborns with penicillin rapidly increased
the frequency of penicillin-resistant Staph bacteria from a minority to 100%”
Pathogens at home greatly reduced, less chance of being infected by others
Hypothesis – if attendant borne transmission increases virulence, the severity of infections
should increase as the extent of institutional transmission increases
o Tested and confirmed – when the outbreaks in nurseries lasted a short amount of time
(around one week), there were few deaths. When it lasted for weeks to months, one in
10 babies died.
Isolation periods, antibiotics, and the closing of infected wards helped terminate and control the
outbreaks
Note - This is very similar to what we encountered in the Defoe reading “Journal of the Plague Year”.
Victims of the plague, according to Defoe, were kept in isolation, with family members and house mates,
to prevent the spread of the disease. Similarly, in this reading, Ewald mentions the usefulness of closing
down infected wards with strict isolation period, along with antibiotics, as the only methods that proved
to effectively control and even terminate the vicious outbreaks. This section of the reading brought to
mind the dangerousness of hospitals, especially for newborns. As Defoe mentions, staying at home
when sick is more beneficial than travelling to a hospital. Perhaps this can be applied to newborns as
well? Traditional methods of birthing at home, rather than hospitals, safer?

Severity of infection linked with whether infecting organism infected the bloodstream
o Causes death in 1/3 – 1/2 of patients
o Most of these patients got these infections from hospitals…ex. “50 -98% of bloodstream
infections of pneumonia causing bacterium were acquired in hospital”
o A bacterium that causes a severe bloodstream infection in hospitals rarely causes severe
disease outside of hospital


Regular usage of antibiotics causes evolution of increased virulence…the pathogens changed to
become resistant to antibiotics…more and more bacterium are evolving resistance without a
subsequent increase in effective antibiotics…we can’t keep up.
Three-Pronged approach to solve this problem
o Hygienic Standards: many people(nurses and doctors) do not follow proper protocol of
hygiene…hand-washing, gloves etc. This needs to be improved.
 Ewald suggests increasing staff to patient ratio. – very important because more
staff to every patient means less attendant vector of transmission…nurses and
doctors have less patients to take care off, reducing the risk of passing on
pathogens to other patients
o Maternal Contact: stresses a sort of lack of hygiene when it comes to the contact
between mother and child…less hygienic measures are better because it gives the
mother a chance to pass on benign bacteria to the child…increasing acquired immunity
 Support breast feeding!
o Selective Antibiotic Usage: wide usage of antibiotics lead to the evolution of antibiotic
resistance leads to more dangerous pathogens...more virulent.
During this reading, I thought a lot about Florence Nightingale’s Notes on Nursing article, along
with Defoe’s Journal of the Plague Year. Nightingale, who presented staunch Anti-Contagion views, felt
that disinfectants were useless, and the leading cause of illness was poor caregiving by nurses and
doctors. This seems to echo what Ewald highlights in this chapter, to a degree. Of course, Ewald does
not deny the role of bacterium, but his views on hospital causing severe illness via attendant-borne
vectors, which are not seen to be as severe outside healthcare institutions, follow Nightingale’s theory.
In her Notes, Nightingale says, “The life duration of babies is the most delicate test of sanitary
conditions” (p.33). Eerily, resonating Ewalds chapter, as he uses the ill health of babies, must commonly
infected with life-threatening diarrheal diseases, passed on via nurses and doctors. I was also really
surprised at the types of numbers given supporting hospital and institution-borne diseases, and how
recent the data was, as recent as the mid-1980s!
Chapter 7 - War and Virulence

Use of microbes in war is not useful because they can be transmitted to human populations that
they were not intended for, they act slowly and can mutate. Example of bomb with anthrax set
off in Scotland with experimentation with sheep; 50 years later cannot go to this island r/t
dormant spores. if you won this land in war = useless!

Infectious disease killed more soldiers than warfare did. What are the possible effects of war on
the evolution of pathogen characteristics? Look into the influenza pandemic of 1918. The
conditions responsible for the extreme virulence of this influenza.
o
Sick individuals were moved between crowded rooms to crowded vehicles and vice
versa. This is considered a cultural vector because they allow transmission from an
immobilized person to susceptible people.
o
The hospital turnover rate for beds for influenza patients were extremely, high a 360
bed unit received and passed on 824 people per day. These rooms and beds could not
have cleaned effectively which would yield more disease.
o
When the ill were taken out of the trenches, new susceptible soldiers replaced them.
This would continue the cycle of transmission.

Conditions and activities at the western front were responsible for the enhanced virulence of
the 1918 pandemic - typically less than one death per 1000 infections. During the several
months just before and just after the end of the war, mortality per infection was 10X higher and
declined three years after the war, virulence gradually declined to normal levels.

Age distribution of 1918 pandemic - most lethal in young to middle aged adults, primary group
in which enhanced virulence evolved. Normally most lethal in very young and very old.

virulence in wars before the germ theory:
o
In the American civil war, the troops were densely packed into camps by the hundreds
and thousands for months without pure water and sanitation. Deaths related to
diarrhea cases. First year 4/1000, last year of the war 21/1000. To fix the situation a US
medical official James Tilton enacted decentralized care: heads of patients were spread
apart from one another with the fire bringing fresh air to the patients and relieving stale
air through the roof. Also called for burning of straw, washing of bedding and exposing
the bedding to sun --> reduced the potential for transmission by direct transmission and
air borne transmission. Decline in mortality after these interventions, and the high
lethality among doctors and nurses --> death not simply a result of soldier’s
compromised state of hygiene and stress but enhanced virulence of pathogens.
Ebersole Class 3 Notes:

HIV/AIDS- difficult exception to the rule that person to person contact is benign related to the
fact that the ease of transmission favors transmission. Ebersole used a diagram to show that
the perception of science at the time that AIDS was discovered was flawed. A low virulent strain
of HIV/AIDS does not cause transmission easily but does allow the host to live longer. A highly
virulent strain of HIV/AIDS with a high titer causes transmission in every partner exchange but
kills the host quickly. In this diagram the person with a low virulent strain of HIV/AIDS and a low
partner exchange rate caused more transmission than the highly virulent strain because the low
virulent strain did not kill its host as fast therefore that person had more time/opportunity to
infect more partners. This can be simply stated by saying with low partner exchange
transmission favors the low virulent strain. With high partner exchange, transmission favors the
highly virulent strain. However, this theory does not match up with the reality of AIDS since it is
ALWAYS highly virulent.

It is difficult to make a vaccine for the virus as it keeps changing its structure. HIV relies on
mutation to keep one step ahead of host and medical interventions. Mutation is a very
uncommon event, so increase the chance of mutation the virus replicates itself exponentially.

Adaptive virus creates nasty bugs- transmitted in hospitals by healthcare workers where there
are patients with compromised immunity leads to a vulnerable host and a large transmission
(hospital acquired infection –nosocomial).

Most people have had the flu but not many die from it. This was not the case during the 1918 flu
pandemic. Ewald comes up with idea related to ease of transmission (similar to AIDS
transmission). The poor health conditions in the trenches combined with the poor hygiene in
hospitals and of the transport vehicles increased the rate of transmission. The flu pandemic in
the civilian population can be traced back to when the troops evacuated from the front lines
and came home.

How to prevent highly virulent strain: hand washing is number one, decrease the number of
patients per nurse to decrease the chance of transmission with the nurse as the vehicle.
Major Themes and Points
Ease of transmission: Both Ewald and Ebersole bring this point up that it is the ease of transmission of a
virus that yields a “nasty bug”. In the case of the flu pandemic it was the unsanitary conditions that lead
to an increase ease of transmission from one soldier to another. When they soldiers returned home,
they spread the bug to those susceptible people in the population. In the case of AIDS the ease of
transmission determines the epidemic. As we learned from Ebersole AIDS is ALWAYS highly virulent
therefore if the person infected with the virus has a high partner exchange rate there is a great ease of
transmission. However, as the diagram showed if a virus is highly virulent and has a low partner
exchange rate, transmission is low because the virus kills the host before the virus can be passed on. It is
through prevention that the HIV/AIDS transmission can be cut down. As we read in previous articles, this
is easier said than done related to the vulnerability of the population, HIV/AIDS drug treatment costs,
and availability of health education classes. This idea also tends to exclude those who are already
infected.
Prevention of highly virulent strains: I thought it was very interesting the discussion at the end of the
class regarding prevention of nosocomial infections. Even with all the precautions that healthcare
workers take to protect the transmission of diseases to patients, there are still incidences. It would be
interesting to examine the factors that cause the transmission and the deficiencies in healthcare
precautions (such as shoe covers). Until we test out all hypothesis and understand the mechanisms of
how the pathogen function we cannot stop transmission. Similar to how smallpox spread through the
hospital by climbing the outside walls, did not understand this until experimenting with the smoke
machine.