Bio171-F08-lec38 - Biology 171 Lecture 38: Friday December...

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Unformatted text preview: Biology 171 Lecture 38: Friday December 5, 2008 Today’s Topic: Emerging Infectious Diseases Human
Disease:
Transmission
Modes
 Human‐Human
–
tuberculosis,
HIV/AIDS
 Water‐borne
‐
cholera
 Vector‐borne
diseases
 


human
only
–
dengue
fever
 


zoonotic
diseases:
 


West
Nile
fever,
Lyme
disease

 Announcements Course Evaluations online Final Exam Tues. Dec 16 7-9PM – covers lectures 30-39 & last 3 discussions Review Sun. Dec 14 4-6PM - 1800 Chem Text Reading Lec.
38:
none
 Lec.
39:
none
 The
phrase
‘emerging
infectious
diseases’
was
coined
by
Nobel
Prize

 winner
Joshua
Lederberg.
It
is
applied
to
infections
that
newly

 appear
in
a
population,
or
have
existed
but
are
increasing
in

 incidence
or
geographic
range.
 Throughout
history,
disease
causing
pathogens
and
 parasites
have
acted
as
selective
pressures
on
 human
populations.
In
14th
century
Europe,
plague,
 caused
by
the
bacterium
Yersinia
pestis,
and

 transmitted
by
fleas,
killed
one‐third
of
the
 population.
 Yersinia
pestis
 Rat
flea,
 Xenopsylla
cheopis
 The
field
of
Epidemiology
is
the
study
of
disease
 transmission
through
human
populations.
 Human
diseases
are
transmitted
via
several
modes:
 1.  Directly
from
person
to
person
 2.  Via
inanimate
objects

 






(e.g.
food
or
water)
 3.


Via
animal
vectors
 Reservoirs
of
disease
 An
Anthroponosis
is
a
disease
that
affects
only
humans
 e.g.
smallpox,
malaria
 A
Zoonosis
is
a
disease
that
has
animal
reservoirs
 e.g.
Lyme
disease,
Ebola
hemorrhagic
fever
 Tuberculosis
 Tuberculosis is a bacterial infection caused by Mycobacterium tuberculosis that affects mainly humans (animal reservoirs are rare) . Throughout history, tuberculosis has killed millions of people. TB kills between 2 and 3 million people each year and is the leading cause of death among young adults and a major cause of death among women of childbearing age. Tuberculosis
 Perhaps
the
most
alarming
aspect
of
the
present
epidemic
is
the
rise
in
multidrug‐resistant

 TB
(MDR‐TB).
According
to
a
survey
conducted
by
the
WHO,
up
to
four
percent
of
all
TB
 cases
worldwide
are
resistant
to
more
than
one
anti‐tuberculosis
drug.
In
parts
of
Eastern
 Europe,
nearly
half
of
all
TB
cases
resist
at
least
one
first‐line
drug.
Most
of
the
burden

 of
MDR‐TB
falls
on
poor
countries,
but
the
United
States
has
seen
outbreaks
of
drug‐
 resistant
TB
as
well.
In
early
1990s,
New
York
City
had
an
epidemic
of
MDR‐TB
that
cost
 almost
$1
billion
to
control.
(NIH,
2005) Tuberculosis
 Why
is
tuberculosis
an
emerging
disease?
 Encapsulated
bacteria
are
difficult
to
kill,
 leading
to
many
people
not
completing
 antibiotic
treatments.
This
selects
for
resistant
 strains.
 Many
cases
are
asymptomatic.
 Crowded
conditions
foster
spread.
 Immune‐compromised
people
are
at
particular
risk.
 HIV/AIDS
 AIDS (Acquired Immune Deficiency Syndrome) was first described in 1981. The virus now known as HIV (Human Immunodeficiency Virus) was first characterized in 1983. Evidence of the virus was recovered from tissue samples from a Congolese man taken in 1959, the oldest known record of the virus in humans. HIV
parasitizes
and
destroys
helper
T
cells
and
macrophages,
components
 of
the
human
immune
system
(Figure
35.3).
When
the
T‐cell
count
drops,
 the
body
is
less
able
to
fight
infections. Clinical symptoms typically do not begin to develop until after a long latency period, up to 8 to 10 years after the initial infection with HIV. During this long interval, carriers of HIV have no clinical symptoms but are apparently fully infectious, which makes the spread of HIV very difficult to control. Several
distinct
strains
of
HIV
have
successfully
jumped
from
other
 primates
to
humans
in
recent
decades.

HIV‐1
most
probably
from

 Chimps
(multiple
times);
HIV‐2
most
probably
from

 Mangabey
Monkeys
‐
see
phylogenetic
tree
below
 Fig.
35.16
 Factors
necessary
for
successful
cross‐species
transfer
of
a
pathogen
 1.  a
large
human
population;
 2.  a
large
nearby
population
of
the
appropriate
host
animal;
 3.  an
infectious
pathogen
in
the
host
animal,
that
eventually
produces
a
mutation
that

 






can
spread
from
animal
to
human;
 4.  interaction
between
the
species
to
transmit
enough
of
it
to
humans
to
establish

 






a
human
foothold,
which
may
take
millions
of
individual
exposures;
 5.  a
mutation
of
the
same
pathogen
that
can
spread
from
human
to
human;
 6.  some
method
that
allows
the
pathogen
to
disperse
widely.
This
prevents
the
 






infection
from
"burning
out"
by
either
killing
off
its
human
hosts
or
provoking
 






immunity
in
a
local
population
of
humans.
 Geographic
Distribution
of
HIV
Infections
in
2006
 FORENSIC SCIENCE: HIV Strain Analysis Debuts in Murder Trial The Louisiana case began in 1995 when Janet Trahan Allen, a nurse in Lafayette, accused Richard J. Schmidt, a local gastroenterologist, of deliberately infecting her with HIV and hepatitis C. She claimed that after she had threatened to break o her decade-long aair with Schmidt, he infected her with tainted blood in place of one of her regular vitamin injections. The blood, the state argued in court, came from two of Schmidt's patients, one of whom had hepatitis C and the other of whom had HIV. As part of its case, the prosecution arranged for an analysis of the HIV strains in blood samples from Schmidt's HIV-positive patient and from Allen. The analysis was performed by Michael Metzker, at the time a graduate student in the lab of molecular biologist Richard Gibbs of Baylor College of Medicine in Houston. Metzker compared the gene sequences of the strains to see how closely related they were, using a technique called phylogenetic analysis. He reported that the strains from the two samples were more closely related to each other than to a set of controls from other HIV-positive patients in the Lafayette area. Phylogenetic analysis of HIV sequences Tree based on sequences from local HIV population sample (LA); the patient (P) and the alleged victim (V) The smaller set of boxed sequences represents the sequences from the victim, and the larger set of boxed sequences represents the patient plus victim sequences. The victim sequences were found to be embedded within the patient sequences in all analyses and for all models of evolution examined. Because the alleged victim’s HIV infection represented a genealogical subset of the patient’s, this finding was consistent with the direction of transmission from the patient to the victim. Schmidt was convicted of attempted murder and is now serving a 50-year prison sentence. Biology 171 Lecture 38: Friday December 5, 2008 Today’s Topic: Emerging Infectious Diseases Human
Disease:
Transmission
Modes
 Human‐Human
–
tuberculosis,
HIV/AIDS
 Water‐borne
‐
cholera
 Vector‐borne
diseases
 


human
only
–
dengue
fever
 


zoonotic
diseases:
 


West
Nile
fever,
Lyme
disease

 Announcements Course Evaluations online Final Exam Tues. Dec 16 7-9PM – covers lectures 30-39 & last 3 discussions Review Sun. Dec 14 4-6PM - 1800 Chem Text Reading Lec.
38:
none
 Lec.
39:
none
 Cholera
 Cholera
is
a
bacterial
infection
caused
by
Vibrio
cholerae.
It
infects
the
 intestinal
tract
and
produces
a
toxin
that
causes
severe
diarrhea,
often
 leading
to
death
by
dehydration
in
less
than
24
hours
after
infection.
People
 heterozygous
for
the
allele
causing
cystic
fibrosis
are
resistant
because
their
 intestinal
lining
does
not
respond
to
the
toxin
and
allow
water
loss.
 Cholera
 Cholera
has
been
responsible
for
numerous
pandemics
in
the
19th
and
20th

 centuries,
primarily
in
Asia,
Africa
and
Latin
America.
It
is
spread
by
 water
or
food
contaminated
by
human
feces
 Cholera
 Cholera
commonly
emerges
in
periods
of
social
disruption
when
water
supplies

 are
compromised
and
is
the
most
feared
disease
following
natural
disasters.
 A
current
outbreak
in
Zimbabwe
started
in
November
2008
and
has
affected
 over
11,000
people,
resulting
in
over
600
deaths
so
far.
This
resulted
from
a
 breakdown
in
water
treatment.
 Biology 171 Lecture 38: Friday December 5, 2008 Today’s Topic: Emerging Infectious Diseases Human
Disease:
Transmission
Modes
 Human‐Human
–
tuberculosis,
HIV/AIDS
 Water‐borne
‐
cholera
 Vector‐borne
diseases
 


human
only
–
dengue
fever
 


zoonotic
diseases:
 


West
Nile
fever,
Lyme
disease
 Announcements Course Evaluations online Final Exam Tues. Dec 16 7-9PM – covers lectures 30-39 & last 3 discussions Review Sun. Dec 14 4-6PM - 1800 Chem Text Reading Lec.
38:
none
 Lec.
39:
none
 Dengue
Fever
 Dengue
is
a
very
important
emerging
disease
caused
by
four
strains
of
a
Flavivirus.

 Symptoms
include
severe
headache
and
muscle
aches.
The
common
name
is

 "breakbone
fever ”
because
the
muscle
pain
is
so
severe.
There
are
four
strains
of

 varying
severity
(serotypes
DEN‐1,
DEN‐2,
DEN‐3,
DEN‐4).
 The
dengue
viruses
strictly
infect
humans;
there
are
no
animal
reservoirs.
 Dengue
is
only
transmitted
by
mosquitoes,
 primarily
the
“yellow
fever
mosquito,”

 Aedes
aegypti,
and
the
“Asian
tiger
mosquito,”
 Aedes
albopictus.
 Dengue
Fever
 Dengue
is
primarily
a
tropical
disease,
following
the
distribution
of
its
 mosquito
vectors.
It
is
a
major
cause
for
concern
for
the
southeastern
 United
States
where
A.
aegypti
occurs,
and
possibly
the
whole
country
 following
the
introduction
of
A.
albopictus
in
1985.
 Dengue
Fever
 Dengue
in
Puerto
Rico,
2008.
 Dengue
Fever
 Dengue
hemorrhagic
fever
is
an
often
fatal
 Complication
that
often
follows
infection
by
 More
than
one
strain
of
Dengue
virus.
 Open
containers
are
typical
breeding
habitat
for
vector
mosquitoes.
 West
Nile
Virus
 West
Nile
Virus
is
another
Flavivirus,
but
disease
in
humans
is
a
zoonosis.
 The
natural
hosts
of
this
virus
are
birds,
many
of
which
do
not
show
disease.
 The
native
distribution
of
the
virus
is
in
Africa,
the
Middle‐East,
and
Europe.

 West
Nile
was
introduced
into
eastern
North
America
in
1999.
The
first
cases
 were
in
New
York
City,
and
the
virus
genotype
matched
a
strain
from
Israel,
 suggesting
an
infected
mosquito
flew
by
airline.

 West
Nile
virus
was
detected
in
Michigan
in
2001.

 The
disease
caused
9.3%
mortality
in
2002,

 especially
in
elderly
individuals.

 West
Nile
Virus
 West
Nile
Virus
is
now
known
to
infect
70
species
of
birds
in
the
US,
with
severe

 mortality
noted
in
crows
and
blue
jays.
A
number
of
native
mosquitoes,
primarily

 Culex
species,
can
serve
as
vectors,
notably
the
“house
mosquito,”

 Culex
pipiens.

 Culex
pipiens
 West
Nile
Virus
 Biology 171 Lecture 38: Friday December 5, 2008 Today’s Topic: Emerging Infectious Diseases Human
Disease:
Transmission
Modes
 Human‐Human
–
tuberculosis,
HIV/AIDS
 Water‐borne
‐
cholera
 Vector‐borne
diseases
 


human
only
–
dengue
fever
 


zoonotic
diseases:
 


West
Nile
fever,
Lyme
disease

 Announcements Course Evaluations online Final Exam Tues. Dec 16 7-9PM – covers lectures 30-39 & last 3 discussions Review Sun. Dec 14 4-6PM - 1800 Chem Text Reading Lec.
38:
none
 Lec.
39:
none
 Lyme
Disease
 Lyme
disease
(named
for
the
town
of
Old
Lyme,
CT,
where
it
was

 First
characterized,
is
caused
by
a
spirochete
bacterium,
Borrelia
burgdorferi.
 Symptoms
include
a
skin
rash,
but
secondary
complications
can
include
severe
 neurologic,
cardiac,
and
arthritic
conditions.
 Erythema
migrans
 Borrelia
burgdorferi
 Lyme
Disease
 Borrelia
burgdorferi
occurs
in
many
parts
of
the
world,

 especially
N.
America
and
Europe.

 Habitat
in
Old
Lyme,
CT
 Lyme
Disease
 Lyme
disease
is
a
zoonosis.
In
the
US,
the
primary
reservoir
is
the
 white‐footed
mouse,
Peromyscus
leucopus.
 Peromyscus
leucopus
 ‐NOTE:
the
concept
of
"reservoir
competence"
=

 the
ability
of
a
reservoir
host
to
transmit
a
pathogen
to
a
vector.
 This
is
distinguished
from
the
concept
of
"vector
competence"
=

 the
ability
of
a
vector
to
transmit
a
pathogen
to
a
recipient
host.
 Peromyscus
leucopus
is
a

 competent
reservoir
of
 Lyme
disease
 Tamias
striatus,
the
eastern
 chipmunk,
is
not.
 Lyme
Disease
 The
vectors
of
Lyme
disease
are
ticks:

Ixodes
scapularis
(the
“deer
 tick”)
(Eastern
N.
America),
I.
pacificus
(West
Coast),
I.
ricinus
 (Europe),
I.
persulcatus
(Eurasia)

 Ixodes
scapularis
 Ixodes
ricinus
 Lyme
Disease
 Infection
transmitted
to
humans
typically
through
bite
by

 nymphal
tick,
which
acquired
it
by
feeding
as
a
larva
on
an
 Infected
mouse.

 Lyme
Disease
 Occurrence
of
Lyme
disease
in
humans
depends
on
many
factors
 of
the
environment.
 Processes
leading
to
emerging
diseases
 1.  Overpopulation
–
crowding,
social
disruption,
breakdown
of
 






sanitation
 2.  Interaction
with
natural
environments
–
deforestation,

 






agricultural
changes,
“bushmeat ”
consumption
 3.  Globalization
–
increased
travel,
commerce
 4.


Evolution
of
pathogens/parasites
–
antibiotic
resistance,

 






host
shifts
 ...
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