Download “living together” Symbiosis Phoresis

Microbio590S
Parasitology
Lecture 2: Terms and
Concepts – Example of reemerging neglected disease
Michele Klingbeil
Office: Morrill IVN Room 222
By appointment only
[email protected]
Symbiosis
“living together”
•  Intimate association between two different
species
–  Usually a larger organism is the host, the
smaller is the symbiont
•  Give some examples of symbioses
Specific types of association
Phoresis - Traveling Together
•  No dependence from
either participant
•  One participant is
usually machanically
carried by the other
•  Hitch-hiking
Crab + Barnacle
Commensalism
•  “Sharing at the table”
•  One partner benefits,
but the other is neither
helped nor harmed.
Clownfish + Sea anemone
Mutualism
Endosymbiosis - mitochondria
•  Interspecific interaction that
benefits both members
Lichen on tree bark
•  Frequently, the relationship
is essential for survival of at
least one of the members
–  Obligate interaction
Moray + cleaner wrasse
Parasitism
•  Parasite and parasitism
are terms that define a
way of life rather than a
coherent evolutionary
related group of
organisms.
Phoresis and
Commensalism
Parasitism
Mutualism
•  Numerous definitions
–  the intimate association of two species where one species (the
parasite) benefits at the expense of the other (the host).
–  the parasite relies on the host for nutrients and as a place to live.
Is this Parasitism?
•  The benefit in these
relationships are clearly
skewed toward the lion
and the spider.
•  Predator vs. prey
•  Predators tend to be
larger than their prey, and
consume many prey in a
lifetime.
What is a Parasite?
•  Parasites are usually
much smaller than their
host, and do not kill the
host before taking a
meal.
Is This Parasitism?
•  Micropredation - the
mosquito is certainly gaining
a nice blood meal.
•  Blurry lines between these
definitions.
•  The host is the food source,
and a specific niche for the
parasite.
•  Many parasites show strict
specificity for a single host
species.
Parasite Diversity!
  Parasitology as a scientific discipline historically covers a
diverse collection of multi- and unicellular eukaryotic
organisms
  Protozoa: unicellular eukaryotes (this is a historic term,
protozoans are not really a monophyletic group)
  Platyhelminthes: flatworms these include flukes and tape
worms
  Nematodes: elongated worms with rigid cuticule
  Arthropodes: insects, ticks and mites which either are
parasitic or transmit parasites as vectors
  (we only have time to discuss the most important groups
causing human and some animal disease, there are
many additional parasites outside these groups)
Parasite Diversity!
•  Not a phylogenetically related group of organisms
–  Single celled eukaryotes - Protists (protozoa)
–  Mutlicellular worms - Helminths
•  Many are Vector transmitted disases
•  Zoonoses - transmission of the infectious agent to
humans from an animal reservoir.
No establishment of a permanent new life cycle solely
in humans (still requires animals).
Ecto- vs Endoparasites
•  Ectoparasites live on, but
not in their hosts.
Protozoan Ichthyophthirius that
causes fish “Ick”
 
Endoparasites live within
the body and tissue of their
hosts. The majority of
parasites to be discussed.
Protozoan Trypanosoma that
causes African Sleeping
sickness.
Facultative vs. Obligate
•  Facultative - usually a
free-living organism
but can invade host
under certain
conditions. Can cause
severe disease.
  Obligate - most parasites
require a host for at least
one stage of its life cycle.
Some parasitic worms
have free-living larval
stages.
Naegleria fowleri
Trypanosoma cruzi
Intermittent vs. Permanent
•  Intermittent/ temporary
- micropredation “parasite” feeds on the
host and then leaves.
•  Permanent - parasite
that lives its entire
adult life on or within
the host. Most of the
parasites we discuss
are permanent.
Life Cycles
•  Direct Life Cycle parasite passes from one
host to the next through
contaminated food/water,
air, or sexual intercourse.
 
Indirect Life Cycle - parasite
passes from one host to the
next through a vector and/
or intermediate host. Many
parasites have complex
indirect life cycles.
Entamoeba
histolytica
Diphyllobothrium
latum
Vectors
for Transmission
Vectors
- Actively
transmit parasites
•  Mechanical Vector no multiplication or
development of
parasite takes place.
•  Biological Vector either multiplication or
development takes
place.
Horse fly
Tsetse fly
Transmission of 2 related parasites
Tsetse fly
Horse fly
•  Feeds often moving
front legs and mouth
parts vigorously.
–  Trypanosoma evansi
remains on the
mouth parts - no
biological
development occurs.
•  Proboscus used for
blood meal - longer
feeding period.
–  Trypanosoma brucei
bloodstream form is
ingested - develop to
procyclic form - migrate
and develop to infective
epimastigotes (new
form).
Host Definitions
•  Definitive host - where sexual reproduction occurs. If
there is no sexual reproduction documented, then it is the
host that is most important to humans.
–  Typically a vertebrate. Exception - Plasmodium
•  Intermediate host - where asexual replication or parasite
development occurs.
•  Paratenic host - transport host, but parasites do not
develop in this host.
•  Reservoir host - any animal that carries an infection that
can serve as a source of infection to human and other
animals.
•  Accidental host - parasite enters or attaches to other than
the normal host. Parasites usually do not survive in the
wrong host, but can cause serious disease (Toxocara).
Life Cycle Example
Intermediate
Host
Paratenic
Host
Bridging the gap between human
And small fish/copepod.
Copepod
Intermediate
Host
Monoecious
Hermaphroditic
Diphyllobothrium
latum
Definitive
Host
Free-swimming
stage
Summary of Introduction
commensalism, mutualism, parasitism, ecto,
endo, obligate, facultative, intermittent
parasitism …)
  Hosts (final, intermediate, paratenic,
accidental, reservoir …)
  Disease terminology (infection, infestation,
acute, chronic, patency, incubation
period, crisis, convalescence …)
Parasites Among Us
“…no matter how we set ourselves off from
nature we remain a part of it, and thus we
invariably share parasites with the other
species in which we live.”
Julius P. Kreier
PARASITIC PROTOZOA
Emerging Infectious Disease
 
Infectious diseases whose incidence in humans has increased in the
past 2 decades or threatens to increase in the near future have been
defined as "emerging." These diseases respect no national boundaries
include:
 
 
 
 
New infections resulting from changes or evolution of
existing organisms (host and/or pathogen)
Known infections spreading to new geographic areas or
populations
Previously unrecognized infections appearing in areas
undergoing ecologic transformation
Old infections re-emerging as a result of antimicrobial
resistance for known agents or breakdowns in public health
measures.
Emerging(re) Infectious Disease
-HIV
Species Jumping -Influenza
-Hepatitis C and E
Zoonoses
-E. coli 0157:H7
-Cryptosporidium
-Ebola
-Hantavirus
-Lyme disease
-nvCJD
-Trypanosomiasis
-West Nile Virus
Zoonoses
Zoonoses - transmission of the infectious agent to
humans from an animal reservoir.
No establishment of a permanent new life cycle
solely in humans (still requires animals).
Species jumping - the infectious agent derives from
an ancient animal reservoir, but has established a
new life cycle in humans that DOES NOT require an
animal transmission phase any longer.
Contributing Factors for Zoonoses
 
Pathogen evolution (adaptation)
 
Host condition
 
 
 
 
Vaccination
Immunological disorders
Host population
 
 
 
 
Mutations
Urban crowding (land use)
Host demographics & behavior
Global travel
Environmental
 
 
 
Climate
Destruction
Public Health breakdown
Dealing with Zoonoses
 
 
 
 
 
Why are the pathogens jumping?
Can we predict this?
Who will be the world’s doctor?
WHO, UN - need to get rid of political links?
Who will be the world’s expert on zoonoses?
Develop new strategies to deal specifically with
emerging zoonoses.
Surveillance will be key, but also greater
involvement of field and basic science research.
Numbers of People with Parasitic Diseases
Disease with HIGH mortality:
– 
– 
– 
– 
Malaria - 489 M
Sleeping Sickness 0.5 M
Chagas disease - 18 M
Visceral Leishmaniasis - 4 M
Estimated World Pop by UN
10/31/11
7 Billion
Disease with HIGH morbidity
and QL losses:
– 
– 
– 
– 
– 
– 
– 
– 
Schistosomiasis - 200 M
Onchocerciasis - 37 M
Filiariasis - 350 M
Ascariasis – 807 M
Hookworm diseases – 600 M
Trichuriasis – 605 M
Cutaneous leishmaniasis - 8 M
Food and waterborne
protozoan - 1.5 B
Human African Trypanosomiasis
•  Classical example of a zoonotic emerging infection,
1890-1930.
•  Leading public health problem in Africa at that time,
colonialism brought the disease to new areas with a 2/3 death
rate.
•  Nearly eliminated by 1960 using population screening, case
treatment, chemoprophylaxis, and vector control.
•  Currently classified by WHO as a re-emerging and
uncontrolled disease.
HAT
Nearly
Eliminated
inin1960s
HAT
Nearly
Eliminated
1960!
Human African Trypanosomiasis, central Africa, 1926-1999
HAT: re-emerging, Neglected Tropical Disease
How Was Control Successful?
……..and now
Card agglutination Test
Anion Exchange
Centrifugation Technique
Time consuming
Expensive
Additional equipment
Molecular Tools
Sensitive
Still under development
Large # of
false +’s
Estimating Disease Burden
> 60 M people at risk, only about 3-6 M are screened for
HAT.
Health facilities lacking in disease foci areas.
Little if any public health measures being implemented.
Huge political conflict and insecurity in epidemic foci.
Clinical diagnosis is difficult until late stage.
Intermittent fever - malaria?
Weight lose - AIDS?
Diagnostics - false negatives
Barriers to Control HAT
 
 
 
 
Insufficient resources - developing countries
War and civil disturbances = refugees
No vaccine = no prevention
Crisis in chemotherapeutics
 
 
 
Melarsoprol was 95% effective, but in 1997
resistance up to 30% was emerging in Uganda,
Sudan and Angola (DRofC little data).
Arsenal of therapeutic drugs is minimal (~6)
Toxicity - drugs kill 4-10% of the patients.
Do you know
these public
health
workers?
•  World’s first peer-reviewed, open-access journal
devoted to the NTDs
•  Launch supported by Bill and Melinda Gates
Foundation
•  Papers on pathology, epidemiology, treatment,
control, prevention
•  Magazine section devoted to policy and advocacy
•  International editorial board—half of the
Associate Editors are from endemic countries
“It is expected that the journal will be both catalytic and transformative
in promoting science, policy, and advocacy for these diseases of the poor.”
—Peter Hotez, Editor-in-Chief