Transcript Toxoplasma gondii - Amazon Web Services

The mind altering powers of
parasites!
Sheena Cruickshank,
University of Manchester
Parasitism
•“the relation between two different kinds of
organisms in which one receives benefits usually at
the expense of the host”
•>50% of all animal species are parasites!
•Most animals are parasitised all the time!
•Most parasite infections are NOT fatal.
Have you heard of
Parasites?
There are many types
of parasites….
But our immune system has
adapted to fight them…
Parasites and host behaviour
• Many different parasites are thought to manipulate
their host’s behaviour for their own benefit.
Why?
• Many parasites have a complex life cycle in >1 host
• Many parasites cannot reach maturity(sexually
replicate) in the intermediate host therefore need
host to be eaten by predatory definitive host
Infection risk posed by cats revealed
By Michelle Roberts Health editor, BBC News online
Beware of the cat: Britain's
hidden toxoplasma problem
New research shows 350,000 Britons a year are being
infected with pet-borne parasite linked with schizophrenia
and increased suicide risk
http://www.independent.co.uk/
How toxoplasma
spreads... and spreads
Life > Health & Families > Health News
FSA set to review advice to pregnant women
on dangers of cat parasites
Agency also attacked for failing to warn of
risk of contamination from eating undercooked
lamb
•Toxoplasma gondii is THE most common parasitic
infection in the world!
•WHY?
•It can infect any nucleated cell in the body
•It causes a “chronic” infection ie life long!
•It infects ALL mammalian species
•That includes us….
•20-80% of people are infected with T.gondii
•France has one of the highest incidences in peoplewhy?
Parasite Life Cycle:
Toxoplasma gondii
Definitive
Host
(Cat)
Possible
transmission
via placenta
Infected
foetus
Oocysts shed in
poo
(10 million
over 1-3 days)
Oocysts in feed,
water or soil
Tissue Cysts
in Meat
Intermediate
Hosts
Adapted from JP Dubey,
2006
Why does France have one of the
highest incidences of Toxoplasma
infection in the human
population???
(A)
French people love cats?
(B) French people love rare meat?
How do you know if you have
Toxoplasma gondii
•You probably don’t know!
•Most cases have no symptoms!!
•So why could it matter?
•T.gondii persists in the body forming “cysts” in the
muscle and CNS!
•Significant risk to:
•
Unborn children of T. gondii naive mothers.
•
Immunosuppressed e.g.Transplant patients
•
Immunocompromised e.g. AIDS patients
What does it do in the CNS:
Rodents (Mice and Rats)
• Mice and Rats amongst typical cat prey
• ie AN INTERMEDIATE HOST
• Infected animals show
• increased activity
• preference for exposed areas
• And…….
What does our mouse do: does it go to
Wee (1) or Wee (2)
Toxoplasma infected mice and rats have a
preference for cat wee!!!
In fact Toxoplasma infected animals
REALLY love cats!
Toxoplasma gondii and the Manipulation
Hypothesis
• Observations support the manipulation hypothesis.
• Infected rats (and mice) are bolder, more active and less
likely to avoid cats
– they are more likely to be eaten!
• So parasite transmission rate and the possibility of
sexual recombination are increased!
Does Toxoplasma modulate us????
• Up to 80% of the human population are infected.
• But are we predated by cats?
•T. gondii infects all known species of cats…….
Big cats
Does T.gondii modulate us????
• Up to 80% of the human population are infected (around 30% in
UK).
• Flegr reported possible effects of infection on psychomotor
performance (reaction time):
• Decreased psychomotor performance (reaction time) correlated
with blood levels of T. gondii-specific antibodies.
What might the consequences of this be? Can they be measured?
Toxoplasma gondii – Road Traffic Accidents
• Czech Republic (Flegr et al, 2002): The risk of being in car
accidents is 2.65 times higher in T.gondii infected people
(passenger or driver!!!)
• Turkey (Yereli et al, 2006): increased frequency of T.gondii
infected people in accidents (eg Toxo specific IgG 24.32% versus
6.48%)
• But is this causative criteria?
• Are some personality types more likely to be involved in car
accidents and more likely to have T.gondii???
How your Cat is Making you
Crazy
J Flegr
Blog article based on Flegr’s work in The Atlantic:
ideashttp://www.theatlantic.com/magazine/archive/2012/03/howyour-cat-is-making-you-crazy/8873/
Are Humans a Target of Parasite Manipulation?
•
Humans are very rarely eaten by cats!
•
Tissue cysts are commonly found in the brain. Could these damage
motor performance?
•
•
•
A classical “manipulation” effect seems unlikely!
Unlikely to be as specific as the effects that are seen.
Most likely that effects seen in humans are:
• consequence of mechanisms evolved by the parasite to manipulate
rodent behaviour are manifested in humans because of similarities
in brain biochemistry between humans and rodents.
• And/or because certain personalities are more likely to be
infected?
• Altered levels of neurotransmitters?
Might parasite-induced alterations in neurotransmitter levels have
other effects?
Toxoplasma gondii and Schizophrenia
• Schizophrenia is a severe and debilitating disorder
• Range of symptoms including hallucinations, delusion, self neglect,
social withdrawl
• Attributed to disruption of areas of the brain associated with
thought, perception, attention, motor behaviour and emotion.
• Higher incidence of T.gondii infection in patients with
schizophrenia
• Is T.gondii one of the risk factors for schizophrenia?
So is T.gondii “making us
crazy”
•We don’t know!
•Data conflicts:
•Some studies even suggestT.gondii may
benefit some brain diseases!!!
•Lack of mechanisms…..
•Lack of robust research
Can We Reduce Risk of
Infection?
• Wash hands after handling pets
(especially dogs) or handling cat litter
• Wash fruit and vegetables
• Freeze meat before use
• Cook meat thoroughly
Homework!!
Can you think of or find out about any
other mind altering parasites??
Wasps, sticklebacks, beetles, ants………
Want to find out more?
We run fun activities about our
research throughout the year. Come
see us at Manchester Museum on the
27th October or 30th October
Check our resources on:
http://www.mig.ls.manchester.ac.uk/impact/
resources/
Guinea Worm: Does this
“alter” behaviour?