The mind altering powers of parasites!

Sheena Cruickshank, University of Manchester

•“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.

Parasitism

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 riskhttp://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 people- why?

Parasite Life Cycle: Toxoplasma gondii

Definitive Host

(Cat)

Infected foetus

Possible transmission via placenta

Oocysts shed in poo

Adapted from JP Dubey, 2006

Oocysts in feed, water or soil

Tissue Cysts in Meat

(10 millionover 1-3 days)

Intermediate Hosts

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?

Big cats

•T. gondii infects all known species of 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/how-your-cat-is-making-you-crazy/8873/

Are Humans a Target of Parasite Manipulation?

• Humans are very rarely eaten by cats! A classical “manipulation” effect seems unlikely!

• Tissue cysts are commonly found in the brain. Could these damage motor performance?

• 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?

Check our resources on:

http://www.mig.ls.manchester.ac.uk/impact/resources/

We run fun activities about our research throughout the year. Come see us at Manchester Museum on the 27th October or 30th October

Guinea Worm: Does this “alter” behaviour?