Toxoplasmosis 2017-02-28T12:40:43+00:00

One man’s meat…

Horror stories about Toxoplasmosis rear their head on a fairly regular basis and, once again, cats are supposedly to blame. So here is the Proper PURRspective!

Toxoplasma gondii is a nasty little parasite if you happen to strike it during a critical stage of pregnancy or immuno-incompetence. However, several factors have to line up in order for unborn children (or adults occasionally) to be clinically affected.

The primary factor is a dodgy immune system.  Most adult ‘toxo’ occurs when the immune system is ‘down’ – either due to cancer or, in fact, to chemotherapy for cancer or after organ transplant.  The most regular immune derangement is, in fact, pregnancy – the maternal immune system has to be down-regulated in order to prevent the baby being rejected and ejected.  It is one of the marvels of the mammalian reproduction system, but it does leave a window of opportunity  for some fungal infections as well as toxoplasma.  21% of adults who first come in contact with the toxo parasite can develop a retinal inflammation in the eye (which can be treated and thus prevent vision loss).

The second factor is exposure to the toxoplasma parasite – a single-celled organism that exists as eggs (oocytes) outside the body, and as cysts (bradyzoites) inside the body in muscle. It takes a week for the eggs in the cat’s faeces to become infective, and most cats only shed the oocytes for 3 – 14 days in their whole lifetime (and usually when they are kittens).

Which means, a person has to eat either undercooked muscle from the cat or one of the other mammals that can be infected, or eat cat faeces from an infected cat, that are a week old. It does mean that sandpits and gardens where stray cats can use the sand as a litter tray can be a major source of infection – especially if you (or your child) does not wash their hands before putting them in their mouth or after handling raw meat or uncooked vegetables.  Most infection actually comes from eating raw or undercooked meat, although contaminated water (and soil) comes a close second.  You will not pick up any toxoplasma oocytes from your cat’s coat – she has already licked any way and they are destroyed in the intestine of the cat, or they move into the muscle, the same as any other mammal.  Dogs, on the other hand, because they roll in rather unpleasant things in the park, can have toxoplasma eggs on their coat.  Vets and vet nurses have no higher incidence of toxoplasma antibodies nor toxoplasma infections than the general population, which is basically down to hygiene and not consuming under cooked mammal meat.

The lifecycle  of the parasite is complex, which is why it took years to figure out how infection occurred.  The only part of the cycle that has ‘stuck’ in the media though, is that cats are the ‘engines’ of infection – they produce the oocytes that remain in the environment ready to go into any mammal and some birds that consume them (see diagram).

Dr Kim’s advice to concerned cat owners is this:  keep the litter tray and the sand pit clean (faeces less than 3 day old is not infective). Filter and boil your (and the cat’s water.  Do not eat the cat or any other meat under cooked.  So far, no one has advised that they would like to break these rules!  So, take the media’s Toxo Terror beatup with a grain of salt if you must – but make sure it is not on steak tartare!

For the official lowdown on Toxo: www.cdc.gov

And to keep it in perspective:

  • The feral pig / feral cat story is going to prevent the problem ever being eradicated in Australia.  However, even in the USA, there are only 750 deaths per year from toxoplasmosis (toxo infection) and 50%are due to eating undercooked meat, not related to cat owning at all. Even 24% of the vegetarian Seventh Day Adventists have toxo titres (exposure to the parasite at some time in their lives) while in the general population it is 50%.  The rates of infection in the USA and Europe are declining, mainly due to meat hygiene, and antenatal health care and serotesting.
  • Toxoplasma infects between 1 baby and 10 babies per 10,000 live births, and the rates are declining. Thus the number of births in Australia was 301,600 in 2011 so that means 30 to 300 neonates infected that year. Toxo is a rare cause of stillbirths (miscarriage), but is a frequent cause of (treatable) eye inflammation in adults.
  • Drowning kills 27 toddlers (< 5 years old) a year in Australia
  • Cars kill 40 babies and toddlers a year (numbers maimed are unavailable), as 1 in 5 fatalities is a child less than 5yrs old, and again rates are declining due to improved safety measures.  If the proportion of toddlers injured is the same as killed (1 in 5) then of the 50,000 people catastrophically injured each year in Australia, 10,000 will be toddlers.

So Cars vs Cats in the danger stakes = 10,000 against 300. Per Year. Purrspective is important.