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Sunday, 10 November 2019

Toxoplasmosis (Things We Don’t Know about Pregnancy Series #6)

I once heard someone talking about arranging a hen do and struggling for ideas that would be okay for pregnant participants. At the time, I couldn’t see why it was so difficult… they were pregnant, not dead! …But I guess it depends how risk averse you are. If you’re avoid absolutely everything that could pose any tiny risk that includes alcohol, caffeine, household chemicals, saunas, certain foods, sports, paint, gardening, cats, non-stick frying pans and any person who could have an illness. In fact, staying locked indoors without human contact.

The outdoors thing intrigued me.

The great outdoors © TWDK.

So what is the risk?


Cat and mouse © TWDK.
The panic is over toxoplasma gondii, a protozoan parasite that will infect a third of people over their lifetimes. Most people never know: the zoonotic infection is asymptomatic in healthy adults, and humans are considered dead-end accidental hosts, because toxoplasma gondii can only reproduce in cats – and wants to get back in cats.

Some unlucky people can experience flu-like symptoms: headaches, fatigue, swollen glands, and body aches; those with a compromised immune system, such as HIV sufferers, may experience more severe effects, including fever, lung problems, blurred vision and seizures.

There is a suggestion that toxoplasmosis can change your behaviour, driving you to like cats, hang out with cats and, if you’re a rat, end up eaten by cats so the parasite can get back in cats where it belongs – research into this is still ongoing.

Risk during pregnancy

 

If you’ve had toxoplasmosis before becoming pregnant, you’re immune, and your foetus is safe. The danger is contracting it for the first time whilst you’re pregnant and passing on congenital toxoplasmosis, which is much more dangerous. The risk of passing it to your baby is greatest if you get it during your third trimester, but the earlier you get it, the worse the complications.

Complications can start with miscarriage or stillbirth, or birth defects that are sometimes picked up in babies but, in the majority of cases, don’t emerge until the teens or adulthood. These include seizures, jaundice, liver enlargement, hearing or vision loss, low IQ, neurological disorders and mental disability.

 

How do you treat it?

 

You don’t. Doctors can test for toxoplasmosis and try to mitigate its spread and effects, but don’t understand the mechanism behind how it works, so can’t truly eliminate it. Vaccines are used in cats and livestock that can limit its spread, and new anti-malaria, anti-schizophrenia and nanoparticle-borne Estersantibody drugs are being explored.

 

How do you catch it?

 

Whilst cats are ultimate host of toxoplasma gondii, contracting it from cats is very unlikely. First, you can’t get it directly from cats: you have to handle cat poo (where the eggs are excreted) and, second, it has to be poo from cats that have contracted the parasite for the first time: after that, like humans, they become immune. Research has shown that exposure to three or more kittens increases your risk (yet apparently one or two is not statistically significant!)[1].

Another risk factor is handling soil, possibly because cats toilet outdoors. This is a bigger risk but can be mitigated by wearing gloves and hand-washing.

This is why some foods, such as “unwashed greens” are best avoided during pregnancy – they might be soil contaminated and the soil might contain toxoplasma gondii. Greens themselves are not a risk factor, however, and may be safely eaten, provided they’re washed with clean, treated water. Uncooked meats (especially pork, lamb, and venison), cured meats (like salami), unpasteurised dairy products or raw oysters, clams, or mussels may contain toxoplasma gondii cysts. Meat is the primary source of toxoplasmosis.
Avoid lambing if pregnant © TWDK.

Some more unusual risks include handling pregnant sheep or newborn lambs, having a blood transfusion or organ transplant and, of course, inheriting it from your mother in the womb.

In summary, if you don’t want to contract toxoplasmosis whilst you’re pregnant, don’t eat raw meat, don’t eat dirt, don’t birth lambs, and don’t play with cat poo.

 

Data variations

 

Risks vary with cultural eating habits, livestock health and local soil, which means every country has different statistics.

In Europe, between 30 and 63% of infections are down to meat consumption – but which meats differed[2]. In Italy, salami was two or three times more likely to be linked to the disease than it was elsewhere (10-14%), and in most other places, lamb was the primary culprit.

Social trends also play a role, such as the fashions to eat raw food diets, including uncooked vegetables and meats. Free-range and organic meats are more likely to carry the parasite, simply because the animals spend more time outdoors on untreated land. This is especially true for pork and poultry, but can be mitigated by thoroughly cooking the meat, and avoiding tasting whilst cooking[3].

Salami by André Karwath via Wikipedia Commons.

However, one study showed that 14 to 49% of infections still had an unidentified cause, primarily because of the difficulties involved in monitoring, detecting toxoplasma gondii in food, and in confirming sources[4] [5]. Scientists think there may be other unidentified sources in food and the environment[6].

Sensible precautions

  • Garden wearing gloves
  • Wash your hands/equipment before and after eating or touching food
  • Wash any foods you’re planning to eat raw (such as salad)
As an outdoors person, I have not abstained from walking and have been doing gardening. I admit I’ve been a little more paranoid about soil under the fingernails than usual, but even with gloves I haven’t been able to avoid contact entirely. Like when I went foraging for fruit (not easy to do in gardening gloves, and hawthorn can rip nylon gloves), or when I had to climb a tree to rescue my cat. However, it’s important to remember that the risk is small, that I have probably already been exposed (after all… I have a cat), and there are still unidentified sources out there.

My cat stuck up a tree © TWDK Everything in moderation.


There are many unknowns when it comes to pregnancy, and over the next few months, I’ll be exploring more of them with you. Look out for my next blog post, which will be about reproductive immunology.

To read our full article on the things we don't know about pregnancy, check out our site. This article will be updated as we add posts across the coming months.



References
why don't all references have links?

[1] Emily Ostler, Expecting Better: Why the Conventional Pregnancy Wisdom is Wrong - and What You Really Need to Know (2013) Penguin Press.
[2] Cook AJ, Gilbert RE, Buffolano W, Zufferey J, Petersen E, Jenum PA, Foulon W, Semprini AE, Dunn DT. Sources of toxoplasma infection in pregnant women: European multicentre case-control study. European Research Network on Congenital Toxoplasmosis. BMJ. 2000 Jul 15; 321(7254):142-7.
[3] Guo M, Buchanan RL, Dubey JP, Hill DE, Lambertini E, Ying Y, Gamble HR, Jones JL, Pradhan AK. Qualitative Assessment for Toxoplasma gondii Exposure Risk Associated with Meat Products in the United States. J Food Prot. 2015 Dec; 78(12):2207-19.
[4] Robert-Gangneux F, Dardé ML. Clin Microbiol Rev. Epidemiology of and diagnostic strategies for toxoplasmosis. 2012 Apr; 25(2):264-96.
[5] Singh A.K., Verma A.K., Jaiswal A.K., Sudan V., Dhama K. Emerging food-borne parasitic zoonoses: A Bird’s eye view. Adv. Anim. Vet. Sci. 2014;2:24–32. doi: 10.14737/journal.aavs/2014/2.4s.24.32.
[6] Hussain, Malik, et al. Toxoplasma gondii in the Food Supply. Pathogens 6.2 (2017): 21.

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