Last updated January 11, 2018 at 10:27 am
Toxoplasmosis is a great excuse to not have to clean out a kitty litter tray when you’re pregnant. While somewhere in the order of 30-50% of all humans carry the Toxoplasma gondii parasite that leads to toxoplasmosis, in most cases infection will produce mild flu like symptoms, if any at all. For people with compromised immune systems or pregnant women, infection can be catastrophic.
Even in mild cases, the latent cyst form of the parasite has been shown to be able to hijack the brain, leading to changes in behaviour including a tendency to take risks, trust strangers and be more outgoing. A study earlier this year linked toxo infection to neurological diseases including epilepsy, Parkinson’s disease, Alzheimer’s diesase and even cancer.
Immune cells (red, with blue stained nucleus) infected with Toxoplasmosis tachyzoites (green) Source: PLOSPathogens
In most cases It’s not just humans who suffer from this parasite either. While the sexual stage of the parasite’s life cycle need to take place in a cat, the rest of its life cycle can take place in almost any other mammal.
A series of studies have previously shown that the parasite can manipulate the behaviour of infected rats, so that they lose fear of cats and even become attracted to the smell of cats, making them easy prey.
Feral cats spread toxo to native wildlife
It also means that apart from killing them outright, feral cats are wreaking havoc on native wildlife by spreading Toxoplasmosis to native species. Australian marsupials are susceptible to infection, where it has been known to kill bandicoots, Tammar wallabies, koalas and wombats.
The main route for infection is through contact with cat poo, hence the advice to lay off kitty litter duty to pregnant women. Touching or consuming undercooked pork, lamb or kangaroo, or drinking unpasteurized milk, can also lead to infection.
New research has shown how the parasite takes control and forces our own immune system to spread it around the body. Once the parasite reaches the stomach, it passes through the intestinal wall. Usually at this point immune cells would intercept and destroy the invading parasite. But Toxoplasmosa pulls a molecular trick to turn the immune cells into “Trojan horses”.
“We have decoded how the parasite takes control of immune cells, converting them into moving “zombies” which spread the parasite in the body,” said Antonio Barragan, professor at Stockholm University and one of the authors of the new study.
How the parasite spreads and disease occurs
The infected immune cells secrete GABA, a neurotransmitter, which then switches on a calcium dependent signal pathway that leads to “hypermotility” – the ability of the cell to move to new sites in the body and spread the infection.
“The neat thing is that the signal can be inhibited by regular blood pressure medicine. When mice received the medicine, the spread of the parasite was inhibited. We do not want to say that blood pressure medicine can cure toxoplasmosis, but we have discovered a new signalling pathway in immune cells that is linked to their motility and that the parasite utilizes in a very smart way.” Said Antonio Barragan.
“This helps us understand how the parasite is spread and disease occurs. In the longer term, it may help us develop targeted treatments for infection.”
