People can become infected with toxoplasmosis by eating food or drinking water contaminated with parasites shed in the faeces of infected cats.

Researchers identify changing epidemiology of this harmful foetal disease.

Human toxoplasmosis rates have been declining in high-income countries over the past six decades, according to new research.

However, an epidemiological "peak shift" - where more women contract the disease for the first time during pregnancy rather than before motherhood - can cause transient spikes in high prevalence countries.

The study by the Royal Veterinary College (RVC) and published in the journal Trends in Parasitology analysed six decades of data from more than a quarter of a million people from 19 countries. 

As well as highlighting the changing epidemiology of toxoplasmosis, the study also found gaps in the current understanding of the parasite Toxoplasma gondii (T. gondii) in low- and middle-income countries, and calls for this to be addressed in future research.

It also suggests that pregnant women from countries predicted to experience a rise in cases may benefit from the introduction of temporary screening programmes and a reassessment of the cost-effectiveness of these programmes to consider related disorders.

RVC lead researcher and postdoctoral scientist Dr Gregory Milne said: “Toxoplasma causes a large public health burden, from severe congenital disease among infants, to fatal infections among people with compromised immune systems, to other more subtle changes in host behaviour. It is therefore promising news to find consistent evidence of decreases in parasite exposure in many populations and countries. 

“We show that more data are needed to assess the trajectories of exposure trends in lower-income countries. Our findings nonetheless caution against complacency: in high-prevalence countries, despite decreasing parasite exposure, cases of congenital disease may counterintuitively increase as more women acquire primary infections in pregnancy.”

Toxoplasmosis affects some 190,000 pregnancies globally every year and occurs when pregnant women become infected with the parasite T. gondii for the first time, passing the infection to the foetus. Of the 19,000 annually reported cases, three per cent of infected infants die before one month of age, sometimes before birth, and those who survive can experience issues with their vision and development.

Around one-third of the human population is thought to have been exposed to T.gondii. People can become infected by eating food or drinking water contaminated with parasites shed in the faeces of infected cats.