16 Nov 2022
Although there is a decline in exposure across high-income countries, scientists at the RVC say more still needs to be done to understand changing causes and how the condition is diagnosed.
Allister Webb
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Image: © Africa Studio / Adobe Stock
RVC scientists have warned against complacency despite new research indicating a long-term decline in levels of exposure to the parasite that causes congenital toxoplasmosis (CT) among pregnant women.
The study, published in Trends in Parasitology, also argues more research is needed into the condition in low and middle-income nations, together with new diagnostic methods to understand changes in infection rates.
CT is caused when pregnant women are infected with the Toxoplasma gondii parasite for the first time and the infection is passed on to the fetus.
The condition is estimated to affect around 190,000 pregnancies globally each year, with 3% of affected babies dying within a month of birth.
The parasite is transmitted either through consumption of meat containing its cysts, or raw unwashed foods or water that contains parasites shed in infected cats’ faeces.
The study, which was funded by the Biotechnology and Biological Sciences Research Council, analysed data from more than 250,000 people in 19 countries across Europe and the Americas.
Although it confirmed that rates of exposure in high-income countries have been falling over several decades, it also reveals spikes of CT cases in nations where more women become infected for the first time during, rather than before, their pregnancy.
Lead researcher 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.”
But he added: “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.”
The paper also argues that prenatal screening could be used on a temporary basis to aid diagnosis and treatment in countries where CT cases are expected to rise.
