Toxoplasma gondii is a protozoan so widespread throughout the world that one in three inhabitants of the planet is parasitized at some point in life by it. The infection, toxoplasmosis, is almost always very mild and those affected do not even think that the slight discomfort and fatigue they suffer may have an external cause. With two exceptions: immunocompromised people and pregnant women. In the first case, complications can be fatal, while in the second contagion is a major threat to the fetus that can cause abortions or serious neurological and visual sequelae that prevent the normal development of the child. It is called congenital toxoplasmosis.
In recent years, this ailment is at the center of a gigantic controversy that divides scientific societies, experts and governments. The reason is whether or not all expectant mothers should undergo screening tests to see if they have contracted the parasite. Until 2018, these blood tests were generally done in Spain. That year, however, the Spanish Society of Gynecology and Obstetrics (SEGO) stopped recommending them after reviewing all the scientific evidence. Other entities, such as the Spanish Society of Paediatric Infectology (SEIP), maintain the opposite position.
The result of this division between the medical class is a great disparity between autonomous communities, with some following the opinion of gynecologists and others that of pediatricians. Asturias, Cantabria, Catalonia, Valencia, Madrid, Murcia and the Basque Country have stopped doing the tests in recent years, as confirmed in writing to EL PAÍS.
The arguments for doing so are those presented at the time by the SEGO and that the Public Health Commission – formed by the Ministry of Health and the communities – updated last year in a document that states that "screening does not meet the necessary criteria to be considered effective". The reasons are that there are no diagnostic means "that can differentiate acute or recent infection from past infection"; that it is not possible to know whether the foetus is infected without "resorting to invasive methods not without risk", such as amniocentesis (a test in which amniotic fluid is removed); and that "there is no scientific evidence of the effectiveness of pharmacological treatment" to prevent the "transmission of the infection from mother to fetus." According to this position, only in some at-risk pregnancies, such as that of mothers with HIV, screening is indicated.
Castilla-La Mancha, Extremadura, Navarra and La Rioja, on the other hand, perform the test three times during pregnancy, one per trimester. In the first the objective is to know if the future mother has or has had the infection in the past, while in the next two is to check if it has occurred during pregnancy (the possible symptoms are often confused with the pregnancy itself). Andalusia and Castilla-León, on the other hand, only do the test in the first quarter. "This test has all the scientific evidence and is the only way to prevent and treat the baby early if it is affected," says Castilla-La Mancha.
Four communities – Aragon, the Balearic Islands, the Canary Islands and Galicia – have not answered the questions of this newspaper, although an extensive document from the Carlos III Health Institute reveals an even more fragmented picture, with differences in some cases between hospitals in the same community and even within the same hospital. This disparity between governments is repeated on the international scene. The United Kingdom, for example, does not carry out screenings considering that they are not cost-effective, while in France screenings during pregnancy are monthly. The differences also occur with private health, where the performance of tests is widespread.
What is the ultimate reason for such a difference in criteria even between specialists, who are the ones who must set the guidelines for health policies, and also between the different governments that must execute them?
Anna Suy, president of the Section of Perinatal Medicine of the SEGO, believes that, if you look at the current scientific evidence, there is not much room for controversy. "Official data from the National Epidemiological Surveillance Network and the Carlos III Health Institute tell us that between 2019 and 2021 only one case of congenital toxoplasmosis was detected. It doesn't make sense to test all pregnant women [330,000 in Spain in 2022] for a single proven case in three years," she says.
Suy warns that testing can even be counterproductive: "It is a disease in which it is very difficult to know with the available tests if the infection is current or past. This means that you will end up treating many women for an infection that they no longer have with drugs that carry their risks and have their toxicity for the mother and the baby. With the current evidence, screening doesn't make sense."
The decision to stop screening, however, has met with the rejection of a sector of the medical class, mostly formed – although not only – by pediatricians. As a result of this malaise, the State Research Network on Congenital Toxoplasmosis (REIV-TOXO) emerged, which today has professionals from 122 hospitals and collaborates closely with the Carlos III Health Institute, from which it receives public funds. In 2021, the group sent a letter to the Ministry of Health "supporting gestational screening."
Clara Carreras, pediatrician at the Germans Trias i Pujol Hospital (Barcelona) and member of the group, focuses on the loss of diagnostic opportunity. "If we withdraw screening, we're going to diagnose fewer cases and we're going to do it late. More serious neurological disorders are commonly detected on pregnancy follow-up ultrasounds. But then they have already occurred and the opportunity to try to prevent the infection from reaching the fetus has been lost. Other cases are detected as the child grows, especially ocular cases, when it is already difficult to diagnose that the origin is in pregnancy," he explains.
Between 2010 and 2020, the National Epidemiological Surveillance Network declared 17 cases in Spain, a figure that for many specialists is lower than the real one. The estimated incidence, according to several sources, would be at least one case per 10,000 births. This means that, with 330,000 births in 2022, more than 30 cases per year would remain unreported in Spain.
The REIV-TOXO has identified about 60 cases in the hospitals that form the network. Researchers from the Carlos III Health Institute have presented this week at the congress of the Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC), held in Santiago de Compostela, a study that offers even higher data. "The Specialized Care Activity Registry (RAE-CMBD) detected 547 hospital discharges with this diagnosis between 2010 and 2020 (3% of reported cases)," says the presentation.
Isabel de Fuentes, one of the authors, admits that these data can be approximate due to the source used and that, in any case, they are provisional since they are preliminary results of an extensive investigation still underway. "But in any case, what they do make evident is that there is a great ignorance of the real situation of congenital toxoplasmosis in Spain. There is a clear underdiagnosis and underreporting that requires further study. This needs to be done because if we don't know how many cases occur, we can't properly assess the need for screening."
According to a document from the Carlos III Health Institute, if the mother contracts the parasite in the first 14 weeks of pregnancy, it will also infect the fetus in less than 10% of cases. But if infection occurs, more than 60% of babies will suffer "eye and intracranial injuries that can be severe." Between 14 and 28 weeks of gestation, the infection will reach up to half of the fetuses, but the percentage of those who will suffer damage is reduced to 25%. In these cases, the injuries are mainly ocular and "are generally not serious." Beyond week 28, up to 80% of babies will be infected, although less than 15% will be affected and generally mildly.
"We are starting to have enough evidence that we can significantly reduce the impact of the disease. Drugs help us prevent infection of the fetus and reduce damage when it occurs. But it is important to have screening to treat cases early, "says María de la Calle, head of the Obstetrics section at the Hospital de La Paz (Madrid) and supporter of screening.
Anna Suy, on the other hand, believes that the current recommendation against screening cannot be changed until new evidence emerges. "SEGO, as a scientific society, and governments must make decisions with the available evidence. And this is what it is today. Obviously, new data and publications in scientific media may emerge that change this position. This is how science advances. But that time has not yet come," he concludes.
What all parties agree on is the need to maintain during pregnancy the prevention measures that prevent the contact of the pregnant woman with the parasite. These are to avoid consuming raw meats and cured sausages (although freezing them for two days can reduce the risks), wash all fruits and vegetables that are going to be eaten well and avoid contact with cats that are part of their life outside. Domestic cats that do not leave the house and eat feed are not a source of contagion.
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