In addition to the greater susceptibility to presenting severe Covid-19 and dying from the disease, men are more firstly infected and, consequently, can be the main transmitters of Sars-Cov-2. This is what a study by researchers at the Center for the Study of the Human Genome and Stem Cells (GHG-CEL) suggests — one of the Research, Innovation and Diffusion Centers (CEPIDs) funded by FAPESP — based on an epidemiological survey which involved 1,744 Brazilian couples.
The results of the work were published on the medRxiv platform, in an article that has not yet been peer reviewed.
“This finding corroborates and is in line with findings made in recent studies that we carried out, which already indicated that men can transmit more of the new coronavirus”, says to the Fapesp Agency Mayana Zatz, professor at the Biosciences Institute of the University of São Paulo (IB- USP) and coordinator of the CEGH-CEL.
A study published in early August by researchers at the Center in the journal Diagnostics, based on a test for detecting Sars-Cov-2 in saliva developed at the HGH-CEL, found that men have a virus load in the fluid of about 10 times higher than women, particularly up to 48 years of age. This difference in viral load was not detected in tests with nasopharyngeal samples, pointed out the authors of the study, coordinated by Professor Maria Rita Passos-Bueno.
“Since the virus is transmitted mainly by saliva droplets, we deduced that this would explain why men transmit more viruses than women,” says Zatz.
In addition to this observation, the researcher began to hear reports from couples – many of them both doctors – in which the woman was infected with the new Sars-Cov-2 and showed mild or moderate symptoms, while the man remained asymptomatic. A few months later, the spouse was also infected after contact with male patients, which reinforced the theory that men transmit more of the new coronavirus.
In order to assess the hypothesis, the HGH-CEL researchers began to collect, between July 2020 and July 2021, data through e-mails and questionnaires from more than 2,000 couples, with an average age of 45 years until then not vaccinated against Covid-19, in which at least one spouse was infected, diagnosed and showed symptoms of the disease.
To eliminate the influence of behavioral biases, such as the fact that men are more reluctant than women to wear protective masks and respect social distancing, as demonstrated by studies during the pandemic, the transmission of the virus in more than 1,000 couples who lived together during the period of infection without taking protective measures.
Couples were divided into concordant groups – in which both partners were infected – or discordant – in which one of the spouses remained asymptomatic despite close contact with the infected.
The combination of data collected showed that men were the first or the only ones infected in most cases, both among concordant and discordant couples.
“We saw that men were first infected much more than women, in both concordant and discordant couples. In total, 946 men were infected first compared to 660 women,” says Zatz.
The investigation received funding from FAPESP through two other projects: 14/50931-3 and 20/09702-1.
The researchers also analyzed the genetic material of couples in which only one spouse was infected with Sars-Cov-2, although both were exposed, with the aim of understanding why some people are naturally resistant to the infection.
Preliminary results of the study, also published on the medRxiv platform, indicated that more frequent genomic variants in susceptible partners would lead to the production of molecules that inhibit the activation of defense cells known as natural killers or NK (read more at: agencia.fapesp.br/ 35752/).
The complete results of the study, carried out in collaboration with Professor Erick Castelli, from the Universidade Estadual Paulista (Unesp), campus of Botucatu, will soon be published in the journal Frontiers in Immunology.