A person can become infected with Zika virus twice

Can the coronavirus be transmitted while kissing?

Photo: Can the new coronavirus or the Zika pathogen be transmitted when kissing?

No kissing: the defense mechanism in saliva does not stop SARS-CoV-2

Virologists from Ulm University Medical Center have examined whether kissing becomes risky behavior during the coronavirus pandemic. In a current study, they are researching to what extent the Zika virus and the new coronavirus (SARS-CoV-2) can be passed on from person to person via saliva. The researchers have discovered a new defense mechanism for the Zika virus that can prevent infection. However, this saliva component has no effect on the risk of infection with SARS-CoV-2.


In fact, both viruses can be found in large quantities in saliva. In a current study, virologists from Ulm have investigated whether they are also passed on from person to person via this body fluid. In doing so, they discovered a new defense mechanism in saliva that can prevent infection with the Zika virus. However, this saliva component has no influence on the risk of infection with the novel coronavirus (SARS-CoV-2).

How do emerging viruses spread from person to person?

This is the question that researchers at the Ulm Institute for Molecular Virology are asking themselves for both the Zika virus and the new coronavirus. Both pathogens have recently passed from animals to humans as zoonoses. Since then, SARS-CoV-2 has mainly spread through droplet infection and aerosols. The main carriers of the Zika virus, however, are yellow fever mosquitoes, but human-to-human transmission through sexual intercourse has also been reported. In earlier studies, the virologists at Ulm University Medical Center were able to show that so-called extracellular vesicles in human seminal fluid inhibit this transmission path for Zika viruses and related pathogens. Researchers led by Professor Jan Münch, Dr. Janis Müller, Rüdiger Groß and Carina Conzelmann in their recently published specialist article.

In laboratory experiments, the authors brought human saliva together with the respective virus (SARS-CoV-2 or Zika virus). Cell lines and primary oral mucosal cells were then exposed to these mixtures. In order to prove an infection with the respective pathogen, the scientists measured the amount of viruses in the cells - with contradicting results. They found out that a Zika virus infection is almost impossible with high saliva concentrations. This effect could not be demonstrated for SARS-CoV-2. The real challenge, however, was identifying the salivary component that prevents Zika virus transmission. Due to their previous research in sperm samples, the group focused on extracellular vesicles. “With the help of highly specialized methods, the vesicles had to be purified from the saliva. We were then able to determine their number, size, identity and antiviral activity, ”explains Dr. Janis Müller, who carried out these analyzes during a guest stay at the renowned Karolinska Institute in Stockholm.

Overall, the virologists show that the Zika virus is able to infect cells of the oral mucosa. However, an infection - similar to human sperm - is inhibited by the body's own extracellular vesicles in the saliva. “The vesicles ensure that the Zika virus cannot dock on the target cell and infect it,” explain the first authors Carina Conzelmann and Rüdiger Groß. However, this defense mechanism has no influence on infection with the novel coronavirus. Accordingly, saliva transmission does not seem to play a major role in the Zika virus, but possibly in SARS-CoV-2.

The virus researchers have identified a new component of the human immune system with extracellular vesicles, which apparently exerts its effect in various body fluids. This protective mechanism seems to be directed specifically against properties of flaviviruses (Zika virus, dengue virus, West Nile virus). In further studies, the researchers want to find out what this defense mechanism is based on.

The result of the current study in the "Journal of Extracellular Vesicles" underpins reports that no Zika virus is known to be transmitted through kissing - although the infectious virus can be detected in the saliva of infected people. However, if a coronavirus infection is suspected, the researchers advise against kissing.

The investigations were funded as part of the Fight-nCoV project to identify antiviral agents against SARS-CoV-2 and the Collaborative Research Center 1279 (“Use of the human peptidome for the development of new antimicrobial and anti-cancer therapeutics”). Dr. Janis Müller was also supported by the "Elite Program for Postdocs of the Baden-Württemberg Foundation" on the topic of "Transmission of the Zika Virus" and through his first DFG application for research into antiviral properties in body fluids.

Source: Ulm University

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