Zika infections unlikely to be passed by kissing, casual contact: study

August 1, 2017, University of Wisconsin-Madison
Transmission electron microscope image of negative-stained, Fortaleza-strain Zika virus (red), isolated from a microcephaly case in Brazil. The virus is associated with cellular membranes in the center. Credit: NIAID

Saliva is no way to pass a Zika virus infection.

According to researchers at the University of Wisconsin-Madison who conducted studies with , casual contact like kissing or sharing a fork or spoon is not enough for the to move between hosts. Their findings were published today (Aug. 1, 2017) in the journal Nature Communications.

Scientists believe that mosquito bites are the source of most Zika virus infections in people. After infection, the Zika virus is present in blood and for up to about two weeks, but it remains in bodily fluids like breast milk for weeks and semen for months. The virus can also be spread by sexual intercourse, but much about Zika remains unknown—including, until recently, whether the saliva of an infected person posed a danger.

"If passing the virus by casual contact were easy, I think we would see a lot more of what we would call secondary transmission in a place like the United States," says Tom Friedrich, a virology professor at the UW-Madison School of Veterinary Medicine. "But we're not seeing clinically apparent spread of Zika throughout the continental U.S. without the presence of the mosquitoes that carry the virus, and our study helps to put into context some of the transmission risk."

Last week, Texas public health authorities announced a case of Zika virus infection likely caused by a mosquito bite. The saliva study was funded by the National Institutes of Health in 2016 amid uncertainty about other potential ways Zika could spread between people. In particular, officials were concerned by a mysterious case of Zika transmission—between an elderly man and his caretaker son in Utah—that ruled out better-understood routes such as mosquitoes or sexual activity.

In the study results reported today, at the Wisconsin National Primate Research Center were infected with the strain of Zika virus that has been circulating in North and South America in recent years, and saliva was collected from the infected monkeys.

The researchers swabbed the tonsils of five uninfected monkeys with the saliva, and swabbed the tonsils of three monkeys with a concentrated high dose of Zika virus in solution.

None of the saliva-swabbed monkeys developed an infection—nor did a pair of monkeys who had infected saliva swabbed in their nostrils or eyelids. However, all three monkeys who had high-dose virus applied directly to their tonsils in the absence of saliva got infected (though the infection took slightly longer to develop than in monkeys infected under their skin).

Dawn Dudley, a scientist in UW-Madison's School of Medicine and Public Health, says the tonsils were chosen as a site for testing because they are typically a source of infection for influenza and Epstein-Barr virus.

But saliva itself may do a lot of work to thwart Zika's infection potential.

Matthew Aliota, a research scientist in the UW-Madison School of Veterinary Medicine, conducted experiments with monkey saliva and cells in the lab.

"He found that if you add monkey saliva to the virus you reduce the ability of the virus to infect cells," Friedrich said.

The study's infected monkeys had very little active virus in their saliva, compared to the amounts typically passed into people or monkeys by mosquito bites. The monkeys who were swabbed with the high dose of virus encountered nearly 80,000 times the number of Zika particles the researchers counted in the saliva from the infected monkeys.

"The viral loads in the saliva in general are low, but there are also anti-microbial components in saliva making that low level of virus even less infectious than it might be in another medium," says Christina Newman, co-first author of the study with Dudley and also a scientist with the UW-Madison Zika Experimental Science Team.

"Saliva is also viscous stuff," Dudley said. "That hinders the ability of the virus to move and get to cells that they could infect."

This does not add up to an environment friendly to .

"The case in Utah was an outlier—by orders of magnitude—in terms of the amount of virus that was present in his blood," Friedrich said. "Transmission via saliva is theoretically possible, but it would require extraordinarily high viral loads that just aren't present in the vast majority of infected people."

Explore further: Zika virus persists in the central nervous system and lymph nodes of rhesus monkeys

More information: Nature Communications (2017). dx.doi.org/10.1038/s41467-017-00246-8

Related Stories

Zika virus persists in the central nervous system and lymph nodes of rhesus monkeys

April 28, 2017
Zika virus can persist in cerebrospinal fluid (CSF), lymph nodes and colorectal tissue of infected rhesus monkeys for weeks after the virus has been cleared from blood, urine and mucosal secretions, according to a study published ...

Maternal-fetal transmission of Zika virus and therapeutic approaches to prevent it

June 5, 2017
The devastating effects of Zika virus on the brain of the developing fetus during infection in pregnancy have led to intensive research to understand the routes of Zika virus transmission and how the virus travels to and ...

New scientific evidence of sexual transmission of the Zika virus

April 15, 2016
A study by researchers from Inserm, the Paris Public Hospitals (Bichat Hospital, AP-HP), Aix-Marseille University, and the National Reference Centre for Arboviruses confirms that the ZIKA virus can be transmitted sexually. ...

Zika detected in urine, saliva: top Brazilian researchers

February 5, 2016
Brazil's top research institute said Friday that Zika has been detected in urine and saliva, but added that there is no proof the virus can be transmitted through those fluids.

Argentina: 1st local transmission of Zika, likely by sex

February 26, 2016
Argentine authorities say they've detected the country's first case of local infection with the Zika virus and say it's apparently due to sexual transmission.

Zika infections could be factor in more pregnancies

May 25, 2017
Zika virus infection passes efficiently from a pregnant monkey to its fetus, spreading inflammatory damage throughout the tissues that support the fetus and the fetus's developing nervous system, and suggesting a wider threat ...

Recommended for you

More frequent checks control MRSA in newborns, but can hospitals afford them?

May 22, 2018
The more often a hospital can check its newborns for deadly MRSA germs, the more likely it will be that they are contained, according to a new study.

Could we predict the next Ebola outbreak by tracking the migratory patterns of bats?

May 22, 2018
Javier Buceta, associate professor of bioengineering, Paolo Bocchini, associate professor of civil and environmental engineering, and postdoctoral student Graziano Fiorillo of Lehigh University have created a modeling framework ...

Helping preterm infants grow bigger kidneys would prevent kidney disease later in life

May 21, 2018
Nephrons are the microscopic blood-filtering units inside our kidneys that convert waste products into urine, regulate our electrolyte levels and our blood pressure.

Kidney docs worry over no dialysis for undocumented immigrants

May 21, 2018
(HealthDay)—Undocumented immigrants in the United States are often denied treatment for kidney failure until they have a life-threatening emergency. Now a new study finds that the doctors and nurses who treat them are frustrated ...

Clues found to early lung transplant failure

May 21, 2018
Among organ transplant patients, those receiving new lungs face a higher rate of organ failure and death compared with people undergoing heart, kidney and liver transplants. One of the culprits is inflammation that damages ...

How to ethically conduct clinical research during public health emergencies

May 21, 2018
Following the 2014-2015 Ebola outbreak in West Africa, the U.S. National Academy of Sciences, Engineering and Medicine established a committee to assess the clinical trials conducted in Guinea, Sierra Leone and Liberia. In ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.