If researchers had earlier reported the presence of Zika virus in urine and saliva samples (besides semen, blood and breast milk), a new study has been able to find infectious Zika virus particles in urine and saliva samples of two patients during the acute phase of infection. While in theory the presence of Zika virus in urine and saliva can lead to yet another route for Zika transmission, at this point in time, it is not clear whether it can actually happen. It is extremely important to know this as it will help in controlling Zika virus transmission.

According to the results of a study published in the journal PLOS Neglected Diseases, the viral concentration was as high as 80 plaque forming units per ml in a saliva sample of a patient in his acute phase of infection.

The urine and saliva samples from nine patients from Rio de Janeiro suspected of Zika virus infection were examined. The samples were collected between January 14, 2016 and February 2, 2016. Six of the seven women were pregnant with gestational ages varying from 18 to 33 weeks.

Of the nine patients studied, Zika virus was detectable in urine and saliva samples in only two patients (patients 1 and patient 6). Generally, whenever urine and saliva samples are collected from the same patients, the viral load is higher in urine than saliva. Yet, the researchers were able to detect more number of plaques in saliva samples. Also, the virus was found in the urine sample of only one patient (patient 1) though the viral load in the urine sample of patient 1 was 100 times lower than patient 6.

Viral detection and recovery from urine and saliva samples might be related to severity of infection as well as the period of specimen collection after the onset of Zika symptoms. The pH of saliva and urine also affects the ability to recover the virus. The pH in urine varies from 4.5 to 8.0 while saliva assumes values near neutral pH. The pH of the urine sample of patient 6, which was mildly acidic at 5.6, might be the reason why no virus was detected.

“The importance of Zika virus in urine for human transmission is unexplored, but the effect of acidic pH on viral viability might represent a serious restriction for viral spreading,” writes Myrna C. Bonaldo, the senior author of the paper, from Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro, Brazil.

Virus in saliva

At the same time, the very presence of viable Zika virus in saliva “does not always indicate that the virus can be transmitted orally and become epidemiologically relevant”.  This is because saliva contains antiviral molecules.

Despite the protective nature of saliva, ulcer or disruption of oral skin can facilitate the entry of the virus into the body. As the latest study has found infectious Zika virus in saliva samples, there is a possibility of person-to-person oral transmission of Zika virus when the oral cavity mucus membrane is disrupted. More studies are needed to confirm this.

“In conclusion, the detection of infective Zika virus in saliva and urine of patients deserves a more detailed study to establish whether or not these fluids contribute to viral transmission. Surely, these findings will be extremely relevant to prevent and control Zika virus transmission,” the authors write.