Eurosurveillance: Prolonged Shedding Of Zika Virus RNA In Saliva - Italy

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Traces of Zika virus RNA have been detected in urine or saliva since 2014 (see Detection of Zika virus in saliva), What hadn't been demonstrated - until about 5 weeks ago - was the presence of live Zika virus in these bodily fluids (see FIOCRUZ: Statement On Detection Of Zika Virus In Saliva and Urine).


Since then, concerns have been raised over the possibility that saliva might be a potential route for human-to-human transmission. Evidence is lacking, however, and  yesterday's ECDC Risk Assessment had this to say:

Risk of sexual transmission
 
(Excerpt)

Zika virus genome has also been detected in saliva during the acute phase of the disease [52]. Data about the presence of viable virus, viral load or kinetics are lacking, and at this point in time the risk of transmission via saliva cannot be further assessed.

 

Adding incrementally to our current knowledge of Zika is a report today from the Journal Eurosurveillance, which extends the length of time that Zika virus has been detected in saliva to nearly a month.

The authors suggest their findings  pose questions on the potential risk of human-to-human transmission of the virus through saliva.

While this type of H-2-H transmission of an arbovirus has never been documented, not so very long ago sexual transmission of Zika was considered a very remote, almost theoretical possibility. Today, all major public health agencies are actively providing guidance to prevent sexual transmission.

Eurosurveillance, Volume 21, Issue 10, 10 March 2016

Rapid communication 

Isolation of infectious Zika virus from saliva and prolonged viral RNA shedding in a traveller returning from the Dominican Republic to Italy, January 2016

L Barzon ^{1 2} , M Pacenti ² , A Berto ¹ , A Sinigaglia ³ , E Franchin ^{1 2} , E Lavezzo ¹ , P Brugnaro ⁴ , G Palù ^{1 2}

Received:03 March 2016; Accepted:10 March 2016

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We report the isolation of infectious Zika virus (ZIKV) in cell culture from the saliva of a patient who developed a febrile illness after returning from the Dominican Republic to Italy, in January 2016. The patient had prolonged shedding of viral RNA in saliva and urine, at higher load than in blood, for up to 29 days after symptom onset. Sequencing of ZIKV genome showed relatedness with strains from Latin America.

(BIG SNIP)

Discussion and conclusions

In this report, we described the isolation of infectious ZIKV in cell culture from saliva collected from a patient during acute ZIKV infection. This finding poses questions on the potential risk of human-to-human transmission of the virus through saliva.

In particular, the virus was isolated from saliva collected on day 6 after symptom onset. It is conceivable that viral isolation is more successful from saliva samples characterised by high viral load and collected during the first week after symptom onset, before the appearance of antibodies. However, further analyses in other patients are required to assess the infectivity of ZIKV in saliva.

Shedding of ZIKV RNA in saliva has been reported in the literature. In particular, it has been observed in 48% of patients tested during the first week after symptom onset, i.e. more frequently, although not for a longer time, than in plasma [25]. For this reason, testing ZIKV in saliva by RT-PCR has been recommended as a non-invasive and sensitive method for the direct diagnosis of ZIKV infection during the first week after symptom onset [25].

In the case reported here, ZIKV RNA was present at high titre during the first week after symptom onset and remained detectable for a relatively long period, up to 29 days after onset of symptoms. Viral RNA was also excreted in urine for a long-time, in agreement with previous reports on ZIKV detection in urine for more than 10 days after onset of disease [26,27]. Shedding in saliva and urine has also been demonstrated for other vector-borne flaviviruses, i.e. DENV [28,29] and West Nile virus [30,31], and these samples are used for direct diagnosis based on viral nucleic acid or antigen detection.

While isolation of ZIKV in cell culture from urine, semen, and breast milk has been described [22,32,33], to our knowledge, isolation of ZIKV from saliva has not been reported so far. Epidemiological data and experimental studies are needed to assess the potential risk of ZIKV spread and transmission through saliva. Interestingly, a human case of ZIKV infection following a monkey bite has been reported [34]. In addition, CHIKV, a mosquito-borne alphavirus, has been isolated in oral fluids of patients with severe infection and in the saliva of experimentally infected mice and monkeys, and mouse-to-mouse transmission of CHIKV without an arthropod vector was demonstrated [35].

Finally, from the laboratory perspective, the results of this study showed that saliva is a useful sample not only for ZIKV nucleic acids detection, but also for virus isolation.