|Credit CDC PHIL|
Although there was only one case on record at the time (from 2008 see Probable Non–Vector-borne Transmission of Zika Virus, Colorado, USA), in late January the UK PHE Warned On Potential Sexual Transmission Of Zika strongly recommending that:
Sexual transmission of Zika virus has been recorded in a limited number of cases, and the risk of sexual transmission of Zika virus is thought to be very low. However, if a female partner is at risk of getting pregnant, or is already pregnant, condom use is advised for a male traveller :
- for 28 days after his return from a Zika transmission area if he had no symptoms of unexplained fever and rash
- for 6 months following recovery if a clinical illness compatible with Zika virus infection or laboratory confirmed Zika virus infection was reported
Less than a week later, a second case was confirmed (see Dallas, Texas: DCHHS Confirms Locally Acquired Sexually Transmitted Zika Infection), and soon other public health agencies were issuing similar advice.
Today we may know what prompted the UK's initial strong recommendations.
A letter, published ahead of print today in the CDC's EID journal, describes the detection of ZIKV by rRT-PCR in a 68 year old man's semen by the UK's PHE in 2014, more than 2 months after the onset of his illness.
While live virus was not cultured from the sample, it suggests that sexual transmission may be possible weeks or even months after initial infection. Not unlike what we've seen (albeit, very rarely) with Ebola.
While the persistence of ZIKV in semen for weeks or months increases the risks of sexual transmission, the mosquito-vector remains the primary way the virus is transmitted to humans.
Volume 22, Number 5—May 2016
LetterAtkinson B, Hearn P, Afrough B, Lumley S, Carter D, Aarons EJ, et al.
To the Editor: As an increasing number of autochthonous Zika virus (ZIKV) infections are reported from several South America countries (1), we read with interest the report from Musso et al. on the potential sexual transmission of ZIKV (2). We report additional evidence for this potential route of transmission after identification of an imported case of ZIKV infection into the United Kingdom.
After an outbreak alert for ZIKV in French Polynesia, active ZIKV screening was implemented at Public Health England (Porton Down, United Kingdom). In 2014, a 68-year-old man had onset of fever, marked lethargy, and an erythematous rash 1 week after returning from the Cook Islands. Serum samples taken 3 days into the febrile illness tested negative for dengue and chikungunya viruses by real-time reverse transcription PCR (rRT-PCR). Test results for dengue virus IgM and chikungunya virus IgM also were negative; a test result for dengue virus IgG was indeterminate.
An rRT-PCR test result for ZIKV (3) was positive and indicated a crossing threshold value of 35 cycles. This low viral load, commonly observed even in the acute phase of disease (3), meant that attempts to obtain sequence data were unsuccessful.
Convalescent-phase serum, urine, and semen samples were requested; only semen was positive for ZIKV by rRT-PCR, , at 27 and 62 days after onset of febrile illness. These results demonstrated stronger signals than those obtained in tests of the original serum sample, with crossing threshold values of 29 and 33 cycles, respectively. ZIKV-specific plaque reduction neutralization test results were positive on convalescent-phase serum samples.
Although we did not culture infectious virus from semen, our data may indicate prolonged presence of virus in semen, which in turn could indicate a prolonged potential for sexual transmission of this flavivirus. Moreover, these findings could inform decisions regarding what control methods are implemented and which specimen types are best suited for diagnostic detection.