TWiV 399: Zika la femme

The latest Zika virus news from the ConTWiVstadors, including a case of female to male transmission, risk of infection at the 2016 summer Olympics, a DNA vaccine, antibody-dependent enhancement by dengue antibodies, and sites of replication in the placenta.

You can find TWiV #399 at microbe.tv/twiv, or listen below.

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TWiV 393: Lovers and livers

Possible sexual transmission of Zika virus, and a cell protein that allows hepatitis C virus replication in cell culture by enhancing vitamin E mediated protection against lipid peroxidation, are the subjects discussed by the TWiVerati on this week’s episode of the science show This Week in Virology.

You can find TWiV #393 at microbe.tv/twiv, or listen below.

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TWiV 383: A zillion Zika papers and a Brazilian

TWiVEsper Kallas and the Merry TWiXters analyze the latest data on Zika virus and microcephaly in Brazil, and discuss publications on a mouse model for disease, infection of a fetus, mosquito vector competence, and the cryo-EM structure of the virus particle. All on episode #383 of the science show This Week in Virology.

Audio and full show notes for TWiV #383 at microbe.tv/twiv or listen below.

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TWiV 378: Herpes plays DUBstep

TWiVOn episode #378 of the science show This Week in Virology, Greg Smith joins the TWiVirate to reveal how his lab discovered a switch that controls herpesvirus neuroinvasion, and then we visit the week’s news about Zika virus.

You can find TWiV #378 at microbe.tv/twiv, or you may listen below.

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Person to person Zika virus transmission

FlavivirusThe title of a Eurosurveillance article, “An autochthonous case of Zika due to possible sexual transmission, Florence, Italy, 2014” was written to make the headlines. The title should be “An autochthonous case of Zika due to person to person contact, Florence, Italy, 2014.”

An Italian man returns from a 10 day holiday in Thailand and a day later develops a rash with fever and headache. Within 6 days the rash has subsided. About two weeks later his girlfriend develops a similar disease. As this was 2014 no one looked for Zika virus and both were presumed to have dengue virus infection.

The serum samples taken from the patients were pulled from the freezer after Zika virus becomes a household word in 2015. Both patients’ sera are shown to contain neutralizing antibodies against Zika virus, with a clear rise between samples taken early in illness and after recovery.

Apparently the couple had sex between the time the man’s rash subsided, and the onset of the girlfriend’s symptoms. The authors of the paper conclude that transmission by semen is suggested.

Inexplicably, the authors write:

Other transmission modalities (i.e. direct contact with other bodily fluids) are unlikely to play a role but may not be completely ruled out.

Why is it unlikely that the man had a residual rash, possibly leaking virus, which he then transferred to the woman, perhaps on one or more mucus membranes? This mode of transmission is also known as ‘close contact’ between individuals. I am waiting for a similar case report in which the couple used condoms, yet Zika virus infection was still transmitted.

Like everyone else, the authors are seduced by the possibility of sexual transmission of Zika virus. I have yet to see any clear, convincing evidence of sexual transmission of Zika virus. At worst, the risk is extremely low, although probably not zero, given that Zika virus RNA (not virus) has been found in semen of one individual. Consider these facts and act accordingly.

Zika from sex, the byway but not the highway

FlavivirusCan Zika virus be sexually transmitted? Perhaps in very rare cases, but the main mode of transmission is certainly via mosquitoes. That’s why I’ve shamelessly stolen a quote on this topic from Dr. William Schaffner of Vanderbilt University:

Mosquito transmission is the highway, whereas sexual transmission is the byway. Sexual transmission cannot account for this sudden and widespread transmission of this virus.

If you just read the news headlines, which many people do, you will think that Zika virus spreads like HIV. But it does not.

Let’s make a clear distinction between sexually transmitted viruses (like HIV – sex is the main mode of transmission, along with contaminated blood), versus sexually transmissible viruses. The latter includes viruses that now and then might be sexually transmitted under certain circumstances, but which normally are transmitted by another route. Zika virus is transmitted among humans by mosquitoes. If sexual transmission occurs, it is very, very rare, given the large number of Zika virus infections that have been documented.

Is Zika virus sexually transmissible?

The first hint of sexual transmission of Zika virus came from the story of two American scientists working in Senegal in 2008, where they were sampling mosquitoes. Between 6-9 days after returning to their homes in Colorado, they developed a variety of symptoms of infection including fatigue, headache, chills, arthralgia, and a maculopapular rash. The wife of one patient had not traveled to Africa, yet she developed similar symptoms three days after her husband. Analysis of paired acute and convalescent sera from all three patients revealed antibodies against Zika virus. The authors of the study do not conclude that transmission from husband to wife was via sexual activity – they suggest it as a possiblity. Their data could not prove sexual transmission.

More recently infectious Zika virus was detected in semen of a French Polynesian male who had recovered from infection. The presence of virus in semen is compatible with sexual transmission, but the patient was not known to have transmitted infection to anyone.

The CDC has concluded that Zika virus was transmitted to an individual in Texas who had sex with a traveler returning from Venezuela. As of this writing I do not know exactly how the CDC came to this conclusion.

What would be needed to prove that Zika virus is sexually transmissible?

Polymerase chain reaction (PCR) is used to diagnose many viral diseases. This assay detects small fragments of viral nucleic acid and can be very specific. However as we are trying to establish for the first time that Zika virus can be transmitted sexually, more than PCR must be done – infectious virus should be recovered from the donor and recipient. A positive PCR result does not mean that infectious virus is present in the sample, only fragments of the genome, which of course would not be infectious. It is important to correlate the presence of infectious virus with sexual transmission.

Not only should infectious virus be recovered from both donor and recipient, but the viral genome sequences should be nearly identical, providing strong evidence for sexual transmission. If the viral genome sequences were substantially different, this result could imply that the infection was acquired from someone else.

Looking for anti-viral antibodies in serum is a good way to confirm virus infection when virus is no longer present. However it is not as specific as PCR or virus isolation, and does not provide information about the genome of the donor and recipient virus.

Sexual transmission of Ebolavirus still remains speculative. There are several suspected cases, and many examples of PCR positive semen samples from men who have recovered from the disease. It’s not easy to prove that a virus can be transmitted sexually, especially when it is a rare event.

Just as we are not sure that Zika virus causes microencephaly, we are not sure if it can be sexually transmitted.

TWiV 368: Infected, you will be

On episode #368 of the science show This Week in Virology, a plaque of virologists explores the biology of Zika virus and recent outbreaks, and the contribution of a filamentous bacteriophage to the development of biofilms.

You can find TWiV #368 at www.microbe.tv/twiv.

TWiV 361: Zombie viruses on the loose

On episode #361 of the science show This Week in Virology, the TWiVsters discuss Frederick Novy’s return from retirement to recover a lost rat virus, and evidence for persistence of Ebolavirus in semen.

You can find TWiV #361 at www.microbe.tv/twiv.

TWiV 334: In vino virus

On episode #334 of the science show This Week in Virology, the TWiVles talk about endogenous viruses in plants, sex and Ebolavirus transmission, an outbreak of canine influenza in the US, Dr. Oz, and doubling the NIH budget.

You can find TWiV #334 at www.microbe.tv/twiv.

TWiV 322: Postcards from the edge of the membrane

On episode #322 of the science show This Week in Virology, the TWiVodes answer listener email about hantaviruses, antivirals, H1N1 vaccine and narcolepsy, credibility of peer review, Bourbon virus, influenza vaccine, careers in virology, and much more.

You can find TWiV #322 at www.microbe.tv/twiv.