Could the Zika virus be spread through sex? Two cases suggest it might

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New York: Zika virus has already been linked to brain damage in babies and paralysis in adults. Now scientists are facing another ominous possibility: that on rare occasions, the virus might be transmitted through sex.

The evidence is very slim; only a couple of cases have been described in medical literature. But a few experts feel the prospect is disturbing enough that federal health officials should inform all travellers, not just pregnant women, of the potential danger.

Officials at the Centres for Disease Control and Prevention, however, say the evidence is insufficient to warrant such a warning. While the two instances suggest a "theoretical risk" of sexual transmission, they note the primary vector is clearly mosquitoes.

Marcio Nehab, a pediatrician and infectious disease specialist at Fiocruz, a research institute in Rio de Janeiro, Brazil, said much more research was needed to definitively prove that Zika can be transmitted during sex.

Estafany Perreira holds her five-month-old nephew David, who has microcephaly, in Recife, Brazil.Credit: Getty Images

"At the moment we need to be more concerned with the mosquito, the vector known for transmitting the virus," Dr Nehab said in an information bulletin about Zika geared toward women and children.

At present, experts know of just one case in the medical literature of live Zika virus being detected in a man's semen.

The man was an unidentified 44-year-old Tahitian, exposed during an outbreak of Zika virus in French Polynesia in 2013. French scientists helping to investigate found high levels of the virus in semen samples taken from the patient, even after it disappeared from his blood.

It was unclear how long the virus had persisted in his body: He had had two episodes of fever that might have been caused by the Zika virus, one shortly before he was tested and another about two months earlier. The virus was also found in his urine.

Health workers fumigate to prevent dengue, chikungunya and Zika virus, at El Angel cemetery, in Lima last week. Credit: AP

A more unusual episode – the first clue that Zika could be sexually transmitted – occurred in 2008.

Brian Foy, a biologist specialising in insect-borne diseases at Colorado State University, was in rural Senegal with a graduate student, Kevin Kobylinski, collecting mosquitoes for a malaria study. Both were bitten many times.

Dejailson Arruda holds his daughter Luiza at their house in Santa Cruz do Capibaribe, Brazil. Luiza was born in October with microcephaly, her mother was infected with the Zika virus.Credit: AP

About a week after they flew back to Colorado, Dr Foy and Mr Kobylinski each fell ill with rashes, fatigue and headaches, symptoms typical of several mosquito-borne illnesses.

A few days later, Dr Foy's wife – Joy Chilson Foy, a nurse and mother of four, showed similar symptoms, slowly developing a rash worse than that of either man, along with greater headache pain and bloodshot eyes.

Army soldiers apply insect repellent as they prepare for a clean-up operation against the Aedes aegypti mosquito in Sao Paulo. Credit: AP

All three eventually recovered. Late in his illness, however, Dr Brian Foy had genital pain and what appeared to be blood in his semen.

Blood was drawn from all three patients and tested for the usual West African suspects: malaria, dengue and yellow fever. All were negative.

Spreading the Zika virus ... A female Aedes aegypti mosquito in the process of acquiring a blood meal from a human host. Credit: AP

Their infection remained a mystery until a year later, when Mr Kobylinski, back in Senegal, met another scientist who suggested it could be Zika virus. The blood samples, which Dr Foy had frozen, tested positive. That left the question of how his wife had been infected.

She had not left northern Colorado, which has none of the mosquitoes that transmit Zika. And it seemed unlikely that she and her husband had been bitten by the same mosquito: The virus needs more than four days to move from the insect's gut to its salivary glands.

Neither had passed the disease to their children, so even close family contact seemed non-infectious. The most likely explanation, the couple realised, was that they had had sex shortly after Dr Foy's return, before he fell ill.

Dr Foy wrote about his experience in 2011 in the journal Emerging Infectious Diseases.

In an interview, Dr Foy said he had been trying to get research money to study the phenomenon, but there had been obstacles: Until the past few weeks, there had been little interest in the obscure virus.

Zika virus is hard to study, because it does not infect mice, rats or most other lab animals. It does infect monkeys, but that research is difficult, expensive and controversial. Colorado State did not have a monkey research colony, Dr Foy said.

Dr William Schaffner, chief of preventive medicine at Vanderbilt University Medical School, said it was imperative that research on possible sexual transmission of Zika be done in Brazil or another Latin American country experiencing an outbreak.

Two suspect cases "are not really enough to warrant a large public health recommendation from the CDC," he said. "But it's provocative, so someone else could recommend it. And it certainly should be studied."

Testing men for the virus in their semen should be easy, he added. After that, researchers should look for couples like the Foys, in which one partner had been in a mosquito-infested area and the other had been in a mosquito-free one.

"If I was a man and I got Zika symptoms, I'd wait a couple of months before having unprotected sex," said Scott Weaver, director of the Institute for Human Infections and Immunity at the University of Texas medical branch in Galveston and an expert on the virus. "If my wife was of childbearing age, I'd want to use protection, certainly for a few weeks."

A spokeswoman for Brazil's Health Ministry said studies about how Zika can be contracted needed to be evaluated more closely.

"These analyses need to be accompanied by scientific work so the Health Ministry can provide the population with safe advice about transmission of the virus."

The ministry has advised Brazilian women to postpone getting pregnant until more is known about the virus and microcephaly, a neurological disorder that causes babies to be born with a small head and underdeveloped brain.

On Monday, the Pan American Health Organisation warned that Zika virus was likely to spread to every country in the Americas except Canada and Chile where the Aedes aegypti, which transmits the virus, is not present.

In the United States, CDC experts have said they expect the disease to follow the same pattern as dengue: limited outbreaks in hot, wet regions including Florida and other states along the Gulf Coast and Hawaii, where the mosquito which also transmits yellow fever and dengue, is common. They hope that aggressive mosquito control will contain the infection.

The CDC has warned pregnant American women not to travel to Latin American countries.

The New York Times