The US Centers for Disease Control and Prevention (CDC) today expanded its recommendation for men potentially exposed to Zika virus who are considering trying to conceive with their partners to wait at least 6 months, regardless of symptoms, in line with new scientific evidence and recently updated World Health Organization (WHO) guidance.

In other developments, Thailand confirmed two Zika-linked microcephaly cases, its first, and CDC researchers published a case series on US children who contracted Zika during travel, suggesting that their infections are usually mild, as they are for most adults.

Lingering virus in semen drives guidance

The CDC spelled out its new recommendations today in an early edition of Morbidity and Mortality Weekly Report (MMWR). It said the new guidance combines its pregnancy planning and sexual transmission advice into one document.

The new recommendation for couples trying to conceive extends the waiting period if a man had Zika symptoms or possible exposure from at least 8 weeks to at least 6 months. Expanding the waiting period is intended to cut the risk of sexual transmission during conception and prevent early fetal exposure to the virus.

The WHO expanded its recommended waiting period to 6 months on Sep 6, based on evidence that the virus can persist in semen for that long, longer than previously thought. At that time, the CDC said that it was aware of the new information—part of rapidly changing scientific development—and would update guidance when its review was complete.

Besides men who have Zika symptoms, asymptomatic men should also wait 6 months after the last possible exposure before attempting to conceive, the WHO said.

The CDC hasn't changed its recommendation for women with possible Zika exposure who are trying to conceive: They should wait at least 8 weeks after symptom onset or last possible Zika exposure.

Couples who aren't trying to conceive should minimize the risk of sexual spread by using a condom or abstaining from sex for the same periods described for men and women trying to get pregnant.

Potential risk from Southeast Asian strain

Thailand has confirmed two Zika-linked microcephaly cases, prompting the WHO, in a statement today from its regional office, to urge countries in Southeast Asia to take extra steps to prevent, monitor, and respond to the Zika virus threat.

Genetic analysis of recent Zika viruses from Singapore and Malaysia suggests that the strain linked to outbreaks is related to an Asian strain that has circulated in Southeast Asia in the past, not the one fueling outbreaks in the Americas.

The WHO said in its statement that the virus has been detected in Southeast Asia in recent years, including in Thailand, Indonesia, Maldives, and Bangladesh.

Experts aren't sure if the Southeast Asian strain can cause the type of birth defects seen with the Asian stain, so the announcement of the two Zika-associated microcephaly cases seems to suggest the potential for fetal complications. Thailand has identified two suspected microcephaly cases, one in an unborn baby, and a few days ago ruled out Zika links for two others.

According to a Reuters report today, Thailand has confirmed 349 Zika cases since January, 33 of them in pregnant women, and Singapore has reported 393 Zika cases since August, including 16 in pregnant women.

Today's announcement comes a day after the CDC issued a travel warning for pregnant women to avoid nonessential travel to 11 Southeast Asian countries.

No complications in peds case series

The CDC published its Zika profile in children in an early online edition of MMWR. Researchers analyzed 158 cases of confirmed or probable postnatal Zika reported from US states this year from January through July.

The illnesses were reported in 30 states, mostly in Florida, New York, and California. All of the cases were contracted abroad, with the most common destinations being the Dominican Republic, Puerto Rico, Honduras, Nicaragua, and Jamaica. Ages ranged from 1 month to 17 years, with a median age of 14. Girls made up 56% of those infected. Five girls were pregnant.

Common symptoms included rash, fever, conjunctivitis, and joint pain. No meningitis, encephalitis, or Guillain-Barre syndrome (GBS) complications were reported, and only two of the children were hospitalized: a 4-year-old with fever, cough, and poor oral intake and a 1-year-old with a cough and a rash. No deaths were reported.

The CDC said the findings are similar to other reports and that protecting kids from mosquitoes is the best way to prevent Zika infections. Researchers also noted that the pregnancies in the case series underscores the point that sexually active teens are also at risk for sexual transmission of Zika virus, with the resulting threat to unborn babies.

Because symptoms can mimic other childhood infections, health providers should consider Zika in the diagnosis if kids live in or have traveled to an area where the virus is circulating.

See also:

Sep 30 MMWR report on Zika sexual transmission

Sep 30 CDC press release

Sep 30 WHO statement

Sep 30 Reuters story

Sep 30 MMWR report on Zika in children