Two new cases of Zika virus — including one death — in Utah and the upcoming Olympic Games in Brazil have thrust this public health concern back into the headlines, just as a new study summarizes the particulars of known cases of the virus to date.

The Zika virus gained widespread public attention when a late 2014-early 2015 outbreak in Brazil led to a dramatic increase in cases of newborns with microcephaly — a head circumference significantly less than expected for the child's age. Abnormally small head size causes severe delays in cognitive function, reasoning and learning skills, growth, and neuromuscular development and coordination.

The earlier the rash appeared in pregnancy, the smaller the head circumference.

Infants with microcephaly and their families face significant long-term problems. While there are several causes of microcephaly at birth, including other infections (such as toxoplasmosis, cytomegalovirus and rubella), the brain imaging of the babies with microcephaly related to Zika showed particular abnormalities including malformations of the brain cortex, abnormally large ventricles, underdevelopment of the cerebellum and poor density of the white matter.

Since being brought to the world's attention in Brazil, Zika virus has been recognized worldwide as travelers to countries with Zika-infected mosquitoes contract the virus and bring it home. While travel to an area with Zika was behind the infection of the elderly person infected in Utah who died of the virus, the second Utah case was surprising and involved a person who was a family contact of the deceased. That second patient has recovered.

The CDC is investigating how the virus was spread and whether there may now be infected mosquitoes in Utah which can transmit the disease.

By June 2016, 61 countries have reported cases of Zika. It is spread by the bite of infected mosquitoes, and it can also be transmitted through sexual contact. The risk is highest for pregnant women and their developing fetuses. When adults contract the virus, they often show no symptoms or have mild symptoms such as conjunctivitis, fever, rash and joint pain. Rarely, adults develop Gillian-Barre syndrome, a neurologic complication causing rapidly developing muscle weakness that may last days to weeks.

There are currently almost 1000 identified cases of the virus in the US. With the exception of the one Utah infection, they are all related to travel to Zika-infected countries or to having sex with a partner who contracted the virus.

Research efforts are being directed to infection prevention with vaccines or by control of mosquito carriers, as there is little that can be done, other than supportive therapies, to treat infants who are born with evidence of congenital Zika infection.

Accurate identification of adults and infants with the virus is critical in order to allocate research funds and direct public health measures. Zika in infants has primarily been suspected when infants are born with small heads. Pregnant women have primarily been suspected of Zika infection when they report a rash.

A recent study in The Lancet looks at the pregnancy history, clinical characteristics and neuroimaging of 602 cases of definite or probable congenital Zika in Brazil. It suggests that these criteria are too narrow and will miss cases of the infection and underestimate its prevalence. Investigators propose that screening guidelines must be revised.

The researchers found that not all Zika babies had small heads. When the babies' mothers reported their rash late in pregnancy, they might actually have a normal head size, but the brain tissue imaging reflected Zika-related brain damage. The earlier the rash appeared in pregnancy, the smaller the head circumference.

They suggest that limiting Zika investigations to infants with measurably small head circumference at birth will miss many cases. They also note that not all women whose babies showed congenital Zika reported a rash during pregnancy. Thus, only screening women and babies with a history of pregnancy-related rash will also miss cases. The researchers also found that among the cohort of babies they identified with definite or probably Zika infection, there was a four-fold increase in mortality compared to the general population.

The message from this research is that relying on microcephaly at birth or a history of a rash during pregnancy to identify cases of congenital Zika infection are not sufficiently accurate to inform research and preventive measures.

Internationally, health organizations have been developing policies to help travelers make informed decisions. This has become particularly relevant because of the upcoming Brazil Olympic Games.

The World Health Organization (WHO) has provided guidelines for travelers to Zika-infected areas. They particularly target women who are pregnant or might become pregnant.

WHO recommends that:

  • Pregnant women should not travel to areas where Zika is present.

  • Women's sex partners who have been in Zika-endemic areas should abstain from sex or practice safe sex during the pregnancy because of the high risk of sexual transmission of the infection.

  • For couples or women planning a pregnancy, living in or returning from areas where transmission of Zika virus is known to occur, it is strongly recommended that they wait at least 8 weeks before trying to conceive; and 6 months if the male partner was symptomatic.

  • Men and women of reproductive age, living in areas where local transmission of Zika virus is known to occur, should consider delaying pregnancy and follow recommendations (including the consistent use of condoms) to prevent HIV, other sexually transmitted infections and unwanted pregnancies.

    • Zika virus constitutes a significant risk to the health of developing fetuses and is spreading rapidly worldwide. Research, supported by accurate information, is critical to prevention and control efforts. Until a vaccine is developed, individual measures, as outlined by the World Health Organization, can provide effective guidelines for safer pregnancies.