The Centers for Disease Control and Prevention (CDC) directed healthcare providers yesterday to ask pregnant women if they have traveled to regions with an ongoing outbreak of Zika virus that is spreading across the Americas and to test those who have for presence of the virus. This comes on the heels of the travel alert issued by the CDC with special precautions for pregnant women – asking them to consider postponing travel to regions with an ongoing Zika outbreak.
Why specifically pregnant women? In December, Brazilian and other health officials reported that outbreaks of Zika have been associated with sharp increases in a birth defect known as microcepahly – a condition in which babies are born with smaller than normal heads leading to major concerns expressed by physicians and experts. Though a causative link has not been established, based on current data researchers strongly suspect that Zika infections during the first trimester of pregnancy underlie the defects.
Several important issues are being dissected such as what experts know about the virus, what it can do and what is being done to tackle this epidemic.
What’s Zika and where did it come from?
Zika is a virus that belongs in the same family of viruses as dengue and West Nile, called flaviviruses. It gets its name from the Zika forest in Uganda where it was first isolated in monkeys in 1947. The first human detection was in Uganda in 1952. Since then there are two distinct lineages that have been detected, an African lineage and an Asian lineage. According to health officials, the current outbreak is thought to be caused by the Asian lineage of the virus.
How and where is it spreading?
Zika spreads through the bites of mosquitoes. The Aedes mosquitoes, whcih also transmit dengue and chikungunya are the major carriers of Zika. While the species Aedes aegypti is thought to be the primary carrier, knowledge is still limited. Once an infected mosquito bites an individual, he or she can carry the virus in the blood for up to a week after the infection. During this period mosquitoes that bite the person can get infected and then pass on the virus to others. There have been a few reports of transmission through sexual contact or via blood transfusion, but these are rare cases.
The bigger concern though is that the virus could be passed on from mother to child during pregnancy, and that is the cause of the increase in birth defects. Though experts suspect this to strongly be the case, a link has not been conclusively proven. “I think that the link between Zika virus infection and microcephaly has become reasonably strong with the detection of viral RNA in several fetuses diagnosed in Brazil,” said Scott Weaver, an infectious diseases professor at the University of Texas Medical Branch in a comment to the Genetic Expert News Service (GENeS) which provides journalists with expert analysis on important issues in genetics and biotechnology. However, “an alternative cause cannot yet be ruled out until the maternal infection is linked directly to the onset of microcephaly in the absence of other viruses,” he said
The most recent reports from the World Health Organization indicate that Zika outbreaks have been detected in 18 countries and territories in the Americas including Brazil. From the first reported outbreak in May 2015 in Brazil, over 1.5 million people are estimated to have been infected in Brazil alone with thousands more in the other countries.
Local transmission in the mainland US has not been reported, though it has been observed in Puerto Rico. More than one incident of people returning from Central or South America with infection has been reported and some experts believe that local transmission in parts of Florida and Texas could be detected soon.
What can Zika cause?
According to the CDC, infection with Zika in most cases causes only mild flu-like symptoms with fever, skin rash, red eyes and joint paint being the most common symptoms. In other words, if you had Zika infection, a doctor would be hard pressed to suspect it was anything other than a mild flu – unless of course you lived in or visited any of the regions of the outbreak. What makes it harder to detect is that only 1 in 5 people even develop symptoms, which could be one of the reasons why it spread so fast. For the vast majority of people though, this will be the extent of their illness.
However, links between Zika outbreaks and Guillian Barre Syndrome (GBS), an illness in which the body’s own immune system attacks the nerves, have been reported in the past. In severe cases of GBS, the individual can be completely paralyzed. Outbreak related GBS illnesses have been minimal however, and similar reports have not appeared for the current outbreak.
More concerning however, has been the potential for Zika to cause birth defects, specifically microcephaly.
What is basis for added concerns about birth defects?
Between 2010 and 2014, Brazil saw an average of 163 cases of microcephaly per year. But since October 2015, 3,530 cases have been recorded — a more than 20-fold increase. Further investigations by Brazilian health officials revealed that the virus could be isolated from stillborn infants with microcephaly. More recently, the mother of a Hawaiian infant born with microcephaly was also reported to have been infected while being pregnant in Brazil.
Nikos Vasilakis, an associate professor of pathology and a Zika expert at the University of Texas Medical Branch said in comments to the Genetic Expert News Service, “There is strong evidence providing a link between Zika virus infection during the first trimester of pregnancy and microcephaly. Furthermore, the presence of Zika viral RNA in the amniotic fluid in pregnant women of fetuses diagnosed with microcephaly as well as in the brains of newborns that were delivered stillborn or died at birth suggests infection during pregnancy.
A few more pieces of evidence are needed to make the link causative, said Daniel Lucey an infectious diseases specialist at Georgetown University when GENeS reached out to him for comment. This includes finding the presence of viruses in children born with microcephaly and their mothers, along with ruling out other viruses such as rubella or cytomegalovirus that can also cause the defect. Additionally epidemiological studies to show that pregnant women with Zika are more likely to have children with microcephaly will have to be performed. And lastly, an animal model that can make clear the mechanism behind how exactly Zika leads to a birth defect would need to be developed.
The Genetic Expert News Service gathered reactions from experts on different aspects of the unfolding Zika virus outbreak in Central and South America.
Is there a way to vaccinate against it?
The short answer? No. “There are no licensed vaccines against the Zika virus anywhere in the world,” said Lucey. The Brazilian government has recently announced that it will fund efforts to develop a vaccine in “record time,” according to the Health Minister Marcelo Castro which is expected to take three to five years. According to Lucey, an effort led by the National Institutes of Health to develop a Zika vaccine has also only recently begun.
There is some good news. Nikos Vasilakis of the University of Texas Medical Branch said, “given the existence of highly successful and efficacious vaccines against yellow fever and Japanese encephalitis viruses, which are closely related to Zika virus, development of a live attenuated or chimeric vaccine would be straightforward.” However, Lucey cautioned that expecting that a solution is around the corner might be too optimistic. “Assuming that the scientific and pharmaceutical industry challenges can be met as quickly as possible, based on past new vaccine development timelines, we are several years away from having an FDA-licensed Zika vaccine,” he said to GENeS.
Genetically engineered solution?
The first line of action in almost all cases is to get rid of the mosquitoes and prevent them from breeding further. This involves fumigation and removing sources of stagnant water where mosquitoes can breed. Brazilian authorities have even deployed army troops to hasten this process.
A more biotech based vector control solution is the use of genetically engineered mosquitoes developed by the British firm Oxitec. The modified male Aedes aegeypti mosquitoes mate with females in the wild population and produce offspring that do not survive to adulthood, essentially making the males sterile. Such a mosquito was approved for use in the city of Piracicaba, Brazil last year in the middle of the dengue outbreak and trials showed that they reduced vector populations by as much as 82 percent. Yesterday, Oxitec announced that it was expanding its production facilities in Piricicaba in view of a potentially increased demand to combat dengue and Zika.
Though a similar trial was proposed in Florida which also has a high Aedes mosquito population, it’s adoption has been controversial in the United States. The FDA is currently reviewing the application for a trial and it is not known whether the rapid spread of Zika and its potential to quickly move to the US will hasten the process in any way.
The biological basis of this control strategy is well understood and similar strategies have been used for decades for insects mainly of agricultural significance.
When GENeS asked experts about the expansion plans of Oxitec, the reactions were mostly positive.”In my opinion [it] is generally an encouraging sign that this and related genetics-based technologies for the control or local elimination of mosquitoes is moving towards the mainstream,” said David O’Brochta, a professor of Entomology at the University of Maryland.
What can we expect in the near future?
There appears to be little chance of Zika slowing down. The US aside, Brazil is expecting to host thousands, if not millions of travelers from around the world first for Carnival in February and then in the 2016 Summer Olympics. It could lead to the rapid spread of Zika to other parts of the world, said some experts, though local officials in Brazil suggest that by then the rainy season would be over, allowing the outbreak to subside. Summer is also when things might ramp up in the US, especially in the southern parts where conditions are more ideal for mosquitoes to breed. Better quality of resources and healthcare may prevent the virus from spreading as fast though.
“I anticipate Zika becoming much worse in the near future,” said professor Lucey of Georgetown University.
Arvind Suresh is a science media liaison at the Genetic Expert News Service. He is also a science communicator and a former laboratory biologist. Follow him @suresh_arvind.