Notícia

Mongabay (EUA)

Zika: from obscure virus to global health emergency

Publicado em 25 maio 2016

Por Jenny Gonzales

“The evolution of science [occurs] by means of questions that are made — not by the answers.” So said Pedro Vasconcelos in an interview with Mongabay. He is director of the Evandro Chagas Institute (IEC) — one of the 15 research centers around the world urgently seeking a vaccine against the Zika virus.

His search for the right questions inspires hope, but also reveals that the path to understanding and controlling this infectious agent — which has spread throughout Latin America and the Caribbean, and threatens the rest of the world — is still likely to be long.

Here’s what we do know so far: transmitted by the female Aedes aegypti mosquito — also the vector for chikungunya, dengue fever and yellow fever — the virus was reported in 66 countries and territories between January 2007 and the end of April 2016, according to the World Health Organization (WHO). Of that total, 45 countries saw their first outbreak from 2015 onward — a very sudden increase.

There is no historical precedent of contagion by arthropods — the phylum to which insects belong — with such a rapid expansion. Dengue fever, for example, took decades to achieve a similar extent.

In Brazil, where the epidemic began in the Americas, the pathogen was identified in May of last year, but patients with the disease’s symptoms (intermittent low fever and red spots on the body) had already arisen two months before that. Those mild symptoms were misinterpreted as a lesser version of dengue, early on.

The destructive effect of Zika was only recognized in November 2015, when it appeared in a growing number of newborns with microcephaly — a condition characterized by an undersized brain that can be genetically or environmentally caused. Children with microcephaly often have developmental problems, and there’s currently no treatment for the condition, according to the Mayo Clinic.

Researchers in Brazil and around the planet are now racing to develop more reliable Zika diagnostics, create an effective vaccine, and determine the environmental, biological and genetic factors that allowed a once innocuous virus to morph into a serious global health emergency.

The crisis arrives

It was a Brazilian specialist in fetal medicine, gynecologist Adriana de Melo, who first presented clear evidence of the relationship between Zika and the growing number of microcephaly cases. In October, 2015 she examined two pregnant women carrying babies with atrophied brains and calcifications in their skulls in the northeast state of Paraíba.

“I’d never seen such destruction in the brain of fetuses before,” she said.

Melo wanted to analyze the amniotic fluid that surrounded the fetuses, but the Paraíba State Health Secretary refused the request. Undaunted, she shifted her request to the Oswaldo Cruz Institute (IOC-Fiocruz), affiliated with the Ministry of Health. Melo sent samples to Rio de Janeiro, paying for their transport out of her own pocket.

Faced with a sudden increase of newborns with microcephaly, the Ministry decreed a public health emergency in Brazil on November 11, 2015. Six days later, IOC-Fiocruz announced that Zika was capable of crossing the placental barrier and reaching the amniotic fluid of pregnant women.

Before the outbreak, national microcephaly cases averaged 150 annually. In 2015, that number jumped to 4,000 registered cases, while the number of Brazilian births remained practically the same, 2.8 million per year.

The latest Brazilian government report reflects not only the seriousness, but also the uncertainty, connected with the epidemic: between October 2015 and May 18, 2016, 7,534 suspected cases of microcephaly were detected in Brazil — 76.5 percent of which were found in the country’s Northeast. But of this total, only 1,384 cases were confirmed, while another 2,818 diagnoses were discarded, and 3,332 are still under investigation.

Because cases of microcephaly were so low before Zika’s surge, the Ministry of Health makes the assumption that babies who receive a final diagnosis of microcephaly were infected by their mothers with Zika, although there are other factors that could cause brain malformation.

On February 1, 2016, with Zika already in more than 20 countries and territories of the Americas, the World Health Organization (WHO) declared an international public health emergency, recognizing the connection between the virus and microcephaly — although that connection had not yet been scientifically proven.

A day later Chile and the United States confirmed their first cases of Zika (via sexual transmission), with similar cases reported in Argentina, Peru, Canada, France, Italy, Portugal and New Zealand since then.

Counting cases

When an old and existing, but rarely seen disease, suddenly surges to epidemic proportions, a scramble ensues to determine the number of cases so as to measure the current scope and spread of the disease.

But to perform such a count, accurate diagnostics are needed — diagnostic tools that may not exist at the outset, which can lead to early misestimates.

The understandable difficulty in quantifying the number of Zika virus infections is evident in Brazil’s recent withdrawal of earlier statistical data, and the country’s regular reappraisal of the epidemic’s proportions.

Until March 2016, the Ministry estimated that 400,000 to 1.3 million Brazilian women had been infected with Zika in 2015, but then it decided to reassess that data and removed the statistics from its previous online epidemiological bulletins (though those old estimates can still be found at a WHO link).

On April 26 of this year, the Ministry of Health released new estimates for the number of Zika cases: from February 2015 to April 2, 2016 they said, 91,387 cases were reported. Of that total, 7,584 are pregnant women and, of these, 2,844 cases were confirmed.

One of the chief problems in the registration of cases is that about 80 percent of those who contract the virus don’t present symptoms and so are not evaluated. And when symptoms do appear, they can look very similar to those of dengue fever — an epidemic of which hit record levels in Brazil in 2015, with 1.6 million probable cases. This year there are more than 800,000 dengue fever cases already in the country, so the diagnostic confusion between it and Zika infections is likely to remain.

The diagnostic challenge

Also to be expected with any new and unfolding epidemic, hurriedly developed Zika diagnostic tests still have their limitations. The PCR genetic material test, for example, only manages to identify the virus in the first five to seven days of infection, and exams by serology frequently have cross-reactions with other infections, such as dengue fever.

But there is some good news: there are promising new diagnostic tests on the way.

In March of this year, Marie-Paule Kieny, WHO assistant director-general for Health Systems and Innovation, informed the world that new detection tests are at a more advanced stage than the development of a vaccine against Zika.

In the same month, the Institute of Biomedical Sciences of the University of São Paulo (ICB-USP) announced the creation of a serology test that identifies antibodies to the virus even after it has been eliminated by the body. The test found that the majority of eight mothers of babies with microcephaly tested positive for Zika. Other serological tests hadn’t identified the presence of the virus in these women, who live in a Brazilian town with high rates of microcephaly.

“The antibody test will verify if pregnant women had contact with the virus before pregnancy,” Paolo Zanotto declared with confidence. He is the coordinator of the Zika Network, a task force that includes 40 research groups in São Paulo state.

The discovery of this diagnostic tool is leading quickly to its mass production. ICB-USP has partnered with Butantan Institute (responsible for 90 percent of the serums and vaccines produced and consumed in Brazil) to manufacture a diagnostic kit in large scale. Their goal is to distribute it free of charge in hospitals and blood banks across Brazil, according to the virologist. “We are making adjustments,” said Zanotto. The diagnostic test’s “efficiency has been proven, but there are still some problems regarding its sensitivity in mass applications.”

The search for a vaccine

While accurate diagnostics are crucial to tracking and managing an epidemic, the obvious hoped for next step is an effective vaccine against it.

The search for a Zika vaccine is involving numerous public health institutions and companies. According to WHO, the two vaccines currently in the most advanced stage of development are from the National Institute of Health (NIH) in the U.S. and the Bharat Biotech Company in India.

NIH, partnering with Brazil’s Instituto Butantan, has created a vaccine against dengue fever that is in its final stages of development. The two organizations now want to transform that vaccine from being a tetravalent — able to fend off the four dengue virus subtypes — to a pentavalent version that will also work against the Zika virus. One problem with this approach is that it’s still too early to know with certainty whether the Zika virus has more than one subtype.

In March, a preliminary clinical test conducted by NIH and John Hopkins University showed that the new dengue vaccine protected 100 percent of immunized persons. The third phase of clinical trials, involving 17,000 volunteers in Brazil, may be ready in 2018.

“With the studies we have of dengue and [it] being very similar to Zika, we can move faster towards the vaccine,” predicted Marcelo De Franco, substitute director of Butantan Institute.

Brazilian research slowed by bureaucracy

Diagnostic and vaccine development are crucial to controlling Zika, but so too is having sufficient financial resources and administrative capabilities to apply those tools to a large population at risk from the epidemic.

That’s why the timing of Zika’s appearance is so dangerous. The disease has reached epidemic levels at a time when the Brazilian government is stumbling through an intractable national corruption scandal, a presidential impeachment, and an economic free fall that is the worst since the 1930s.

Add to that the country’s bureaucracy, well-known for its inefficiency, plus high levels of poverty and the lack of services in rural areas where Zika is present, plus the Rio Olympics planned for this summer — with visitors arriving from around the planet who might contract the disease and take it home with them — and you have an historically unprecedented set of logistical challenges faced by epidemic researchers, medical and public health professionals.

Brazil’s federal government has been slow to respond to the crisis with funding. “Four months ago, we came to an agreement with the Ministry of Health, but nothing has arrived until now,” said Zanotto of ICB. “We are in an intense operation, working 24-hour shifts, and if it weren’t for the support of FAPESP (the São Paulo Research Foundation), which cut the bureaucracy to almost zero for the release of funds — redirected, in fact, from other research projects — we would be in a critical situation.”

At Butantan, virus research (including a serum development project) began in January. The institute signed a contract with the federal Ministry of Health in February for US $8.5 million, with the first US $2.3 million promised in just thirty days. But “not even [that] initial amount has arrived, and it’s been more than two months,” reported De Franco. “This delay is unbelievable — the government places an emergency situation in the same ditch [as the rest of the] bureaucracy.”

Another US $28 million meant to pay for the final stages of dengue/zika vaccine development is also stuck in that same bureaucratic ditch. Help finally came on April 11, when a delegation of the Biomedical Advanced Research and Development Authority (BARDA), a division of the U.S. Department of Health and Human Services, arrived in São Paulo and partnered with the institute, which has now received US $1.2 million for their Zika studies.

“The vaccine is the only thing that will offer an [effective] response to childbearing-age women, whether or not pregnant,” said Pedro Vasconcelos, of the Evandro Chagas Institute (IEC).

Based in Pará state, IEC is working in close partnership with the University of Texas Medical Branch (UTMB) on the development of an immunizing drug. Preclinical trials are being done on mice in Galveston, Texas, and with monkeys at Belém, in Pará state, Brazil, and should be complete by February 2017.

“After that, we want to speed up the process safely by shortening the stages of human trials. This will be difficult to manage with WHO and Anvisa — the health regulatory agency in Brazil,” said the virologist. “There are precedents, however. The Ebola vaccine was created in record time and proved to be highly effective.”

In May, The University of Texas Medical Branch announced that a team of researchers has developed a Zika virus clone. The genetically engineered replica is of the type that’s spreading throughout the Americas and has been associated with the cases of microcephaly. “The cDNA clone represents an advance towards deciphering why the virus is tied to serious diseases,” said lead author Pei-Yong Shi, UTMB professor. “The new clone is a critical step in developing a vaccine and antiviral drug against Zika.” The study was published in the Cell Host & Microbe journal.

Tracing Zika’s origins

The John Hopkins University School of Medicine has long been studying diseases related to neural development through its stem cell research. This March — only a month after beginning work with the Zika virus — John Hopkins determined that the virus has the ability to infect a type of neural stem cell that gives rise to a baby’s cerebral cortex — the area of the brain responsible for intellectual capabilities.

“More importantly, it leads to thinning of the cortical layers, a feature that closely resembles microcephaly,” said Guo-Li Ming, one of the research coordinators. To speed results for this research, the US study was divided among four university laboratories. “If it had been done by a single laboratory, it would have taken us six months to a year to reach this result,” said the neuroscientist.

On March 31, 2016, the World Health Organization officially recognized that Zika causes microcephaly and other birth defects — although several Brazilian scientists had supported that position since the end of 2015. On April 13th, the Centers for Disease Control and Prevention (CDC) also declared their acceptance of this conclusion, saying that there is sufficient evidence to establish the causal relationship.

To understand why the virus has suddenly become so severe, causing microcephaly, scientists need to perform full genome sequencing of the Zika virus on as many samples as possible. Genetic mapping of the virus from multiple samples allows scientists to pinpoint possible mutations in the genome that may have resulted in congenital malformations.

Data from NIH’s GenBank — a collection of genetic sequences from around the world — shows that Zika sequencing is on the upswing. Between 1998 (the year of the first registered Zika sequencing at GenBank) and 2012, only 13 sequences were registered; in 2014 and 2015, the number of sequences mapped jumped to 196 (of which 11 were done in Brazil). By April 15, 2016, 88 more were sequenced (with 41 from Brazil).

“We need many samples with high viral load to do more sequences. The problem is that Zika stays in small quantities in the blood,” said Renato Aguiar, a member of the Federal University of Rio de Janeiro (UFRJ) team that, along with Fiocruz, did the first complete genome sequence of Zika in Brazil.

The gene sequencing effort resulted in the discovery that the virus in Brazil is the same as that which caused a 2013 Zika outbreak in French Polynesia — the same, but also different: “We know that it suffered mutations when it arrived [in Latin America], and that it’s more neurotoxic than the [original] African virus. A greater number of [genetic] sequences will help us understand that evolution,” said the UFRJ biologist. He also made it a point to note that a severe lack of resources for Zika research in Brazil is hampering work: “We had to divert funds from other projects to not interrupt the [Zika] studies.”

Originally found in Uganda’s Zika forest during a yellow fever control expedition, the Zika virus was isolated from blood samples of a Rhesus monkey first in 1947. In the following 60 years, there were only 14 records of people infected in Africa and Asia, and no major epidemics. But in 2007, the first serious outbreak emerged on the Island of Yap (Micronesia), with 73 percent of the population of just over 11,000 inhabitants above the age of three-years becoming infected.

In a strange twist, WHO reported on May 20, 2016 that the new Zika strain which causes microcephaly has now found its way to Africa — where the harmless form of Zika was first detected in 1947.

Into the unknown

Almost 70 years after Zika’s discovery in Africa, ICB researchers found the virus in South America. Then between July and November of 2015, a group of scientists took blood samples from fifteen marmosets (Callithrix jacchus) and nine capuchin monkeys (Sapajus libidinosus) captured in different areas where occurrences of Zika and microcephaly had occurred in Ceará state.

“The material was for rabies research, but we decided to test the samples for Zika as well [using the PCR diagnostic]. It was a surprise that 29 percent of the primates gave positive [results] for the virus,” said Edison Durigon, professor of the ICB microbiology department. Preliminary results of this study were published on the website bioRxiv on April 20.

The possibility that monkeys could function as a reservoir for the virus, thus helping perpetuate the contamination of people, is worrisome, said Durigon. “These animals are not totally wild; they often go to nearby houses to get food and may have been contaminated there.” Each of the monkeys had a microchip implanted before being released to their natural habitat. The team plans to return to Ceará this month for further research.

Vector control is also proving especially difficult. In the 1950s, the Aedes aegypti mosquito was eradicated from Brazil, and from other countries in Latin America and the Caribbean in the following decade. Gradually, however, the mosquito returned.

“We stopped having strict policies [against Aedes] because it seemed no longer a threat. It came back, and with several complications,” said Jorge Kalil, director of Instituto Butantan in a recent televised debate. “Studies show that the current mosquito is faster and reproduces at a greater speed. It can lay eggs in not so clean waters, contrary to what we thought, and survives better in cooler temperatures, [while] in the past [we thought it only thrived] in hot weather.”

While important discoveries have been made about the Zika virus, there’s still many more key questions to ask, and much to understand.

Scientists want to know: what caused the virus’ mutation, and why did it become so neurotoxic? How does the immune system eliminate it from the body? What is the mechanism by which it can cross the placenta’s double barrier in pregnant women? How does it cross the blood-brain barrier to wreak havoc on a fetus’ brain? What is the relationship between the newly returned, and tougher, Aedes aegypti mosquito and Zika? And what are the risks from a virus that can hide in Latin American monkey species?

“What frightens me is that we don’t know the future impact on the new generation [of infants] affected,” said ICB’s Zanotto. “[T]he consequences of [this] virus are unpredictable.

“What we know,” Zanotto concludes, “is that Zika’s spread, and the potential emergence of other viruses, are linked to population growth and environmental degradation. The human being invades nature and — along with poverty and precarious urbanization — we have the current scenario as a result; that will continue in the future.”

Article published by Glenn Scherer on 2016-05-25