TWiV 375: Zika and you will find

TWiVOn episode #375 of the science show This Week in Virology, the TWiVziks present everything you want to know about Zika virus, including association of infection with microcephaly and Guillain-Barré syndrome, transmission, epidemiology, and much more.

You can find TWiV #375 at

Zika virus

FlavivirusThe rapid spread of Zika virus through the Americas, together with the association of infection with microcephaly and Guillain-Barré syndrome, have propelled this previously ignored virus into the limelight. What is this virus and where did it come from?

Zika virus was first identified in 1947 in a sentinel monkey that was being used to monitor for the presence of yellow fever virus in the Zika Forest of Uganda. At this time cell lines were not available for studying viruses, so serum from the febrile monkey was inoculated intracerebrally into mice. All the mice became sick, and the virus isolated from their brains was called Zika virus. The same virus was subsequently isolated from Aedes africanus mosquitoes in the Zika forest.

Serological studies done in the 1950s showed that humans carried antibodies against Zika virus, and the virus was isolated from humans in Nigeria in 1968. Subsequent serological studies revealed evidence of infection in other African countries, including Uganda, Tanzania, Egypt, Central African Republic, Sierra Leone, and Gabon, as well as Asia (India, Malaysia, Philippines, Thailand, Vietnam, Indonesia).

Zika virus moved outside of Africa and Asia in 2007 and 2013 with outbreaks in Yap Island and French Polynesia, respectively. The first cases in the Americas were detected in Brazil in May 2015. The virus circulating in Brazil is an Asian genotype, possibly imported during the World Cup of 2014. As of this writing Zika virus has spread to 23 countries in the Americas.

The virus
Zika virus is a member of the flavivirus family, which also includes yellow fever virus, dengue virus, Japanese encephalitis virus, and West Nile virus. The genome is a ~10.8 kilobase, positive strand RNA enclosed in a capsid and surrounded by a membrane (illustrated; image copyright ASM Press, 2015). The envelope (E) glycoprotein, embedded in the membrane, allows attachment of the virus particle to the host cell receptor to initiate infection. As for other flaviviruses, antibodies against the E glycoprotein are likely important for protection against infection.

Zika virus is transmitted among humans by mosquito bites. The virus has been found in various mosquitoes of the Aedes genus, including Aedes africanus, Aedes apicoargenteus, Aedes leuteocephalus, Aedes aegypti, Aedes vitattus, and Aedes furcifer. Aedes albopictus was identified as the primary vector for Zika virus transmission in the Gabon outbreak of 2007. Whether there are non-human reservoirs for Zika virus has not been established.

Signs and Symptoms
Most individuals infected with Zika virus experience mild or no symptoms. About 25% of infected people develop symptoms 2-10 days after infection, including rash, fever, joint pain, red eyes, and headache. Recovery is usually complete and fatalities are rare.

Two conditions associated with Zika virus infection have made the outbreak potentially more serious. The first is development of Guillain-Barré syndrome, which is progressive muscle weakness due to damage of the peripheral nervous system. The association of Guillain-Barré was first noted in French Polynesia during a 2013 outbreak.

Congenital microcephaly has been associated with Zika virus infection in Brazil. While there are other causes of microcephaly, there has been a surge in the number of cases during the Zika virus outbreak in that country. Whether or not Zika virus infection is responsible for this birth defect is not known. One report has questioned the surge in microcephaly, suggesting that it is largely attributed to an ‘awareness’ effect.  Current epidemiological data are insufficient to prove a link of microcephaly with Zika virus infection. Needed are studies in which pregnant women are monitored to see if Zika virus infection leads to microcephaly.

Given the serious nature of Guillain-Barré and microcephaly, it is prudent for pregnant women to either avoid travel to areas that are endemic for Zika virus infection, or to take measures to reduce exposure to mosquitoes.

There are currently no antiviral drugs or vaccines that can be used to treat or prevent infection with Zika virus. We do have a safe and effective vaccine against another flavivirus, yellow fever virus. Substituting the gene encoding the yellow fever E glycoprotein with that from Zika virus might be a good approach to quickly making a Zika vaccine. However testing of such a vaccine candidate might require several years.

Mosquito control is the only option for restricting Zika virus infection. Measures such as wearing clothes that cover much of the body, sleeping under a bed net, and making sure that breeding sites for mosquitoes (standing water in pots and used tires) are eliminated are examples. Reducing mosquito populations with insecticides may also help to reduce the risk of infection.

Closing thoughts
It is not surprising that Zika virus has spread extensively throughout the Americas. This area not only harbors mosquito species that can transmit the virus, but there is little population immunity to infection. Infections are likely to continue in these areas, hence it is important to determine whether or not Zika virus infection has serious consequences.

Recently Zika virus was identified in multiple states, including Texas, New York, and New Jersey, in international travelers returning to the US . Such isolations are likely to continue as long as infections occur elsewhere. Whether or not the virus becomes established in the US is a matter of conjecture. West Nile virus, which is spread by culecine mosquitoes, entered the US in 1999 and rapidly spread across the country. In contrast, Dengue virus, which is spread by Aedes mosquitoes, has not become endemic in the US.

We recently discussed Zika virus on episode #368 of the science show This Week in Virology. You can be sure that we will revisit this topic very soon.

Added 1/28/16 9:30 PM: The letter below to TWiV provides more detail on the situation in Brazil.

Esper writes:

Hi TWIVomics

I hope this email finds you all well and free of pathogenic viruses.

My name is Esper Kallas, an ID specialist and Professor at the Division of Clinical Immunology and Allergy, University of São Paulo, Brazil.

I have been addicted to TWIV since a friend from U. Wisconsin participated in the GBV-C episode (David O’Connor, episode #260). Since then, never missed one episode. After long silent listening, I decided to write for the first time, motivated by the ongoing events in my country, potentially related to the Zika virus.

In the last episode, Emma wrote about events taking place in the small town of Itapetim, State of Pernambuco, Northeastern Brazil, which I will describe a bit later in this email. Before, let me bring some background information on the current situation.

Most believed Zika was a largely benign virus, causing a self-limited disease, clearly described in episode #368. Its circulation was documented after an outbreak became noticed in the State of Bahia (NE Brazil) by a group led by Guilherme Ribeiro, a talented young Infectious Diseases Scientist from Fiocruz (PMID: 26584464, Emerg Infect Dis. 2015 Dec;21(12):2274-6, free access)

However, things started to get awkward around October 2015, when a single hospital in Recife (NE Brazil) and some other practicing Obstetricians and Pediatricians from the region started reporting a mounting number of microcephaly cases in newborns, later confirmed by the national registry of newborns. The numbers are astonishing. The graph below depicts the number of cases per year prior to the surge in 2015. Only this year, 2,975 cases were reported by December 26, the vast majority in the second semester of the year. Cases are concentrated in the Northeast (map), with 2,608 cases, including 40 stillbirths or short living newborns.

Microcephaly, Brazil

In response to the situation, the Brazilian Ministry of Health has declared a national public health emergency (

The Brazilian Ministry of Health has been presenting updates every week (see link: It is important to observe some imperfections in these numbers: 1. There may be an over reporting after the news made to the big media, suggesting an association between microcephaly and Zika virus. 2. The criterion to consider a microcephaly case has been changed after the current epidemic from 33cm to 32cm; this is because 33cm of head circumference is sitting in the 10th percentile of newborns at 40 weeks of pregnancy and the adjustment would bring the limit to the 3rd percentile, increasing the specificity to detect a true microcephaly case (this may result in an over reporting in the beginning of the epidemic).

The association between Zika virus infection and microcephaly was suspected since the beginning, when Brazilian health authorities ruled out other potential causes, together with the fact that the microcephaly epidemic followed Zika virus spread. Further evidences were the two positive RT-PCR for Zika RNA in two amniotic fluids obtained from two pregnancies of microcephalic fetuses and a stillborn microcephaly case with positive tissues for Zika RNA. In fact, French Polynesia went back to their records and also noticed an increase of microcephaly case reporting, following their epidemic by the same virus strain in 2013 and 2014.

Now, Zika virus transmission has been detected in several countries in the Americas (

Although strong epidemiological data suggest the association between Zika virus and the microcephaly epidemic, a causal link between the virus and the disease is still lacking and is limited to few case reports. Many questions still remain. Does the virus damage embryonic neural tissue? What is the percentage of fetuses getting infected when the mother acquires Zika virus during pregnancy? Does the stage of pregnancy interfere with virus ability to be transmitted to the fetus and the development of neurologic effects? Are there other neurological defects related to Zika virus infection? Is there another cofactor involved, such as malnutrition or other concurrent infection? All these questions are exceedingly important to provide counseling to pregnant women and those who are planning to become pregnant, especially in Northeastern Brazil. In fact, Brazilian authorities have been recommending avoiding pregnancy until this situation is further clarified.

The microcephaly epidemic impact is unimaginable. It is a tragedy. These children are compromised for life and the impact on their families is beyond any prediction.

Back to the story sent by Emma. A small town in the North of Pernambuco State, named Itapetim, has almost 14 thousand inhabitants and has reported 11 cases of microcephaly in the past 3 months. This very same town has been suffering from a prolonged drought, since September 2013 when the last reservoir went dry. Perhaps the storage of clean water or the limited resources has led to the best environment for arbovirus spread and the development of microcephaly.

But the Zika virus’s impact may be reaching further. An increase in Guillain-Barré syndrome cases has also been noticed in the Northeast of Brazil, possibly related to the epidemic.

Several groups have been trying to establish animal models to study the interaction of Zika virus with neural tissue. The forthcoming developments are critical to better understand the virus immunopathology and confirm (or refute) the association between the virus infection and neurologic damage in fetuses and in the infected host developing Guillain-Barré syndrome. Many things still shrouded in mystery.

Keep on the good work. I will keep on listening!


TWiV 317: Brazil goes viral

On episode #317 of the science show This Week in Virology, Vincent travels to Brazil and joins Eurico to speak with three four young virologists, Gustavo, Cintia, Tatiana, and Suellen, about their work and their prospects for careers in science.

You can find TWiV #317 at

Implications of finding poliovirus in sewers of Brazil and Israel

Poliovirus by Jason RobertsWild poliovirus has been detected in the sewers of Brazil and Israel. Fortunately, no cases of poliomyelitis have been reported in either country. Why is poliovirus present in these countries and what are the implications for the eradication effort?

Wild type poliovirus (e.g. not vaccine-derived virus) was detected in sewage samples that had been collected in March 2014 at Viracopos International Airport in the State of Sao Paulo. Wild type poliovirus had not been detected in Brazil since 1989 when the last case of poliomyelitis was reported in that country, and has not been found since March 2014.

Sequence analysis of the RNA genome of the wild type poliovirus found in the Brazilian sewer indicates that it is closely related to an isolate from a case of poliomyelitis in Equatorial Guinea. It seems likely that this virus was carried to Brazil in the intestine of an infected person who did not have symptoms of paralytic disease (only 1 in 100 poliovirus infections lead to paralysis). This individual might have traveled from Equatorial Guinea to the Brazilian airport where use of the bathroom lead to introduction of poliovirus into the sewer.

There have been 8 reported cases of poliomyelitis in Equatorial Guinea in 2014, from which we can extrapolate that there have been approximately 800 infected individuals. Given the number of cases of poliomyelitis that have been reported globally over the past 20 years, it is surprising that virus has not been detected previously in Brazilian sewage, especially at the airport. I suspect that wild type poliovirus would be detected in sewage in the US, given the number of individuals who enter that country each day. However the US does not conduct routine surveillance for poliovirus in sewage.

Brazil utilizes the Sabin vaccine to control poliomyelitis, and in the past 8 years over 95% immunization coverage has been achieved. The Sabin vaccine is taken orally and replicates in the intestine where it induces mucosal immunity. The intestine of Brazilians do not support the replication of wild type poliovirus, which is why the presence of wild type virus in sewage is not a threat – it is unlikely to spread in the population.

The isolation* of wild type poliovirus from sewage and from stool samples in Israel is a far more serious matter. As with Brazil, there have been no reported cases of poliomyelitis in Israel since 1989. Yet ten different sites in central and south Israel have been persistently positive for wild type poliovirus since February 2013. Wild type poliovirus has been found intermittently at 8 of 47 different sampled sites in southern and central Israel, and in stool from healthy persons collected in July 2013.

Two major lineages of wild type polioviruses currently circulate in endemic countries: the South Asian (SOAS) lineage in Pakistan and Afghanistan, andthe West African lineage in Nigeria. Nucleotide sequence analysis of the wild type poliovirus isolates from Israel indicate that they are closely related to the South Asian lineage, and in particular to polioviruses that circulated in Pakistan in 2012 and in Egypt in 2012. Molecular clock analysis of the sequences indicate that poliovirus was probably transmitted in 2012 from Pakistan into Egypt and Israel, and then spread in the latter country.

The central point of poliovirus circulation is within Bedouin communities in the south of Israel. The main virus reservoir within this community is children less than 9 years of age who had been immunized with inactivated poliovirus vaccine (IPV). This vaccine has been exclusively used in Israel since 2005, with overall vaccination coverage between 92-95%, and 81-100% within individual districts. The last nine birth cohorts in this country have been immunized solely with IPV.

The response to isolation of wild type poliovirus in Israeli sewers was to complete IPV immunization of all children in the south, raising coverage to above 99%. Then from August 2013 onwards, all children up to the age of nine years old were given a dose of bivalent oral poliovirus vaccine (OPV) containing types 1 and 3 poliovirus. All children who received OPV had previously been immunized with IPV, a strategy that prevents vaccine-associated poliomyelitis.

The finding of sustained circulation of wild type poliovirus in Israel shows that the virus can circulate silently in a population that has been well immunized with IPV. Such circulation occurs because IPV does not sufficiently protect the intestinal tract against poliovirus infection. However poliomyelitis does not occur in such populations because IPV-induced antibodies in the blood prevent virus invasion into the central nervous system. The US now exclusively uses IPV and it is likely that wild polioviruses are present in US sewage, although as mentioned above the US does not search for poliovirus in sewage. Silent circulation of wild type poliovirus in countries that use IPV poses a threat to other countries where immunization coverage is low.

These findings indicate that immunization with IPV will not lead to eradication of wild type poliovirus. This observation is problematic because the World Health Organization has recommended a gradual shift from OPV to IPV. In the past I have also supported such a transition, but I have also remained cautious about the ability of IPV to immunize the human gut. The experience in Israel confirms my suspicions.

The US shifted from using OPV to IPV because the associated vaccine-associated poliomyelitis was not acceptable in a country with no paralytic disease caused by wild type poliovirus. Now it seems that eradication cannot be achieved with IPV. What can be done about this conundrum? OPV should be used to eradicate remaining pools of wild type poliovirus in endemic countries (Nigeria, Afghanistan, Pakistan). At the same time environmental surveillance must be done in all countries that exclusively use IPV. If wild type poliovirus is found in the sewage of such countries, then introduction of OPV, in children previously immunized with IPV, should be considered to eliminate the reservoir of will type virus. It will be important to observe the effect of the distribution of OPV in Israel on the circulation of wild type poliovirus.

*Infectious poliovirus was isolated by adding sewer and stool filtrates to monolayers of L20B cells, which are mouse fibroblasts that produce the cellular receptor for poliovirus. These cells were produced in my laboratory, and are useful for isolating polioviruses because they are not susceptible to infection with non-polio enteroviruses. I am pleased to be able to contribute to efforts to control poliomyelitis.

Popularização da ciência através de podcast

luizaFor those who do not read Portuguese, the title of this post is “Popularization of science through podcast”. During my visit to Brazil last month, I was interviewed by a Ph.D. student, Luiza Montenegro Mendonça, from the Federal University of Rio de Janeiro. Luiza is taking a course on scientific divulgation, and students are required to produce a podcast each week which is published on the course website. Luiza’s brief (~5 min) conversation with me can be found on the ICB (Instituto de Ciências Biomédicas) website, and it’s available in both English and Portuguese. If you read Portuguese, you should also check out the home page of the ICB website.

Luiza is very interested in teaching the public about science, but does not feel that podcasting is right for her. Instead, she plans to write a science blog in Portuguese. When her blog launches we will be sure to note it here.

TWiV 155: XXII Brazilian National Virology Meeting

sbv_logoenv2011Hosts: Vincent Racaniello, Grant McFadden, Eurico de Arruda Neto, Paulo Eduardo Brandão, Francisco Murilo Zerbini, and Janice Reis Ciacci Zanella

Vincent, Grant, Eurico, Paulo, Francisco and Janice discuss their work on bocavirus, infectious bronchitis virus, begomoviruses, and circoviruses at the Brazilian Virology Society meeting in Atibaia, São Paulo, Brazil.

Click the arrow above to play, or right-click to download TWiV 155 (56 MB .mp3, 93 minutes).

Subscribe to TWiV (free) in iTunes , at the Zune Marketplace, by the RSS feed, by email, or listen on your mobile device with the Microbeworld app.

Links for this episode:

Weekly Science Picks

Vincent – AAM Colloquium Program
Grant – The Disappearing Spoon by Sam Kean

Listener Pick of the Week

Antonio2011 Nobel Laureates Lectures at Lindau

Send your virology questions and comments (email or mp3 file) to, or call them in to 908-312-0760. You can also post articles that you would like us to discuss at and tag them with twiv.

The World of Viruses

Keynote SBV 2011I was honored to present the Keynote Address at the XXII meeting of the Brazilian Virology Society on 23 October 2011. In my talk entitled The World of Viruses, given to an audience of 640 virologists, I shared my enthusiasm for these amazing microbes by discussing ten seminal virologists and ten compelling virology stories of recent years.

Before I began the presentation, I asked the audience to smile and took the photograph at left. Within a few minutes there were no empty seats in the room.

Watch the video of The World of Viruses below, or view at YouTube.

TWiV 95: Does a virus shift in the woods?

Hosts: Vincent Racaniello, Dickson DespommierAlan Dove, and Rich Condit

On episode #95 of the podcast This Week in Virology, Vincent, Dickson, Alan, and Rich consider the end of the influenza H1N1 pandemic, dengue in Florida, vaccinia virus infection in Brazilian monkeys, and viruses in the faecal microbiota.

Click the arrow above to play, or right-click to download TWiV #95 (68 MB .mp3, 94 minutes)

Subscribe to TWiV (free) in iTunes , at the Zune Marketplace, by the RSS feed, or by email, or listen on your mobile device with Stitcher Radio.

Links for this episode:

Weekly Science Picks

Alan – Families Fighting Flu
Rich –
Food, Inc.
Dickson –  Fuel
Vincent – MIT Open Courseware
Michael –  Waiting for Superman and Can Science Feed the World? (Nature)

Send your virology questions and comments (email or mp3 file) to or leave voicemail at Skype: twivpodcast. You can also post articles that you would like us to discuss at and tag them with twiv.

Brazilian influenza H1N1 isolate is not novel

3184877559_e8bbb242ba_mReaders of virology blog have no doubt seen news reports that a Brazilian influenza isolate called A/Sao Paulo/1454/2009 (H1N1) is novel strain with mutations that enable it to infect new hosts. Here is one example of such a report, from The Australian:

Brazilian scientists have identified a new strain of the H1N1 virus after examining samples from a patient in Sao Paulo, a research institute says. The variant has been called A/Sao Paulo/1454/H1N1 by the Adolfo Lutz Bacteriological Institute, which compared it with samples of the A(H1N1) swine flu from California. The genetic sequence of the new sub-type of the H1N1 virus was isolated by a virology team led by one of its researchers, Terezinha Maria de Paiva. The mutation was comprised of alterations in the Hemagglutinin protein which allows the virus to infect new hosts, it said.

There is nothing novel about this Brazilian isolate. Comparison of the amino acid sequence of the HA protein of A/Sao Paulo/1454/H1N1 with those of other isolates of the current pandemic strain reveals no alterations in the HA protein which would allow the virus to infect new hosts. The HA protein of this virus and many other 2009 H1N1 isolates are identical. The few amino acid differences with other 2009 H1N1 isolates are in areas that would not be expected to influence antigenicity or host range.

I’ll give the journalists the benefit of doubt: perhaps they misinterpreted the statements of the Brazilian scientist. But they should have confirmed their story with a virologist. They would have learned within a few minutes that there is nothing novel about A/Sao Paulo/1454/2009 (H1N1).