Is the Zika virus a serious threat?

Question

An article on WGNO.com makes the following claims on the Zika virus:

A relatively new mosquito-borne virus is prompting worldwide concern because of an alarming connection to a neurological birth disorder and the rapid spread of the virus across the globe.

...

The WHO estimates 3 million to 4 million people across the Americas will be infected with the virus in the next year

The Zika virus is a flavivirus, part of the same family as yellow fever, West Nile, chikungunya and dengue. But unlike some of those viruses, there is no vaccine to prevent Zika or medicine to treat the infection.

...

Since November, Brazil has seen 4,180 cases of microcephaly in babies born to women who were infected with Zika during their pregnancies. To put that in perspective, there were only 146 cases in 2014. So far, 51 babies have died.

So the questions are:

1. Is the Zika virus "relatively new"?

2. Is it true that the Zika virus is prompting worldwide concern by health officials?

3. Is it true that "the WHO estimates 3 million to 4 million people across the Americas will be infected"?

4. Is there "no medicine to treat the infection"?

5. Does the Zika virus cause microcephaly?

Answer 1

The best summary is probably to quote from the WHO director general Margaret Chan's statement on announcing that zika had been declared a "Public Health Emergency of International Concern":

The experts agreed that a causal relationship between Zika infection during pregnancy and microcephaly is strongly suspected, though not yet scientifically proven. All agreed on the urgent need to coordinate international efforts to investigate and understand this relationship better.

The experts also considered patterns of recent spread and the broad geographical distribution of mosquito species that can transmit the virus.

The lack of vaccines and rapid and reliable diagnostic tests, and the absence of population immunity in newly affected countries were cited as further causes for concern.

After a review of the evidence, the Committee advised that the recent cluster of microcephaly cases and other neurological disorders reported in Brazil, following a similar cluster in French Polynesia in 2014, constitutes an “extraordinary event” and a public health threat to other parts of the world.

So, it's being taken very seriously - and a big part of that is because there are so many uncertainties, and difficulties in controlling the rapid spread.

It's also not just pregnant women who are affected - another, seemingly rarer, linked complication, Guillain-Barré syndrome, can cause paralysis and, in rare cases, death - although there doesn't seem to be any evidence so far that such serious complications for the infected individual are as common as the (also relatively rare) serious or fatal possible complications from dengue fever.

On to the specific claims in the original question:

1. Is the Zika virus "relatively new"?

   No. The way it is behaving is relatively new, but was still seen prior to this outbreak that begin in Brazil.

   It was first discovered in Uganda in 1947, and was found to be prevalent across much of Africa and Asia, but wasn't considered a major concern and no major outbreaks were recorded until 2007 in Micronesia. Compared to other diseases in the flavivirus family, like Yellow Fever and Dengue, it was relatively benign, and these populations appeared to have relatively strong immunity to it. What is relatively new is:

   • The apparent (not yet proven) link to microcephaly and Guillain–Barré syndrome, the first evidence for which is from the 2013-14 outbreak in French Polynesia (note that the association with microcephaly wasn't observed until the French Polynesia data was re-examined following the South American outbreak, but the association with Guillain–Barré was observed at the time)
   • Its rapid spread through South America - a population who appear to have poor immunity to it (although it was also very fast spreading through the South Pacific islands after the 2007 outbreak - not as fast, but this is to be expected given the differences in population density)

   The strain in Brazil comes from the Asian lineage (there's also a separate African one). It is possible it might have mutated, and there is evidence suggesting that the exact strain in Brazil is related to the 2013 French Polynesia outbreak:

   Phylogenetic studies showed that the closest strain to the one that emerged in Brazil was isolated from samples from case-patients in French Polynesia and spread among the Pacific Islands

2. Is it true that the Zika virus is prompting worldwide concern by health officials?

   Yes, very much so, but it's their job to be concerned, and it's mostly precautionary - we don't yet know how serious it is, just that the risk is high enough to take urgent coordinated action.

   They've been describing its growth as "explosive", and an International Health Regulations Emergency Committee meeting was held on Monday 1st Feb 2016, at which:

   Members of the Committee agreed that the situation meets the conditions for a Public Health Emergency of International Concern.

   They're promoting research on a vaccine and increasing surveillance immediately. Here's that "explosive" comment in context - in an official, on-the-record speech by WHO Director General, Margaret Chan:

   In the wake of Ebola, health officials are more alert to alarming signals coming from the microbial world. Last year’s MERS outbreak in the Republic of Korea showed the devastation a new disease can cause, even in a country with an advanced health system.

   The explosive spread of Zika virus to new geographical areas, with little population immunity, is another cause for concern, especially given the possible link between infection during pregnancy and babies born with small heads. Although a causal link between Zika infection in pregnancy and microcephaly has not been established, the circumstantial evidence is suggestive and extremely worrisome.

   The American Centre For Disease Control (CDC) did issue a travel warning, but this was:

   Out of an abundance of caution

   Even after declaring it an international emergency, WHO are advising against such travel bans or trade restrictions, and instead recommend avoiding mosquito bites while staying informed in case of developments.

3. Is it true that "the WHO estimates 3 million to 4 million people across the Americas will be infected"?

   This is a ball-park figure given by Marcos Espinal, an infectious disease expert at the WHO's Americas regional office:

   We can expect 3 to 4 million cases of Zika virus disease

   I can't find any evidence that it's an official estimate, and there's nothing resembling this estimate in any of WHO's official fact sheets or information pages that I can see. I'd be amazed if they were publishing official estimates when so little is known. Bare in mind that 60%-80% of cases are asymptomatic - which makes it very hard to judge how many people have had it. It looks like this was an unguarded ball-park comment by one official which the media have jumped on.

4. Is the number of people potentially infected large compared to other tropical diseases?

   The speed and rate at which it is spreading is very high - even in an article questioning the claimed risks, Nature describe it as:

   an unprecedented epidemic in Brazil

   In terms of total numbers, projections are comparable to Dengue Fever, of which there were 1.5 million cases in 2015 in Brazil alone, and don't look likely to overtake, for example, malaria, which had 2.35 million suspected new cases in Brazil alone in 2012 and, worldwide, an estimated 214 million new cases in 2015. But the fact it could shoot from seemingly nothing to numbers not far off malaria in South America in one year is remarkable.

   Don't forget, of course, that many of these cases have no symptoms or known side effects.

   This is within the Americas. In theory, populations in Asia and Africa have good immunity and so its worldwide growth would be limited - and another limitation is climates suitable for the species of mosquito. The NY Times published a map showing areas in the Americas believed to be at risk.

5. Is there "no medicine to treat the infection"?

   This is true, however, your article is being a touch alarmist by talking as if this makes Zika worse than related diseases. It's identical to the closely related Dengue Fever. CDC say:

   No vaccine or medications are available to prevent or treat Zika infections

   ...and advise rest, plenty of fluids, and painkillers if necessary (but not aspirin or anti-inflamatories like Ibuprofen, which might increase risk of haemorrhage). Their advice on Dengue is near-identical - but for the fact that Dengue is more likely to require urgent hospitalization.

6. What percentage of Zika virus victims are estimated to conceive babies with microcephaly?

   This is unknown right now - many of the suspected cases of microcephaly are proving to actually be false positives. From a previously-linked article in Nature:

   Many experts agree the reported size of the microcephaly increase so far is probably inflated — and this chimes with the latest figures from the Brazilian government. On 27 January, it said that of 4,180 suspected cases of microcephaly recorded since October, it has so far confirmed 270 and rejected 462 as false diagnoses

   We won't know rates until we've weeded out the false diagnoses that result from heightened awareness of a rare condition.

   I'm trying to find a plausible published ball-park estimate, no success so far. But as always, beware of alarmist reporting of relative increases in rates. Plenty of sources talk plausibly about 1,000% increases - but a ten-fold increase in something very rare is still rare.

7. Do other mosquito-born diseases cause birth defects and how does their threat level compare to the Zika virus?

   It does appear to be unusual:

   • Dengue Fever - not notably, although it seems to often cause premature birth
   • Yellow Fever - not notably. Vaccination isn't recommended while pregnant, but the risk of harm to the baby is purely theoretical
   • Malaria while pregnant has major risks including low birth weight, but there doesn't seem to be any specific commonly associated birth defects
   • West Nile in pregnancy seems to not harm the baby

   I can't find any other mosquito-borne disease with a link to a specific pattern of birth defects.

   It's worth mentioning that there are other infections that cause microcephaly, notably:

   • Rubella (virus, aka German Measles)
   • Toxoplasmosis (parasitic infection, often contracted from cat litters)
   • Cytomegalovirus (virus, related to herpes, aka CMV)

8. Is there a reason for an average person living in an area infected by the Zika virus to worry about it more than other diseases?

   We simply don't know yet. Questions that need answering:

   • What exactly is the link with microcephaly? A key unanswered question here is, why hasn't any link been found in regions where Zika has been known to be present for decades
   • How often does it cause microcephaly, and can this be prevented any other way? It's been theorised that there might be some additional factor necessary
   • Is there also a link to Guillain–Barré syndrome (also theorised after an outbreak in Polynesia, but unproven)
   • Why exactly has it spread so rapidly in Brazil (compared to, for example, Dengue fever, which has been increasingly rapidly in incidence recently but has taken years to reach millions of cases)

   60-80% of cases have no effect, which might seem like a reason to think it's not too bad (most individuals are unaffected) - but if it is true that a small but significant minority have a very serious effect, this actually makes it much worse from a public health point of view. As Jeremy Farrar, head of the Wellcome Trust, was quoted in the Guardian:

   In many ways the Zika outbreak is worse than the Ebola epidemic of 2014-15. Most virus carriers are symptomless. It is a silent infection in a group of highly vulnerable individuals – pregnant women – that is associated with a horrible outcome for their babies.

   It's a matter of perspective. One average individual is likely to suffer less from contracting Zika than they would from many other diseases, including the much more unpleasant and more often deadly Dengue Fever. But looking at whole populations, Zika is much harder to monitor, trace, predict, control or treat - for many people, there may be little to no sign they had it or were even at risk until it's too late. The (very effective) strategy used against Ebola was all about tracking and tracing, isolating people and beginning treatment as soon as they were found to be at risk, before symptoms developed.

   And there's another good reason why it's difficult from a public health point of view, quoted from Mike Turner, head of infection and immuno-biology at the Wellcome Trust, in the same article:

   The real problem is that trying to develop a vaccine that would have to be tested on pregnant women is a practical and ethical nightmare

Answer 2

So the questions are:

1. Is the Zika virus "relatively new"?

From WHO.int:

Zika virus is an emerging mosquito-borne virus that was first identified in Uganda in 1947 in rhesus monkeys through a monitoring network of sylvatic yellow fever. It was subsequently identified in humans in 1952 in Uganda and the United Republic of Tanzania.

To compare, Malaria has been around since humans have - although it was only discovered in 1880.

It has also been prevalent in Africa for a while - so it's not a "discovered last year" issue.

2. Is it true that the Zika virus is prompting worldwide concern by health officials?

Yes and No. Yes, they're concerned, they're calling this meeting. No, because the meeting hasn't happened yet:

WHO Director-General, Margaret Chan, will convene an International Health Regulations Emergency Committee on Zika virus and observed increase in neurological disorders and neonatal malformations.

The Committee will meet on Monday 1 February in Geneva to ascertain whether the outbreak constitutes a Public Health Emergency of International Concern.940s and has since become endemic in parts of Africa.

They won't decide for another two days.

As Dr Margaret Chan, she is "Asking the committee for advice on the appropriate level of international level of concern".

3. Is it true that "the WHO estimates 3 million to 4 million people across the Americas will be infected"?

I can find no statement from WHO.int that contains "million" in referece to the number of expected infections. That's not to stop The BBC, The Independent, Reuters, The Guardian, CNN, and more from reporting the statement "3 to 4 million cases" - normally attributed to Marcos Espinal.

4. Is the number of people potentially infected large compared to other tropical diseases?

WHO says that

There are between 1.4 million and 4.3 million cases a year, and as many as 142 000 deaths [from Cholera].

and also

According to the latest WHO estimates, released in September 2015, there were 214 million cases of malaria in 2015 and 438 000 deaths.

finnaly, TB (Tuberculosis)

In 2014, 9.6 million people fell ill with TB and 1.5 million died from the disease.

We don't have numbers of people who will get infected (and if you assume 3 - 4 million, no timeframe). But the number of people in affected countries is around 3.34 Billion. Compare that to the 3.2 Billion at risk from malaria.

Map and Population Data.

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^{These questions have since been removed from the original question post}

5. Is there "no medicine to treat the infection"?

As WHO.int says, "There is no specific treatment or vaccine currently available".

6. What percentage of Zika virus victims are estimated to conceive babies with microcephaly?

Note that Zika doesn't necessarily cause it:

Dr Aylward: Association between #Zika and microcephaly or Guillain-Barrè syndrome is not necessarily causation #ZikaVirus

7. Do other mosquito-born diseases cause birth defects and how does their threat level compare to the Zika virus?

I can't find anything caused by mosquitoes. Fleas / Ticks might do something.

8. Is there a reason for an average person living in an area infected by the Zika virus to worry about it more than other diseases?

No. The "average" person is not pregnant. There are 7,256,000,000 humans, and only 49.75% are female.

Of that 57.32% are of childbearing age, so just 2,069,171,752 could be pregnant. The number of pregnant women can be estimated from the birth rate - 256 worldwide births per minute. Each of those women were pregnant for 9 months, and there are 394,200 minutes in 9 months, suggesting 100915200 pregnant women at any given minute. That's about 4.87% of fertile women, or 1.39% of people. No, most people are not pregnant women.

Numbers from CIA "The World Factbook"

The other possible issue is Guillain–Barré syndrome. As CDC says:

Guillain-Barré syndrome (GBS) is a rare disorder where a person’s own immune system damages the nerve cells, causing muscle weakness and sometimes, paralysis. These symptoms can last a few weeks or several months. While most people fully recover from GBS, some people have permanent damage and in rare cases, people have died.

We do not know if Zika virus infection causes GBS. It is difficult to determine if any particular pathogen “caused” GBS. The Brazil Ministry of Health is reporting an increased number of people affected with GBS. CDC is working to determine if Zika and GBS are related.

Right now, there are no proven links to serious issues, and even if these are proven, very few people are vulnerable.

About 1 in 5 people infected with Zika will get sick. For people who get sick, the illness is usually mild. For this reason, many people might not realize they have been infected.

The most common symptoms of Zika virus disease are fever, rash, joint pain, or conjunctivitis (red eyes). Symptoms typically begin 2 to 7 days after being bitten by an infected mosquito.

Answer 3

Now that two years have passed since January 2016, let's review again what scientists have learned about microcephaly and Zika.

In October 2018, Regina Grazel and Pamela Harris-Haman write in Advances in Neonatal Care:

ZIKV infection during pregnancy has been shown to cause a multitude of neurologic abnormalities; however, the magnitude of the risk is unknown. The clear majority of pregnancies exposed to ZIKV result in normal-appearing infants at birth. The estimated prevalence of microcephaly is between 2.0% and 3.0%, depending on the stratification used. The probability of microcephaly occurring increases if Zika infection is contracted in the first trimester of pregnancy.

Zika Virus Infection: A Vector-Borne Threat to Pregnant Women and Infants