ZIKA: Climate Change Threat?

Guest Essay by Kip Hansen

ZIKA!  A frightening new disease that burst onto the front pages in 2016 as “linked to thousands of babies being born with underdeveloped brains.”  Over the next two years, current outbreaks of Zika had spread from Brazil through South America, Mexico, the Caribbean, and even a few cases in southern Florida.

As of May 2019, the U.S. Centers for Disease Control and Prevention gives this brief:

Q: What is Zika?

• A: Zika virus disease is caused by the Zika virus, which is spread to people primarily through the bite of an infected mosquito (Aedes aegypti and Aedes albopictus). The illness is usually mild with symptoms lasting up to a week, and many people do not have symptoms or will have only mild symptoms. However, Zika virus infection during pregnancy can cause a serious birth defect called microcephaly and other severe brain defects.

What we know:

Zika is spread mostly by the bite of an infected Aedes species mosquito (Ae. aegypti and Ae. albopictus). These mosquitoes bite during the day and night.

Zika can be passed from a pregnant woman to her fetus. Infection during pregnancy can cause certain birth defects.

There is no vaccine or medicine for Zika.

The New York Times brings Zika back onto the news scene with an article written by  Andrew Jacobs titled:   ”The Zika Virus Is Still a Threat. Here’s What the Experts Know”.   The news item was prompted by “the World Health Organization issued a report on Zika that listed 61 such countries, among them densely populated behemoths like China, Egypt and Pakistan as well as much of Africa.”

Zika is a tricky viral disease; the NY Times quotes Dr. Karin Nielson of UCLA:

“Zika has completely fallen off the radar, but the lack of media attention doesn’t mean it’s disappeared,” said Dr. Karin Nielson, a pediatric infectious disease specialist at U.C.L.A. who studies Zika’s impact in Brazil. “In some ways, the situation is a bit more dangerous because people aren’t aware of it.”

“The virus, which is mostly spread by mosquitoes but also through sex with an infected person, is still circulating in Brazil and other countries that were at the center of the epidemic, and two years ago the same strain from the Americas arrived in continental Africa for the first time. That strain, researchers recently discovered, had been causing birth defects in Asia long before the Zika epidemic of 2016.”

It is this  risk to pregnant women of subsequent birth defects in their unborn children, primarily microcephaly (and other severe brain defects), that is so worrying, particularly for those who have the least access to health care and long-term assistance for the affected children.

The primary defense against mosquito-transmitted diseases is a three pronged attack, as I explained in an earlier essay on dengue:

1. Rapid knock-down of mosquito populations in and around the area of an outbreak through spraying.

2. Identifying and isolating infected persons where they can receive treatment and not be bitten by mosquitoes, further passing on the disease.

3. Public education of eliminate mosquito-breeding sites — rain barrels, trash piles, old tires, etc.

Here’s how dengue, yellow fever and Zika are primarily spread:

We see on the left the most usual case: uninfected mosquito bites an infected person (symptomatic – showing the symptoms of the disease) — mosquito becomes infected — mosquito bites uninfected human — human becomes infected — back around again to — uninfected mosquito bites infected human.

On the right we find the trickier case in which all members of a family become infected, but only one (in this case) shows symptoms.  Isolating only the obviously sick member of the family (the symptomatic member) doesn’t stop the chain of infection because mosquitoes can bite the asymptomatic (showing no symptoms) members of the family, thus becoming infected and spread the disease to other families.   This is often the case with Zika:

“Q: What are the symptoms of Zika virus disease?

A: The most common symptoms of Zika virus disease are fever, rash, headache, joint pain, red eyes, and muscle pain. Many people infected with Zika won’t have symptoms or will have mild symptoms, which can last for several days to a week.” (CDC)

These mild Zika infections are easily misdiagnosed even if reported to a doctor where they can be mistaken for a cold or the flu, thus making isolation of Zika infected individuals less likely.

What is the Threat of Zika in the United States?

 Andrew Jacobs of the NY Times, following his editor’s narrative for climate change, includes this in his article:

“Warming temperatures associated with climate change are expected to expand the range of Aedes, according to a recent study, putting tens of millions more people at risk for Zika and other mosquito-borne diseases.”

The link leads to the NY Times’ earlier piece on the possible threat of the spread of dengue, which features a map grossly misrepresenting “the risk” of dengue in the continental United States — based on a study with some complex modelling of the possible expansion of the range of Aedes aegypti.  As with dengue, this “increased risk” is a fallacious claim.  The area of “increased risk” in the quoted study is smaller than the current (as of 2017) range of Ae aegypti.  There is no endemic dengue in the continental United States now, and there is no biological plausibility of dengue becoming endemic here.

Here Mr. Jacobs of the Times does a better job of journalism than his colleagues who write for the Times’ Climate section — he does real journalism and fact checks the subject.  Thus he reassures us:

“In the United States, the Aedes mosquito can be found across significant swaths of the country during summer, though epidemiologists say the potential for large-scale American outbreaks is limited by the near ubiquity of air conditioning, window screens and local mosquito control efforts.

“It also helps that people in the U.S. tend to live fairly far apart in single-family homes,” said Dr. Lyle R. Petersen, who oversees vector-borne diseases at the Centers for Disease Control and Prevention. “This is a mosquito that doesn’t fly very far.””

Quoting myself in the earlier dengue essay;

“Note that Aedes mosquitos can only fly about 100 meters in the wild, so suitable breeding sites have to be ubiquitous in the environment and many infected human hosts have to be present and live close together.  This is why dengue has such prevalence in the tropical third world.”

Of course, the same applies to Zika.  However,  “Zika can be spread by a person infected with Zika to his or her sex partners.” (CDC)

What is our risk in the United States now? 

The CDC reports: “In 2018 and 2019, no local mosquito-borne Zika virus transmission has been reported in the continental United States.”

Here’s the map: (lack of counties in green indicate zero cases of Zika)

Things are not so good in Puerto Rico, where the climate is more tropical and living standards can be a bit more like other Caribbean nations.  However, the US Virgin Islands, comprising St. Thomas, St. John, and St. Croix, have no Zika recorded.

On the international scene, the situation is also better, though it may be skewed by lack of reporting from some areas, with the current CDC travel risk map:

So, that’s the good news, despite (or, possibly, as a result of) increased attention from the World Health Organization, there are no current Zika outbreaks.

So what happened?

 Quoting the Times again:

“Arboviruses like dengue, chikungunya and yellow fever provide something of a template for the future of Zika. During the 1940s and 50s, successful eradication campaigns aimed at quelling deadly yellow fever outbreaks vanquished Aedes from Brazil and much of the region. But by the 1970s, as those efforts were abandoned, the mosquito quickly re-established itself, leading to increasingly intense outbreaks of dengue and yellow fever, and more recently the emergence of new arboviral pathogens like chikungunya and Zika. These days, dengue infects over 100 million people globally a year, killing 10,000.”

It was not only Brazil that ended or cut back on vector control (mosquito spraying) — many parts of the US did as  well.

As in so many other things, we humans have trouble learning things and once having learned, when the immediate threat has passed, we let that hard-earned knowledge slip away, dropping our guard and letting known threats return to plague us.

Climate, changing or not, will not increase the risk of Zika (or any other tropical diseases) — only the spread of poverty and lowered living standards will do that.

There will be outbreaks as the people from areas with endemic tropical diseases continue to move into Europe and the United States — bringing with them their sick — but these outbreaks will be quickly quelled by the higher levels of public health access and  generally higher living and housing standards.  Increased spending by the U.S. federal government in Puerto Rico, in conjunction with rebuilding in the aftermath of Hurricane Maria, which must include restored vector control (neighborhood spraying for mosquitoes) and improved public health access, will eliminate Zika there.

The Bottom Line:

As with malaria, yellow fever and dengue defeating Zika and keeping it at bay requires:

1. Constant public health vigilance to identify and isolate infected individuals
2. Increased and continuous vector (mosquito) control
3. Public Health education on tropical diseases, their symptoms, their relationship to travel and educational campaigns on how to eliminate mosquito-breeding sites in potentially-affected neighborhoods.

All of the above require caring governments with adequate resources to carry out the necessary work.

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Author’s Comment Policy:

As with so many other alleged climate change threats, the spread of Zika “because of climate change”  is a fairy-tale hobgoblin.  It just isn’t so.  The spread of Zika, though, is a real problem, mostly because it is not a serious disease for the majority of people infected — only causing serious harm for babies born of infected mothers.  For that reason, work on a vaccine must be accelerated.  It may be possible, as past infection seems to provide immunity.

The Times’ Andrew Jacobs gets credit for avoiding the worst of the climate change fear mongering and writing in some reassuring reality regarding the lack of any real threat to those of us living in the continental United States (and, I assume, that the same applies for most of Europe as well).

My personal experience includes humanitarian work in Puerto Rico and the Virgin Islands (US and British) in the 2000s.    Puerto Rico had endemic dengue and HIV  at the time but no Zika.   Many of the poorer homes we visited lacked effective window and door screens and most homes had to have mosquito bed nets.  Hurricane Maria was very hard on Puerto Rico and surely made matters of public health worse.  Readers in Puerto Rico might let us know the current situation for the average rural citizen.

Those spreading fear of the future are enemies of the public mind and need to be countered wherever and whenever they find a public voice.  There are enough real things to concern  modern man without the continuous injection of bogus threats into the daily news-stream.

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