Study: Zika virus transmission isn’t as dependent on warmer temperatures as previously thought

From the University of South Florida and the  “we’ll have to find some other angle to blame it on global warming” department, comes this study.

TAMPA, Fla. (May 9, 2017) — Transmission of mosquito-borne diseases, such as Zika, occur at lower temperatures than previously thought, a recently released study co-authored by two University of South Florida researchers shows.

The study, led by Stanford University and published in the journal PLoS Neglected Tropical Diseases, found that transmission of dengue, chikungunya and Zika is highest at around 84 degrees Fahrenheit. Scientists had long considered 90 degrees to be the peak-transmission temperature. The finding is significant, especially as climate change causes temperatures to climb.

“This means that future transmission is much more likely to occur in subtropical and even temperate areas, such as the southern United States and northern Mexico,” said Jeremy Cohen, PhD, a postdoctoral researcher studying integrative biology.

He and Jason Rohr, PhD, an associate professor of integrative biology, are coauthors on the study. From 2015-2016, they collected data on the incidences of dengue, chikungunya and Zika, as well as climate, gross domestic product and tourism, in Latin America and the Caribbean.

Their data were used to create a model that shows the potential effects of temperatures and temperature change on the transmission of dengue, chikungunya and Zika around the world, three diseases that are mosquito-vectored and increasing in the United States.

The map at the left depicts the number of months where there is a greater than 97.5 percent chance of disease transmission by the mosquito Aedes albopictus, based on the model. Map at right depicts Aedes aegypti, the species most likely to transmit the Zika virus. The darker the red, the more months per year that transmission is likely. The areas outlined in black delineate the current ranges of the mosquitoes within the United States. CREDIT Image courtesy of study authors

“Our findings should help to predict the areas at the greatest risk of dengue, chikungunya and Zika outbreaks,” said Rohr.

Temperature affects how often mosquitoes bite, the amount of time it takes for them to ingest a virus from one human and inject it into another, and their life cycle. Cohen, Rohr and other members of the research team found that mosquitos posed the greatest risk to humans at 84 degrees and risk declined in cooler and warmer temperatures.

“Given that the predominant thinking was that transmission was most likely to peak at very hot temperatures, which would mostly limit the diseases to the tropics, we were certainly surprised that the model and the field data suggested that high rates of transmission could occur at lower temperatures, possibly impacting more northern regions in the future,” Cohen said.

Pinpointing the optimal temperature for disease transmission is critical for predicting future disease rates and how diseases will spread with climate change, and more effectively implementing mosquito-control measures, said lead author Erin Mordecai of Stanford University.

“If we’re predicting a 29-degree optimum and another model is predicting a 35-degree optimum, the other model will say that climate change will increase transmission,” she said in a Stanford-issued media release, adding that if local temperatures are already near optimal temperature, infections may decline as temperatures rise.

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54 thoughts on “Study: Zika virus transmission isn’t as dependent on warmer temperatures as previously thought

  1. “Our findings should help to predict the areas at the greatest risk of dengue, chikungunya and Zika outbreaks,”

    except that..

    “Their data were used to create a model”

    in which they presumably assumed that temperature was the deciding factor so… good luck with that?

  2. We already know how to combat mosquito-borne diseases for which humans are the main source of infection. Knock down mosquito populations by public spraying, quarantine infected individuals indoors where they cannot be bitten by mosquitoes thus spreading the infection. This has been hugely successful in fighting malaria in the united States. The public health fight must be taken to poor neighborhoods where trash-filled yards, junkyards, and empty lots create lots of small bodies of water which promote Aedes species mosquito breeding. “The mosquitoes prefer to breed in areas of stagnant water, such as flower vases, uncovered barrels, buckets, and discarded tires [as well as tin cans and any small cavity that will retain a small pool of water], but the most dangerous areas are wet shower floors and toilet tanks, as they allow the mosquitos to breed in the residence. ”

    It doesn’t take much to knock out an outbreak of dengue….though it is a long hard slog to eliminate it altogether from a locality. The most effective tool in increasing standard of living and readily available basic health care.

  3. Clearly, temperature is a threat to the human race. We must find/fund ways to eliminate it.

  4. Was this study done on more than one species of mosquito? The high latitude ones may well peak at lower temps. A recentl visit to Canada gives me that impression.

    • The genus Aedes can tolerate a wide range of climate. They’re originally tropical and subtropical, but cities can provide microclimates for them to survive in higher latitudes of the temperate zones.

      One species recently invaded North America in car tires, which make such good water collectors and incubators of eggs and larvae.

    • I would assume so.

      Worst mosquito swarm I’ve ever ran into was at 9,000′ near Lime Creek, CO. We approached a deep red colored alpine pond out of curiosity, but were quickly running away from so many biting mosquitos that it looked more like a swarm of flies. This was in June, with temperatures between 30-60 degrees at that altitude.

      • Try Nova Scotia in July – you don’t go out without repellant on – and even then jeans and thick shirts are no protection.

      • Particularly aggressive Alaskan mosquitoes are alleged to have carried of small animals for later feasting.

      • Scotland – not New Scotland – has a reputation for swarms of mozzies that darken the Sun, and strip people to skeletons.
        I dare say that that is (seriously – ye-es?) exaggerated.
        But there is a hazard.
        Happily – to date – none of these are reported to carry real nasties – malaria, dengue, chikungunya and Zika – but my model [ a six-sided cuboid, which is user-handy] – suggests it could happen by 2517 AD.

        Please revert then. Thanks.

        Auto

      • “. . . mosquitos at 9,000. . .”

        True. Wouldn’t recommend camping outdoors if you’re traveling the Al-Can Highway, northern Canada or Alaska when warm-up begins. Swarms are thick, black, endless, maddening.

      • And all these places you tout are actually mosquito-free compared to northern Scandinavia and Siberia.

  5. There was a yellow fever epidemic in Philadelphia in 1787, after the Constitutional Convention. That was still during the Little Ice Age, so I doubt the vector is that particular as to temperature.

      • Also Europe.

        Swamp and marsh drainage helped, which would never be allowed by today’s Econ@zis, just as vector control spraying has been so drastically curtailed.

      • In Scandinavia malaria reached the Arctic Circle in the Torne Valley in the early 19th Century.

      • Chimp, whatta u bet the folks who outlaw spraying and complain about the bugs are the same sort that kill beneficial snakes and then complain about all the mice.

    • The whole “plague of mosquitoes from warming” schtick is ridiculous on its face.

      The biggest, deadliest outbreak of malaria in the history of the civilized world was in Europe during the Little Ice Age.

      That has been known since… the Little Ice Age.

    • The whole “plague of mosquitoes from warming” schtick is ridiculous on its face.

      The biggest, deadliest outbreak of malaria in the history of the civilized world was in Europe during the Little Ice Age.

      That has been known since… the Little Ice Age.

  6. Don’t mosquitoes see in the infrared scale and aren’t they attracted by carbon dioxide emissions from their prey?

  7. New study: Climate change will cause all areas to be 84 degrees at all times of year. First borns will eat the younger just to survive.

  8. If 84 degrees Fahrenheit is the optimal temperature for mosquitoes to bite and transfer these diseases, then they may need to move there map projections a lot farther north. In southern Alberta, Canada,84 degrees Fahrenheit is a very common temperature in the summer. Some nights we get lucky if it cools off that low at night.

  9. ‘ The recent emergence and spread of vector-borne viruses including Zika, chikungunya and dengue has raised concerns that climate change may cause mosquito vectors of these diseases to expand into more temperate regions. However, the long-term impact of other anthropogenic factors on mosquito abundance and distributions is less studied. Here, we show that anthropogenic chemical use (DDT; dichlorodiphenyltrichloroethane) and increasing urbanization were the strongest drivers of changes in mosquito populations over the last eight decades in areas on both coasts of North America. Mosquito populations have increased as much as tenfold, and mosquito communities have become two- to fourfold richer over the last five decades. These increases are correlated with the decay in residual environmental DDT concentrations and growing human populations, but not with temperature. These results illustrate the far-reaching impacts of multiple anthropogenic disturbances on animal communities and suggest that interactions between land use and chemical use may have unforeseen consequences on ecosystems.’

    https://www.nature.com/articles/ncomms13604

  10. There is this common misconception that mosquitoes don’t survive in cold weather.
    Most people don’t know that in the Arctic, where there are few predators of mosquitoes, huge swarms of mosquitoes exist.
    Just ask anybody from Sweden about the camping trips to the Arctic, where men sit around campfires covered in mosquitoes.

    • Ah yes, sitting around swatting mosquitoes, another Scandinavian tradition, like soaking fish in lye, or invading London on the weekend, (I think this later one was invented by the Danes). In Michigan’s Upper Peninsula the transplanted Finns have substituted deer flies for mosquitoes…

      good times, yes good times.

    • I’ve always been curious about the energy balance budget of UUGE swarms of tundra mosquitoes with only an occasional passing mammal or herd to feed on.

      When I walked the JMT I wore the elbows out of my wool shirt and used a paste of mud and soap for protection.

      • I’ve always been curious about the energy balance budget of UUGE swarms of tundra mosquitoes with only an occasional passing mammal or herd to feed on.

        My understanding — which could be total nonsense — is that mosquitoes mostly dine on plant fluids. They only drink blood when it chances to become available and even then, it’s only the females that attack mammals.

      • Don,

        Males don’t suck blood at all. Some don’t even eat as adults.

        Some species can feed on a variety of vertebrates. Others are limited to a few or possibly even only one victim species.

        Many females won’t find a blood meal, but there are lots of “hosts” on the tundra during fly season.

        Thanks to the pipeline, there are now more caribou than EVAH! Unprecedented numbers. Worse than we expected!

      • Moose are bitten so frequently that they lose about 1.5 pints of blood a week to mozzie bites in summer.

      • “I’ve always been curious about the energy balance budget of UUGE swarms of tundra mosquitoes with only an occasional passing mammal or herd to feed on.”

        Caribou, moose, lemmings, hares, voles, ground squirrels, humans

  11. The map would also suggest that the incidence of Zika is inversely to per capita GDP and therefore to general standards of public hygiene. After all Malaria used to be endemic in many parts of Europe, including the UK

    • Control measures can be expensive. Spraying is opposed by some environmentalists, so other approaches are being investigated, to include releasing sterilized males. Only females bite and suck blood, which they use to make their eggs. Now if we can just make the sterilized males more aggressive, so that they win breeding rights in the swarm, we’ll be on to something.

      It used to be thought that only male Aedes mosquitoes pollinated orchids in northern climes, but females have now been observed doing so as well, presumably incidentally, since they only drink blood. Blood types 0 and A and blood from younger persons are preferred.

      Mosquitoes evolved from “sap-suckers”, and those males who do feed still do so on plant liquids and nectar.

      • There are ‘laser curtains’ which can hear and target them with lasers, 2000 mosquitoes per second. I think they are illegal everywhere.

        Hitting a mosquito with a bright blue light causes them to fall paralysed to the ground where they die. No one knows why.

  12. I highly doubt that climate change fueled the Zika outbreak. These mosquitoes only travel miles. And, they are tropical, so they can withstand hot temperatures.

    The most likely culprit: Wolbachia.

    Wolbachia is responsible for the most widespread pandemics in the animal kingdom (LePage and Bordenstein, 2013).

    Safety tests were never carried out on vertebrate species, birds, Culex, waterways, or aquatic species prior to Wolbachia-infected Aedes mosquito releases (carried out in Brazil, Columbia, India, Indonesia, Vietnam, China, Australia, California, and Florida). FDA approval was not required, only EPA.

    I feel it is akin to putting genetic dynamite into a species and introducing it into the food chain where it never belonged.

    Wolbachia can survive about a week in a dead host; Zika can survive for about five days. And lateral gene transfers to other species have happened.

    Culex that naturally acquire Wolbachia are actually better vectors of malaria and West Nile virus (very similar to Zika).

    Over 300 species of birds carry West Nile virus. It’s extremely likely that birds are amplifying Zika. Birds can have up to a billion times more viral particles in their blood than similarly infected humans. A single “super amplifier” bird can infect 100s of mosquitoes.

    Wolbachia has been introduced into Aedes which means the eggs and larvae contain it. Many bird and aquatic species feed preferentially on the Aedes genus.

    Includes citations: http://www.infobarrel.com/Tracing_Zikas_Path_to_Florida_Culex_and_Wolbachia

  13. It is now generally accepted that the global hysteria before and during the last Olympics in Brazil with regard microcephaly in infants being caused by the zika virus was false news. It appears that the microcephaly was caused by environmental pollutants directly administered by Brazilian authorities

  14. The elephant in the Zika room is sexual transmission. Many of the reported infections had no indication of any mosquito involvement. And the sexual transmission route has been curiously vaguely outlined.

    In reports from Singapore, which was reporting more than 30 new cases per day in late August early September of last year, there’s a mention of dengue fever being endemic, offering this as an explanation of the rapid spread of Zika there.

    Is dengue fever sexually transmitted too? Is there a way of determining whether someone got the disease from a mosquito or by sexual contact?

    The CDC’s latest Zika update reports that “many” of the infected are asymptomatic isn’t much help. It offers as fact that “the virus can stay in semen longer than in other body fluids”, without defining those “other fluids”, or “longer”. Are saliva or tears infectious?

    The report implies that an infectiousness will end at some time, but gives no time frame. Not very reassuring…

    https://www.cdc.gov/zika/prevention/sexual-transmission-prevention.html

    How many unwitting but infectious Zika carriers might be out there? I’ve found no news on the course of the disease in Brazil during the past summer.

    • Both dengue and Zika virus are transmitted through “bites” of mosquitoes of genus Aedes. Mosquitoes pick up the virus after biting an infected person and continue to transmit it to other individuals through bites.

      For Zika, transmission can also occur from mother to fetus, sexual contact and blood transfusions. Dengue, OTOH, is only transmitted through mosquito bites and not through blood transfusions or sexual intercourse.

      In Zika, once you are infected you become immune to that virus. There are four different dengue strains, and a person will only be protected against the strain with which he was infected, but not any other.

  15. In other words, heads or tails, you’re screwed. No matter what, WE ARE ALL GOING TO DIE.

    The maximum “allowable” increase in temperature by 2100 just got lowered again…

  16. Another factor omitted in the study is humidity. Where I live on the High Plains of Texas the summer temperatures are routinely in the 80’s and 90’s, but the humidity is so low that mosquitoes cannot find many places to breed. Our native wildlife includes coyotes, pronghorn, roadrunners, lizards, tarantulas, and others adapted to the dry climate (20 in average annual rainfall). Mosquitoes are hardly a problem.

  17. Zika, Chik, dengue, yellow fever, and several; other arthrovectored virus in the same genus are transmitted by Aedes aegypti, the yellow fever mosquito. Recently the news media and some government officials have blamed the “emergence” actually re-emergence of such diseases on “global warming.” At least most of the responsible government officials got the message when they were reminded that one of the major yellow fever epidemics in USA history was in Philadelphia in 1793, during the Little Ice Age. Yellow fever, dengue and malaria (not vectored by aegypti but anopheles species) were once common in the southern USA and are but an airplane ride or a walk across the border. It has been thanks to modern and professional mosquito control that we have, until very recently avoided significant new outbreaks. We now face a variety of factors that are presenting difficult challenges for mosquito control professionals, world travel, including illegal immigration, pesticide resistance, especially for Aedes aegypti, a general lack of understanding of the problem by the average person, overzealous regulation, naive and misinformed environmental advocates. All the diseases listed above present a problem because a person might have the disease yet be asymptomatic, get on a plane in South America and be in a US city within a few hours.

    • You have that a little mixed up.

      Aedes aegypti & albopictus, spread dengue fever, chikungunya, Zika fever, Mayaro and yellow fever viruses, and other diseases.

      ~ 40 Anopheles species spread Malaria, canine heartworm Dirofilaria immitis, the filariasis-causing species Wuchereria bancrofti and Brugia malayi, and a number of viruses.

      • Aedes aegypti with blood in her gut:

        Anopheles freeborni female pumping same:

        Nasty little bitches.

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