What the rise of Zika (and other viruses) might tell us about our planet

John Ross, MD, FIDSA
John Ross, MD, FIDSA, Contributing Editor

Follow me at @JohnRossMD

Zika virus, a pathogen that was almost unknown a few months ago, is now rampant in Central and South America and the Caribbean. In Brazil, it has already infected about 1.5 million people and caused nearly 4,000 cases of microcephaly, a severe birth defect. It is almost certain to spread to every country in the Americas, except Canada and Chile, which lack the Aedes mosquitoes that spread Zika.

Zika is not the only virus that has come from the tropics to menace the United States. Dengue, an unpleasant and potentially fatal viral infection, has broken out in Texas, Florida and Hawaii in the past 10 years. Chikungunya, a virus that can cause prolonged joint pain and ruin your vacation, has caused recent outbreaks in Florida, Puerto Rico and the U.S. Virgin Islands. All three of these viruses are spread by Aedes mosquitoes.

Globalization for mosquitoes: Have Zika, will travel

Globalization, the explosion of international trade and travel, is one factor in the spread of Zika, dengue, and chikungunya. Viruses may travel the globe via infected humans, or via mosquitoes that are riding in freight containers. One mosquito species that transmits Zika and other viruses, Aedes albopictus (also known by the more formidable name of the Asian tiger mosquito), probably arrived in the U.S. in the 1980s in shipments of old tires from Asia. (Aedes aegypti, another virus-spreading mosquito, probably arrived in the United States from Africa in colonial times.)

Climate change helps Aedes mosquitoes reach new frontiers

Climate change might be another reason for the surge in strange and unfamiliar infections. According to Dr. Aaron Bernstein of the Center for Health and the Global Environment at the Harvard T.H. Chan School of Public Health, there are currently not enough data to make a definite connection between climate change and the emergence of tropical viruses such as Zika. However, says Bernstein, “If I wanted to limit the spread of mosquito-borne diseases like Zika, I’d choose a future more like the past, instead of the one that climate science tells us is coming.”

Dr. Richard Ostfeld of the Cary Institute of Ecosystem Studies in Millbrook, New York, acknowledges that the link between emerging pathogens and climate change is “still controversial.” But, Ostfeld adds, “There’s little doubt that climate warming is expanding the ranges of both Aedes species in North America and elsewhere, increasing the length of the biting season, and accelerating viral replication in the mosquitoes.” The northern limit of Aedes albopictus is currently Long Island, but if climate change continues, it is predicted to push as far north as Maine in the coming decades. In another climate change simulation, Aedes albopictus is predicted to expand throughout the entire eastern United States and into most of Europe.

The role of ecosystem change

Another possible factor in the spread of Zika is loss of biodiversity. Habitat loss, climate change, and invasive species are threatening to lead to mass extinctions. In complex ecosystems, mosquitoes may bite a greater variety of birds and animals. Some of these will be poor hosts that fail to support viral replication, thus breaking the cycle of transmission.

Ostfeld, whose research has shown that the rise of Lyme disease is related to a decline in biodiversity, says that “There’s not a clear cut extrapolation from the effects of biodiversity loss on Lyme disease to biodiversity effects on diseases like Zika, dengue, and chikungunya.” However, he adds, “Aedes albopictus, which is a major vector of dengue and chikungunya, and almost certainly of Zika virus, does bite wild birds and mammals, and so I’d expect that vertebrate diversity could indeed deflect mosquito blood meals away from people and towards these dead-end hosts.”

If Zika is indeed the product of rapid climate change, ecosystems in disarray, and environmental degradation, it might be a disease that points to a greater and more dangerous malady. As bad as Zika is, it might be only a warning of worse to come.

Comments:

  1. Shelley

    Can anyone substantiate the sexual transmission theory?

  2. Eva V

    “In Brazil, it has already infected about 1.5 million people and caused nearly 4,000 cases of microcephaly, a severe birth defect.”

    It is premature to say that Zika is causing microcephaly. Colombia has reported thousands of pregnant women with Zika and no microcephaly. In addition, there are thousands of cases of microcephaly reported in the US with no Zika epidemic. What we know for sure is that Brasil has been heavily spraying with insecticides and still uses chemicals that have been phased out in other countries.

  3. An Sarris

    YOU HAVE NOT MENTIONED MASSIVE IMMIGRATION LIKE THE ONE THAT SUFFOCATES GREECE.

  4. D Shea

    Read an interesting article from UK. There are activist in Brazil that are saying the Zika virus has been in Brazil for 70 years! Without problems. The new policy of requiring pregnant women a to receive a version of the Tdp vaccine is the only thing that has changed. This vaccine has not been tested in pregnant women and is not known to be proven safe. And that these activist want that to be addressed as to whether that is the true culprit of the microcephalic babies! Hmmm!

  5. Charles

    Jack-elyn:
    Better hope you aren’t…it’s becoming clear that the Zika virus has likely been transmitted through sexual contact (blood-semen borne)!!

    Monique:
    Changes in weather patterns (precipitation and temperatures) can effect hundreds of things in nature that have a ripple effect. Further, it is clearly documented that certain conditions, particularly the extremes, create havoc in the environment, and specifically certain conditions that insects thrive in. The article does not state that climate change is definitely the reason for the Zika virus becoming such a public health concern, only that it MIGHT be part of a complex sequence of events that has resulted in the current circumstances. That seems very plausible.

  6. Jennifer Graziano

    This is a very well-thought piece. There is a growing amount of concern which is, in part thanks to digital media, I am glad to see members of my beloved school writing about this!

  7. Charles

    Jack…Read the article more carefully…it discusses a much broader range of factors and variables that MAY have impacted the spread of Zika and other mosquito borne diseases. While 1947 is the currently documented timeframe when Zika was first identified, it is believed that cases outside of Africa did not occur until 2007 when it spread to the South Pacific, 60 years later! Yes, it has been followed, but the recent “epidemic” being described in Brazil MAY be more identifiable because of the likely connection between Zika and the astronomical rates of Microcephaly among newborn children. The Zika virus MAY have mutated the way many viruses can, now causing much more serious illnesses than previously identified. Until public health officials from many countries and the World Health Organization (WHO) track the spread of Zika, much more than climate change remains hypothetical. For more detailed information check bulletins and updates issued by WHO and the U.S. Centers for Disease Control.

  8. Monique houghton

    you disappoint me by sending this climate change garbage based on lie after lie I expected more from you cancel my subscription. Monique Houghton

  9. Richard, M.D.

    To Jack: …….and the moon missions were staged in a warehouse, right?
    Richard, M.D.

  10. Jack

    What a bunch of garbage. The Zika virus was indentified in 1947 and has been followed since. Then throw in the climate change foooey! Unmitigated garbage article – just a bunch of unsubstantiated opinions.

  11. Margarita Rozillio

    How to stop it , to spread?