For the past 10 years, the world has seen extraordinary increases in viral and parasitic infections transmitted by insects and snails. (Yes, snails — they carry parasitic diseases in much the same way insects do) These infections, also known as vector-borne tropical diseases, will significantly and adversely affect the major economies of Europe, the Middle East, Oceania, and the Americas.
Recent disease pattern shifts in southern Europe are among the most prominent. Malaria has returned to Greece after it was eliminated there 50 years ago, while mosquito-borne virus infections such as dengue fever, chikungunya, and West Nile virus are arising in Portugal, Italy, and Spain. Schistosomiasis, a devastating parasitic disease that causes damage to the bladder and ulcers in the female genital tract, is the ultimate neglected tropical disease, in no small part because it's often been viewed as affecting only the world's poorest people in Africa and the Middle East.
But suddenly, it appeared in Corsica off the coast of France.
The Middle East and Afghanistan have also experienced a marked increase in leishmaniasis, a parasitic disease of the skin that can cause disfiguring ulcers on the face and is transmitted by sandflies; there have been more than 100,000 new cases in the last several years. We have also seen dengue become widespread in the Middle East and Africa.
The New World has hardly been immune. In 2013, chikungunya appeared on the Caribbean island of Saint Martin, and over the course of a year it spread with unprecedented speed across Latin America and the Caribbean; today transmission occurs in almost every country in the Western Hemisphere. In Venezuela, rates of malaria have increased and there have been recent urban outbreaks of schistosomiasis and Chagas disease, a cause of heart disease transmitted by kissing bugs.
And now it's happened again. Zika virus made its way across the Pacific Ocean to Micronesia, French Polynesia, and finally Easter Island off the Chilean coast before it rapidly spread into Brazil and then Colombia. By the end of March, Zika will be found in most of Central America and on almost every Caribbean island.
The United States is also vulnerable, especially on the Gulf Coast where there are multiple species of mosquitoes capable of transmitting West Nile virus, dengue, yellow fever, chikungunya, and Zika. Texas has consistently led the nation in West Nile virus infections, and it is one of the only states where Chagas disease is transmitted by kissing bugs. Samples collected in Houston from 2003 to 2005 found dengue in the spring and summer. We're now waiting for chikungunya and Zika.
The profound poverty found in the US Gulf Coast means we might see significant Zika outbreaks and cases of microcephaly arise there.
So far we do not fully understand how these vector-borne diseases appear seemingly out of nowhere and then, in the case of Latin America, spread with such alarming speed to occupy entire the entire continent in the course of a year. I tell my medical students and graduate students that these sudden outbreaks remind me of the movie Ghostbusters – a floating green blob feasts at a hotel table, a skeleton drives a taxi, but no one has yet figured out the unifying theme that explains all the weird behavior.
That said, there are several possible explanations for the rise of vector-borne diseases — most of them resulting from human activities.
Poverty is an important factor. Some of the areas now most severely affected by vector-borne diseases, including Brazil, Venezuela, and Southern European nations, have recently experienced marked economic downturns. Vector-borne diseases strike poor nations because governments cannot afford to maintain insect control programs, while people living in poverty can become vulnerable because their housing lacks adequate screens and their surrounding environments are littered with debris such as plastic containers or old tires that fill with water and breed insect larvae. The profound poverty found in places such as Haiti or even the US Gulf Coast mean we might see significant Zika outbreaks and cases of microcephaly arise in these places.
Large-scale human migrations are also contributing. Beginning in the 1990s, dengue fever is believed to have been introduced into Saudi Arabia from Africa or Asia as a result of the annual Hajj pilgrimage, and there are worries that Zika could follow. Refugees fleeing the conflicts in Syria, Iraq, Libya, and Yemen may be disseminating diseases across the Middle East and North Africa, as might a diaspora escaping the violence and economic collapse in Venezuela. Human migrations into urban areas place excessive demands on city infrastructures that cannot maintain adequate control of water, sewage, or quality housing.
Southern Europe, together with Europe's far north and Arctic regions, has experienced significant temperature increases in recent decades. It's also been noted that the spread of Zika across Latin America and the Caribbean coincide with the rise in Pacific Ocean temperatures linked to an El Niño event. These changes in weather associated with elevations in temperature or altered rainfall patterns help insects and snails flourish in previously uninhabitable areas.
Epidemics of vector-borne diseases may become a new normal for areas of our planet where poverty, conflict and human migrations, temperature and rainfall alterations, or some combination of these factors are having their greatest impact. This year, the United Nations launched a new set of 17 Sustainable Development Goals, which touch on health, poverty, inequality, and the environment. Global leaders will need to be tackle these issues in future G7 and G20 summits if they hope to successfully battle these new disease epidemics.
In addition, the world will need new technologies — including new vaccines to prevent vector-borne diseases such as Zika, dengue, and schistosomiasis — while developing a new generation of safe and effective insecticides or other insect control measures. But this scientific innovation will require innovation in financing through public funds.
My recent finding that neglected diseases disproportionately occur among the poor living in G20 nations — the largest economies in the world, including America and EU countries — presents an opportunity for them to further support global health research and development. The world's wealthiest countries must address this next generation of vector-borne diseases.
Dr. Peter Hotez is dean of the National School of Tropical Medicine at Baylor College of Medicine, where he is president and director of the Sabin Vaccine Institute and Texas Children's Hospital Center for Vaccine Development. He is also a Baker Institute Fellow in Disease and Poverty at Rice University, and serves as US Science Envoy for the State Department and White House. Follow him on Twitter: @PeterHotez