Nine-year-old Nowa Paye is shown last year being taken to an ambulance in her village in Liberia after showing signs of the Ebola infection. (Jerome Delay/Associated Press)

Peter J. Hotez is president of the Sabin Vaccine Institute and Texas Children’s Hospital Center for Vaccine Development and dean of the National School of Tropical Medicine at Baylor College of Medicine. In 2014, he was named a U.S. science envoy by the State Department. The views expressed are his own.

While global attention has been focused on strengthening health systems in West Africa in the aftermath of the Ebola outbreak there, a new wave of tropical infectious disease is threatening Southern Europe, North Africa and the Middle East.

The unprecedented appearance of tropical diseases in Southern Europe in recent years has been well documented. Dengue fever appeared on Madeira off the coast of Portugal in 2012, and chikungunya arrived in Spain this year. Malaria has returned to Greece after being eliminated in the 1960s, and West Nile virus has gained a foothold throughout Southern Europe. These infections are transmitted by mosquitoes that now inhabit the region. Schistosomiasis, a parasitic blood fluke infection transmitted by snails, just made its first recorded appearance on the island of Corsica, while outbreaks of opisthorchiasis, a liver fluke that causes bile duct cancer, have occurred in Italy.

We are still investigating the forces responsible for the transformation of Southern Europe into a tropical disease “hot zone.” Among the possible causes are the severe economic downturns in Greece, Italy and Spain, which may have slowed national public-health efforts, and global warming, which is creating temperature and rainfall conditions better suited for insects and other carriers of disease adapted to tropical climates.

But a third factor must also be considered: The conflicts in the Middle East and North Africa. Ebola arose in Guinea, Sierra Leone and Liberia, in part because the health systems of the affected countries had been weakened by years of conflict and human migration. That same combination is now present in the Islamic State-occupied areas of Syria, Iraq and Libya, as well as in Yemen.

We are already seeing the consequences of drawn-out Islamic State occupation and the subsequent halting of public-health interventions in places under the terrorist group’s control. These include the reemergence of vaccine-preventable diseases such as polio and measles but also a dramatic increase in leishmaniasis. Known in Syria as “Aleppo evil” because of its ability to disfigure the faces of young people, leishmaniasis is a parasitic disease transmitted by sandflies. Dengue fever is also now widespread in the Middle East and parts of North Africa, while deadly Middle East respiratory syndrome coronavirus infections appear regularly on the Arabian Peninsula. These diseases pose additional threats to Southern Europe.

The extent to which Southern Europe’s new wave of tropical infections is due to human migrations from across the Mediterranean Sea or the Middle East remains unclear. But it is apparent that an enormous band of territory extending from Spain and Morocco in the west to Asia Minor, Iran and the Arabian Peninsula in the east is under threat and could become a source for epidemics that imperil the world.

Action is urgently needed to answer this threat. Key needed measures include expanded surveillance for selected tropical infections, as well as studies to better understand how these infections are transmitted and where they originate. A global health-security agenda launched last year and endorsed by the G-7 countries is intended to address some of these urgent issues. Wherever possible, public-health preparedness efforts must be intensified on both sides of the Mediterranean and in the Middle East.

Finally, we need to start developing new medical interventions, and especially vaccines, in preparation for these coming plagues . Last year, Ebola vaccines were not available to fight the epidemic in West Africa even though the technology to produce them had been available for years; a lesson learned was that, because vaccines for tropical diseases are not financially remunerative, we cannot depend on big pharmaceutical companies to produce them. Instead, nonprofit product-development partnerships, such as our Sabin Vaccine Institute and Texas Children’s Hospital Center for Vaccine Development, must step in to do this work, including building parallel capacity for vaccine development infrastructures in the Middle East and North Africa. However, we need innovative financing mechanisms to develop these products in a timely manner and provide them at low cost to vulnerable populations living in these newest hot zones.

The world slept as Ebola overtook West Africa. We should not make the same mistakes in the Middle East and the Mediterranean.