By Jonny Lupsha, News Writer

An illness affecting North American officials in Cuba may be pesticide related, The Guardian reported. The mysterious cognitive ailments injured dozens of diplomats in Cuba in 2016 and 2017. It adds another chapter to the evolving relationship of humans and disease, as some are cured and others arise.

According to The Guardian, the condition known as “Havana syndrome” affected 40 U.S. and Canadian diplomats, causing them to suffer from several cognitive ailments, “ranging from dizziness and blurred vision to memory loss and difficulty concentrating.” While the exact nature of the illness is still unknown, a recent study in Canada proved that cases coincided with spikes in pesticide spraying in Cuba. The increased use of the pesticides, which targeted mosquitoes, came from fears over a Zika virus outbreak. Oddly, locals seemed to be unaffected by exposure to the same pesticides, leaving doctors wondering why only those from Canada and the United States became afflicted by the chemicals.

The Evolving Human-Disease Relationship

Some problems that faced early humans have died out almost completely with advancements in science and medicine or changes in sociological patterns. At the same time, other problems have come up for the same reasons. The first major shift in our relationship with disease was a spike in mortality during humans’ early agricultural days.

“One of the reasons that mortality was so high is because people were now living in much closer quarters with one another and with their animals,” said Dr. Alyssa Crittenden, Associate Professor of Anthropology at the University of Nevada, Las Vegas. “This created a perfect storm for disease transmission and particularly zoonotic diseases—the ones caused by viruses, bacteria, or parasites that were spread from animals to humans.”

Dr. Crittenden said this is known as “the first epidemiological transition.” The second epidemiological transition began in the last two to three centuries and was caused by a decline in infectious diseases in exchange for the start of degenerative diseases, which she said included heart disease, asthma, high blood pressure, and so on. Now, while still fighting off the second epidemiological transition, we find ourselves in the middle of the third epidemiological transition.

Drug-Resistant Diseases

“The third epidemiological transition is the emergence and re-emergence of drug-resistant infectious diseases—things like Ebola and Zika,” Dr. Crittenden said. “It’s characterized by a resurgence of highly virulent infectious diseases that are affecting populations at a very large scale. It’s timed from about the mid-1970s until now.”

All three epidemiological transitions happened at different rates around the world, Dr. Crittenden said, and the United States is currently experiencing both the second and third transitions. The third transition often includes diseases from the first—zoonotic diseases that are transmitted from animals to humans.

“One of the most well-known examples is Ebola,” Dr. Crittenden said. “Fruit bats are thought to be natural Ebola hosts. The virus is contracted initially from close contact with the blood, organs, or bodily fluids of animals that are infected; the virus is then spread through human-to-human contact with blood, organs, or other bodily fluids of an infected person. It can also be spread from contact with surfaces contaminated with these fluids, like countertops or bedding.”

The Zika virus, which led to the pesticide spraying thought to cause Havana syndrome, is similar. “It is primarily spread by a particular genus of mosquitoes, Aedes, that bites during the day and the night,” Dr. Crittenden said. “It’s also passed from a pregnant woman to her fetus, which is why the World Health Organization was urging pregnant women to avoid mosquitoes at all costs during the most recent outbreak.”

Researchers don’t know yet why the pesticides used in an effort to control the Zika virus in Cuba seemed to only affect U.S. and Canadian diplomats. Perhaps, the reason is related to the epidemiological transitions around the world occurring at different rates from one another. The North American population had just started its exposure to Zika and the pesticides used to control the outbreaks.

Dr. Alyssa Crittenden contributed to this article. Dr. Crittenden is an Associate Professor of Anthropology at the University of Nevada, Las Vegas, where she is also an Adjunct Associate Professor in the School of Medicine. She received her M.A. and Ph.D. in Anthropology from the University of California, San Diego.