A study started in 2014 recently concluded ten years later that microorganisms such as bacteria and fungi can be found at between 1,000 and 3,000 meters above sea level, which was believed to be impossible. This data was found by monitoring ten different airplanes that traveled over Japan. The scientists gathered information about the aircraft as well as the ecological conditions it was flying over before swabbing it upon landing and incubating the samples. The study, published in Proceedings of the National Academy of Sciences, found that over 266 fungi and 305 bacteria genera had hitched a ride on the aircraft. 

Many of these species are typically found in soil or plants, and were furthermore more common in China, meaning that they had traveled over 2,000 kilometers in air to get on the planes. Scientists cited farming practices as a reason this could have happened, and the species likely came from areas where pesticides and fertilizers are used frequently. Unfortunately, viruses were found on the aircraft as well as the fungi and bacteria, and many living organisms found on these planes are associated with health risks. 

Furthermore, because of the poisons used in the farmlands where the organisms originate, the only surviving organisms are often the ones that are resistant to common control methods. Biologists are constantly having to change formulations and come up with new solutions, as many pests have short lifespans and their populations can become resistant to a certain treatment quickly. A common example is antibiotics: some illness-causing bacteria have become immune to certain antibiotic drugs because the ones that have the resistance gene survive and reproduce.

Those who work with pest control and farmers are well-aware of these risks, but international travel could speed up the process. If a strain of bacteria or fungi moves to another country, farmers may not be equipped to handle it and protect their crops. Worse, some of the specimens found could be dangerous for animals and humans as well. In a post-coronavirus world, the more pessimistic view is that this could spread illnesses globally. It is a marvel that these microscopic organisms can cover so much distance and live far from the ground, however. The concept of a human illness traveling via aircraft and having a large effect on a population is still unlikely, but this study found it to be not impossible.