Mosquitoes are the deadliest animal on the planet. U.S. Army Force Health Protection measures are in place to protect soldiers from the diseases they carry. But mosquitoes aren’t alone in their risk to soldiers' health and well-being. Flies such as house flies, blow flies, and one known as the “Dog Dung Fly” can not only be a nuisance, but can harbor and transmit pathogens such as E.coli, Shigella, and many other organisms that can make soldiers sick. Also, their sheer numbers can be a source of significant annoyance, often being worse than mosquitoes.
It has been known for many years that flies play a role in transmitting pathogens but in our modern era the threat has become more complicated. Now flies are known not only to transmit pathogens, but many of them are drug resistant, and often the bacteria are “multi-drug” resistant, meaning they are resistant to more than one antibiotic. This is a One Health issue impacting both humans and animals. Flies carrying these drug-resistant pathogens have become a problem with the rise in antibiotic resistance around the world due to the overuse and misuse of antibiotics in people and in agriculture. Flies that are a nuisance for humans often breed on farms where livestock are raised and treated with antibiotics, providing ample breeding material, such as feces contaminated with antibiotics that have passed through the animal. Flies transmitting these bacteria can not only make you sick from what you eat, but the flies are also often attracted to open wounds and can directly transfer drug-resistant bacteria into the open wound.
The threat is even more complicated. The best way to control flies is through sanitation, ensuring that waste is properly disposed of following military sanitation guidelines. But sometimes insecticides are needed to control flies as part of preventive medicine activities. DDT was developed for use by the Department of War in 1944. By 1949, house flies were already exhibiting resistance to DDT. And that resistance has conferred resistance to more modern insecticides such as pyrethroids. Flies in many parts of the world are resistant to the insecticides approved for use by the Department of War leaving deployed warfighters with few or no effective pesticide to use.
Now, when you encounter flies in the field, there is a very good chance that those flies are not only carrying drug-resistant bacteria, but they are also resistant to insecticides, making them difficult to control when engineering sanitation controls are not possible.
Flies are a problem in almost every country in the world during warm weather, so soldiers are facing this threat no matter where they deploy. To address this threat, Army and Navy Entomologists, microbiologists, and Biochemists are partnering with other government agencies, such as the USDA Agricultural Research Service, to identify resistance genes in the bacteria to better plan for treatment options and resistance genes in the flies to better plan what insecticides will work to control the flies.
Researchers at the USDA ARS Arthropod-borne Animal Diseases Research Unit have developed methods to look at the fly “Resistome,” simultaneously identifying resistance genes in bacteria and insecticide resistance. Flies are collected in the field. They are held in tubes where they are allowed to defecate and vomit. The flies are removed from the vials, and these excreta are used to look for bacterial resistance genes. The flies are then placed in another vial and preserved to look for insecticide resistance genes.
Through programs like the Global Emerging Infections Surveillance (GEIS) program, flies are collected during pre-exercise vector surveillance and preserved for testing. With this information, medical providers can better understand what drugs will be effective in an area, and environmental health personnel, such as 68S, ESEOs, and entomologists, can better plan fly control missions with the proper knowledge. And military entomologists can work with private industry partners to develop novel insecticides for use by deployed soldiers.
So, the next time you see a fly land on your lunch, understand that fly is even more dangerous now than it was in the past and it’s critically important to ensure that sanitation is a top priority in the field.
Craig A. Stoops, PHD, BCE
Entomologist
Joint Base Lewis–McChord, WA 98433