.jpg)
Blood-sucking flies might be the newest way to identify emerging infectious diseases in wild animals before they spread to humans.
A team of researchers have discovered that these flies can act as ‘flying syringes’ because pathogens such as malaria are preserved in the blood meals of flies.
These blood meals could be used as an indirect, non-invasive way of studying the circulation of pathogens in wild animals, improving scientists’ ability to identify and control the global outbreak of new and re-emerging infections including the Ebola and Zika viruses.
There are seven new pathogens identified worldwide each year and that number is predicted to reach 15 to 20 annually by 2020 due to increased human contact with wildlife species that are potential reservoirs of disease.
Despite significant scientific advances, researchers are unable to predict where, when and how epidemics arise.
“This is a huge public health issue that urgently requires new tools for the active monitoring of outbreaks and rapid diagnosis of the pathogens involved,” senior author and evolutionary geneticist Franck Prugnolle, from the National Center for Scientific Research (CNRS) in Montpellier, France, said in a statement. “We wanted to investigate whether blood-feeding insects could act as a sampling tool out in the wild environment, allowing us to monitor the presence and emergence of infectious disease.”
According to the study, about 60 percent of emerging infectious diseases in humans are zoonotic in origin. That increasing number requires the development of new methods for early detection and monitoring of infectious agents in wildlife.
Existing methods for studying the circulation of pathogens in wild habitats involve analyzing animals caught for food, which represent only a fraction of a region’s wildlife, or directly trapping animals to study the presence of infection in their organs and tissues, which is difficult as well as dangerous to protected species.
Over 16 weeks, the research team conducted a field study in four national parks in the forests of Gabon by setting traps for three types of flies. The researchers analyzed the insects’ blood meals to determine the origin of the blood and the species of any malaria parasites present.
They caught more than 1,230 flies—30 percent of which spread African sleeping sickness—that were engorged with blood.
Lead author Paul-Yannick Bitome-Essono, from the National Center for Scientific and Technological Research, France, said the majority of the infected flies were tsetse flies—which is known to transmit diseases to human beings.
“We thought the tsetse fly might be a good candidate in our study, as both sexes feed on blood, they are large and easily trapped, present in large numbers in Central Africa and are opportunistic feeders with no strong preference for a particular host animal, so would feed on a large range of wildlife,” Bitome-Essono said in a statement.
They used a new technique for closely studying host blood DNA and determined the host origin of three-quarters of the samples, which shows that the flies had fed on over 20 different species, ranging from elephants and hippopotamuses to reptiles and birds.
The researchers found malaria parasites in nearly 9 percent of the blood meals, including 18 cases of previously undocumented malaria species. The method also allowed them to identify the natural hosts of some malaria species whose preferred host was previously unknown.
“These results show that blood meals of the engorged flies can be successfully used to analyze the diversity of known malaria parasites,” Prugnolle said.
The researchers will now look at ways to improve the method with next-generation sequencing and high-throughput pathogen detection methods.
“This approach of ‘xenosurveillance’ could detect pathogens before they spread to humans, as well as the emergence of new diseases in wild animals that may threaten their long-term survival,” Prugnolle said.
The study was published in eLife.
