Researchers observed the single-celled organisms that cause African sleeping sickness mating for the first time.

The organisms, called trypanosomes, are found in the blood of those who have been diagnosed with the illness, a University of Bristol news release reported.

A research team looked at the microbes' behavior inside tsetse flies, which transmit African sleeping sickness to humans. The trypanosomes were observed using fluorescent markers.

The team watched the organisms "twirling and gyrating together," and eventually combining into one hybrid cell. The researchers made this discovery by tagging each trypanosome with a different colored fluorescent. The resulting hybrid cells were found to have colors from both of its "parents."

"It's not only bigger animals that have intricate courtship - but you need a powerful microscope to see this!" Professor Wendy Gibson, who led the research, said in the news release.

The sexual patterns of the microbes allow for genes to be "swapped" which can lead to different, and possibly stronger, strains. Microbes like the trypanosome can use sex to create new combinations of harmful genes.

Researchers once believed these microbes reproduced by splitting in half. This new research shows the trypanosomes actually reproduce to "swap genes between strains."

"These new results suggest that sex is not an optional or rare part of this microbe's life cycle, but probably happens every time two different trypanosomes find themselves together in the same tsetse fly," the news release reported.

The finding could help researchers understand how new strains of diseases such as African sleeping sickness are formed. It could also help medical researchers pinpoint how drug resistance arises in microbes.

African sleeping sickness causes symptoms such as "anxiety, day drowsiness, fever, headache, insomnia, mood changes, sleepiness, excessive sweating, swollen lymph nodes, swelling at the site of the fly bite, and weakness, the New York Times reported.