Leishmania, a tropical parasite carried by sand flies, spreads prolifically to mammals by forcing the flies to regurgitate as they bite their prey, a new study finds.
While still in the sand fly, the parasite secretes—and then multiplies in—a gel that obstructs the fly's throat. When the fly bites a person or another mammal to feed on blood, the insect is forced to expel the parasite-laden blob of gel into the victim's bloodstream, the researchers report in the July 22 Nature. Inside the new host, the gel appears to promote the parasite's survival.
A fly remains infected for life. So, by obstructing the sand fly's digestive tract, the parasite could also be forcing the insect to take more blood meals than normal, prompting more bites and hence greater spread, hypothesizes Matthew E. Rogers, a parasitologist at the University of Liverpool in England.