Leishmaniasis parasite protects the fly that transmits it to
13 August 2014
The Leishmania parasite, which causes the human disease
leishmaniasis, acts as a probiotic in the insect that transmits it
to humans, protecting them from infection by bacteria.
The research, by Lancaster University and published in the open
access journal Parasites and Vectors , suggests that
using bacterial controls to stop the spread of leishmaniasis could
sometimes have the opposite effect to that intended, by benefiting
flies carrying the parasite.
Around 12 million people are currently infected with
leishmaniasis worldwide, mostly in South America, Africa and Asia.
It is estimated to kill 20-50,000 people per year. Sandflies
transmit the parasite by feeding on an infected mammal and, if they
survive long enough, feeding on another mammal, and passing the
parasite on to them.
The team from Lancaster University studied sandflies’
interactions with bacteria, to find a new way to control the sandfly
populations, and curb the spread of leishmaniasis. They set out to
study the effects on the sandfly of carrying both the Leishmania
parasite and the bacterial pathogen Serratia marcescens, a
naturally occurring disease in sandfly populations.
The team took a population of Lutzomyia longipalpis
sandflies and fed them blood meal containing the Leishmania
parasite, and a second group with uninfected blood meal. They then
fed both groups with the Serratia pathogen. The group that were
carrying the Leishmania parasite had a survival rate of 56% after
six days, in contrast to the control group, which had a survival
rate of just 11%. This showed that carrying both the Leishmania
parasite and the bacterial pathogen protected the flies and
increased their lifespan.
The authors say that this finding is important for efforts to
develop biological controls against vectors of disease using
bacterial pathogens, as these may have unexpected effects in the
Researcher Dr Rod Dillon said: “We’re looking at using bacteria
to stop the spread of Leishmaniasis, but it turns out that the
Leishmania parasite works as a kind of probiotic and reduces the
mortality of the fly.”
Dr Fernando Genta said: “Finding out that sandflies can benefit
from Leishmania infection was a surprise. It changes the way we
think about the vector-parasite interaction. From an evolutionary
point of view, it may be interesting for sandflies to have a part of
its population permissive to Leishmania infection. This may be one
explanation for the maintenance of this interaction throughout time.
“Our finding states an alert for vector control strategies. If
you try to use a pathogen to reduce sandflies population, you may
favor the Leishmania infected insects. In the end, it may increase
the chance of human infections.”
Sant’Anna MRV et al. Colonisation resistance in
the sand fly gut: Leishmania protects Lutzomyia longipalpis from
Parasites & Vectors 2014 7: 39