Actualité scientifique
Actualidad científica
Scientific news
N° 481
June 2015
Leishmania parasites reveal their sexuality
Human immune cells infected by Leishmania (© IRD / B. Vergnes).
With 16 million people affected worldwide, mainly in developing countries,
leishmaniosis (also called leishmaniasis) is a major public health problem. It
is, however, a neglected disease, from the point of view of both treatment and
research effort spent on it. In particular, little is yet known in biological terms
about the parasites responsible, called Leishmania. How do they reproduce?
How do they evolve and adapt to their environment and hosts, and to drugs, and
so on? A recent study by IRD lifts the veil on their complex biology.
Key points
Transmitted by the bite of small insects called Phlebotominae, there are three different types of leishmaniosis, namely cutaneous,
mucocutaneous and visceral, the latter being fatal if left untreated. Approximately 350 million people are exposed in Southern Europe, East
Africa, Southern Asia and South America, and 2 to 2.5 million new cases are reported every year.
The appearance or re-emergence of epidemic outbreaks and a growing number of Leishmania/HIV co-infections are very worrying from a
public health viewpoint.
Glossary
Genetic recombination or mixing: the mixing of genes from both parents during sexual reproduction. This is a key mechanism for
diversity and evolution in species.
Genome: the set of genetic material of an individual or species.
DNA: deoxyribonucleic acid. The molecule carrying the thousands of genes making up the genome. DNA is the support molecule for
genetic information.
Contacts
Leishmania parasites live in an extremely
diverse range of ecosystems. There are
more than twenty species, able to infect
a broad range of wild and domesticated
mammals. The majority of infections
in humans are asymptomatic. When
the disease does present, it does so in
three different forms, namely cutaneous,
mucocutaneous or visceral, being the most
serious. Genetically, biologically, ecologically
and epidemiologically, Leishmania are
consequently complex parasites about which
researchers still have much to learn.
A “mixed” reproduction method
The reproduction strategy of Leishmania
parasites is the subject of much debate.
For a long time, scientists thought they
were asexual, in other words, that they
reproduced clonally, with occasional genetic
recombination. However, as IRD researchers
have just revealed, matters are not as
simple as that in reality. Statistical analysis
of the genetic data available actually shows
that the genome of different species of the
Leishmania genus bears the hallmarks of
sexual reproduction.
DNA samples of parasites from Europe, Asia,
Africa and Latin America in fact show genetic
mixing by sexual recombination, usually
between related individuals, hence the high
consanguinity. More precisely, biologists
deduce from this that a feature of Leishmania
parasites is a “mixed” reproduction
method, alternating between clonal and
sexual reproduction. It seems, however,
that depending on the ecosystem and the
Leishmania species involved, these parasites
use one or other method to a greater degree.
Widely heterogeneous populations
The discovery of this “mixed” method of
reproduction in Leishmania is a major step
forward for the genetics of these parasites’
populations. The reproduction method is in
fact an influence on the distribution of genetic
information within populations. This data then
makes it possible to deduce the structure
and breakdown of natural populations, in
particular for organisms that are difficult to
observe, such as parasites. During this study,
scientists accordingly noted that naturallyoccurring Leishmania populations are
structured into small sub-populations, where
genetic evolution is rapid. Hence, the widely
heterogeneous parasite populations in any
given environment.
Coordination
Gaëlle Courcoux
Information and Culture
Department
Although some aspects of these organisms
and their method of natural evolution
remain obscured, this work shed new
light on genetic studies of Leishmania
populations. Understanding the precise role
of clonal or sexual reproduction, somewhat
consanguineous, will make it possible to
understand how these parasites evolve, adapt
to their environment and their hosts, and how
they develop resistance to treatment.
T. +33 (0)4 91 99 94 90
[email protected]
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Media Contact
References
Rougeron V., De Meeûs Thierry, Bañuls Anne-Laure. A
primer for Leishmania population genetic studies. Trends
in Parasitology, 2015, 31 (2), p. 52-59. ISSN 1471-4922.
Scientific contacts
Cristelle DUOS
T. +33 (0)4 91 99 94 87
[email protected]
Anne-Laure Bañuls, IRD researcher
T. +33 (0)4 67 41 61 80
[email protected]
Virginie Rougeron, CNRS researcher
T. +33 (0)4 67 41 61 80
[email protected]
UMR Maladies infectieuses et vecteurs : écologie,
génétique, évolution et contrôle – Mivegec (IRD / CNRS
/ Universités de Montpellier)
Thierry De Meeûs, IRD researcher
T. +226 20 97 00 75
[email protected]
UMR Interactions hôte-vecteur-parasite-environnement
dans les maladies tropicales négligées dues aux
trypanosomatidés – Intertryp (IRD / CIRAD)
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© IRD/DIC, Mars 2015 - Conception et réalisation graphique : L. CORSINI
A range of environments, hosts and forms
of infection