Actualité scientifique
Scientific news
December 2010
Chikungunya is
transmitted by mosquitoes
of the genus Aedes. The
disease is spreading in the
world and periodically
sparks new outbreaks.
Africa, Asia, the Indian
Ocean and even Southern
Europe are now affected.
The viral infection can be
expressed in many
different ways. Patients
can suffer forms ranging
from a simple fever to
severe pain in the joints.
This high variability in
symptoms arises from the
variability of humans’
individual immune defence
systems. Blood analyses
conducted during the
2007 Gabonese epidemic,
studied by IRD
researchers and their
partners1, recently showed
the key role of innate
immunity, the organism’s
first line of defence, in the
clinical course of the
infection. Control of the
disease thus closely
depends on the underlying
configuration of each
patient’s immune system.
The serious cases would
therefore be due to a
defect in the innate
response, as happens in
pregnant women, the
aged, and other vulnerable
groups.
These investigations have
brought new insights into
this disease, insufficiently
studied and neglected by
public authorities.
Chikungunya : The key role
of “innate immunity”
© IRD / Michel Dukhan
N° 363
Actualidad cientifica
Over recent years Chikungunya, transmitted by female mosquitoes of the genus Aedes (here Aedes albopictus or “tiger mosquito”), has spread to new areas of
the world: Indian Ocean, Central Africa and even Southern Europe.
Chikungunya virus, first isolated in Tanzania in 1953,
caused a great number of epidemics in Africa and
South-East Asia in the course of the 20th Century.
A global threat
This infectious disease, like yellow fever and
dengue, is caused by an arbovirus, transmitted by
blood-sucking arthropods, ticks and Phlebotominae or sand flies. Its main vectors are mosquitoes of the genus Aedes. Particularly concerned is
Aedes albopictus, nicknamed the “tiger mosquito”,
whose eggs* enable it rapidly to conquer new
ter ritories. Increasing human travel, which
spreads the larvae, and the rising resistance of
mosquitoes to insecticides have contributed to
the rapid expansion of epidemics over the past few
years, to new regions of the world: islands in the
Indian Ocean, Central Africa and even, very recently,
Southern Europe are now affected. The outbreak in
Réunion Island in 2005-2006 hit over 260 000 people.
The recent epidemic in southern Italy, in 2007,
and also the first reported case of fever in the
South of France illustrate the potential for worldwide diffusion, making this disease, rarely fatal
but severely incapacitating, a major threat to
public health.
Strong innate immunity
Ranging from a simple bout of fever to severe pain
in the joints, chikungunya can take on many
different forms. This very broad variability of symptoms is due to variations in the individual immune
response of each patient. IRD researchers and
their partners1 recently showed the key function of
“innate immunity”, the organism’s first line of
defence, in the clinical course of the disease.
Challenged by the presence of foreign DNA in the
organism following a viral, bacterial or parasitic
For further information
infection, or the presence of tumoral cells, the
organism activates its immune system. This
immune, or inflammatory response, occurs in two
major stages: non-specific defence, also called
“innate immunity”, which does not take account of
the nature of the micro-organism it is fighting, and
the specific response, which targets the pathogenic
agent in the infected cells.
In chikungunya patients, the first stage response is
highly effective. Detailed analysis of nearly 70 blood
plasma profiles taken during the 2007 epidemic in
the Gabonese capital Libreville, revealed the
presence, during the first four days of symptoms,
of a high quantity of interferons, cytokines and
chemokines2, immune-system substances akin to
hormones- Interferons play a prime role in the
immediate inflammation defence system. As the
name indicates they interfere with replication of
the virus in host cells and thus inhibit the virus
early in the process. The function of cytokines and
chemokines is to activate the second stage: the
specific response. These proteins attract immune
cells -leucocytes- to each virus replication site and
direct the deployment of the organism’s antiviral
defences.
Control of the disease therefore depends closely on
the underlying immune status of each patient.
Severe cases could therefore be the result of a
defect in the innate response mechanism, as can
occur in pregnant women, elderly people or Aids
patients.
A highly disabling disease
Contact
Serious forms can consequently appear, inducing
highly disabling stiffening of the joints, the reason
for the name of the disease: chikungunya meaning
“bent man disease” in the Makonde language of
Southern Africa. These symptoms generally last
three to seven days, the time for the immune cells to
work, but can also become chronic and persist for
months, even years. Neurological and hepatic
complications can also occur in the most severe
forms. There is currently no specific treatment, so
therapeutic care aims solely to alleviate these symptoms, using analgesic and anti-inflammatory drugs.
Éric LEROY,
director of research at the IRD
Tel: +241 07 85 06 13
eric.leroy@ird.fr
UMR Émergence des pathologies virales
(IRD et université de la Méditerranée
Aix-Marseille 2)
Address
Centre international de recherches
médicales de Franceville (CIRMF)
BP 769, Franceville
Gabon
References
wauquier n., becquart pierre, nkoghe d.,
padilla c., ndjoyi-mbiguino a., leroy Éric.
The Acute Phase of Mild Chikungunya
Virus Infection in Humans is Associated
with Strong Innate Immunity and T CD8
Cell Activation, Journal of Infectious
Diseases, 2010.
doi: 10.1093/infdis/jiq006
Medical professionals are at the dawn of their
research on the disease, long neglected by government authorities. The research team is similarly
exploring the role, in pathogen inhibition, of cells
called Natural Killer, capable of killing directly the
infected cells. In parallel, investigations are also
under way on modulation of the immune response
in cases of co-infection with dengue virus, recently
discovered in Gabon*, a new threat involving a
simultaneous attack by the two severely debilitating
diseases.
Key words
Chikungunya, virus, innate immunity
*See Scientific news bulletin n°312 – Dengue and chikungunya:
when both diseases strike at once.
Copy editor – Gaëlle Courcoux - DIC, IRD
Translation – Nicholas FLAY
Coordination
Gaëlle Courcoux
Information and Culture
Department
Tel.: +33 (0)4 91 99 94 90
Fax: +33 (0)4 91 99 92 28
fichesactu@ird.fr
1. These research studies have been conducted jointly with research scientists from the Centre international de recherches médicales
in Franceville (CIRMF), the université des sciences de la santé at Libreville in Gabon and from INSERM.
2. Interferons, cytokines and chemokines are proteins produced by the cells of the immune system.
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This research on the 2007 Gabonese epidemic has shown the key role of innate immunity in the infection’s clinical course.
© IRD / Michel Dukhan
© IRD / Xavier Pourrut
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