Chikungunya Virus

Chikungunya (in abbreviated chik) is an infectious tropical disease caused by an arbovirus (CHIKV noted for chikungunya virus), an Alphavirus of the family Togaviridae, transmitted by Aedes mosquitoes. The name comes from makondea and means "to curl, which cowers, like the fallen leaves of trees that curl while drying, it was also translated in french chikungunya disease which breaks bone "or" man's disease bent "because it causes extreme pain associated with stiffness, which gives patients infected a curved characteristic.

The transmission of the virus from a human patient to a mosquito is by blood aspirated during the injection. Contamination of a healthy man is produced by the saliva of mosquitoes that were infected a few days or weeks before. Only female mosquitoes bite.

Several species of mosquitoes can transmit the chikungunya, but only Aedes aegypti and Aedes albopictus have so far been identified as vectors of epidemics, because of their adaptation to human settlements. These same species are also involved in the transmission of other arboviruses: dengue, dengue haemorrhagic fever (DHF), yellow fever, etc..

The chikungunya is not a new disease. The virus was first isolated in 1952-1953 during an outbreak of fever that was rampant on the Makonde plateau in the province of Newala to Tanganyika (now Tanzania). The disease is responsible for conditions prevailing in endemic rural areas of tropical Africa and in epidemic form in non-immune populations, particularly urban, both in Africa and South Asia (India, Vietnam).

There are two major outbreaks of chikungunya:

* An Asian who regularly hits Java, and India (nearly 1.3 million people infected).
* The other Africa. Scientists at the National Reference Center for Arboviruses of the Pasteur Institute have identified as early as May 2005 the virus in Reunion. The first case was registered on 22 February. In late November, 4 500 people were contaminated. 24 February 2006, the chikungunya virus infected more than 150 000 people, or 20% of the population of the island, with nearly 120 000 new cases just for the beginning of 2006. The meeting is not the only island in the affected region. Chikungunya has emerged in the Comoros in July 2004. Northern Madagascar, Mauritius, Seychelles and Mayotte, with more than 5 000 cases officially reported, were not spared, even if it is talked quite low (if the figures announced at the meeting are close to reality you can make serious doubts about the other 4 regions mentioned above). Disease imported exceed the 1 000 cases leading to a potential risk of spread if there is an insect vector.

The first European outbreak is identified in the summer of 2007. On 30 August 2007 the Italian health authorities inform their European counterparts a hundred cases of chikungunya virus infection are to be deplored in the north-eastern Italy (district of Ravenna, Emilia-Romagna region), information relayed by the french Ministry of Health. At this stage, the number of new cases per week decreased by these same authorities.

Outbreaks of chikungunya prior to 1952 were identified retrospectively in the light of current knowledge of the disease. Thus, Carey argued that certain epidemics attributed to dengue virus, were in fact outbreaks of chikungunya: Cairo and Jakarta-Batavia in 1779, Zanzibar in 1823 and 1870, India in 1823, 1824-1825 and 1871 -- 1872, Hong Kong, Burma (now Myanmar) and Madras, 1901-1902. The reallocation of these retrospective virus chikungunya epidemics is based on the coexistence of dengue virus and chikungunya in these regions, and on descriptions reports of pain and complications type of arthritis more compatible with chikungunya fever with a dengue.

The clinical picture is dominated by high fevers such as dengue (dengue and chikungunya were often combined) associated with disabling pain and sometimes a rash. But there are severe forms hitherto ignored: fulminant hepatitis, attacks the heart muscle, the meningo-encephalitis ... Many other togavirus the alphavirus genus, belonging to the complex of Semliki Forest, as Ross River, O'nyong-Nyong, Sindbis and Mayaro are associated with similar symptoms.

The mosquito is the vector of local transmission of chikungunya. A few cases of blood contamination, however, exist in the medical literature. They are extremely rare and carers who had unwittingly infecting virus.

The larva of the mosquito
The egg hatches, giving a first stage larva. The larva is experiencing an evolution in four stages before turning into pupa. The nymphal stage lasts 48 hours from which emerges the adult who makes a nuptial flight over the larval shelter. While this cycle lasts from six to ten days, six more days when heat and humidity are ideal.

The Aedes is not very difficult on the quality and size of its place lay a bobbin is sufficient as long as it contains a little water. However, it does not pond water than in fresh, stagnant, and not foul in the shade (used tire). In addition, the egg is resistant to desiccation and survive in the absence of water, n'eclosant to the restoration of its water instead of laying.

We should not limit the anti-mosquito eradication of the only adults. It is much easier and efficient to deal with a puddle of water containing hundreds of larvae immobile, that chasing the same number of adult mosquitoes and thus flying.

Cycle of the virus
As in all species of mosquitoes, only females are hematophagous (ie it must feed on blood to ensure the development of her ovaries and eggs) and therefore able to transmit the chikungunya. The tube of the female is equipped with 2 parallel pipes: one to inject saliva and the virus, the other to pump the blood after local anesthesia by saliva. Males are sucking sap from grass or fruit nectar, they are deprived of mouthparts can pierce the skin of vertebrates. This ability to "vector" of the female Aedes explained by an ability to replicate the virus (and not the amount of blood absorbed well enough). And contrary to popular belief, it is not absorbing the blood, but just before, injecting a bit of saliva anticoagulant in a blood vessel of his victim, that infects the mosquito host. A mosquito is infected by biting into effect (strictly speaking, should be talking about not biting mosquito bites) a human or an animal infected. The blood then passes through the border stomach of the animal to move in its salivary glands. Females become infective else all his life, about a month. However, it stings and pond every four days. Seven to eight transmissions of the virus by the mosquito are possible contamination with as many people. A female Aedes lays about 300 eggs in her lifetime. Eggs may persist for several months in the wild during unfavorable conditions (drought, before transforming into larvae and then pupae from the water nesting site. The adult (imago) and then flew mates fast.

There is vertical transmission, ie the eggs laid by infected females are infected in a very small proportion (1 to 2%), and thus no real impact on the transmission of the disease.

The incubation of the illness lasts four to seven days on average. Viremia, ie the period of the virus in the bloodstream and therefore transmission possible spread during this period during which the viral genome can be identified in the body by RT-PCR. Immunoglobulin M antibodies (IgM) appear to the 5th day of illness and persist for several months. IgM are not very specific and false positives are due to polyclonal stimulation mechanisms by other infectious diseases. Then appear IgG from day 15, which for several years, even decades, are specific chikungunya (antibodies directed against membrane proteins of the virus) and protectors. The immunity acquired is estimated to life, which means the current state of knowledge that a person with chikungunya was not possible to achieve a second time.

The first symptoms may suggest a crisis of malaria or influenza or leptospirosis, or septicemia, meningitis etc. According to WHO, the Chikungunya is a disease known as dengue-like, ie it is very similar to dengue (muscle and joint pain, high fever, rash on the skin ...). The disease was usually a very high fever, sometimes above 40 ° C, for about 3 days. The fever is followed by erythema (rash of buttons) and very painful aches and pains of the joints nailing sick in bed. Children rarely do these pains. Home chikungunya is a simple flu. However, Reunion, two children of 9 and 10 years died in boards myocarditis and encephalitis (brain damage and heart).

The pain may persist or recur for several months, particularly to vulnerable joints (old sprains or fractures in athletes, for example). Particular attention should be paid to vulnerable people: infants whose pain can block the jaw and make it impossible for any food, elderly failures organ particularly sensitive to the effects of fever (increased heart rate, dehydration) . Are particularly exposed to these risks fever secondary to any people suffering from diabetes, heart failure, renal, respiratory ... Alcoholics suffering from chikungunya have increased risk of fatal hepatitis.

Care and treatment
Direct transmission of the virus from person to person does not exist. Transmission is called indirect because it requires the presence of a mosquito vector: Aedes aegypti and albopictus mainly. Alongside "chikungunyés" presents no direct risk, unless they are bitten by Aedes who fill their blood so rich in virus. There is an in-utero transmission of HIV from mother to child (about forty cases have been reported in 2005-2006 in La Réunion). Chikungunya can cause serious neurological damage in the fetus, which can cause death in utero during the second quarter (3 cases in La Reunion). But the main risk is the delivery viraemic period, ie while the mother is sick with chikungunya. In half the cases the child is infected with the virus and encephalitis in 10% of cases. By biting an infected person, the mosquito gets the virus and can spread it. The female Aedes will then infesting after several days of development of the virus in his body: the extrinsic cycle which causes the virus to the gut of the mosquito salivary glands.

No drug has been developed to date, only an experimental vaccine was developed by the Research Institute of the United States Army. Vaccine (strain 1962 from Thai attenuated by successive passages on Vero cells of monkey), was released by the Research Institute of the United States Army at INSERM currently working on the preparation of test phase III in humans (in retraining courses - mid 2007). The vaccine is currently retraining in France under the auspices of INSERM. If requalification positive vaccine trials could be conducted in 2007 in France (tolerance test), and later during outbreaks in a french overseas territory (efficacy trials).

There is no treatment virucidal ( "killer virus"). Ex vivo, choloroquine (Nivaquine) has been very effective on the virus. However, studies of proof of concept (choloroquine as curative and preventive) conducted in mid-2006 to the meeting failed to conclude, given the low number of people included in the study, the epidemic to an end. The tests were therefore continued on animal models (macaques) and have concluded unequivocally that chloroquine is not effective against the virus in vivo.

Absence of etiological treatment, treatment therefore remains purely symptomatic: fever control and pain with paracetamol. As during the dengue fever, aspirin should not be used because of the risk of bleeding and that this molecule that causes chikungunya (decrease of aggrégabilité and number of blood platelets).

The virus was not known to be fatal, but cases of encephalitis and organ failure have been reported during the outbreak of the Meeting. Chikungunya can no longer be considered a benign disease. There are asymptomatic forms (ie without fever or pain), but in a very small percentage (6 - 10% of cases, based on seroprevalence studies conducted in Reunion and Mayotte in 2006).
Monkeys are also carriers of chikungunya, and many other wild animals, domestic and annuities. A study conducted on about 1 500 animals in Reunion and Mayotte, can learn more about the animal reservoir, and its role in the epidemic in the Indian Ocean.

The protective clothing is long and clear and the use of repellent lotions early morning and late in the day, but they have a limited effective duration (4 to 8 hours depending on the product), the mosquito net impregnated with repellent The installation of fences on the open houses. Because of the high viremia during the illness (up to 10 power 12 copies of virus per milliliter of blood in the patient during the first week of illness), it must also stress the need to isolate patients (containment home ...), repellents to reduce the spread of the disease. Indeed, during epidemics, is the sick man who is the main reservoir of virus and is therefore a danger to those around her.

The only real prevention to date is to combat the replication and the proliferation of mosquitoes by eliminating breeding sites of stagnant water such as vases cemeteries, tarpaulins pools, abandoned containers, gutters, tires stored outside, the waste. Aedes albopictus, the mosquito vector of Chikungunya is closely related to human activities.

The chikungunya is part of the list of notifiable diseases in France, the Caribbean, the Pacific french, and the Meeting on 19 December 2008. It is not enough to protect oneself, one must also think about the community. There exist already a monitoring device in INVS.

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