This article treats disease. For the epidemic of chikungunya to the Meeting of 2004-2006, to see the dedicated article.
The transmission of the virus of a human patient to a mosquito is done by the blood aspired at the time of the puncture. The contamination of a healthy man is carried out by the saliva of mosquitos which were infected a few days or a few weeks before. Only the mosquitos females prick.
Among more than 950 species of mosquitos, several of them are likely to transmit the chikungunya, but only Aedes aegypti and Aedes albopictus was to date identified like epidemic vectors, because of their adaptation to the zones of human habitat. These same species are also implied in the transmission of other arboviruses: Dengue, hemorrhagic fever dengue (DHF), Yellow fever,… etc
HistoryThe chikungunya is not a new disease. The virus was isolated for the first time in 1952-1953 at the time of an epidemic of Fièvre which prevailed on the plate of Makonde in the province of Newala to Tanganyika (current Tanzania). The disease is responsible for affections prevailing in endemic form in rural areas of subtropical Africa, and in epidemic form in populations not immunes, in particular urban, as well in Africa as in Asia of the south (India, Vietnam).
Two principal hearths of chikungunya are counted:
One Asian, which strikes Java regularly, or the India (nearly 1,3 million infected people).
- other African. The scientists of the National Reference Center of the arboviruses of the Institut Pasteur identified as of the month of May 2005 the virus with the Meeting. The first case was recorded there the February 22nd. At the end of November, 4500 people were contaminated. At February 24th, 2006, the virus of Chikungunya infected more than 150.000 people, that is to say 20% of the population of the island, with nearly 120.000 new cases only for the beginning of the year 2006. the Meeting is not besides the only island touched in this area. The chikungunya made its appearance with the the Comoros in July 2004. The north of Madagascar, Maurice, the Seychelles and Mayotte, with more than 5000 officially declared cases are not saved, even if one speaks about it finally enough little (if the figures announced with the Meeting are close to reality, one can express serious doubts concerning the 4 other above mentioned areas). The imported diseases exceed the 1000 cases involving a possible hazard of dissemination if there exists an insect vector.
The first European hearth is identified during the summer 2007. August 30th, 2007 the Italian health authorities inform their European counterparts that a hundred case of infection with Chikungunya virus are to be regretted in the North-East of Italy (district of Ravenne, area of Emilie-Romagna), information relayed by the French ministry of Health. This stage, the number of new weekly cases decrease according to these same authorities.
Epidemics of chikungunya former to 1952 could be identified retrospectively in the light of current knowledge of the disease. Thus, Carey has advanced that certain epidemics allotted to the virus of the Dengue, were in fact of the epidemics of chikungunya: Cairo and Batavia - Jakarta in 1779, Zanzibar in 1823 and 1870, the India in 1823,1824-1825 and 1871-1872, HongKong, Burma (current Myanmar) and Madras in 1901-1902. The retrospective reallocation of these epidemics to the virus chikungunya rests on the one hand on the coexistence of the Virus of the dengue and the chikungunya in these areas, and on the other hand on descriptions making state of joint pains and complications with type of arthritis more compatible with a fever chikungunya than with a dengue.
The clinical picture is dominated by a fever raised like that of the dengue (dengue and chikungunya were often confused) associated with invalidating joint pains and sometimes an cutaneous eruption. But there are severe forms ignored up to that point: fulminant hepatitises, attacks of the cardiac muscle, meningoencephalites… Many others Togavirus of the kind Alphavirus and pertaining to the complex of Semliki forest, like Ross To rivet, O' nyong-nyong, Sindbis and Mayaro are associated with similar symptoms.
The mosquito is the vector of local transmission of the chikungunya. Some cases of blood contaminations exist however in the medical literature. They are extremely rare and concern of the medical staff which involuntarily inoculated the virus.
Larva with the mosquitoThe egg becomes larva. The Larve knows an evolution in four phases, before being transformed into nymph. The phase nymphale lasts 48 hours and is closed by a nuptial flight above the larval lodging. All this cycle lasts from six to ten days. Rather six days when the circumstances, moisture and heat, are ideal.
The Aedes is not very difficult on the quality and the size of its place of laying: a quill is enough for him for little that it contains a little water. On the other hand, it lays only in fresh water, stagnant, not stagnated and in the shade.
One should not limit the fight anti-mosquito to the only eradication of the adults. It is much simpler and effective to attack a water puddle pool containing of the hundreds of motionless larvae, to run behind the same number of adult mosquitos and thus wheels.
Cycle virusAs at all the species of mosquitos, only the Femelle is hematophagous (i.e. that it must nourish blood to ensure the development of its ovaries and its eggs) and thus able to transmit the chikungunya. The horn of the female is provided with 2 parallel pipes: one to inject saliva and the virus, the other to pump blood after the local anesthesia by saliva. The males being nozzles of sap the herbaceous ones or fruit nectars, they are thus stripped oral parts able to transpierce the skin of the vertebrate ones. This “vectorial” capacity of the female Aedes is explained by a faculty to duplicate the virus (and not quantity of absorptive blood, quite insufficient). And contrary to the generally accepted ideas, it is not by absorbing the Sang front but right, by injecting a little anticoagulant Salive in a blood-vessel of its victim, that the mosquito infects the host. A mosquito infects itself indeed by pricking (strictly speaking, it is advisable to speak about bite and not about punctures of mosquitos) human or a contaminated animal. Blood crosses then the stomachic border of the animal to pass in its salivary glands. The female become infecting the remainder all its life, is approximately a month if it does not cross on its way the human one provided with spray. However, it pricks and lays every approximately four during the days. Seven to eight transmissions of the virus by the mosquito are thus possible with contamination of as many people. A Aedes female lays approximately 300 eggs during its existence. The eggs can persist several months in nature in the event of adverse conditions (dryness, before transfomer in larvae then in nymphs as of the setting in water of the site of laying. The adult (imago) flies away then and couples himself quickly.
There exists a vertical transmission, i.e. the eggs laid by an infected female are contaminated in a very small proportion (1 to 2%), and thus without real effect on the transmission of the disease.
The incubation of the disease lasts from four to seven days on average. Viremy, i.e. the period of presence of the Virus in blood and thus of possible transmission, is spread out for this period during which the viral genome can be highlighted in the organization by RT-PCR. The antibodies Immunoglobulines M (IgM) appear about the 5th day of the disease and persist several months. IgM are rather not very specific and of the false-positives are due to mechanisms of stimulation polyclonale by other infectious illness. Then, appear IgG as from the 15th day, which during several years, even decades, are specific chikungunya (antibodies directed against proteins of the membrane of the virus) and guards. Immunity is thus considered acquired at life, which means in the actual position of knowledge that a person having had the chikungunya cannot be reached second once.
The first Symptôme S can make think of a crisis Paludisme or of influenza, or leptospirosis, or with a septicaemia, a meningitis etc According to WHO, the chikungunya is a disease known as dengue-like, i.e. it resembles the dengue much (muscular and articular pains, high fever, eruption on the skin…). The disease is generally declared by a very strong Fièvre, sometimes beyond the 40°C, lasting approximately 3 days. This fever is followed of an erythema (eruption of buttons) and of very painful Courbature S, as of sharp pains of the articulations nailing the patient with the bed. The children present only seldom these joint pains. On their premises the chikungunya is translated like a simple influenza. However, with the Meeting, two children of 9 and 10 years died in tables of encéphalite and myocarditis (reached brain and heart).
The joint pains can persist or reappear during several months, in particular with the weakened articulations (old distorsions or fractures in sportsmen for example). An special attention must however be carried to the fragile people: the infants whose pains can block the jaw and make impossible any food, elderly with the failures of bodies particularly sensitive to the effects of the fever (acceleration of the heart rate, dehydration). At these secondary risks with any fever the people are particularly exposed suffering from diabetes, cardiac failure, renal, respiratory… The alcoholics reached of chikungunya presented increased risks of hepatitis mortal.
Precautions and treatmentThe direct transmission of the virus of man with man does not exist. The transmission is known as indirect because it requires the presence of a mosquito vector: Aedes aegypti or albopictus primarily. Côtoyer of “chikungunyés” does not present a direct risk, except if those are piqués by of Aedes which is gorged thus with their blood rich in virus. There exists a transmission in-utero virus of the mother to the child (forty case were described in 2005-2006 with the Meeting). The chikungunya can then induce serious neurological lesions at the Fœtus, being able to involve its death in utero during the second quarters (3 cases with the Meeting). But the essential risk is consisted the childbirth in viremic period, i.e. while the mother-to-be is sick chikungunya. In half of the cases, the child is then contaminated by the virus and makes a encéphalite in 10% of the cases. By pricking an infected person, the mosquito recovers the Virus and can thus propagate it. Aedes female will be then infesting only after several days of development of the virus in its body: it is the extrinsic cycle which brings the virus of the digestive tract to the salivary nipples of the mosquito.
No Médicament was developed to date; only a experimental Vaccin was developed by the Research institute of the army of the United States. The vaccine stock (stock inhabitant of Thailand going back to 1962 attenuated by successive passages on cell vero of monkeys), was yielded by the Research institute of the army of the United States to the INSERM which currently works on the preparation of tests of phase III at the man (requalification in progress - mid 2007). The vaccine stock is in the course of requalification in France under the aegis of the INSERM. In the event of requalification positive, vaccine tests could be carried out in 2007 in metropolis (tests of tolerance), then later on in period of epidemic in a French territory of overseas (tests of effectiveness).
There does not exist virucide treatment (“killer of virus”). Ex vivo, the choloroquine (Nivaquine) was shown very effective on the virus. However, the studies of proof of concept (choloroquine on a purely curative and preventive basis) led to semi-2006 to the Meeting did not make it possible to conclude, because of the low number of people included in the study, the epidemic touching at its end. The tests thus continued on animal model (macaques) and made it possible to conclude without ambiguity which chloroquine is not effective against the virus in vivo.
Etiologic fault of treatment, the treatment thus remains purely symptomatic: control fever and pain by means of Paracétamol. As during the dengue, aspirine should not be used because of the risks of bleeding only this molecule and that the chikungunya cause (reduction in the aggregability and the number of the blood plates).
The Virus did not have the reputation to be mortal, but cases of encéphalites and failures of bodies were described at the time of the epidemic of the Meeting. The chikungunya cannot thus be regarded as a minor illness any more. There exist asymptomatic forms (i.e. without fever nor pains), but in a very small proportion (6 - 10% of the cases, on studies of séroprévalence led with the Meeting and to Mayotte in 2006).
The monkeys are also carrying the chikungunya, like much of other wild animals, servants and of revenues. A study led on approximately 1.500 animals with the Meeting and Mayotte, will allow more on the animal tank, like its role in the epidemic of the Indian Ocean.
Individual protection is by long and clear clothing and the use of repulsive lotions early the morning and in end-of-day, but those have one effective duration limited (4 to 8 a.m. according to the products), the impregnated mosquito net the repulsive ones, the installation of nettings on the openings of the houses. Because of the very strong viremy during the disease (up to 10 power 12 copies of virus by millitre of blood at the patient during the first week of the disease), it is also necessary to insist on the need for isolating the patients (containment in residence, repulsive…), in order to limit the proliferation of the disease. Indeed, in epidemic period, it is the sick man who constitutes the principal reserve of virus (the viremy can reach 10 power 10 viruses by millitre of blood) and which is thus a danger to its entourage.
The only true prevention to date thus consists in fighting the reproduction and the proliferation of the mosquitos by elimination of the larval stagnant water lodgings for example the vases of the cemeteries, the covers of the swimming pools, the given up containers, the gutters, the tires stored outside, waste. Aedes albopictus, mosquito vector of the chikungunya is very related to the human activities.
The chikungunya belongs to the list of the Notifiable diseases in Metropolitan France, the Antilles and French Pacific, but not Meeting where it is endemic. It is not enough to protect oneself, it is also necessary to think of the community. There exists with this intention a surveillance device with INVS.
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