Verno-estival meningoencephalitis

The known verno-estival (MEVE) English meningoencephalitis under the name of Early summer meningoencephalitis (ESME) is caused by a virus with ARN of the group of the Flavivirus transmitted by the puncture of a Tique (common tick or Ixodes ricinus)

Two different diseases before were distinguished:

the encéphalite of Central Europe
the verno-estival encéphalite Russian

It was thought whereas the verno-estival encéphalite Russian (Russian Spring-Summer Encephalitis, RSSE) was due to a more virulent alternative of the virus of the MEVE. The last analyzes show however only negligible differences between the isolates of Europe and those of the Japan, not justifying at all a distinction between two types different of virus. The gravity of the infection in the oriental party of the zone at the risk also corresponds to a species of vector (tick) different.

Zones at the risk of the virus

The zones at the risk of MEVE are the south of the Germany, the Suisse and the Alsace, certain areas of ex-Germany of the East, the Sweden and the Austria as all Eastern Europe, they extend to the east until in Russia and to the Japan. The continents American and Australian are deprived of virus MEVE.

Three genotypes of virus MEVE were identified: sub-types of the Central Europe, of the the Far East and of the Siberia.

Epidemiology

The qualified hosts as vectors are the ticks belonging to the family of the Ixodidae (hard ticks). Many species of hard ticks can transmit the virus, but two species play a paramount role in the transmission of virus MEVE: Ixodes ricinus and Ixodes persulcatus .

Ixodes ricinus is widespread in Central Europe and of the west, where it transmits the European sub-type of the MEVE (encéphalite of Central Europe). Ixodes persulcatus is disseminated in Russia and the Far East, where it transmits the sub-types of the Siberia and the Far East (encéphalite vernoestivale Russian). Certain sub-types overlap in areas of Eastern Europe. The zones at the risk extend on a good part of Europe, since the east of France until the south of the Scandinavia and the Croatia and to the east until the north of the Japan.

Biological cycle of the tick and transmission of the virus

The tick crosses 3 developmental stages lasting approximately 1 year and the virus can be transmitted to all the stages. The ticks hibernate preferably in the wet underwoods, close to the rivers. The female lays hundreds of eggs which can already be infected. The larvae with six legs resulting from eggs make their first meal of blood as of the first hot days of spring, awaiting their victim on a grass bit they hang them in the passing. During their meal, they can transmit the virus to their host (a small animal: mouse, squirrel etc…) or on the contrary to infect itself if their victim is carrying the virus. After its meal the larva drops itself and becomes after metamorphosis a Nymphe with 8 legs. After another blood meal 1 to 2 years later the tick reaches the adult stage. It measures a few millimetre length then and can climb the bushes up to 80 cm height to reach a larger animal (fox, big game). After its blood meal the tick couples, lays eggs and the cycle begins again. The human beings are an occasional host who constitutes a dead end for the cycle since in this case the tick generally does not turn over in nature after its meal of blood. At the human being the tick generally goes up along the legs to reach a mean cutaneous zone, easier to prick where it niche, the umbilical point, the armpit or the root of the hair on the level of the nape of the neck and the puncture is painless. After one period from 2 to 3 days the tick begins its meal of blood which lasts 1 day then, repue of blood it drops itself on the ground. The virus multiplies in particular in salivary glands of the tick.

Private clinic

In half of the cases the concept of puncture of Tique is not found, it was not even noticed by the victim.

The disease often presents a two-phase form like much of viral infections.

After one incubation period from 1 to 10 days (being able to go up to 30 days) appear grippaux symptoms which last a few days.

Then at the end of 1 to 10 days one enters the phase of the central nervous system disorders which often requires a hospitalization:

Paralysis of the cranial nerves or the ends of the upper limbs
Meningitis or Meningoencephalitis (in the child)

One can especially observe cases of death by neurological complications among old patients.

The long-term consequences are frequent. A third of the patients presents residual disorders several years after the disease (Céphalée S, sensitive or vegetative-nervous disorders).

Variety of the Far East :

The disease is monophasic and more severe, developing quickly towards a neurological attack. The rate of lethality amounts to 20%, and up to 60% of the survivors present residual neurological after-effects.

Diagnosis

Presence of anti-MEVE antibody. The presence of IgM allow to make the difference between an infection in progress and the serologic trace in an old infection last unperceived (IgG).

The detection of the infectious germ is possible by means of the Chain reaction by polymerase (PCR). Because of the reliability of serology, this technique is however not used in routine for the diagnosis of MEVE

Disease prevention

There does not exist any specific treatment of the disease. Since the Seventies one has a Vaccin with effective killed virus and tolerated well it is recommended for the people remaining in a zone of endémie during the season of the ticks (February at November).

To avoid the punctures and the infection by the ticks, the experts advise the following precautions:

particularly To avoid the zones infested by the ticks during the hottest months.
To wear clothing of clear color so that the ticks are more easily visible. To wear a long shirt, a hat, long pants, and to go up the socks over the legs of the pants.
To go in the center of the paths to avoid grass and the bushes.
To regularly check at the end of a few hours the absence of ticks on your body when you spend much time outside in zones infested by the ticks. The ticks are generally found on the thigh, the arms, the armpits and the legs. The ticks can be very small (not larger than a pinhead). To carefully inspect all new “freckle”.
To use a Repulsive insect containing of DEET on your skin or of the Perméthrine on clothing.
To extract immediately the ticks piqués in the skin.

Extraction of a tick

The ticks should be removed quickly and carefully with grips tweezers and by applying a regular and soft traction. the body of the tick should not be crushed at the time of the extraction and the tweezers should be as placed close to the skin as possible to avoid leaving pieces of the mouth of the tick in the skin. The ticks should not be extracted with naked hand. Hands should be protected by gloves and/or a fabric and be carefully washed with water and the soap and after the operation. This operation should be carried out with the greatest care.

External bonds

HTTP: /www.medicalforum.ch/pdf/pdf_f/2006/2006-11/2006-11-247.PDF MEVE in Switzerland
HTTP: /www.baxter.fr/downloads/a_propos_de_baxter/dossiers_presse/tiques_alsace_23-03-2007.pdf MEVE in Alsace
HTTP: /www.maladies-a-tiques.com/TAP/Haller%20Meningoencephalites%20a%20tiques.pdf Thesis MEVE in Alsace
HTTP: /www.phac-aspc.gc.ca/publicat/ccdr-rmtc/06pdf/acs-32-03.pdf Encéphalite with ticks
HTTP: /horizon.documentation.ird.fr/exl-doc/pleins_textes/cahiers/entomo/19148.pdf Ticks and arbovirus

Random links: