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Which arbovirus infections may be encountered in Europe? Describe the laboratory diagnosis of any one of these infections.

 

Arboviruses are viruses which could infect man via an insect vector. Often, a mammalian or avian reservoir for the virus exist. However, in some cases, the insect vector serves as the main reservoir and transovarial transmission plays the main role in the maintenance of the virus. Being in the temperate region, arboviruses are not as active in Europe as other parts of the world such as Africa and Asia since the arthropod vectors are not as common. Nonetheless arbovirus infections are seen in Europe. Arboviruses comprises of viruses from three different families: togaviruses, bunyaviruses, and flaviviruses, representatives of each are seen in Europe.

Togaviruses: the genus alphaviruses contain arboviruses which are pathogenic for man. The only alphvirus which is known to cause disease in Europe is the Ockelbo virus, which is found in Sweden, Finland and Western parts of the previous USSR. It causes a febrile disease with rash and polyarthralgia. The virus is closely related to Sindbis virus and the vector is a mosquito.

Bunyaviruses: members of the bunyavirus, phlebovirus and Nairovirus genus are known to cause arbovirus disease in Europe.

Bunyavirus - the Calovo virus of the Bunyamwera serogroup is widely distributed throughout Central Europe. Infection gives rise to a mild febrile illness only. The Tahyna virus of the California virus serogroup is widely distributed in Central Europe. The spectrum of disease ranges from a mild febrile illness to aseptic meningitis. The inkoo virus is found in Finland and infection is usually silent. The vector involved in all three viruses is the mosquito.

Phlebovirus - most phleboviruses are associated with sandflies and there is evidence for transovarial transmission. Phleboviruses which are known to be active in Europe include the Naples and Sicilian sandfly fever viruses and the Toscana virus. Naples and Sicilian sandfly fever viruses are found throughout the Mediterranean region and extends as far east as India and Transcaucasia. They cause a self-limiting disease which consists of high fever, headache, joint pains, malaise, and occasionally nausea and vomiting and drowsiness. The Toscana virus is widely distributed in the Mediterranean region and is thought to cause aseptic meningitis.

Nairovirus - all known nairoviruses are transmitted by ticks. Crimean-Congo haemorrhagic fever virus is widely distributed over Eastern Europe, the Middle East, the Indian subcontinent and Africa. It causes a severe haemorrhagic fever with a mortality rate of 15-30%. Since blood is highly infectious, nosocomial infections had been reported.

Flaviviruses: flaviviruses may be mosquito or tick-borne. The only mosquito-borne flavivirus known to be active in Europe is the West Nile virus. A number of tick-borne flaviviruses are active in Europe.

West Nile virus - this virus is widely distributed throughout Europe, Africa and Asia. However, it usually causes subclinical infection and seldomly a mild encephalitis.

Tick-bourne encephalitis - The Louping ill virus is confined to the British Isles. It is usually an infection of sheep. Human infection results in a influenza-like illness and occasionally a mile meningoencephalitis. The Eastern and Western form of tick0borne encephalitis virus occurs widely throughout Europe and states of the former USSR. The disease is usually transmitted by tick bites but may be transmitted by unpasteurized goat's milk. The clinical presentation of tick-borne encephalitis vary from asymptomatic infection to fulminant encephalitis and rapid death. The Eastern form of the disease is more severe.
 

Diagnosis of Crimean-Congo haemorrhagic fever

A large variety of tests are available for the diagnosis of Crimean-Congo haemorrhagic fever, but none are entirely satisfactory.

Virus Isolation - virus may be readily isolated from the blood within the first week of illness. The most widely used test is the intracranial inoculation of suckling mice. The mice usually die in four to eight days with paralytic disease and brain tissue may be tested by complement-fixation or fluorescent antibody. Cell cultures such as Vero E6 and LLC-MK2 may also be used where a cytopathic effect may be seen and viral antigens produced may be detected by immunofluorescence. However, cell culture is less sensitive than suckling mice but they produce a result more rapidly.

Virus-antigen detection - sensitive antigen-detection ELISAs have been developed. The rapid diagnosis possible with this technique is valuable since treatment of the disease is available.

Serology - several methods for serological testing area available, including complement-fixation tests, agar gel precipitin, mice and plaque neutralization, haemagglutination-inhibition and indirect immunofluorescence. The diagnosis may be made by the demonstration of rising titres of antibody or the presence of specific IgM.

Because of the cold climate, arbovirus infections are not that active in Europe because of the lack of vectors. However, this means that vigilance is often low when such a rare infection arises. This is also the case with diagnostic tests as very laboratories are able to diagnose arbovirus infections.
 

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