What are alphaviruses?

Alphaviruses are viruses from the genus Togaviridae. About 20 enveloped single-stranded RNA viruses with a diameter of about 60 to 70 nanometres can be classified in this genus. The viral envelope has typical spikes that consist of glycoproteins. These replicate in the cytoplasm, whereby the nucleic acid alone is highly infectious. Alphaviruses are spread all over the world. The pathogens are mainly transmitted by mosquitoes.

In humans, alphaviruses can cause epidemic, sporadic or endemic diseases. In most cases, there are febrile infections, sometimes accompanied by joint inflammation and exanthema.

In animals, lethal infections involving the central nervous system can also occur. This includes in particular encephalomyelitis in horses. This disease is also a notifiable animal disease.

What are the different types of alphaviruses?

The human pathogenic alphaviruses include the following species:

• Chikungunya virus,
• Ross River virus,
• O'Nyong-nyong virus,
• Mayaro fever virus,
• Sindbis virus,
• Semliki Forest virus,
• Mucambo virus,
• Everglades virus,

How often do alphaviruses occur?

Europe-wide infections with the alphavirus are rare, although travel infections do occur. The viruses are transmitted by bloodsucking vectors such as mosquitoes and are also returned to the vector through the bite or sting . The Sindbis viruses are among the most widespread, .

What diseases are triggered by alphaviruses?

Depending on the type of virus, the diseases also vary. Most often, infectious arthritis, encephalitis, exanthema and fever occur.

Infectious arthritis

Acute infectious arthritis caused by the alphavirus usually develops quickly. Usually such arthritis is acute, only rarely does a chronic form develop. Acute infectious arthritis can affect not only people with certain risk factors but also completely healthy people. The cartilage mass, which is necessary for the joint to function properly, can be completely destroyed within a few hours or days.

Alphavirus-related encephalitis

Alphaviral encephalitis is an inflammation of the brain parenchyma. It is caused by direct entry of alphaviruses. Symptoms may include headache, fever and altered mental status, focal neurological deficits and seizures.

Exanthema caused by alphaviruses

Exanthema is when a rash affects large areas of the skin . In most cases, it is caused by an infection with measles or rubella. But in some cases, alphaviruses are also responsible.

Alphavirus-induced fever

In an infection with alphaviruses, fever occurs in the vast majority of cases. The body temperature can rise to 40 degrees. After a few days, the fever goes down again.

How do alphaviruses make themselves felt?

Many infections with alphaviruses proceed completely without symptoms. If signs of illness occur , they usually begin with mild, unspecific flu-like symptoms, which can, however, develop into syndromes. The following syndromes can occur, among others :

• Lymphadenopathy,
• Exanthema,
• aseptic meningitis,
• Encephalitis,
• Joint pain,
• Arthritis,
• Non-cardiac pulmonary oedema.

 
In many cases there is also fever and an increased tendency to bleeding. Decreased synthesis of vitamin K-dependent coagulation factors, altered functions of platelets and disseminated intravascular coagulation play a major role.

How are alphaviruses diagnosed?

To detect an infection with alphaviruses, cultures are taken and blood tests are carried out. It is also possible to test the blood for certain antibodies that are formed against the antigen of alphaviruses . When cultures are set up, microorganisms are allowed to grow in the laboratory from samples of body fluids, blood or other materials taken from the infected area. This is done at until a sufficient quantity has formed, which can then be determined .

With the help of the polymerase chain reaction test, or PCR test for short, doctors are able to identify the alphavirus quickly and accurately . If there are serious symptoms or an infection poses a huge risk to public health as a whole, these tests are often carried out quickly.

Important notes:

• Before taking a blood sample, it is advisable to inform the relevant laboratory which viruses are to be tested.
• An, if possible, accurate travel history and a detailed description of the symptoms are mandatory for a fast and efficient analysis.
• If severe and uncontrollable courses, haemorrhagic fever and risk of infection are suspected, a tropical institute should be consulted.

How are alphaviruses treated?

Treatment of most diseases caused by alphaviruses is only possible symptomatically. However, if there is increased bleeding, a therapy with vitamin K substitution may become necessary. It may also be necessary for the affected person to receive transfusions with fresh plasma or red cell concentrates. Treatment with acetylsalicylic acid and other anti-inflammatory drugs is not suitable because of their antiplatelet effect.

How can alphaviruses be prevented?

To prevent alphaviruses, it is essential to prevent bites or stings from mosquitoes or ticks.

• Wear clothing that covers as much of the body as possible,
• Insect repellent,
• Minimise the likelihood of suffering a mosquito bite or a tick bite.

 
According to of the laboratory reporting obligation under the Infection Protection Act, there is a clinical medical reporting obligation of alphaviruses if the clinical picture of haemorrhagic fever is fulfilled.