Sindbis
Widely and continuously found in insects, it can lead to chronic disease

Sinbidis is a relatively rare disease, transferred by the bite of an infected mosquito. It usually will occur in outbreaks where sometimes up to 1500 people are infected. In a significant portion of patients, symptoms of arthritis persist for years and chronic disease shares many features with autoimmune diseases.

This disease is frequently misdiagnosed. Routine screening is not done and little data is available about Sindbis. It does look like this disease is becoming more prevalent.

?

THOUSAND

New infections per year

/

5

%

Develop illness

/

?

PEOPLE

Chronic illness

What causes Sindbis

Sindbis viruses are primarily transmitted by mosquitoes of the genus Culex and Culiseta and the natural reservoir of the virus are birds.

Sindbis virus is an enveloped single-stranded positive RNA virus, which belongs to the genus Alphavirus in the family Togaviridae. Sindbis virus species are further divided into 6 subtypes: Sindbis virus, Babanki virus, Kyzylagash virus and others, where most of them are associated with a particular geographical region.

The virus was first isolated in 1952 in Egypt and today sindbis virus infections are commonly known as Pogosta fever in Finland, Karelian fever in Russia and Ockelbo disease in Sweden.

Photo: Culex mosquito on arm.

Where is Sindbis found

Sindbis virus is widely spread with most symptomatic infections being localized to the South of China, Northern Europe, South Africa and Australia. There are cases of “Pogosta disease” occurring in Finland every year and regular epidemics occurring with a frequency of 7 years.

Migratory birds can carry the virus over long distances and contribute to the spread of the virus. There is no evidence of human-human transmission. Any person who is not immune to the virus may become infected and the incidence is highest in people who are 30-69 years old.

Image: Sindbis geographical distribution.

What are the symptoms of Sindbis

Infection with sindbis is frequently asymptomatic. Median time from mosquito bite to first symptoms is four days. 

The symptoms begin with (often itching) rash,fatigue, mild fever and headache. Some patients also have malaise, nausea, lymphadenopathy and dizziness.

The joint inflammation in wrists, hips, knees and ankles caused by the virus is also known as “epidemic polyarthritis” appear slightly after the initial symptoms. The joint manifestations can resolve after 1-2 weeks but they can also last for years or develop into a chronic disease.

Skin lesions occur in practically all patients and are found on the trunk and the limbs.

Higher age and female gender have been identified as risk factors for severe and prolonged symptoms.

The clinical picture is similar to the infection with Dengue virus. Asymptomatic infections are also common and in rare cases the virus can cause encephalitis.

Photo: cryo-electron micrograph of Sindbis-liposome complex

How can Sindbis be prevented

One of the main prophylaxis is protecting oneself from mosquito bites in endemic areas by wearing long sleeved-clothes and trousers or applying insect repellent on the skin.

There is no vaccine or prophylactic medication for Sindbis infection available.

How is Sindbis diagnosed

The diagnosis is based on the identification of virus-specific IgM antibodies, which appear within 8 days post infection, or IgG antibodies seroconversion within 2 weeks measured by ELISA. The presence of IgG antibodies in the absence of IgM antibodies indicates a previous infection. Antibodies can alternatively be detected by immunofluorescence and hemagglutination inhibition techniques.

PCR tests are available from the WoIDMo but due to low and short viremia it is difficult to detect the presence of the viruses.

How is Sindbis treated

There is no specific antiviral treatment available for sindbis and the treatment remains to be symptomatic. For the treatment of itching rash, antihistamines can be used, while non-salicylate analgesics can be used to alleviate pain in the joints.

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