|BIO Photography Group, Biodiversity Institute of Ontario|
Have you ever heard of Pogosta Disease, Karelian fever or Ockelbo disease? To me these were new but apparently they are all the same viral infection named after the different northern European regions it occurs (Finland, Russia, Sweden). In the 1980s it was shown to be associated with a strain of SINV isolated from mosquitoes. SINV is a mosquito-borne RNA virus, currently divided into five genotypes. One of those comprises of strains from northern Europe and South Africa and is called the African–European genotype.
The symptoms of the disease usually include a rash, as well as mild fever and other flu-like symptoms. Normally the symptoms cease after about 5 days. However, in some cases, patients develop a painful arthritis in the joints that may persist for months or even years. A typical patient is a middle-aged person who has been infected through a mosquito bite while picking berries in the autumn.
In August and September of 2013, an outbreak of Ockelbo disease occurred in northern Sweden, along the coastline of the Gulf of Bothnia, north of the endemic region where SINV is usually found. A group of Swedish researchers investigated the causative agent of this unexpected outbreak by using novel techniques (e.g. DNA barcoding) for vector identification and a high-throughput screening assay for virus detection.
The mosquitoes were initially screened as large pools by SINV-specific quantitative RT-PCR, and the SINV-positive mosquitoes were species determined by single-nucleotide polymorphism (SNP) analysis, followed by sequencing the barcoding region of the cytochrome oxidase I gene. The proportion of the collected mosquitoes was determined by a metabarcoding strategy.
The colleagues were able to isolate a new SINV strain (Lövånger) linked to strains from Ilomantsi, Finland, and Tärnsjö, Sweden. A pool of 1600 mosquitoes composed members of different genera (Culex, Culiseta, Aedes) was identified by metabarcoding. The only SINV-positive species was Culiseta morsitans which is also known to be a vector for Eastern equine encephalitis in North America.