Monday, March 28, 2016

EID Journal: Acute Human Inkoo and Chatanga Virus Infections, Finland


Yesterday, in Yellow Fever In Angola & The Risk Of International Spread - ECDC, I mentioned several other mosquito-borne viruses - including (Usutu Virus, Rift Valley Fever,  Sindbis Virus (SINV), Japanese Encephalitis, etc.) - that might someday pose a larger global threat.

There are others, of course.  Some we know of, and likely many others that have yet to be identified. 

Two relatively obscure viruses - Inkoo and Chatanga - are known to circulate in Scandinavian countries, and parts of Russia. Both are members of the California serogroup in the family Bunyaviridae, and are similar to the mosquito-borne La Crosse Virus found in the United States. 

While West Nile virus is the most common cause of neuroinvasive arboviral disease in the United States, the La Crosse virus (LACV) is the most common cause among children, producing between 80-100 cases of La Crosse encephalitis each year (cite CDC).

Much less is known about the incidence and health burden of the Inkoo and Chatanga viruses in Northern Europe, although recent studies (see Seroprevalence and Risk Factors of Inkoo Virus in Northern Sweden) suggest they are more common than previously appreciated.
As with both  WNV and LACV, most infections are mild or subclinical, and only a small percentage produce significant illness. And like LACV, both Inkoo and Chatanga appear to cause their most severe symptoms in children.

With vector-borne viruses like Dengue, Chikungunya, and Zika on the rise, the following EID journal research article is a good reminder of how much we have yet to learn about mosquito transmitted viruses around the world.

Volume 22, Number 5—May 2016


Acute Human Inkoo and Chatanga Virus Infections, Finland

Niina PutkuriComments to Author , Anu Kantele, Lev Levanov, Ilkka Kivistö, Markus Brummer-Korvenkontio, Antti Vaheri, and Olli Vapalahti


Inkoo virus (INKV) and Chatanga virus (CHATV), which are circulating in Finland, are mosquitoborne California serogroup orthobunyaviruses that have a high seroprevalence among humans. Worldwide, INKV infection has been poorly described, and CHATV infection has been unknown. 

Using serum samples collected in Finland from 7,961 patients suspected of having viral neurologic disease or Puumala virus infection during the summers of 2001–2013, we analyzed the samples to detect California serogroup infections. IgM seropositivity revealed 17 acute infections, and cross-neutralization tests confirmed presence of INKV or CHATV infections. 

All children (less than 16 years of age) with INKV infection were hospitalized; adults were outpatients with mild disease, except for 1 who was hospitalized with CHATV infection. Symptoms included fever, influenza-like illness, nausea or vomiting, disorientation, nuchal rigidity, headache, drowsiness, and seizures. Although many INKV and CHATV infections appear to be subclinical, these viruses can cause more severe disease, especially in children. 

In conclusion, we describe INKV and CHATV infections in humans and the clinical characteristics of acute disease. Symptoms of acute INKV and CHATV infections in patients in our study resembled symptoms of other California serogroup virus infections: influenza-like illness, with fever being most prominent. Most acute cases appeared to be subclinical, and a small minority of patients required hospitalization.
Compared with adults, children were at higher risk for contracting more severe disease and were more often hospitalized because of INKV infection. In adults, CHATV infection appeared to be more severe than INKV infection. Further studies are required to explore in detail the clinical picture, prognosis, incubation period, and antibody kinetics of these infections. Viral isolates or RT-PCR–positive samples from patients are needed to acquire data related to INKV and CHATV strains causing the clinical cases.
Niina Putkuri is a PhD student who works at the Faculty of Medicine, University of Helsinki, where she is finalizing her thesis. Her research interests include molecular epidemiology and disease associations of California serogroup viruses in Finland.


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