Sindbis virus as a human pathogen : epidemiology, virology, genetic susceptibility and pathogenesis

Sindbis virus (SINV), an arthropod-borne, enveloped single-stranded RNA virus belongs to genus Alphavirus in the family Togaviridae. SINV is found in Eurasia, Africa, and Australia but clinical SINV infections occur particularly in Finland where the infection is known as Pogosta disease. SINV epidemics have a peculiar cyclic appearance in Finland and since 1974, major outbreaks involving hundreds or even thousands of cases have occurred approximately every seven years. This study aimed to characterise descriptive, analytical and molecular epidemiology, to develop a PCR-based detection method and to study the pathogenesis and genetic susceptibility to SINV infection. The epidemiology of a SINV outbreak in 2009 was described and compared to the outbreak pattern of previous major epidemics. The anticipated seven-year cycle did not recur as a relatively mild epidemic was observed. The data indicated that changes in grouse population and weather factors may contribute to the human epidemiology of SINV infection as speculated earlier. We identified risk factors for SINV infection in a large population based case-control study and extended the data on clinical features and patient characteristics. In the final multivariable analysis, mosquito bites and spending time in woods or marshland remained as independent risk factors with a significant dose-response effect. Exposure to other arthropods was not positively associated with SINV infection. A new estimate of the median incubation period of SINV infection was 4 days. The SINV-infected patients were found to have previous or ongoing medical conditions affecting joint or connective tissues more frequently than controls. SINV was isolated from mosquitoes in Finland for the first time. Sequence analyses on the full-length coding sequences of all Finnish SINV strains, significantly expanding the available data on SINV sequences, demonstrated that the novel SINV isolate is closely related to Finnish human SINV isolates and to strains isolated previously from mosquitoes in Sweden and Russia. The data further established that SINV has had a local circulation in the endemic Northern Europe during the past decades. Sequence analyses also identified amino acid signatures, particularly in the nsP3 protein, shared by Northern European strains that may be associated with vector or host species adaptation. We developed a specific and sensitive real-time RT-PCR assay for the detection of SINV RNA with a detection limit of 9 copies/reaction. The assay demonstrated low levels of viraemia (< 103 copies/ml) in sera of SINV-infected patients and only 12% of the serum samples were positive in the assay. Thus, the assay was found to have limited value as a diagnostic technique using serum samples but could be used for screening SINV in e.g. wildlife. These findings on low viral load may be associated with the pathogenesis and epidemiology of SINV infection. The pathogenesis of myalgia was studied by examining a unique muscle biopsy obtained from a SINV-infected patient with chronic myalgia and arthralgia and by performing SINV infections of primary human myoblasts and myotubes. Evidence of muscle regeneration due to previous necrosis likely caused by earlier SINV infection was found in the biopsy. We further showed that human primary myoblasts and myotubes were susceptible in vitro for SINV infection. Overall, the study provided new information on SINV tropism and the mechanisms behind myalgia in SINV infection. The role of HLA and complement C4 genes in the susceptibility and outcome of SINV infection were investigated. The frequency of DRB1*01 allele was significantly higher in patients with SINV infection than in the reference population (OR=3.3, P=0.003). The frequency of DRB1*01 allele was particularly prominent among patients who at three years post infection experienced joint manifestations. The data further suggested that the combination of HLA-B*35- DRB1*01 alleles and C4B deficiency may be associated with a more prominent or persistent form of the disease. A set of autoantibodies was measured in SINV-infected patients at the acute phase and three years post infection to assess autoreactivity. The frequency of rheumatoid factor at three years post infection was 29.5% and showed significant increase (P=0.02) during the three-year follow-up. The antinuclear and anti-mitochondrial antibodies were also present in serum three years post infection with frequencies of 15.9% and 6.8%, respectively. Thus, the data demonstrated that symptomatic SINV infections show association to the HLA system and that autoantibody titres are elevated in patients three years post infection. These findings indicate that SINV-induced arthritis shares features with autoimmune diseases.Pogostantauti eli nivelrokko ilmenee ihottumana, kuumena, lihaskipuina ja kivuliaina niveloireita, jotka voivat kestää jopa vuosia. Taudin aiheuttaa Togaviridae-heimoon ja alfavirusten sukuun kuuluva Sindbis-virus. Virusta esiintyy Afrikassa, Euraasiassa sekä Australiassa. Sindbis virus aiheuttaa kliinistä infektiota tuntemattomasta syystä lähinnä vain Pohjois-Euroopassa ja erityisesti Suomessa, jossa peräti 5 %:lla väestöstä voidaan todeta viruksen vasta-aineita merkkinä sairastetusta infektiosta. Pogostantauti on puhjennut satojen tautitapausten epidemiaksi n. 7 vuoden välein. Syyt erikoiseen epidemiasykliin ovat epäselviä. Tässä väitöstutkimuksessa selvitettiin pogostantaudin epidemiologiaa, tautimekanismeja ja geneettisiä riskitekijöitä. Lisäksi tutkittiin aiheuttajaviruksen ominaisuuksia ja kehitettiin taudin laboratoriodiagnostiikkaa. Selvitimme vuodeksi 2009 ennakoitua epidemiaa ja vertasimme sitä aiempiin epidemioihin. Vuodeksi 2009 odotettu epidemia jäi kuitenkin lieväksi ja 7 vuoden sykli ei siten toteutunut ennakoidulla tavalla. Tutkimus antoi viitteitä siitä, että metsäkanalintujen populaatiovaihtelut ja sääolosuhteet saattoivat vaikuttaa epidemian voimakkuuteen. Sindbis-virusinfektion riskitekijöitä ja taudinkuvaa kartoitettiin väestöpohjaisella tapaus-verrokkitutkimuksella. Hyttysenpistoille altistumisen todettiin olevan tärkein virusinfektion itsenäinen riskitekijä ja hyttysten puremat lisäsivät riskiä annos-vaste -efektin mukaisesti. Myös metsässä tai suolla liikkuminen osoittautui pogostantaudin itsenäiseksi riskitekijäksi. Tutkimuksessa tarkentui myös taudin itämisaika neljäksi päiväksi sekä selvisi että sairastetut tai edelleen aktiiviset nivel- tai sidekudossairaudet olivat yleisempiä tapausten kuin verrokkien keskuudessa. Tutkimuksessa eristettiin ensimmäinen suomalainen Sindbis-viruskanta hyttysistä, jonka koko proteiineja koodaavan alueen emäsjärjestys määritettiin. Kyseinen alue määritettiin myös kaikista aiemmin ihmisistä eristetyistä viruskannoista. Viruksen perimän tarkempi analyysi vahvisti käsityksen siitä, että virus kiertää paikallisesti Pohjois-Euroopan endeemisillä alueilla ilman uusien viruskantojen jatkuvaa saapumista Afrikasta. Havaitsimme myös, että pohjoiseurooppalaiset kannat jakavat 9 aminohappomuutosta, jotka saattavat liittyä viruksen sopeutumiseen uusiin vektori-ja isäntälajeihin ja/tai viruksen lisääntymistehokkuuteen. Tutkimuksessa kehitettiin käänteis-PCR-menetelmä Sindbis-viruksen perimän osoittamiseen. Menetelmällä pystyttiin herkästi ja tarkasti tunnistamaan kaikki suomalaiset Sindbis-viruskannat virusviljelynäytteistä. Menetelmä sopii kuitenkin huonosti käytännön laboratoriodiagnostiikkaan, sillä viruksen määrän todettiin olevan seerumissa erittäin alhainen. Vähäisellä virusmäärällä saattaa olla merkitystä taudin epidemiologiassa. Tutkimme virusinfektiossa esiintyvien lihaskipujen taustaa. Havaitsimme Sindbis-infektion jälkeen kroonistuneen potilaan lihaskoepalassa merkkejä lihassolujen uudismuodostuksesta, mikä todennäköisesti johtuu viruksen aikaisemmin aiheuttamasta kudostuhosta. Osoitimme myös kokeellisesti, että virus kykenee infektoimaan eri erilaistumisvaiheessa olevia lihassoluja. Lisäksi selvitimme kudosantigeenin sekä komplementtijärjestelmän geenien yhteyttä altistumiseen oireelliselle Sindbis-virusinfektiolle sekä taudin pitkittymiseen. Tulokset osoittivat, että kudosantigeenialleeli DRB1*01 altistaa selvästi kliiniseen Sindbis-virusinfektioon ja etenkin pitkittyneisiin niveloireisiin. Jopa puolet tutkituista potilaista oli DRB1*01-alleelin suhteen positiivisia ja alleelifrekvenssi oli merkitsevästi korkeampi kuin verrokkiväestössä. Tutkimme myös autoimmuniteetin ja Sindbi-virusinfektion välistä yhteyttä määrittämällä eri autovasta-aineiden esiintymistä potilaiden seeruminäytteissä eri aikapisteissä. Tuloksemme osoittivat, että reumatekijä yleistyi merkitseväsi 3 vuoden seurantatutkimuksen aikana. Lisäksi reumatekijän, tumavasta-aineiden ja mitokondriovasta-aineiden esiintyvyys 3 vuotta infektion jälkeen oli selvästi korkeampi pogostantautipotilaiden keskuudessa kuin normaaliväestössä

Zikavirus

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Health Information-Seeking Patterns of the General Public and Indications for Disease Surveillance : Register-Based Study Using Lyme Disease

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Risk of lymphoid malignancies increased after Puumala virus infection in Finland, 2009-2019: A retrospective register-based cohort study

Objectives: The Puumala virus (PUUV) is a hantavirus that causes hemorrhagic fever with renal syndrome. Studies showing an increased risk of lymphoid malignancies after hantavirus infection, together with the observation that PUUV infects B cells, motivated us to study the risk of lymphoid malignancies after PUUV infection. Methods: We linked data from the Finnish Cancer Registry and National Infectious Diseases Register for 2009-2019. We used a time-dependent Cox regression model to evaluate the hazard of the lymphoid malignancies grouped according to the HAEMACARE classification. Results: We identified 68 cases of lymphoid malignancies after PUUV infection among 16,075 PUUV-infected individuals during 61,114,826 person-years of observation. A total of 10 cases occurred within 3-<12 months and 38 within 1-<5 years after PUUV infection, and the risk of lymphoid malignancies increased with hazard ratios (HRs) of 2.0 (95% confidence interval [CI], 1.1-3.7) and 1.6 (95% CI, 1.2-2.3), respectively. The group of mature B cell neoplasms showed an increased risk 3-<12 months and 1-<5 years after PUUV infection, HR 2.2 (95% CI, 1.2-4.3) and HR 1.8 (95% CI, 1.3-2.5), respectively. Conclusion: PUUV infection is associated with lymphoid malignancies in the Finnish population, supporting the earlier studies. Further research is required to understand the pathophysiological mechanisms behind this association

Modelling habitat suitability for occurrence of human tick-borne encephalitis (TBE) cases in Finland

The numbers of reported human tick-borne encephalitis (TBE) cases in Europe have increased in several endemic regions (including Finland) in recent decades, indicative of an increasing threat to public health. As such, it is important to identify the regions at risk and the most influential factors associated with TBE distributions, particularly in understudied regions. This study aimed to identify the risk areas of TBE transmission in two different datasets based on human TBE disease cases from 2007 to 2011 (n = 86) and 2012-2017 (n = 244). We also examined which factors best explain the presence of human TBE cases. We used ensemble modelling to determine the relationship of TBE occurrence with environmental, ecological, and anthropogenic factors in Finland. Geospatial data including these variables were acquired from several open data sources and satellite and aerial imagery and, were processed in GIS software. Biomod2, an ensemble platform designed for species dis-tribution modelling, was used to generate ensemble models in R. The proportion of built-up areas, field, forest, and snow-covered land in November, people working in the primary sector, human population density, mean precipitation in April and July, and densities of European hares, white-tailed deer, and raccoon dogs best es-timated distribution of human TBE disease cases in the two datasets. Random forest and generalized boosted regression models performed with a very good to excellent predictive power (ROC = 0.89-0.96) in both time periods. Based on the predictive maps, high-risk areas for TBE transmission were located in the coastal regions in Southern and Western Finland (including the angstrom land Islands), several municipalities in Central and Eastern Finland, and coastal municipalities in Southern Lapland. To explore potential changes in TBE distributions in future climate, we used bioclimatic factors with current and future climate forecast data to reveal possible future hotspot areas. Based on the future forecasts, a slightly wider geographical extent of TBE risk was introduced in the angstrom land Islands and Southern, Western and Northern Finland, even though the risk itself was not increased. Our results are the first steps towards TBE-risk area mapping in current and future climate in Finland.Peer reviewe

Sindbis Virus Strains of Divergent Origin Isolated from Humans and Mosquitoes During a Recent Outbreak in Finland

Sindbis virus (SINV) is a mosquito-borne avian hosted virus that is widely distributed in Europe, Africa, Asia, and Oceania. Disease in humans is documented mainly from Northern Europe and South Africa and associated with genotype I. In 2018 under extremely warm climatic conditions, a small outbreak of 71 diagnosed SINV infections was recorded in Finland. We screened 52 mosquito pools (570 mosquitoes) and 223 human sera for SINV with real-time RT-PCR and the positive samples with virus isolation. One SINV strain was isolated from a pool (n = 13) of genusOchlerotatusmosquitoes and three strains from patient serum samples. Complete genome analysis suggested all the isolates to be divergent from one another and related to previous Finnish, Swedish, and German strains. The study provides evidence of SINV strain transfer within Europe across regions with different epidemiological characteristics. Whether these are influenced by different mosquito genera involved in the transmission remains to be studied.Peer reviewe

Destination specific risks of acquisition of notifiable food- and waterborne infections or sexually transmitted infections among Finnish international travellers, 1995-2015

Background: Overnight international travels made by Finns more than doubled during 1995-2015. To estimate risks and observe trends of travel-related notifiable sexually transmitted and food- and water-borne infections (STIs and FWIs) among travellers, we analysed national reports of gonorrhoea, syphilis, hepatitis A, shigellosis, campylobacteriosis and salmonellosis cases and related them to travel statistics. Method: Cases notified as travel-related to the Finnish infectious diseases register were used as numerators and overnight stays of Statistics Finland surveys as denominator. We calculated overall risks (per 100,000 travellers) and assessed trends (using regression model) in various geographic regions. Results: Of all travel-related cases during 1995-2015, 2304 were STIs and 70,929 FWIs. During 2012-2015, Asia-Oceania showed highest risk estimates for gonorrhoea (11.0; 95%CI, 9.5-13), syphilis (1.4; 0.93-2.1), salmonellosis (157; 151-164), and campylobacteriosis (135; 129-141), and Africa for hepatitis A (4.5; 2.5-7.9), and shigellosis (35; 28-43). When evaluating at country level, the highest risks of infections was found in Thailand, except for hepatitis A ranking Hungary the first. During 2000-2011, significantly decreasing trends occurred for most FWIs particularly in the European regions and for STIs in Russia-Baltics. Conclusions: Our findings can be used in targeting pre-travel advice, which should also cover those visiting Thailand or European hepatitis A risk areas.Peer reviewe