Development of specific antibody patterns and clinical symptoms following Ockelbo virus infection

Mosquito-borne viruses causing human disease in Fennoscandia—Past, current, and future perspectives

Five different mosquito-borne viruses (moboviruses) significant to human disease are known to be endemic to Fennoscandia (Sindbis virus, Inkoo virus, Tahyna virus, Chatanga virus, and Batai virus). However, the incidence of mosquito-borne virus infections in Fennoscandia is unknown, largely due to underdiagnosing and lack of surveillance efforts. The Fennoscandian moboviruses are difficult to prevent due to their method of transmission, and often difficult to diagnose due to a lack of clear case definition criteria. Thus, many cases are likely to be mis-diagnosed, or even not diagnosed at all. Significant long-term effects, often in the form of malaise, rashes, and arthralgia have been found for some of these infections. Research into mobovirus disease is ongoing, though mainly focused on a few pathogens, with many others neglected. With moboviruses found as far north as the 69th parallel, studying mosquito-borne disease occurring in the tropics is only a small part of the whole picture. This review is written with the objective of summarizing current medically relevant knowledge of moboviruses occurring in Fennoscandia, while highlighting what is yet unknown and possibly overlooked.

Sindbis virus neutralising antibodies detected in Swedish horses

A number of viruses transmitted by mosquitoes are well known to cause disease in both humans and horses, ranging from mild fevers to mortal neurological disease. A recently discovered connection between the alphavirus Sindbis virus (SINV) and neurological disease in horses in South Africa initiated this serological study in northern Europe, where the same genotype of SINV (SINV-I) is also highly endemic. We tested 171 serum samples, originally obtained from horses for other reasons from April to October 2019, for presence of SINV neutralising antibodies using a plaque reduction neutralisation test (PRNT). The serum from six horses reduced the plaque count more than 80%, and two out of these reduced the plaque count more than 90%. These horses were sampled in six different regions of Sweden, and included individuals sampled from April to August. This study shows that horses in Sweden have become infected with SINV and developed neutralising antibodies. Potential connections between infection and development of disease are important questions for future studies.

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SINV is a arbovirus that has been associated with disease in horses in South Africa.

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SINV is common in Sweden but any connection to equine infection is unknown.

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In this study, neutralising antibodies against SINV were detected in Swedish horses.

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This is the first study to indicate SINV infection in European horses.

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The clinical impact of SINV on horses will be an important focus for future studies.

Arabidopsis thaliana plants expressing Rift Valley fever virus antigens: Mice exhibit systemic immune responses as the result of oral administration of the transgenic plants

The zoonotic Rift Valley fever virus affects livestock and humans in Africa and on the Arabian Peninsula. The economic impact of this pathogen due to livestock losses, as well as its relevance to public health, underscores the importance of developing effective and easily distributed vaccines. Vaccines that can be delivered orally are of particular interest. Here, we report the expression in transformed plants (Arabidopsis thaliana) of Rift Valley fever virus antigens. The antigens used in this study were the N protein and a deletion mutant of the Gn glycoprotein. Transformed lines were analysed for specific mRNA and protein content by RT-PCR and Western blotting, respectively. Furthermore, the plant-expressed antigens were evaluated for their immunogenicity in mice fed the transgenic plants. After oral intake of fresh transgenic plant material, a proportion of the mice elicited specific IgG antibody responses, as compared to the control animals that were fed wild-type plants and of which none sero-converted. Thus, we show that transgenic plants can be readily used to express and produce Rift Valley Fever virus proteins, and that the plants are immunogenic when given orally to mice. These are promising findings and provide a basis for further studies on edible plant vaccines against the Rift Valley fever virus.

Mapping of human B-cell epitopes of Sindbis virus

Mosquito-transmitted Sindbis virus (SINV) causes fever, skin lesions and musculoskeletal symptoms if transmitted to man. SINV is the prototype virus of genus Alphavirus, which includes other arthritogenic viruses such as chikungunya virus (CHIKV) and Ross River virus (RRV) that cause large epidemics with a considerable public health burden. Until now the human B-cell epitopes have been studied for CHIKV and RRV, but not for SINV. To identify the B-cell epitopes in SINV-infection, we synthetised a library of linear 18-mer peptides covering the structural polyprotein of SINV, and probed it with SINV IgG-positive and IgG-negative serum pools. By comparing the binding profiles of the pools, we identified 15 peptides that were strongly reactive only with the SINV IgG-positive pools. We then utilized alanine scanning and individual (n=22) patient sera to further narrow the number of common B-cell epitopes to six. These epitopes locate to the capsid, E2, E1 and to a region in PE2 (uncleaved E3-E2), which may only be present in immature virions. By sequence comparison, we observed that one of the capsid protein epitopes shares six identical amino acids with macrophage migration inhibitory factor (MIF) receptor, which is linked to inflammatory diseases and to molecular pathology of alphaviral arthritides. Our results add to the current understanding on SINV disease and raise questions of a potential role of uncleaved PE2 and the MIF receptor (CD74) mimotope in human SINV infection.

Human cases of Sindbis fever in South Africa, 2006-2010

Sindbis virus (SINV), the prototype positive-sense RNA alphavirus, causes febrile arthritis and is present throughout Afro-Eurasia. Little is known of the epidemiology of Sindbis fever due to insufficient surveillance in most endemic countries. The epidemiological features of Sindbis fever in humans in South Africa are described here based on a retrospective study of suspected arbovirus cases submitted for laboratory investigation from 2006 to 2010. Cases were detected annually mostly during the late summer/early autumn months and an increase in cases was noted for 2010, coinciding with an outbreak of Rift Valley fever. Cases were reported most often from the central plateau of South Africa and involved mostly males. No severe or fatal cases were reported and cases were associated with febrile arthralgia as commonly reported for SINV infection. Further surveillance is required to reveal the true extent of the morbidity of Sindbis fever in South Africa.

Diagnostics of Pogosta disease: antigenic properties and evaluation of Sindbis virus IgM and IgG enzyme immunoassays

Sindbis virus (SINV) is a mosquito-borne causative agent of a fever-rash arthritis, Pogosta disease, as verified recently by virus isolation from acutely ill patients. Pogosta disease occurs annually, but it emerges as unique epidemics every 7 years in Finland; over 10,000 patient samples have been analyzed for SINV antibodies, with over 2000 diagnosed acute SINV infections. However, the performance of these serological tests with a large number of samples has not been described before. The aim of the present study was to characterize and evaluate methods developed for the serodiagnostics of SINV infection, suitable for large sample numbers, and to examine the protein-specific responses to the antigen used. We developed SINV IgM and IgG enzyme immunoassays (EIA) using highly purified SINV. The EIAs were compared to hemagglutination inhibition (HI) and neutralization tests. We studied paired samples from 46 acutely ill patients taken at approximately 2-week intervals, with a verified SINV infection confirmed by a fourfold rise in HI antibody titer. The assay cut-off values and specificity were determined with confirmed negative sera. Protein-specific antibody responses were examined with immunoblot assay. The optical density values of the EIAs correlated well with the HI titers. The sensitivities of the IgM and IgG EIAs were 97.6% and 100%, and specificities were 95.2% and 97.6%, respectively. We consider that a verified serological diagnosis of acute SINV infection requires (1) in addition to a positive IgM result at least a fourfold increase in HI (or IgG) titer between paired sera or (2) a positive IgM result and a negative/borderline IgG result (which excludes old immunity) and specific reaction in HI. Both E1 and E2 glycoproteins of SINV were shown to be recognized by IgM and IgG antibodies early in infection.

Viral zoonoses in Europe

A number of new virus infections have emerged or re-emerged during the past 15 years. Some viruses are spreading to new areas along with climate and environmental changes. The majority of these infections are transmitted from animals to humans, and thus called zoonoses. Zoonotic viruses are, as compared to human-only viruses, much more difficult to eradicate. Infections by several of these viruses may lead to high mortality and also attract attention because they are potential bio-weapons. This review will focus on zoonotic virus infections occurring in Europe.

Sindbis viruses and other alphaviruses as cause of human arthritic disease

Amongst the arthritis-causing arboviruses, i.e. those spread by insects, the alphavirus group is of special interest. These viruses occasionally cause vast outbreaks, such as O'nyong-nyong in Africa in 1959. In Fennoscandia, Sindbis-related Ockelbo, Pogosta, or Karelian fever viruses have been found to cause significant morbidity. The major symptoms in addition to joint inflammation are fever, fatigue, headache and rash. The joint symptoms may persist for weeks, even months. The diagnosis is based on the clinical picture and serology. The causative viruses are closely related but not identical. It appears that at least in Finland the Pogosta disease is more common than thought, and the symptoms may often be overlooked. Several factors related to the viruses, their hosts, and global environmental changes may affect the spread of these viruses. All over the world arbovirus-caused diseases have increased, because of global changes.

Causative agent of Pogosta disease isolated from blood and skin lesions

Pogosta disease is a mosquito-borne viral disease in Finland, which is clinically manifested by rash and arthritis; larger outbreaks occur in 7-year intervals. The causative agent of the disease has been suspected of being closely related to Sindbis virus (SINV). We isolated SINV from five patients with acute Pogosta disease during an outbreak in fall 2002 in Finland. One virus strain was recovered from a whole blood sample and four other strains from skin lesions. The etiology of Pogosta disease was confirmed by these first Finnish SINV strains, which also represent the first human SINV isolates from Europe. Phylogenetic analysis indicates that the Finnish SINV strains are closely related to the viral agents isolated from mosquitoes and that cause clinically similar diseases in nearby geographic areas.

Alphavirus-specific cytotoxic T lymphocytes recognize a cross-reactive epitope from the capsid protein and can eliminate virus from persistently infected macrophages

Persistent alphavirus infections in synovial and neural tissues are believed to be associated with chronic arthritis and encephalitis, respectively, and represent likely targets for CD8+ alphabeta cytotoxic T lymphocytes (CTL). Here we show that the capsid protein is a dominant target for alphavirus-specific CTL in BALB/c mice and that capsid-specific CTL from these mice recognize an H-2Kd restricted epitope, QYSGGRFTI. This epitope lies in the highly conserved region of the capsid protein, and QYSGGRFTI-specific CTL were cross reactive across a range of Old World alphaviruses. In vivo the acute primary viraemia of these highly cytopathic viruses was unaffected by QYSGGRFTI-specific CTL. However, in vitro these CTL were able to completely clear virus from macrophages persistently and productively infected with the arthrogenic alphavirus Ross River virus.