Sensitive enzyme immunoassay for detecting immunoglobulin M antibodies to Sindbis virus and further evidence that Pogosta disease is caused by a western equine encephalitis complex virus

Insights into Antibody-Mediated Alphavirus Immunity and Vaccine Development Landscape

Alphaviruses are mosquito-borne pathogens distributed worldwide in tropical and temperate areas causing a wide range of symptoms ranging from inflammatory arthritis-like manifestations to the induction of encephalitis in humans. Historically, large outbreaks in susceptible populations have been recorded followed by the development of protective long-lasting antibody responses suggesting a potential advantageous role for a vaccine. Although the current understanding of alphavirus antibody-mediated immunity has been mainly gathered in natural and experimental settings of chikungunya virus (CHIKV) infection, little is known about the humoral responses triggered by other emerging alphaviruses. This knowledge is needed to improve serology-based diagnostic tests and the development of highly effective cross-protective vaccines. Here, we review the role of antibody-mediated immunity upon arthritogenic and neurotropic alphavirus infections, and the current research efforts for the development of vaccines as a tool to control future alphavirus outbreaks.

Following the Yellow Brick Road

Charles Calisher was fascinated by microorganisms from the time he was in high school. He attended Stuyvesant High School in New York City, Philadelphia College of Pharmacy and Science (now University of the Sciences) (BS), then University of Notre Dame in South Bend, Indiana (MS), and finally Georgetown University, in Washington, DC (PhD), the latter while employed at a commercial biological house. He was hired by the US Communicable Disease Center (now the Centers for Disease Control and Prevention) in Atlanta, Georgia, was transferred to its Fort Collins laboratories in 1973, and retired from there in 1992. After traveling the world a bit, Calisher joined the faculty of Colorado State University in 1993, then semiretired as professor emeritus in 2010. During all those years, he developed from a would-be virologist to an arbovirologist-epidemiologist, identifying scores of newly recognized viruses from throughout the world and helping to investigate disease outbreaks and epidemics. His interests (always primarily arboviruses but now also rodent-borne viruses and bat-borne viruses) continue to expand, and he continues to be involved in various aspects of virology and to assist and annoy journal editors and others in regard to viral taxonomy.

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.

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.

Standardization of immunoglobulin M capture enzyme-linked immunosorbent assays for routine diagnosis of arboviral infections

Immunoglobulin M antibody-capture enzyme-linked immunosorbent assay (MAC-ELISA) is a rapid and versatile diagnostic method that readily permits the combination of multiple assays. Test consolidation is especially important for arthropod-borne viruses (arboviruses) which belong to at least three virus families: the Togaviridae, Flaviviridae, and Bunyaviridae. Using prototype viruses from each of these families and a panel of well-characterized human sera, we have evaluated and standardized a combined MAC-ELISA capable of identifying virus infections caused by members of each virus family. Furthermore, by grouping antigens geographically and utilizing known serological cross-reactivities, we have reduced the number of antigens necessary for testing, while maintaining adequate detection sensitivity. We have determined that a 1:400 serum dilution is most appropriate for screening antiviral antibody, using a positive-to-negative ratio of >/=2.0 as a positive cutoff value. With a blind-coded human serum panel, this combined MAC-ELISA was shown to have test sensitivity and specificity that correlated well with those of other serological techniques.

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

Sixteen patients with symptoms typical for Ockelbo disease (rash, arthralgia, fever) were enrolled in a 2 1/2 year study, during which clinical symptoms were recorded and ELISA was employed to study specific IgM, IgG and IgG subclass development. Initially, all patients presented with rash and arthralgia, and five patients still suffered from joint symptoms at the end of the study period. Ockelbo virus specific IgM was detected during the first week post onset in 6 patients and in 15 patients by day 14. One patient failed to develop specific IgM and was later diagnosed with a human parvovirus B19 infection. All patients were IgM-negative 2 1/2 years post onset. Seroconversions or significant titer rises for specific total IgG were seen in 15 patients. IgG titers generally peaked within one year but in two patients maximum titers were seen 2 1/2 years post onset. Development of IgG1 followed that of total IgG, while IgG3, after an initial increase in all Ockelbo disease patients, remained at peak levels for one year in four patients, three of whom still had detectable IgG3 at the end of the study period. Ockelbo virus specific IgG2 or IgG4 was not detected in any of the patients.

Medically important arboviruses of the United States and Canada

Of more than 500 arboviruses recognized worldwide, 5 were first isolated in Canada and 58 were first isolated in the United States. Six of these viruses are human pathogens: western equine encephalitis (WEE) and eastern equine encephalitis (EEE) viruses (family Togaviridae, genus Alphavirus), St. Louis encephalitis (SLE) and Powassan (POW) viruses (Flaviviridae, Flavivirus), LaCrosse (LAC) virus (Bunyaviridae, Bunyavirus), and Colorado tick fever (CTF) virus (Reoviridae, Coltivirus). Their scientific histories, geographic distributions, virology, epidemiology, vectors, vertebrate hosts, transmission, pathogenesis, clinical and differential diagnoses, control, treatment, and laboratory diagnosis are reviewed. In addition, mention is made of the Venezuelan equine encephalitis (VEE) complex viruses (family Togaviridae, genus Alphavirus), which periodically cause human and equine disease in North America. WEE, EEE, and SLE viruses are transmitted by mosquitoes between birds; POW and CTF viruses, between wild mammals by ticks; LAC virus, between small mammals by mosquitoes; and VEE viruses, between small or large mammals by mosquitoes. Human infections are tangential to the natural cycle. Such infections range from rare to focal but are relatively frequent where they occur. Epidemics of WEE, EEE, VEE, and SLE viruses have been recorded at periodic intervals, but prevalence of infections with LAC and CTF viruses typically are constant, related to the degree of exposure to infected vectors. Infections with POW virus appear to be rare. Adequate diagnostic tools are available, but treatment is mainly supportive, and greater efforts at educating the public and the medical community are suggested if infections are to be prevented.

Structure of the Ockelbo virus genome and its relationship to other Sindbis viruses

Ockelbo virus was first isolated in 1982 in Sweden. It is the causal agent of disease in humans characterized by arthritis, rash, and fever and is antigenically very closely related to Sindbis virus. We have determined the nucleotide and translated amino acid sequences of the prototype Ockelbo virus isolate (82-5) to determine the relatedness of Ockelbo virus to Sindbis virus at the genomic level and clarify the taxonomic position of Ockelbo virus within the alphavirus genus. The numbers of nucleotides and of translated amino acids in each region of the Ockelbo virus genome were exactly the same as those for the prototype AR339 strain of Sindbis virus except for three small deletions and insertions in the C-terminal half of nsP3 and for three single nucleotide insertions and deletions in the 3' untranslated region. Overall there were 672 nucleotide differences (5.7% divergence), resulting in 97 amino acid changes (2.6% divergence), between the two viruses: more than 85% of the nucleotide changes were silent. Only the C-terminal domain of nsP3 and the E2 glycoprotein showed a higher degree of amino acid substitution than the overall average. The former domain is not conserved among alphaviruses, and the latter is primarily responsible for antigenic variation. Sequence analysis of 420 nucleotides at the 3' end of a number of other Sindbis-like alphaviruses, including Karelian fever virus and South African, Indian, and Australian isolates of Sindbis virus, demonstrated that Ockelbo virus is more closely related to South African strains of Sindbis virus than it is to the prototypic Egyptian AR339 strain. Thus the South African strains, which have caused epidemic disease in humans, may have been introduced into Northern Europe by man or by migratory birds to establish Ockelbo disease there. The Indian and Australian strains form a distinct branch of the evolutionary tree and differ from prototypic AR339 Sindbis virus in 17% of the nucleotides sequenced.

Dot-ELISA for serodiagnosis of human infections due to Western equine encephalitis virus

A standard dot-ELISA (enzyme-linked immunosorbent assay) was modified for use in detecting IgM and IgG class antibodies to Western equine encephalitis (WEE) virus in serum samples from humans infected with this virus. Nitrocellulose membranes were soaked in supernatant fluid from WEE virus-infected cell cultures, air dried, and blocked with bovine protein. Serum samples were pipetted onto sections of the nitrocellulose, incubated, and washed. Addition of antibody to human immunoglobulin conjugated to alkaline phosphatase and enzyme substrate were used to detect the antibodies. Of 13 samples positive for IgM antibody to WEE virus by IgM antibody capture ELISA, 12 were positive by IgM dot-ELISA. IgG antibody to WEE virus was detected by dot-ELISA in 7/8, 10/14 and 7/10 samples with neutralizing, hemagglutination-inhibiting, or complement-fixing antibodies, respectively.

The prevalence of antibodies against viruses causing Kumlinge and Pogosta diseases on the islands of Iniö on the southwest coast of Finland

The prevalence of antibodies against viruses causing Kumlinge (tick-borne encephalitis) and Pogosta disease in the population of Iniö, a small island community in southwest Finland was measured. Antibodies against Kumlinge disease were found in 28% of the population, and increased from 10% in the 0-19 year age group to 42% in the 60-79 year age group. The prevalence varied markedly between different islands, being highest in the outer, bushy islands. Antibodies against Pogosta disease were detected in 2.7%.

Complex-specific immunoglobulin M antibody patterns in humans infected with alphaviruses

Sera from humans with serologically confirmed eastern equine encephalitis, western equine encephalitis, Pogosta (Ockelbo), Mayaro, Ross River, and chikungunya virus infections were tested by immunoglobulin M (IgM) antibody capture enzyme immunoassay. Diagnostically useful IgM antibody titers were detected, and selected sera with high IgM antibody titers were tested for IgM antibody with nine heterologous alphaviruses. The results provide evidence for the complex specificity of IgM antibody and indicate the usefulness of this test in both individual cases and epidemic situations.