[Effect of various adamantane compounds on the reproduction of Sindbis virus. Isolation and properties of a resistant strain]

Rimantadine and its structural analogs, i. e. amide of 1-adamantane carboxylic acid (AACA) and 1-adamantane acetic acid amide, were shown to be able to inhibit reproduction of Sindbis virus in culture Vero cells. AACA had the maximum antiviral activity. Subcultures of the initial sensitive population of Sindbis virus in the presence of AACA led to formation of mutants resistant to AACA as well as to rimantadine, adamantane acetic acid amide and ammonium chloride. The Sindbis virus population was heterogenous in sensitivity to AACA, which was evident from isolation of separate clones with various levels of sensitivity to the above mentioned compounds from the population. It was found that reproduction of the AACA sensitive and resistant strains of Sindbis virus differed: the latent period of the resistant strain was 2 hours longer than that of the sensitive strain. The same effect was observed in the comparative study on synthesis of the virus-specific RNA.

[The identification of alphaviruses by using cDNA probes complementary to the 3'-terminal of the viral genome]

Venezuelan equine encephalomyelitis, Eastern equine encephalomyelitis and Sindbis viruses, as well as members of various serological groups of alphaviruses were identified using synthesized molecular probes complementary to 3'-terminus of the molecule of the appropriate genomic RNA: 32P-single-stranded kDNA and E. coli-cloned 32P-double-stranded kDNA. A high species-specificity of kDNA-probes was demonstrated. The sensitivity of the method was 1 ng of viral RNA overlayed on the nitrocellulose filter.

A novel variant of Sindbis virus is both neurovirulent and neuroinvasive in adult mice

A strain of Sindbis virus (SV), recently isolated from mosquitoes in Israel, was used as a source for variants which differ in neuroinvasiveness and virulence that were generated by serial passage of SV in suckling and weanling mouse brain. At the 15th passage a neurovirulent variant was observed and designated SVN (neurovirulent). After 7 more passages in weanling mouse brains, another variant was observed and designated SVNI (neuroinvasive) and both were isolated and purified. All strains caused similar viremia after intraperitoneal (I.P.) injection of weanling mice, but whereas SV was neuroinvasive but nonvirulent, SVN was neurovirulent but noninvasive and SVNI was both virulent and invasive. SVNI is the first SV variant which is both neurovirulent and neuroinvasive in weanling mice. Co-injection I.P. of SV + SVN resulted in presence of SV alone in the mouse brain; co-injection of SVNI + SVN resulted in full-titered replication of both strains in the brain. We assume that this is achieved through a breach of the blood brain barrier effected by SVNI replication and used by SVN for co-invasion. SV probably invades the brain by a different mechanism. I.P. infection with SVNI of inbred BALB/c mice gave rise to clinical signs only in a few mice even though substantial viremia was demonstrated.

High Resolution Removal of Virus from Protein Solutions Using a Membrane of Unique Structure

We describe a new class of membrane that has the capability of removing particles such as viruses from solution with resolution and reproducibility superior to that of conventional membranes. This composite membrane is composed of a pre-formed microporous membrane plus a thin asymmetric, finely porous retentive layer that is quite different from conventional ultrafilters. The protein sieving characteristics of this membrane are nearly equivalent to, but slightly less than, that of conventional 100,000 Dalton cut-off ultrafiltration membranes. This membrane uniquely shows particle retention characteristics that increase monotonically from 3 to 8 logs as a function of particle diameter in the range of 28 to 93 nm. The performance of this membrane in both a single stage and a two stage system show that 4 to 6 log overall removal of virus particles in the size range 30 to 70 nm is possible with simultaneous high recovery of product protein. Clearance factors exceeding 6 logs are possible with viruses larger than 78 nm. In addition, the performance of process systems containing this membrane is predictable in accordance with the general membrane properties and equilibrium mass balance models. This membrane system is fully validatable and can be used in conjunction with other validated operations in a down-stream process to reliably achieve an over-all reduction of 12 logs of known or putative virus particles.

[The isolation and identification of the Sindbis virus from migratory birds in Estonia]

The data on isolation from birds and identification of two strains of alphaviruses in Estonia in the territory of Vilsandy natural reserve are presented. Electron microscopy of purified virions allowed the isolates to be classified into the family of togaviruses, and serological identification (neutralization test, CFT) using polyvalent sera and monoclonal antibody showed them to belong to Sindbis virus.

Pathogenesis of encephalitis induced in newborn mice by virulent and avirulent strains of Sindbis virus

Strains of Sindbis virus differ in their virulence for mice of different ages; this variation is related in large part to variations in the amino acid compositions of E1 and E2, the surface glycoproteins. The comparative pathogenesis of Sindbis virus strains which are virulent or avirulent for newborn mice has not been previously examined. We have studied the diseases caused by a virulent wild-type strain, AR339, and two less virulent laboratory strains, Toto1101 and HRSP (HR small plaque). After peripheral inoculation of 1,000 PFU, AR339 causes 100% mortality within 5 days (50% lethal dose [LD50] = 3 PFU) while Toto1101 causes 70% mortality (LD50 = 10(2.4) PFU) and HRSP causes 50 to 60% mortality (LD50 = 10(5.1) PFU) with most deaths occurring 7 to 11 days after infection. However, after intracerebral inoculation of 1,000 PFU, Toto1101 is virulent (100% mortality within 5 days; LD50 = 4 PFU) while HRSP is not (75% mortality; LD50 = 10(4.2) PFU). After intracerebral inoculation, all three strains initiate new virus formation within 4 h, but HRSP reaches a plateau of 10(6) PFU/g of brain while Toto1101 and AR339 replicate to a level of 10(8) to 10(9) PFU/g of brain within 24 h. Interferon induction parallels virus growth. Mice infected with HRSP develop persistent central nervous system infection (10(6) PFU/g of brain) until the initiation of a virus-specific immune response 7 to 8 days after infection when virus clearance begins. The distribution of virus in the brains of mice was similar, but the virus was more abundant in the case of AR339. HRSP continued to spread until day 9. Clearance from the brain was complete by day 17. We conclude that the decreased virulence of HRSP is due to an intrinsic decreased ability of this strain of Sindbis virus to grow in neural cells of the mouse. We also conclude that CD-1 mice do not respond to the antigens of Sindbis virus until approximately 1 week of age. This lack of response does not lead to tolerance and persistent infection but rather to late virus clearance whenever the immune response is initiated.

Ecologic studies of mosquitoes and birds as hosts of Ockelbo virus in Sweden and isolation of Inkoo and Batai viruses from mosquitoes

Field studies were conducted in central Sweden from 1983 through 1985 to obtain information on the etiologic agent of Ockelbo disease, described in Sweden in the 1960s and probably identical to Pogosta disease in Finland and to Karelian fever in the western USSR. Mosquitoes (63,644) collected during this 3 year period yielded 21 virus strains. Ockelbo virus isolations were from Culiseta morsitans (5 strains), Culex pipiens and/or Cx. torrentium (6 strains), and Aedes cinereus (3 strains). Inkoo (6 strains) and Batai (1 strain) viruses were recovered from Ae. communis. Blood samples collected March-May from migrating birds on the southeast and est coast of Sweden and in July and August from resident birds in east-central Sweden were tested for neutralizing antibody to Ockelbo virus. Antibody was not detected in 328 birds sampled during spring migrations. Two of 58 (3.4%) birds bled in July and 8 of 78 birds (10%) bled in August had antibody to Ockelbo virus. Ockelbo virus circulates in a mosquito-bird-mosquito cycle, with Cs. morsitans and Cx. pipiens and/or Cx. torrentium as enzootic vectors. Antibody was detected in passerine birds. Other classes of birds or other vertebrates were not sampled. Aedes cinereus may serve primarily to transmit virus to people. The role of other mosquito species as vectors for people is unknown.

Identity of Karelian fever and Ockelbo viruses determined by serum dilution-plaque reduction neutralization tests and oligonucleotide mapping

The causative agents of Ockelbo disease in Sweden, Pogosta disease in Finland, and Karelian fever in the USSR have been attributed to alphaviruses (family Togaviridae) related to Sindbis virus. We compared prototypes Sindbis, Ockelbo, and Karelian fever viruses by neutralization tests. We also analyzed oligonucleotide fingerprint maps of prototypes Ockelbo and Karelian fever viruses and a strain of Sindbis virus from Czechoslovakia. The results indicate that Ockelbo and Karelian fever viruses are essentially identical and suggest that Ockelbo disease, Pogosta disease, and Karelian fever are synonyms for the same disease.

Interaction of Alphaviruses with the serum complement system is a function of method of purification

The interaction of Sindbis and Ross River viruses with the serum complement system in vitro was influenced by the type of density gradient used to purify them. Sindbis virus purified on sucrose gradients activated the alternate serum complement pathway while Ross River virus prepared in an identical manner had no effect on C3 turnover in non-immune serum. Both viruses purified on tartrate gradients inhibited the spontaneous cleavage of C3 in normal serum. At least some of this inhibition appeared to be due to the presence of tartrate adsorbed to the surface of virions.

Basis of neurovirulence in Sindbis virus encephalomyelitis of mice

Neuroadapted Sindbis virus (NSV) was selected by serial passage of wild-type Sindbis virus (SV) in mouse brain. After intracerebral inoculation of weanling mice, NSV causes a severe encephalomyelitis with hindlimb paralysis and high mortality; SV causes nonfatal mild disease. In order to determine the biologic basis of neurovirulence in vivo, these viral infections have been compared by using infectivity assays, light and electron microscopy, in situ hybridization, immunohistochemistry, and double-labeling for neural cell markers and viral RNA. More infectious virus is present in the central nervous system during NSV than during SV infection. After intracerebral inoculation, both viruses enter the central nervous system via the ependyma and spread to gray matter areas, including the ventral horns of the spinal cord. Their cellular targets are not different, and neuronal infection is prominent. NSV infects more neurons, and causes more severe injury than SV. In NSV infection, there is marked swelling of lumbar and thoracic neurons and their processes in the ventral horns. Relatively mild changes are detected in SV infection only by electron microscopy. Neuroadaptation likely occurs by increasing the efficiency of viral replication in neurons, rather than by a fundamental change in the cellular tropism or the topography of the infection in the central nervous system.

Virus removal or inactivation in hemoglobin solutions by ultrafiltration or detergent/solvent treatment

Two procedures to eliminate virus infectivity from hemoglobin solutions at ambient temperature were evaluated. In the first, virus removal was assessed during the ultrafiltration of hemoglobin solutions through a membrane with a nominal molecular weight cut-off of 100,000 Daltons. The results of this study demonstrated that less than 0.1% of any virus originally spiked into the solution was detectable in the ultrafiltrate. In the second procedure the inactivation of viruses in hemoglobin solutions incubated with tri(n-butyl)phosphate mixed with sodium cholate was studied. Greater than 99% of each of the enveloped viruses tested was inactivated during the first 15 minutes of incubation with greater than 10(5) plaque forming units/ml of each being inactivated after one to six hours. No inactivation of the non-enveloped poliovirus was effected by this treatment. The data imply that both ultrafiltration and detergent/solvent incubation may reduce virus infectivity in hemoglobin solutions, but neither method yields a completely virus free product.

Use of enzyme immunoassay and nucleic acid hybridization for detecting Sindbis virus in infected mosquitoes

Aedes aegypti mosquitoes were inoculated intrathoracically with prototype Sindbis virus, held at 26.7 degrees C for from 0-95 h and placed at -70 degrees C. Individual mosquitoes were tested for virus by plaque assay in Vero cells, for viral RNA by nucleic acid hybridization using a cloned cDNA probe, and for viral protein by enzyme-linked immunosorbent assay. Virus was detected by plaque assay as early as 8 h after infection. Sindbis virus RNA was detected by nucleic acid hybridization 18 h after infection and by enzyme-linked immunosorbent assay 10 h after infection. The results of these comparisons suggest that both nucleic acid hybridization and enzyme-linked immunosorbent assay are applicable to direct detection of Sindbis virus in mosquitoes containing virus at levels usually found during arbovirus epidemics.

Elimination of viruses (human immunodeficiency, hepatitis B, vesicular stomatitis and Sindbis viruses) from an intravenous immunoglobulin preparation

More than 10(4) plaque-forming units (pfu)/ml of HIV are inactivated during the alcohol fractionation step from plasma to fraction (Fr)-II+III, greater than 10(4) pfu/ml is inactivated from Fr-II+III to Fr-II and greater than 10(4) pfu/ml is inactivated during the polyethylene glycol (PEG) fractionation process from Fr-II+III to intravenous IgG (IVIG). The total inactivation rate from plasma to IVIG via Fr-II+III or Fr-II was calculated to be greater than 10(8) or 10(12), respectively. The PEG fractionation method produces an intact and unmodified IVIG. In addition, the PEG fractionation method at a low ionic strength was found to be effective for the elimination of greater than 10(5) units of other viruses, including hepatitis B, vesicular stomatitis and Sindbis viruses.

The pathogenesis of spinal cord involvement in the encephalomyelitis of mice caused by neuroadapted Sindbis virus infection

Weanling mice develop an acute encephalomyelitis with high mortality after intracerebral inoculation of neuroadapted Sindbis virus. The mice develop kyphoscoliosis and hindlimb paralysis. Immunohistochemical and in situ hybridization studies have demonstrated virus in the gray matter of the brain and spinal cord. Ventral horn cells are prominently infected, providing an anatomical basis for the clinical poliomyelitis. A novel route of spread of inoculated virus within the central nervous system has been found. The virus enters the ventricular system, and then travels caudally in the central canal of the spinal cord where ependymal cells are infected. The virus subsequently spreads into the gray matter. The distribution of virus in the spinal cord is likely dependent both on variations in the susceptibility of neural cells and on this route of entry and subsequent spread.

Sindbis and West Nile virus infections in the Witwatersrand-Pretoria region

From mid-December 1983 until mid-April 1984, there was an epidemic of Sindbis (SIN) virus infection in the Witwatersrand-Pretoria region in which hundreds of human cases were diagnosed clinically. Twenty-eight of these diagnoses were confirmed in the laboratory by seroconversion as being infections with SIN virus, and 5 cases of infection with West Nile (WN) virus were also found. Attempts to isolate virus from 66 patients, mainly from serum specimens, were unsuccessful. Infection rates for the mosquito vector Culex univittatus, collected at localities on the Witwatersrand in February and March, were mostly higher for both SIN and WN viruses than in previous years. The highest rates determined were 5.4 (SIN) and 9.6 (WN) per 1 000 mosquitoes. It is concluded that an epizootic of both viruses occurred which was manifested by a high level of viral activity in the feral Cx. univittatus-bird transmission cycle. Cx. univittatus efficiently transferred infection of SIN virus from this cycle to man to cause the epidemic of infection with that virus but it is unclear why there were apparently only a few cases of WN virus infection.

Experimental assessment of the vector competence of Culex (Culex) neavei Theobald with West Nile and Sindbis viruses in South Africa

Culex univittatus is the maintenance vector of West Nile (WN) and Sindbis (SIN) viruses on the inland plateau of South Africa and also transfers infection to man. Both viruses have frequently been isolated from this mosquito and human immunity is high on the plateau. In the Natal lowlands where Cx univittatus is replaced by Cx neavei, apparently the main vector there, immune rates are low and few isolations have been made from this species. Vector competence experiments were carried out with Cx neavei to compare with those previously done with Cx univittatus. It was thought that a difference in such competence might explain the contrasting epidemiological situation in the two regions. After infective feeds on chicks with high viraemias of each virus, Cx neavei showed a high transmission rate. However, the 50% infection thresholds determined by exposing birds with differing viraemias to mosquitoes of this species, were 4.4 logs per ml (WN) and 5.8 logs (SIN). These thresholds are both higher than those for Cx univittatus. It is concluded that Cx neavei is a poorer vector of both viruses which accounts for the lower viral activity, including the lower incidence of human infection, in the Natal lowlands.

Isolation of viruses from mosquitoes of the Negev, Israel

In a survey of the mosquito population of the Negev carried out between July 1982 and September 1984, over 85,000 insects belonging to 10 species were tested for the presence of viruses. They yielded 91 virus isolates in C-6/36 mosquito cell cultures; 20 of the isolates were recovered also in Vero cell cultures and in suckling mice inoculated intracerebrally. Of the 20 isolates recovered in the vertebrate systems 17 were identified as Sindbis, and three as West Nile viruses. 71 viruses which have been isolated only in mosquito cell cultures remain unidentified. Sindbis and West Nile arboviruses were isolated only from Culex pipiens and from Cx perexiguus, while the unidentified viruses were isolated from these and from five other mosquito species.

Use of chicken and rabbit antibodies in a solid phase protein A radioimmunossay for virus detection

A new rapid indirect solid phase radioimmunoassay was developed for the detection of Sindbis virus. Chicken antibodies were adsorbed onto wells in microplates to serve as 'capture antibodies' and rabbit antibodies were used as the second antibody. 125I-labelled protein A that does not bind to chicken antibodies, but binds firmly to rabbit antibodies was used as the tracer. All the steps necessary for the development of the assay are described. The minimal amount of Sindbis virus detectable was around 3 x 10(5) PFU/ml and the interassay reproducibility was about +/- 30%.

Sindbis virus isolations from Saudi Arabian mosquitoes

A study in late 1979 to early 1980 was conducted to assess arbovirus activity in the Eastern Province of Saudi Arabia. From 38,245 mosquitoes collected at 3 locations, 16 isolations of Sindbis virus were made: 13 from Culex univittatus and one each from Cx tritaeniorhynchus, Cx pipiens complex, and Culex spp. These isolations represent the first records of a mosquito-borne virus from the Gulf of Arabia and implicate Cx univittatus as the principal vector. A potential risk of human diseases exists due to Sindbis virus in Saudi Arabia.

Association of a Sindbis-like virus with Ockelbo disease in Sweden

An alphavirus isolated from Culiseta mosquitoes has been associated with Ockelbo disease, an exanthema arthralgia syndrome occurring in Sweden. The isolate was made from mosquitoes collected in Edsbyn (central Sweden), an area with considerable Ockelbo disease morbidity. This isolate proved to be indistinguishable from Sindbis virus by complement-fixation and hemagglutination-inhibition tests, and was antigenically related to Sindbis in plaque reduction neutralization tests. Patients with Ockelbo disease developed neutralizing antibodies to the virus in their convalescent sera, suggesting that it is the etiologic agent of the disease.

Evaluation of immunoadsorbent electron microscopic techniques for detection of Sindbis virus

Two immunosorbent electron microscopic techniques (ISEM), the protein A coated grid technique (PA-CGT) and the antibody coated grid technique (AB-CGT) were applied and evaluated for the detection of Sindbis virus from infected tissue culture fluids. At optimal conditions, the efficiency of trapping the virions was only about 1.5 higher with the PA-CGT as compared to the AB-CGT, but the PA-CGT was less dependent on the antiserum dilution used in the test. Both methods were suitable for quantitation experiments, since the number of virions trapped was proportional to the virus concentration. The influence of virus incubation time and temperatures, staining solutions, buffers and washing procedures on the trapping efficiency and specificity was further studied with the PA-CGT. Maximal trapping on coated grids was obtained after 3 h incubation of the virus. At room temperature, less debris was found on the grids, as compared to 37 degrees C, and the numbers of virions counted were only slightly lower. The optimal staining solution was alcohol uranyl acetate. The specificity of the PA-CGT was dependent on washing steps with phosphate buffered saline containing bovine serum albumin. With the standard procedure, at room temperature around 3 X 10(7) virions/ml (1 X 10(6) PFU/ml) were specifically detected in about 1.5 h.

Properties of Sindbis virus variants from infected Culex tarsalis mosquitoes

Plaque-purified Sindbis virus was passed three times in Culex tarsalis mosquitoes and progeny viruses were isolated by plaque purification on a cloned line of Aedes albopictus cells. Nine of ten clones examined differed from wild-type (wt) virus with respect to their plaque morphology characteristics in chick embryo fibroblast (CEF) and/or A. albopictus cells. Seven clones were temperature-sensitive and failed to replicate or synthesize viral RNA in CEF cells at 41 degrees C. At 35 degrees C in CEF cells the majority of isolates synthesized less viral RNA than wt virus. In contrast, all cloned isolates synthesized viral RNA more rapidly than wild-type virus in A. albopictus cells.

Effect of alphavirus infection on mouse embryos

Seven strains and mutants of the alphaviruses, Semliki Forest virus and Sindbis virus, differed in their lethality for mouse embryos and their mothers. The A7 strain and the neurovirulence mutant M103 of Semliki Forest virus were selected for detailed comparison. A7 produced 100% lethality of mouse embryos but was avirulent for their mothers. M103 did not kill embryos or their mothers but did induce postnatal immunity. This immunity could be induced in utero or by suckling to an immune mother. Infectious virus could be recovered from the brain, blood, and embryos of mice infected with A7. Mice infected with M103 developed a viremia of similar titer, but virus could not be recovered from brain or embryos. Electron microscopy showed multiplying virus in trophoblast and fetal tissue after infection with A7, but no virus could be detected in such tissue after infection with M103. Cultures of ectoplacental cone trophoblast cells incubated in the presence of A7 or M103 showed multiplying A7 in the giant cells, but no M103. It is concluded that A7 can traverse both the blood-brain barrier and the placenta, whereas M103 can traverse neither.