Duck Embryo Cell Research Articles

DETERMINATION OF VIRULICIDAL PROPERTIES OF EXPERIMENTAL SUKHODEZ DISINFECTANT

The paper considers the determination of the effectiveness of the virucidal concentration of the new powdered disinfectant «Sukhodez» in relation to DNA-containing and RNA-containing viruses, namely avian smallpox viruses and duck hepatitis.
 The research was conducted in the laboratory of virology of the Department of Pat anatomy, Virology and Poultry Diseases. To determine the effectiveness of virucidal concentrations of the tool against smallpox virus - DNA-containing, cultured on the chorionic-allantoic membrane in 10-12-day-old chicken embryos and hepatitis virus ducklings - RNA-containing, used a suspension of virus-containing material, which virus on primary cultures of duck embryo cells.
 The aim of the work was to investigate a new powdered disinfectant «Sukhodez», namely its virucidal properties.
 The study was conducted in two stages. The first determined the effect of the drug on RNA-containing virus (Avihepatovirus A), and the second stage of research on DNA-containing virus (Fowlox virus).
 Thus, at the first stage of the research, the effect of «Sukhodez» disinfectant on duckling hepatitis virus was determined at a dose of 25, 50, 75 and 100 g of the product per m2 with an exposure of 15, 30 and 60 minutes and the control was treated with sterile water. Thus, at a dosage of 25 g / m2, the product shows a disinfectant ability of 46.3% in 15 minutes, and at an exposure of 30 minutes. completely inactivates the virus; also studies have shown that at a dosage of 75 and 100 g./m2 at an exposure of 15 minutes complete inactivation of the virus took place on the washes.
 In the second stage of the study, the effect of the virucidal action of «Sukhodez» on the DNA-containing avian smallpox virus, which was cultured on the chorionic allantoic membrane of 10-12-day-old chicken embryos, was determined. During the study, it was found that at a concentration of 50 g / m2 disinfectant «Sukhodez» after 15 minutes inactivated the virus by 98.3%. However, after 30 minutes, the effectiveness of the disinfectant increased to 100%. When treating surfaces at the rate of 75 and 100 g / m2 of the tool «Sukhodez» after 15 minutes there was a complete inactivation of the virus. not found.
 According to our research on the virucidal action of the disinfectant, it was found that the experimental disinfectant «Sukhodez» has virucidal properties to RNA-containing and DNA-containing viruses at a rate of 50/75 g / m2 area.

Cytotoxicity and immunolocalization of fumonisin B1 in DEC99 and BALB/C 3T3 cell lines

Fumonisins are widespread mycotoxins, produced by several species of Fusarium moulds that contaminate mainly crops, and food and feed based on cereals. These metabolites represent a significant health treat for humans and animals because of their toxic and carcinogenic effects. The present study aims to ascertain the cytotoxic effects of FB1 on permanent lines and its subcellular localization. In the present study, the cytotoxic effect of fumonisin B1 (FB1) on DEC99 (duck embryo cells) and BALB/c 3T3 (mouse embryo fibroblasts) cell lines was assessed by Neutral Red Uptake (NRU) test and standard Pappenheim and fluorescent AO/PI double staining. Intracellular distribution of FB1 in DEC99 cells was examined by immunofluorescence and immunoelectron microscopy methods. The results from the NRU test indicated that DEC99 cells are more sensitive to the toxic effect of FB1 than BALB/c 3T3 cells. AO/PI double staining revealed morphological features of apoptosis of cells treated with 300 µg FB1/ml. The immunofluorescent and immunogold labeling of FB1 revealed the localization of the micotoxin in the cytoplasm and the nucleus of the cells. The presented results clearly indicate that the cell line DEC99 is a useful model system for studies on the cytotoxic effects of fumonisins.

African Green Monkey Embryonic Stem Cell - a Better Host of Rabies Vaccine

<p>Rabies, an invariably fatal viral disease is transmitted to humans through animal bites, most commonly dogs. The disease is preventable through timely pre-and post-exposure vaccination. However, once the disease occurs, death is inevitable. More than 1.4 billion people are at potential risk of rabies infection in the South-East Asia (SEA) Region, each year around 24 000 people die in the SEA Region due to rabies which accounts for approximately 45% due to rabies worldwide. Vaccines against rabies virus are currently produced in vero cells, chick embryo, duck embryo and human diploid cell lines which are not meeting the demand for rabies vaccines increasing every year. This review portrays the potential and importance of embryonic stem cells as promising host for the production of rabies vaccines. The advantages of using stem cells and its characters have been reviewed with significant references.</p>

Novel Models of Avian Leucosis Virus-induced CarcinogenesisNovel Models of Avian Leucosis Virus-induced Carcinogenesis

The LSCC-SF-MC29 cell culture model system was further characterized by studies on the provirus content of the cells, the host range and the subgroup specificity of the produced virus. The transforming potential of the Mc29 virus was evaluated by the focus-forming and colony-forming assays on primary cell cultures and continuous cell lines of avian and mammalian origin. The in ovo effects of the myelocytomatosis virus Mc29 on 15I line White Leghorn chicken embryos were studied by routine histopathological methods. Six avian leucosis virus-specific proviral sequences were detected by PCR analysis in the genome of LSCC-SF-MC29 cells. The presence of a Mc29 provirus-specific sequence located in the gag-myc region was confirmed. Using primers designed to differentiate ALV subgroups, amplification product was obtained with subgroup B/D-specific PCR primers. As it was expected, the subgroup E-specific PCR primers amplified the endogenous ALV sequences. In vitro studies on the host range of Mc29 virus showed that the primary cultures of chicken and hamster cells and a continuous hamster cell line were susceptible, while the cultures of primary quail cells and of a permanent line of duck embryo cells were resistant to the transforming effect of the virus. In ovo, the inoculated Mc29 virus induced hyperplasic and preneoplastic lesions in the embryonal liver and pancreas and myxomas of the neck.

A comparative study on the safety and immunogenicity of purified duck embryo cell vaccine (PDEV, Vaxirab) with purified chick embryo cell vaccine (PCEC, Rabipur) and purifed vero cell rabies vaccine (PVRV, Verorab)

Rabies is a fatal but preventable disease. Cell culture vaccines (CCV) and purified duck embryo vaccines (PDEV) are currently recommended by WHO for post-exposure prophylaxis. In India, a PDEV (Vaxirab) is being manufactured and is in use since 2003. In the present study, we have evaluated the safety, immunogenicity and tolerance of this vaccine with two other WHO approved CCVs, viz., purified chick embryo cell vaccine (PCEC, Rabipur) and purified vero cell rabies vaccine (PVRV, Veroroab). This study was an open label, randomized phase IV comparative clinical trial. A total of 152 people bitten by dogs and other animals were recruited from 4 different centres from India. They were randomly assigned to receive one of the vaccines by Essen intramuscular regimen (52 subjects received Vaxirab and 50 each Rabipur and Verorab) and rabies immunoglobulin was also administered in all category III exposures. Their blood samples were collected on day 0 (prior to vaccination), 14, 28, 90 and 180. Side effects if any were monitored. The rabies neutralizing antibody titers in their blood samples were estimated by the rapid fluorescent focus inhibition test (RFFIT). Subjects in all three groups had neutralizing antibody titers by day 14 (>0.5 IU/mL) and geometric mean titers (GMT) observed for different vaccines on all days tested did not vary significantly ( p > 0.5). Side effects observed were minimal and did not vary significantly among the groups. The results of the present study indicate that PDEV (Vaxirab) is as safe, tolerable and immunogenic as both PCEC (Rabipur) and PVRV (Verorab). Thus this vaccine can be a good alternative to WHO approved CCVs for rabies post-exposure prophylaxis.

Elimination of human rabies in a canine endemic province in Thailand: five-year programme.

A five-year project to prevent human deaths from rabies in Phetchabun Province, Thailand involved increasing accessibility of post-exposure treatment with the Thai Red Cross intradermal (2-2-2-0-1-1) regimen for humans exposed to potentially and confirmed rabid animals; intensifying documentation of post-exposure treatment; increasing educational awareness through advocacy in provincial schools, television programmes, and newspapers; reducing canine rabies by monitoring the dog population and implementing vaccination and sterilization programmes; increasing the cooperation between the Ministries of Public Health, Agriculture, and Education on a provincial level; and assessing the impact of the programme through intensified follow-up of patients exposed to suspected and laboratory-confirmed rabid animals. Between 1996 and 2001, 10350 patients received post-exposure treatment; 7227 of these received the Thai Red Cross intradermal regimen. Fewer than 3% of exposed patients received rabies immunoglobulin. Seventy-three percent of all patients presented with WHO category III exposures. In a retrospective study, 188 patients exposed to laboratory-confirmed rabid animals were followed to determine their health status. Of these patients, 20 received the intramuscular Essen regimen and 168 the Thai Red Cross intradermal regimen (148 received 0.1 ml purified chick embryo cell rabies vaccine, 10 received 0.1 ml purified vero cell rabies vaccine, and 10 received 0.2 ml purified duck embryo cell rabies vaccine). All patients were alive one year after exposure. Two human deaths occurred in the first two years of the programme - neither patient had received vaccine or rabies immunoglobulin after exposure. No deaths occurred during the last three years of the programme, which indicated that the programme was successful.

Economic issues in postexposure rabies treatment.

Rabies remains a worldwide public health problem even though means to control this disease are known. Logistic problems and cultural barriers for effective dog control in many countries and the high cost of human postexposure treatment, account for much of the remaining worldwide human toll. Efforts to make vaccines, with effective and safe tissue or avian culture products and immune globulin, more affordable have been only marginally successful. Second generation rabies vaccines (purified Vero-, chick and duck embryo cell products) are effective, safe and less expensive than human diploid cell rabies vaccine. Reduced dose intradermal postexposure vaccination works, is affordable, and has helped abolish the use of dangerous and poorly immunogenic brain tissue-derived vaccines in Thailand, the Philippines, and Sri Lanka. The use of purified equine rabies immune globulin has been found to be safe and cost-effective. It is, unfortunately, in short supply worldwide. Preexposure rabies vaccination for travelers to endemic regions is recommended and should be administered by the intramuscular route whenever possible.

Heterologous Gene Expression in Avian Cells: Potential as a Producer of Recombinant Proteins

We have explored the possibility of using avian cells for the expression of human proteins. We found that various avian cells including quail fibrosarcoma cells (QF), duck embryo cells (DE) and primary chicken embryo fibroblasts (CE) could efficiently be transfected with DNA by calcium phosphate coprecipitation, and that promoters which are transcriptionally active in mammalian cells also functioned well in these avian cells. Among the promoters we tested, the major immediate early promoter of human cytomegalovirus drove the highest level of chloramphenicol acetyl transferase (CAT) expression, outperforming the SV40 early promoter and the RSV LTR. Using the bacterial CAT gene as a reporter, we found that levels of CAT activity were higher in QF and DE cells than in mammalian cells such as CHO, HeLa, Vero and 293T cells. We further cloned a sequence encoding human erythropoietin (EPO) and compared its expression in QF and mammalian cells. Consistent with the CAT data, in transient transfection assays, QF cells produced higher levels of EPO than the mammalian cell lines tested. QF cells which can be passaged permanently were stably transfected with an EPO expression vector. The subcloned QF line was able to produce up to 1,700 U/ml EPO from 3 × 10⁶ cells in 72 h. Purified QF-produced EPO showed a broad but discrete protein band, ranging from 33 to 41 kD and was as biologically active as CHO-produced EPO. Although a number of factors still remain to be optimized, our results demonstrate the potential of avian cells such as QF as producers of heterologous proteins.

Identification of Duck Plague Virus by Polymerase Chain Reaction

A polymerase chain reaction (PCR) assay was developed for detecting duck plague virus. A 765-bp EcoRI fragment cloned from the genome of the duck plague vaccine (DP-VAC) virus was sequenced for PCR primer development. The fragment sequence was found by GenBank alignment searches to be similar to the 3' ends of an undefined open reading frame and the gene for DNA polymerase protein in other herpesviruses. Three of four primers sets were found to be specific for the DP-VAC virus and 100% (7/7) of field isolates but did not amplify DNA from inclusion body disease of cranes virus. The specificity of one primer set was tested with genome templates from other avian herpesviruses, including those from a golden eagle, bald eagle, great horned owl, snowy owl, peregrine falcon, prairie falcon, pigeon, psittacine, and chicken (infectious laryngotracheitis), but amplicons were not produced. Hence, this PCR test is highly specific for duck plague virus DNA. Two primer sets were able to detect 1 fg of DNA from the duck plague vaccine strain, equivalent to five genome copies. In addition, the ratio of tissue culture infectious doses to genome copies of duck plague vaccine virus from infected duck embryo cells was determined to be 1:100, making the PCR assay 20 times more sensitive than tissue culture for detecting duck plague virus. The speed, sensitivity, and specificity of this PCR provide a greatly improved diagnostic and research tool for studying the epizootiology of duck plague.

A Monoclonal Antibody to Inclusion Body Disease of Cranes Virus Enabling Specific Immunohistochemistry and Competitive ELISA

Inclusion body disease of cranes (IBDC) herpesvirus kills some infected cranes and persists in convalescent animals. To enable further study and rapid identification of carrier animals, we developed a monoclonal antibody (MAb) to IBDC virus and used it in immunohistochemistry and a competitive enzyme-linked immunosorbent assay (ELISA). We used conventional techniques to make murine MAbs directed against IBDC virus purified from infected duck embryo cells. Hybridomas reacting in an ELISA with IBDC virus but not uninfected duck embryo cells were characterized by radioimmunoprecipitation, in situ immunohistochemistry, and competitive ELISA with neutralizing and nonneutralizing crane sera. MAb 2C11 immunoprecipitated 59-, 61-, and 110-kD proteins from IBDC virus-infected but not uninfected cells and stained glutaraldehyde-fixed IBDC virus plaques but not surrounding uninfected duck embryo cells in vitro. Antibody 2C11 did not react with duck embryo cells infected with falcon herpesvirus, psittacine herpesvirus, infectious laryngotracheitis, pigeon herpesvirus, or duck plague virus. A competitive ELISA using antibody 2C11 identified most sera that were positive in the neutralization test. This antibody will be useful in further characterizing IBDC virus, its pathogenesis, and its natural history.

Progress and achievement of rabies control in Thailand

The breakthrough in production of highly efficacious human and animal rabies vaccines has led to successful rabies control in developed countries, but rabies is still a major health problem in many developing countries. In Thailand, the new cell culture vaccines—purified chick embryo cell (PCEC), purified Vero cell (PVRV), purified duck embryo (PDEV) and human diploid cell (HDCV) are available, and since 1993 have completely replaced the nervous tissue vaccines. The impact of these cell culture vaccines has been considerable, with the number of human rabies deaths decreasing from 200–300 in the early 1980s to 74 in 1995. Rabies prevention has also focused on the vaccination of dogs, and since 1992, the year the Rabies Prevention Act was announced, every owned dog has to he vaccinated at 2–4 months of age annually thereafter. However, only about 20% of dogs have been vaccinated. In 1995, the Ministry of Agriculture and Cooperation collaborated with the Ministry of Public Health to set up a target of no human rabies deaths in 1996, and a rabies-free Thailand by the year 2000. An extensive educational campaign is underway.

Conventional virus detection in cell substrates for the production of biopharmaceuticals

Cocultivation of SIPC-2 myeloma cells with clone A31, BALB/3T3 cells results in the continuous production of a C-type virus by the A31 cells that has been designated S/A-1. S/A-1 virus possessed the essential properties of a murine retrovirus, including a buoyant density of 1.16 g/cm3, C-type morphology, high molecular weight (70 S) RNA, and an RNA-dependent DNA polymerase. After cloning by three endpoint dilution passages in A31, and SIRC cells, the virus was shown to possess ecotropic as well as xenotropic activity. For example, the S/A-1 virus producibility infected mouse cells, including BALB/3T3, NIH/3T3, SC-1, 3T3 FL, and F1 cells as well as non-mouse cells, including normal rat kidney, rabbit corneal (SIRC), Chinese hamster peritoneal, mink lung, Pekin duck embryo, human rhabdomyosarcoma, and guinea pig embryo cells. The S/A-1 virus infected A31, cells do not induce XC-syncytia and the virus does not induce foci in mink lung cells. Thus, the data suggest that it is an amphotropic virus whose ecotropism is different (i.e., NB-tropic) from the previously reported amphotropic viruses (i.e., N-tropic). In addition, S/A-1 virus is different from the mink cell focus-inducing (MCF) viruses (J. W. Hartley, N. K. Wolford, L. J. Old, and W. P. Rowe 1977, Proc. Nat. Acad. Sci. USA74, 789–792) in terms of its lack of focus-inducing activity on mink lung cells, B-tropism, and ability to replicate in human rhabdomyosarcoma and F1 mouse cells. The structural proteins of cloned S/A-1 virus were compared to those of 1504-A virus, a previously described amphotropic virus isolated from feral mice (J. W. Hartley and W. P. Rowe 1976, J. Virol.19 19–26; S. Rasheed, M. B. Gardner, and E. Chan 1976, J. Virol.19, 13–18), by electrophoresis on a linear 7–20% acrylamide slab gel and staining with Coomassie blue. S/A-1 differed from 1504-A in terms of (a) the mobility of a protein with a molecular weight of approximately 12,000 daltons (pl5) and (b) the fact that it has a “double” p30.

No Enhanced Influenza Virus Resistance of Murine and Avian Cells Expressing Cloned Duck Mx Protein

We used polymerase chain reaction techniques to isolate a highly conserved genomic fragment of the Mx gene of a wild duck. This probe recognized the transcripts of two distinct Mx alleles of virus-infected duck embryo cells, which we cloned and sequenced. Duck Mx mRNA was not detectable in uninduced cells, but it accumulated to a high level after infection with Newcastle disease virus or after treatment of cultured duck embryo cells with double-stranded RNA. Duck Mx protein exhibited the characteristic structural features of interferon-induced mammalian Mx proteins, including GTP-binding and leucine zipper motifs. Western blot analysis revealed multiple forms of duck Mx protein with molecular masses between 72 to 82 kDa. In induced cluck embryo cells as well as in murine or avian cells permanently transfected with cloned duck Mx cDNAs, duck Mx protein accumulated predominantly in the cell nucleus. Its immunostaining pattern differed markedly from that of the nuclear mouse and rat Mx1 proteins. A significant portion of duck Mx protein was also found in the cytoplasm where it formed large granules. Duck Mx proteins failed to render permanently transfected mouse or chick cells resistant to different strains of influenza virus. This unexpected result suggests that influenza virus resistance of ducks is not dependent on interferon-induced Mx proteins.

Use of muscovy duck embryo fibroblasts for the isolation of viruses from wild birds

Techniques are described for the preparation, cryopreservation, and inoculation of Muscovy duck embryo cell cultures. The procedure yields a susceptible reproducible cell culture system for the isolation and cultivation of viruses from wild birds.

Anti-rabies treatment of dog-bite victims in Lagos, Nigeria: trial of suckling mouse brain and fetal bovine kidney cell rabies vaccines

Human rabies is common in Nigeria, a country known for rabies endemicity. Yet the supply of anti-rabies vaccines for human use (adult sheep brain origin, produced locally, and duck embryo and human diploid cell vaccines, imported) is grossly inadequate. This study involved controlled treatment of dog-bite victims with suckling mouse brain (SMBV) or fetal bovine kidney (FBKV) rabies vaccines in an effort to determine which type to recommend for production and use in Nigeria. Dog-bite victims treated were aged three to 74 years, with about equal numbers of males and females. Of the 136 patients, 116 (85.3%) completed at least the primo-series of vaccinations, and all have survived without any evidence of clinical rabies. Recipients of the SMBV showed local and generalized reactions in 11.1% and 2.5% of the cases, respectively. Recipients of the FBKV administered subcutaneously showed local and generalized reactions, in 12.5% and 9.4% of cases, respectively. There were no side effects attributable to the vaccine among patients who received the FBKV intramuscularly. By day 7, 26.7% of SMBV recipients and 28.6% of FBKV recipients showed antibody response, with titres of at least one Equivalent Unit ml −1. These percentages increased to 95.1 and 81.1, respectively, by day 14, and by day 20 (for SMBV recipients) or day 30 (FBKV recipients) the response was 100%. Titres dropped by day 90, but in no case to below 1 EU ml −1. We have concluded that both vaccines are equally efficacious and well tolerated. In view of the simple technology required, and the resultant lower cost, the SMBV is being recommended for production and use in Nigeria.

Antigenic relationships of flaviviruses with undetermined arthropod-borne status.

In contrast to most of the arthropod-borne flaviviruses, the flaviviruses with undetermined arthropod-borne status are probably disseminated only by direct contact with excreta (saliva, urine, feces, etc.); however, as yet undescribed arthropod transmission cycles may be found for some of them. Twenty-two of these flaviviruses, including prototype and recently isolated strains, were compared. Biologic properties were defined by infectivity titrations in suckling mice and Vero, LLC-MK2, and primary Pekin duck embryo cells, and antigenic relationships were defined by complement-fixation and plaque reduction neutralization tests. An antigenic classification scheme is proposed. Antigenic and biologic properties delimit two large clusters. The first, comprising a single antigenic complex, includes those which have yet to be isolated from arthropods, but are likely to be so (Israel turkey meningoencephalitis, Koutango, Negishi and Aroa viruses). The second, encompassing five antigenic complexes, is comprised of viruses which have been isolated exclusively from rodents or bats (Saboya, Carey Island, Dakar bat, Sokuluk, Bukalasa bat, Entebbe bat, Phnom Penh bat, Modoc, Sal Vieja, Jutiapa, San Perlita, Cowbone Ridge, Rio Bravo, Apoi, Tamana bat and Montana Myotis leucoencephalitis viruses) but includes three viruses (Saboya, Sokuluk and Entebbe bat viruses) which may be arthropod-borne, as indicated by replication in mosquito cells in vitro.

The Effect of Incubation Temperature on the Propagation of Duck Adenovirus (Virus 127-Like) in Duck and Chicken Cells

Duck adenovirus (Cornell strain) was propagated in duck and chicken embryo cells at 37.5 C and at 40 C. In duck cells, virus levels, as indicated by HA titers, peaked earlier at 40 C than at 37.5 C. High titers were eventually observed in duck cells at both temperatures. In chicken embryo fibroblasts, no titers were observed at 37.5 C, whereas low titers were observed at 40 C. Evidence of virus propagation was not detected in chicken embryo liver and kidney cells.

Transovarial transmission of St. Louis encephalitis virus by Culex pipiens complex mosquitoes.

Experiments were conducted to determine whether transovarial transmission (TOT) of St. Louis encephalitis (SLE) virus occurs in Culex pipiens complex mosquitoes, the principal vectors of SLE virus in the central-eastern United States. In 1978, field-collected mosquitoes from Memphis, Tennessee, and McLeansboro, Illinois, were used; during 1979, colonized mosquitoes from Chicago, Illinois, and Memphis, Tennessee, were used. Mosquitoes were infected by feeding on viremic chicks inoculated with an SLE virus strain isolated from Cx. pipiens complex mosquitoes collected from Memphis, Tennessee, in 1976. During the 1979 experiments, progeny larval and adult mosquitoes were held at two temperatures, 18 and 25 degrees C. Progeny were tested for virus by plaque assay in duck embryo cell cultures and by inoculation of Aedes albopictus C6/36 cells and examination by immunofluorescence. In 1978, most of the progeny tested were from the first ovarian cycle, and a single occurrence of TOT was documented. In 1979, a single TOT occurred from 46,856 first ovarian cycle progeny, whereas 7 of 9,234 progeny of the second ovarian cycle were infected. The rate of TOT was higher for progeny of Memphis than Chicago mosquitoes, and for mosquitoes held at 18 degrees C than at 25 degrees C; however, these differences were not statistically significant. Four positive pools were females, and three were fed on chicks for transmission attempts. The positive Chicago mosquito pool failed to transmit, but both Memphis pools successfully transmitted virus. The overall rates of TOT of SLE virus in progeny of the first and second ovarian cycle were, respectively, 1/45, 151 and 1/1,460. The significance of these results as they relate to the natural history of SLE virus is discussed.

Geographic variation among St. Louis encephalitis virus strains in the viremic responses of avian hosts.

We studied the capacity of 44 strains of St. Louis encephalitis (SLE) virus to induce viremia in an epidemiologically important wild avian host, the House Sparrow (Passer domesticus). Selected virus strains were also inoculated at varying doses into 3-week-old chicks. Viremic responses were analyzed in terms of the proportion of inoculated nestling and adult birds which became viremic, the mean duration and the mean peak titer of viremia. Infectivity of avian sera was determined by plaque assay in primary duck embryo cell cultures. The susceptibility of the House Sparrow to viremic infection with different SLE virus strains varied markedly. Nestling sparrows 6-10 days of age were generally more susceptible than adult birds. All virus strains isolated during Culex pipiens-borne epidemics in the eastern United States were highly viremogenic [viremia in 80% of birds with a mean duration of greater than or equal to 1.6 days in adults or greater than or equal to 2.7 days in nestlings and a mean peak titer of greater than or equal to 10(3.0) plaque-forming units (PFU)/ml in adults and 10(4.0) PFU/ml in nestlings]. All virus strains isolated from Culex tarsalis in the western United States, strains isolated from rodents in South America. and six of 16 strains isolated from various sources elsewhere in tropical America were partially or fully attenuated. A high degree of concordance was demonstrated between experimental viremia in sparrows, viremia in 3-week-old chicks, and neurovirulence for weanling mice. The epidemilogic significance of these findings is discussed.

Erratum

In “Rabies Vaccine Prepared in Human Cell Cultures: Progress and Perspectives” by Stanley A. Plotkin (May–June 1980), part of a sentence was omitted. The sentence that begins on p. 434, col. 2, line 16 should read “Fenje's vaccine has had limited use in Canada, and other inactivated vaccines have been produced in duck embryo cell culture … ”