Impact of wildfire recurrence on soil properties and organic carbon fractions

The recurrence and severity of wildfire is on the rise due to factors like global warming and human activities. Mediterranean regions are prone to significant wildfire events, which cause extensive damage to ecosystems and soil properties. This study focuses on the municipality of Allande in south-western Asturias (Spain), a region highly affected by recurrent wildfires. In this regard, we sought to examine how the recurrence of such fires influences soil organic carbon fractionation and other soil parameters, such as nitrogen fractionation, pH, and cation exchange capacity. The study involved six sampling plots with between varying fire recurrence levels, from 0 to 4 events between 2005 and 2022. The results revealed some significant effects of wildfires recurrence on soil texture, inorganic elemental composition and CEC, but not on pH and CE. In soil affected by recurrent fires, labile carbon fractions (cold-water extractable & hot-water extractable), and fulvic acid concentrations decreased by up to 36%, 5%, and 45%, respectively in comparison with undisturbed soil. In contrast, humic acid concentration remained stable or increased in soils damaged by fire. Additionally, nitrogen species in soil were observed to decrease significantly in high recurrence scenarios, especially nitrate. On the basis of our findings, we conclude that wildfires impact the distinct fractions of organic carbon and nitrogen in soils and that this effect is aggravated by increasing recurrence.

Potentiation of the humoral immune response elicited by a commercial vaccine against bovine respiratory disease by Enterococcus faecalis CECT7121

Vaccination against pathogens involved in bovine respiratory disease (BRD) is a useful tool to reduce the risk of this disease however, it has been observed that the commercially available vaccines only partially prevent the infections caused by Pasteurella multocida and Mannheimia haemolytica. Therefore, it is recommended to search for new adjuvant strategies to minimise the economic impact of this respiratory syndrome. A possibility to improve the conventional vaccine response is to modulate the immune system with probiotics, since there is accumulating evidence that certain immunomodulatory strains administered around the time of vaccination can potentiate the immune response. Considering veterinary vaccines are frequently tested in murine models, we have developed an immunisation schedule in BALB/c mice that allows us to study the immune response elicited by BRD vaccine. In order to evaluate a potential strategy to enhance vaccine efficacy, the adjuvant effect of Enterococcus faecalis CECT7121 on the murine specific humoral immune response elicited by a commercial vaccine against BRD was studied. Results indicate that the intragastric administration of E. faecalis CECT7121 was able to induce an increase in the specific antibody titres against the bacterial components of the BRD vaccines (P. multocida and M. haemolytica). The quality of the humoral immune response, in terms of antibody avidity, was also improved. Regarding the cellular immune response, although the BRD vaccination induced a low specific secretion of cytokines in the spleen cell culture supernatants, E. faecalis CECT7121-treated mice showed higher interferon-γ production than immunised control mice. Our results allowed us to conclude that the administration of E. faecalis CECT7121 could be employed as an adjuvant strategy to potentiate humoral immune responses.

Probiotic activity of Enterococcus faecalis CECT7121: effects on mucosal immunity and intestinal epithelial cells

AIMS

To analyse the effect of Enterococcus faecalis CECT7121 on intestinal epithelial cells (IECs) and its effects on the mucosal immune response.

METHODS AND RESULTS

Enterococcus faecalis CECT7121 showed a high adhesion capacity to completely and heterogeneously differentiated human intestinal epithelial cell line (Caco-2 cells). In addition, the contact of this bacterium with Caco-2 cells did not induce inflammatory chemokines (IL-8 and CCL-20). The presence of IgA(+) and IL-6(+) cells in the small intestine, as well as the production of inflammatory cytokines (TNFα, IL-6 and IL-12) in the gut, was determined after intragastric inoculation of Ent. faecalis CECT7121 in BALB/c mice. The administration of Ent. faecalis CECT7121 increased the number of IgA(+) cells in the intestinal lamina propria without modifying the percentage of IL-6(+) cells. No differences were observed in the cytokines measured in the intestinal extracts between probiotic-treated and control mice.

CONCLUSIONS

Enterococcus faecalis CECT7121 stimulates local mucosal immunity and adheres to IECs without inducing inflammatory signals.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results indicate that, apart from its already reported systemic immune activity, Ent. faecalis CECT7121 has a modulatory effect at a local level.

Production of culture filtrates of Sporothrix schenckii in diverse culture media

Mycelial-form Sporothrix schenckii was studied to determine if growth in complex (Sabouraud-dextrose) or defined culture media (minimal medium, Gibco Medium 199 with and without Hepes buffer) with differing initial pH levels would affect expression of antigen components. Cultures were evaluated by continuous monitoring and serial sampling for various parameters. Great variation was seen in the protein and antigenic patterns induced by the different media. The expression of a 55 kDa component accompanied by significant acidification of the culture medium at the beginning of the stationary growth phase was notable in Sabouraud medium. In the chemically defined media, a 90 kDa component was expressed that reacted with sera from patients with sporotrichosis. The pH in these media showed little change during the different growth phases of the fungus. Among the media studied, minimal medium favored the expression of the greatest number of antigenic components. In all of the assays, the stationary growth phase appeared to be optimal for content of antigenic components. Cross reactions were not observed with any of the culture filtrates using sera from patients with other mycoses.

In vitro anti-inflammatory activity of iridoids and triterpenoid compounds isolated from Phillyrea latifolia L

Two iridoids, oleuropeoside and ligustroside, and two triterpenoid compounds, oleanolic acid and ursolic acid, have been isolated from the leaves of Phillyrea latifolia L. (Oleaceae). These compounds were tested for interactions with the cyclooxygenase (COX) and 5-lipoxygenase (5-LOX) pathways of arachidonate metabolism in calcium ionophore-stimulated mouse peritoneal macrophages and human platelets, and for their effect on cell viability. Structure-activity relationships obtained for in vitro screening results were discussed. These compounds are capable of exerting inhibitory actions on enzymes of the arachidonate cascade. All compounds assayed showed a significant effect on prostaglandin E2 (PGE2)-release, with inhibition percentages similar to the reference drug indomethacin (IC50 = 0.95 microM). The IC50 values of the active compounds are: oleuropeoside 47 microM, ligustroside 48.53 microM, oleanolic acid 23.51 microM and ursolic acid 60.91 microM. In the leukotriene C4 (LTC4)-assay, only oleanolic acid showed a significant effect (IC50 = 16.79 microM). We also investigated the action of compounds on thromboxane B2 (TXB2)-release induced by calcium ionophore in human platelets. Of all the tested compounds, only ligustroside (IC50 = 122.63 microM) and ursolic acid (IC50 = 50.21 microM) showed a significant effect, although with less potency than the reference drug ibuprofen (IC50 = 1.27 microM). Thus, our compounds possess an array of potentially beneficial anti-inflammatory properties which may, alongside other constituents, contribute to the claimed therapeutic properties of the plant from which they are derived.

Simultaneous spectrofluorimetric determination of (acetyl)salicylic acid, codeine and pyridoxine in pharmaceutical preparations using partial least-squares multivariate calibration

A partial least-squares calibration (PLS) method for the simultaneous spectrofluorimetric determination of salicylic acid (SA), codeine (CO) and pyridoxine (PY) is proposed. The determination of SA, CO, and PY has been carried out in mixtures of up to three components by recording the emission fluorescence spectra between 300 and 500 nm (lambda(exc) = 220 nm). Due to the fact of the strong spectral overlap among the excitation and also among the emission spectra of these compounds, a previous separation should be carried out in order to determine them by conventional spectrofluorimetric methodologies. Here, a full-spectrum multivariate calibration PLS method is developed. The experimental calibration matrix was constructed with 14 samples. The concentration ranges considered were 0.1-2.0 (SA), 0.25-3.0 (CO) and 0.10-2.0 (PY) mg x l(-1). The optimum number of factors was selected by using the cross-validation method. The method also allows the simultaneous determination of acetylsalicylic acid (ASA), CO and PY by previous alkaline hydrolysis of ASA to SA. To check the accuracy of the proposed method, it was applied to the determination of these compounds in synthetic mixtures and in pharmaceuticals.

Evaluation of standard reagents for radial-immunodiffusion assays. In vitro control of rabies vaccines

The RID assay is one of the in vitro methods used for in-process control in the production of rabies vaccines for veterinary use. It has been shown to be very useful for determining antigen concentration in the final bulk product. The work presented in this paper, including the production and standardization of candidate standard reagents for use in the Radial Immunodiffusion Assay (RID) was carried out at the Pan American Institute for Food Protection and Zoonoses (INPPAZ/PAHO/WHO). The study was completed with the cooperation of the Faculty of Veterinary Sciences, National University of La Plata (NULP), Argentina, where the validation of the proposed standards and the quality control of samples from 28 different batches of rabies vaccines produced with Pasteur strain rabies virus (PV) in BHK cells were performed. The activity of the vaccines was determined by in vivo (NIH) and in vitro (RID)assays. The results of the candidate reagents for the reagent standardization tests showed stability, sensitivity and reproducibility. The Relative Potency the 1.2 between the problem vaccines and the reference vaccine was estimated by variance and regression analysis. The results of our validation study show that the INPPAZ (PAHO/WHO) is capable of producing and distributing the above-mentioned standard reagents, as well as of providing support for the incorporation of the RID technique (sensitive, rapid and inexpensive) to the laboratories that manufacture rabies vaccines in Latin America and the Caribbean.

A rapid and selective solid-phase UV spectrophotometric method for determination of ascorbic acid in pharmaceutical preparations and urine

Ascorbic acid was determined by a solid-phase UV spectrophotometry technique through the sorption of this on a dextran-type anion-exchange resin, Sephadex QAE A-25 and posterior direct measurement of its absorbance on the resin at 267 and 400 nm, packed in a 1-mm cell. The calibration graph was linear over the range 0.3-5.0 microg ml(-1). The sensitivity obtained is more than 50 times higher than that of the corresponding solution method. The detection limit was 0.05 microg ml(-1) and the relative standard deviation 0.74% (n = 10). This method is very rapid and highly selective for determining ascorbic acid in the presence of other species absorbing in the ultraviolet region and which are normally encountered with it. The one-step method proposed was successfully applied in the determination of ascorbic acid in pharmaceutical preparations and urine and the results were of comparable accuracy as indicated by a statistical analysis of the data, using both t- and F-tests.

Hyperimmune antirabies sera titration by standard mouse neutralization and counterimmunoelectrophoresis tests, comparing results of different laboratories

To determine the rabies antibody level of twenty-four hyperimmune equine sera, Standard Mouse Neutralization (SMN) and Couterimmunoelectrophoresis (CIE) tests were carried out, both at the Instituto Butantan (IB) and Instituto Panamericano de Proteccíon de Alimentos y Zoonosis (INPPAZ). Statistical analysis has shown a correlation (r) of 0.9317 between the SMN and CIE performed at the IB, while at the INPPAZ it scored 0.974. Comparison of CIE data of both laboratories yielded a correlation of 0.845. The CIE technique has shown to be a sensitive and efficient as the SMN in titrating antirabies hyperimmune equine sera. Based on CIE results, a simple, rapid and inexpensive technique, titers of sera antibody can be rellably estimated in SMN test.

Production of monoclonal antibodies to human immunodeficiency virus type-2

The ROD strain of the human immunodeficiency virus type 2 (HIV-2) was used to produce monoclonal antibodies. Virus grown in CEM cells was partially purified by ultracentrifugation and solubilized in a buffer containing Triton X-100. BALB/c mice were inoculated intraperitoneally with 50 micrograms of solubilized virus preparations mixed 1:1 with complete Freund's adjuvant. Animals were boosted on day 28 and sacrificed on day 31. Spleen cells from the immunized animals were fused with SP20/Ag 14 myeloma cells and cultured in HAT medium. Following selection of the hybrids of interest by an HIV-2 ELISA procedure, hybridomas were cloned twice by limiting dilution. Six clones were found to produce antibodies that reacted with HIV-2 antigens as judged by ELISA. These antibodies were concentrated by ammonium sulfate precipitation, and analyzed by the Western blot procedure. Monoclonal antibodies specifically reactive to an HIV protein of 68 KD were obtained. These antibodies did not react with an HIV-2 band of 55 KD. These data showed that the monoclonal antibodies recognized the carboxy terminal region (the RNAse H domain) of the HIV-2 retrotranscriptase enzyme.

Evaluación de la calidad de los reactivos que se utilizan en la tecnica de contrainmunoelectroforesis para la determinación de anticuerpos antirrábicos

En este estudio se comprobó que el Instituto Butantan produce antígenos y sueros indicadores que se pueden utilizar con éxito en la prueba de contrainmunoelectroforesis para titular anticuerpos antirrábicos en personas inmunizadas. No se pudieron demostrar diferencias estadísticamente significativas entre los resultados de las pruebas de estandarización realizadas en el Instituto Butantan y las pruebas de control de referencia llevadas a cabo en el Centro Panamericano de Zoonosis. Se propone que el Instituto Butantan produzca y distribuya a nivel nacional los reactivos para que los laboratorios de diagnóstico apliquen la técnica de contrainmunoelectroforesis para la determinación de anticuerpos antirrábicos.

[Quality of the reagents used in counterimmunoelectrophoresis technique for the determination of antirabies antibodies]

This study demonstrated that the antigens and indicator sera produced by the Butantan Institute may be employed with success in the counterimmunoelectrophoresis technique for the titration of rabies antibodies in sera from immunized individuals. No statistically significant differences were demonstrated between the results obtained in the standardization tests carried out at the Butantan Institute and the reference control tests performed at the Pan American Zoonoses Center. It is proposed that the Butantan Institute be in charge of the production and distribution of these reagents at the national level.

[Antirabies vaccine from the brain of the suckling rat: antigen composition and immunogenic capacity]

Suckling mouse brain (SMB) rabies vaccine is the preparation most widely used in the countries of Latin American and the Caribbean. This vaccine, prepared according to the Fuenzalida and Palacios method, consists of three fixed rabies virus strains (CVS, 51, and 91). However, the World Health Organization recommends that rabies vaccines for human use be prepared using only a single strain of this virus. In order to determine whether any one of the antigens of the SMB vaccine could be eliminated from the preparation, the immunogenic capacity of the standard trivalent SMB vaccine was compared with that of experimental bivalent (CVS-51, CVS-91, and 51-91) and monovalent (CVS, 51, and 91) SMB vaccines. The study was conducted using adult and suckling albino mice provided by the laboratory at the Pan American Zoonoses Center, Buenos Aires, Argentina, and different strains of fixed and street rabies virus. The experimental vaccines were prepared using the Fuenzalida-Palacios method. Potency and cross-immunity tests were conducted. The results showed that the trivalent vaccine was the most effective in protecting the mice against both fixed and street rabies virus infections and also in inducing rapid development of neutralizing antibody at high titers.

Production of monoclonal antibodies to Sp2/O-Ag 14 myeloma cells

The hybridoma technology developed by Kohler and Milstein allows the obtention of antibodies of a single specificity (i.e. monoclonal antibodies). This methodology was first introduced in the Immunology Laboratory of the Department of Microbiology at the Medical Sciences Campus (MSC), University of Puerto Rico (UPR) in 1986. The production of monoclonal antibodies to Sp2/O-Ag 14 reported herein describes the procedure used and is of importance because it constitutes the first work on monoclonal antibodies performed at our institution and in Puerto Rico.

Analysis by fluorescence microscopy and flow cytometry of monoclonal antibodies produced against cell surface antigens

The reactivity of seven monoclonal antibodies against the surface antigens of the murine myeloma cell line Sp2/O-Ag 14 was simultaneously analyzed by fluorescence microscopy and flow cytometry. To 1 X 10(6) Sp2/O-Ag 14 cells were added 200 microliters of the monoclonal antibody and the mixture was incubated at 4 degrees C for 30 min. After washing twice with PBS, the Sp2/O-Ag 14 cells were incubated at 4 degrees C for 30 min with a 1:400 dilution of fluoresceinated goat anti-mouse antibodies. Sp2/O-Ag 14 cells were ready for analysis after washing the cells 3 X with PBS. By fluorescence microscopic analysis different patterns of reactivity with monoclonal antibodies were detected. These patterns were identified as: smooth annular, dot-like annular, dot-like patches, diffuse and homogeneous. The observed patterns may represent different cell surface epitopes being recognized by the monoclonal antibodies. Flow cytometry analysis with the EPICS V system showed reactivity of seven monoclonal antibodies with Sp2/O-Ag 14 cell surface epitopes, which ranged from 79 to 90%. Compared to fluorescence microscopy, flow cytometry provides a faster, more sensitive and more accurate quantitative measurement of the reactivity of different monoclonal antibodies against Sp2/O-Ag 14 cell surface antigens.

Serologic and immune responses to rabies virus during different human treatments with tissue culture and suckling mouse brain vaccines

The antibody response to rabies virus was studied in twenty volunteers immunized with different schemes of suckling mouse brain and human diploid cell culture rabies vaccines. Throughout the study period, titers in serum neutralization and indirect fluorescent antibody tests, as well as the class of immunoglobulins with antirabies activity, varied in different individuals with the treatment scheme and the antigenic potency of the vaccine. The results suggest that measurement of the IgG class of antirabies antibodies, and possibly IgA as well, may be a more adequate criterion to assess the immunogenicity of rabies vaccines than the determination of SN titers alone.

Cross protection of mice against different rabies virus isolates

In an attempt to identify "atypical" strains which could account for vaccination failures, 10 street, one intermediate (DR19) and 4 fixed rabies virus isolates from men, cattle, dogs, cats, mongoose and vampire bats in five countries (Argentina, Brazil, Chile, Cuba, and France) were studied by cross-protection tests in mice. For the purpose of this study, any virus that killed more than 20% of the vaccinated mice challenged with that virus was considered "atypical". When the suckling mouse brain rabies vaccine was used, two "atypical" isolates were found: one, from a human case in Chile (91, 125 mouse passages) and the other, from a vampire bat in Brazil (DR19, 22 mouse passages). However, when mice immunized with a cell culture vaccine (PV-BHK) of a higher antigenic value than the brain vaccine, were challenged with those same isolates, mortality was below 20%. The fact that these two isolates killed enough vaccinated mice to be considered "atypical" could be related to antigenic differences between these viruses and those included in the vaccine. However, since this mortality was observed only in the mice immunized with the vaccine with a lower antigenic value, reasons are given why it could be attributed to other biological characteristics of those strains than antigenic differences. Causes for vaccines failures other than immunological differences of rabies virus strains are also analyzed and discussed.

Evaluation of hyperimmune rabies sera by the counterimmunoelectrophoresis test

This study demonstrates that the counterimmunoelectrophoresis test is a rapid and reliable method for the determination of antibody titres in hyperimmune antirabies sera. The application of this method to the selection of human sera for the production of antirabies globulin and for the final standardization of serum batches is discussed.

Rabies neutralizing antibodies determination by the modified counterimmunoelectrophoresis test and the rapid fluorescent focus inhibition test

The correlation between the modified counterimmunoelectrophoresis and the rapid fluorescent focus inhibition tests for detecting rabies virus antibodies in human sera was studied, using as reference the standard mouse neutralization test. Statistical analyses showed good correlation among the three serological tests. There were no statistically significant differences in titers obtained by serum neutralization and rapid fluorescent focus inhibition tests and the estimated titers based on the results of the modified counterimmunoelectrophoresis test.

Pre-exposure rabies immunization of man with suckling mouse brain vaccine

A case series study is reported which included serologic results obtained in 195 persons recruited from personnel and trainees of the Pan American Zoonoses Center in Buenos Aires, Argentina, and workers from other institutions. The individuals were vaccinated with three doses of suckling mouse brain vaccine administered on alternate days, and some of them were given a booster dose 30 or 365 days after the primary immunization. The sizeable percentage of reactors with a high neutralizing antibody response in a short period of time, the small number of persons requiring a booster dose 30 days after the first vaccine dose, the rapid and intense secondary immune response and the absence of serious post-vaccinal reactions justify encouraging the use of this abbreviated prophylactic course of suckling mouse brain vaccine.

Comparison between a modified counterimmunoelectrophoresis test and the indirect fluorescent-antibody test for detection of antibodies to rabies virus in human sera

The correlation between the modified counterimmunoelectrophoresis test and the indirect fluorescent-antibody test for detecting rabies virus antibodies in human sera was studied, using as a reference the standard mouse neutralization test. Higher sensitivity was observed with the counterimmunoelectrophoresis technique than with the indirect fluorescent-antibody method. The counterimmunoelectrophoresis test provides a practical quantitative alternative to the indirect fluorescent-antibody method.

[Immunization of calves with a rabies vaccine from suckling mouse brain]

This paper summarizes the results obtained in a study on the duration of immunity in calves immunized with suckling mouse brain (SMB) rabies vaccine, supplemented with aluminum hydroxide. Rabies circulating antibodies were detected ten days after vaccination in 100% of the 31 vaccinated calves. They began to decrease 90 days after immunization. Of the 15 calves challenged one year postimmunization, 5 (33%) had no detectable antibodies at serum dilution 1:5, but all were protected against the challenge dose virus which killed 75% (3/4) of the non vaccinated controls. The results obtained suggest that SMB rabies vaccine can be used successfully to immunize calves aged from 7 days to 6 months. Since 15 to 20% of the cattle population of a country is less than one-year-old, the protection of this population against rabies with an inactivated vaccine would decrease the number of susceptible animals and facilitate both the vaccination procedures and the movement of animals from rabies-free areas to those where the disease is enzootic.

Determination of serum neutralization antibodies to rabies virus by a modified counterimmunoelectrophoresis test

A modified counterimmunoelectrophoresis (CIE/SN) technique was developed as a diagnostic procedure for the detection of serum-neutralizing antibodies to rabies virus. CIE/SN test results with sera from individuals undergoing postexposure rabies immunization compared favorably with those obtained by the standard mouse neutralization test procedure. Fractionation of selected sera by Sephadex G-200 column chromatography demonstrated that serological activity involved in both procedures was present in the immunoglobulin G-containing fractions of the sera. The mean advantage of the CIE/SN over the standard mouse neutralization test consists in considerably reducing the time required for results, a factor which can be of clinical importance in evaluating antibody levels to rabies virus. In addition, the CIE/SN method is simple to perform and inexpensive.

Persistence and variation of Mangosta street rabies virus antigens during adaptation into mice

A Mangosta street rabies virus strain antigen not shared by the challenge virus standard (CVS) was identified by counterimmunoelectrophoresis. This strain antigen persisted following nine mouse passages of the virus, during which the CVS strain antigen was not acquired. These observations suggest that the antigen composition of the two virus strains is different. Antigenic differences during the course of adaptation of Mangosta virus were also revealed by crossed serum neutralization tests. The findings are discussed in terms of the occurrence of variations in the number and localizaion of antigen sites in the virus and of the possible existence of antigenic competition by non-infective viral antigens in serum neutralization tests for rabies.

[Suckling mouse brain rabies vaccine supplemented with an adjuvant. Its use in cattle]

This paper describes two experiments carried out in cattle immunized with suckling mouse brain rabies vaccine (SMB) 14, supplemented with 2% Al (OH)3 15 or Freund's modified incomplete adjuvant 2, 26. When determining the vaccinal dose, it was observed that the immune response was independent from the doses used (Table 1), all animals survived the challenge 30 days after vaccination, as compared to a mortality rate of 80% in the controls. To determine the duration of immunity, an amount of 5 ml was chosen as vacinal dose. Two years after immunization, both vaccines protected 96% of the cattle against a viral challenge that killed 63% of the non-vaccinated controls (Table 2). Statistically significant differences were observed between the antibody levels elicited by both vaccines. Antibody levels observed with the oil supplemented vaccine were higher than those produced by the A1 (OH)3 vaccine.

Characteristics of 11 rabies virus isolates in mice: titers and relative invasiveness of virus, incubation period of infection, and survival of mice with sequelae

Mice were inoculated intracerebrally or in the footpad with 11 salivary gland suspensions from rabid foxes, skunks, and bobcats. The 11 isolates differed in their ratios of intracerebral titer to footpad titer, a result indicating that the "invasiveness" of different isolates varies markedly. The degree of invasiveness could not be correlated with the species of animal. The inoculation of the less invasive isolates resulted in an appreciable number of permanently paralyzed animals (survivors with sequelae). These animals had high titers of neutralizing antibody in serum but no neutralizing antibody in the brain, a finding suggesting that virus had invaded only the peripheral nervous system or the spinal ganglia. Pathological examination of the paralyzed mice and normal mice confirmed this finding.

Detection of antigenic differences among street and fixed rabies virus strains by the counterimmunoelectrophoresis test

Using the counterimmunoelectrophoresis test, two street rabies virus strains (Mangosta and Apipe) revealed antigens not detected in the standard challenge virus (CVS). No antigenic differences, however, were found between CVS and another fixed rabies virus strain (strain 91) by this method. The results of serum neutralization tests revealed similar antigenic relationships among the rabies virus strains studied. These findings are discussed in terms of their significance to antigenic variations in rabies virus strains.