Frequency of Neospora caninum infections in beef cow-calf operations under extensive management.

The aim of this study was to evaluate the frequencies of Neospora caninum horizontal and vertical transmissions in beef cow-calf operations under three different extensive management systems: group A: 0.75 head per hectare pasturing on natural grass; group B: 1.1 head per hectare on natural grass and improved cultured pastures; and group C: 2 head per hectare on natural grass, improved cultured pasture and whole corn silage. Serum samples from 72 multiparous cows assigned to each beef cow-calf operations were obtained every 3 months during 2 years. A group of 30 replacement heifers from each group were tested similarly since they were 10-21 months old. Twenty four, 20 and 34 calves from groups A, B and C respectively, were bled before colostrum intake and again 6 months later. The samples were analyzed by indirect fluorescence antibody test (IFAT) for detection of total IgG against N. caninum at a serological titre ≥ 200 for multiparous cows and replacement heifers, and a serological titre ≥ 25 for calves. Serum samples from seropositive cows were assessed by ELISA to evaluate the avidity of their specific antibodies. There were no differences in the proportion of seropositive cows from groups A, B and C at the beginning of the trial (p>0.05). Interestingly, the lowest serological titres in seropositive cows from all groups were observed during the first trimester (p<0.05). Although seropositive cows had medium to high avidity antibodies, suggesting chronic infection; seroconversion associated with low antibody avidity was found in 2, 3 and 3 seropositive cows from groups A, B and C. All replacement heifers remained seronegative. No abortions were recorded but 2, 1, and 2 calves from groups A, B and C were seropositive before colostrum intake, respectively. Seropositive calves born from cows having intermediate or high avidity remained with the same serostatus at 6 months of age. Even under varying extensive management conditions, both N. caninum horizontal and vertical transmission methods do occur in beef cow-calf operations.

First finding of genetic and antigenic diversity in 1b-BVDV isolates from Argentina.

Infection with Bovine Viral Diarrhea Viruses (BVDV) in cattle results in a wide range of clinical manifestations, ranging from mild respiratory disease to fetal death and mucosal disease, depending on the virulence of the virus and the immune and reproductive status of the host. In this study 30 Argentinean BVDV isolates were characterized by phylogenetic analysis. The isolates were genotyped based on comparison of the 5' untranslated region (5' UTR) and the E2 gene. In both phylogenetic trees, 76% of the viruses were assigned to BVDV 1b, whereas BVDV 1a, 2a and 2b were also found. Eight of the BVDV 1b isolates were further characterized by cross-neutralization tests using guinea pig antisera and sera from bovines vaccinated with two different commercial vaccines. The results demonstrated the presence of a marked antigenic diversity among Argentinean BVDV isolates and suggest the need to incorporate BVDV 1b isolates in diagnostic strategies.

Single dilution Avidity-Blocking ELISA as an alternative to the Bovine Viral Diarrhea Virus neutralization test.

This study describes the development and validation of a blocking ELISA that measures avidity of BVDV-specific immunoglobulins (Igs) as an alternative to the classic virus neutralization test. The assay comprises a recombinant soluble E2 glycoprotein as target antigen, a neutralizing serum as detector antibody and a washing-step with a chaotropic agent to determine BVDV-specific Igs avidity. Avidity-Blocking ELISA was validated with 100 negative and 87 positive BVDV-neutralization serum samples from either infected or vaccinated bovines (inactivated commercial vaccines). Specificity and sensitivity of the Avidity-Blocking ELISA were 100% and 98.8%, respectively. The assay was standardized to use a single dilution, so that 90 samples can be tested per plate. Results expressed as Avidity Index (AI) correlated with BVDV neutralizing titers (r=0.94). Unlike the virus neutralization test, the Avidity-Blocking ELISA could discriminate between infected and vaccinated animals (DIVA), suggesting that avidity measurement can be a valuable tool to achieve DIVA compliances. The data show that the avidity of anti BVDV antibodies is related to their capacity to block viral infection in vitro.

Molecular characterization of bovine rotavirus circulating in beef and dairy herds in Argentina during a 10-year period (1994-2003).

Group A bovine rotavirus (BRV) is one of the main causes of neonatal calf diarrhea. The present study reports the incidence of rotavirus diarrhea and the genotypes of BRV strains circulating in beef and dairy herds from Argentina, during a 10-year period (1994-2003). Group A BRV was detected in 62.5% (250/400) of the total studied cases of diarrhea. Positive cases were analyzed by heminested multiplex RT-PCR for P and G genotypes identification. Sixty percent of them were typed as P[5]G6, 4.4% P[11]G10, 4.4% P[11]G6 and 2.4% P[5]G10. Additionally, 9.2% of the cases were initially typed as G8 combined with P[5] or P[11], but sequence analysis revealed they belonged to genotype G6, lineage Hun4-like. Partial typing was assessed in 12.0% of the cases. One of the partially typed samples was closely related to genotype G15. BRV was detected in 71% and 58% of the outbreaks registered in beef and dairy farms, respectively. A clear differential distribution of G/P types was found according to the herd type. P[5]G6 was the prevalent strain in beef herds, while P[11] was the prevalent P-type in dairy herds (71%), associated in similar proportions with G6 and G10, These findings indicate that BRV genotypes included in the current commercially available rotavirus vaccines (G6, G10, P[5] and P[11]) should protect calves from most Argentinean field strains. Nevertheless, continuous surveillance is necessary to detect the emergence of new variants.

Immunohistochemical identification of Campylobacter fetus in natural cases of bovine and ovine abortions.

An immunohistochemistry (IHC) procedure for the detection of Campylobacter fetus antigens using an avidin-biotin complex technique was performed on formalin fixed bovine and ovine fetal tissues from 26 natural cases of Campylobacter spp. abortion (four ovine and 22 bovine). The species of Campylobacter isolated included C. fetus ssp. venerealis from 13 bovine fetuses, C. fetus ssp. fetus from two ovine and one bovine fetus, Campylobacter jejuni from seven bovine fetuses, Campylobacter lari from two ovine fetuses and an unspeciated Campylobacter species in one bovine fetus. Histologic lesions identified in the aborted fetuses included placentitis, serositis, pneumonia, gastroenteritis, hepatitis and encephalitis. Campylobacter fetus antigens were identified by IHC in 13 of 13 bovine fetuses from which C. fetus ssp. venerealis was isolated and in two of two ovine fetuses from which C. fetus ssp. fetus was isolated. The IHC stains were negative in tissues from seven bovine fetuses from which C. jejuni was isolated, one bovine fetus infected with C. fetus ssp. fetus, one bovine fetus infected with the unspeciated Campylobacter and two ovine fetuses infected with C. lari. In positive cases, the IHC stain most frequently identified bacteria in the lung and gastrointestinal tract. The C. fetus IHC procedure performed on formalin fixed tissues is a practical tool for the diagnosis of natural cases of ovine and bovine abortion caused by C. fetus.

[Group A bovine rotavirus: diagnosis and antigenic characterization of strains circulating in the Argentine Republic, 1994-1999]. / Rotavirus bovino grupo A: diagnóstico y caracterización antigénica de cepas circulantes en la República Argentina, 1994-1999.

Group A Bovine Rotavirus (BRV) has been identified as a major cause of neonatal diarrhea in cattle. The study was aimed to determine the prevalence of BRV and to antigenically characterize the G-types of circulating strains in dairy and beef herds in Argentina. A total of 1129 stool samples from diarrheic calves was analyzed from 1994 to 1999. The samples were initially screened for RV by ELISA and PAGE, and then G-typed using monoclonal antibodies (Mab) directed against G1, G2, G3, G6 and G10-specific epitopes. Forty percent (452/1129) of the samples were positive for RV by ELISA, while 24.7% (279/1129) were also positive for PAGE. VP7 was detected in the 70.5% (319/452) of the positive samples using a broadly reactive Mab (C60); 32.6% (104/319) were G6, 15.4% (49/319) were G10, and 6% (19/319) were G1. However, 46.1% (147/319) of the samples remained untypable. Rotavirus diarrhea prevalences were comparable in beef and dairy herds (87.3% and a 74.4%, respectively). Finally, G6 was the most prevalent G-type circulating in beef herds while G10 prevailed in dairy herds. A better understanding of RV epidemiology will contribute to the optimization of current vaccines and prevention programs of RV diarrhea in calves.

Rotavirus bovino grupo A: diagnóstico y caracterización antigénica de cepas circulantes en la República Argentina, 1994-1999 / Group A bovine rotavirus: diagnosis and antigenic characterization of strains circulating in the Argentine Republic, 1994-1999

Group A Bovine Rotavirus (BRV) has been identified as a major cause of neonatal diarrhea in cattle. The study was aimed to determine the prevalence of BRV and to antigenically characterize the G-types of circulating strains in dairy and beef herds in Argentina. A total of 1129 stool samples from diarrheic calves was analyzed from 1994 to 1999. The samples were initially screened for RV by ELISA and PAGE, and then G-typed using monoclonal antibodies (Mab) directed against G1, G2, G3, G6 and G10-specific epitopes. Forty percent (452/1129) of the samples were positive for RV by ELISA, while 24.7 (279/1129) were also positive for PAGE. VP7 was detected in the 70.5 (319/452) of the positive samples using a broadly reactive Mab (C60); 32.6 (104/319) were G6, 15.4 (49/319) were G10, and 6 (19/319) were G1. However, 46.1 (147/319) of the samples remained untypable. Rotavirus diarrhea prevalences were comparable in beef and dairy herds (87.3 and a 74.4, respectively). Finally, G6 was the most prevalent G-type circulating in beef herds while G10 prevailed in dairy herds. A better understanding of RV epidemiology will contribute to the optimization of current vaccines and prevention programs of RV diarrhea in calves.

Rotavirus bovino grupo A: diagnóstico y caracterización antigénica de cepas circulantes en la República Argentina, 1994-1999 / Group A bovine rotavirus: diagnosis and antigenic characterization of strains circulating in the Argentine Republic, 1994-1999

Group A Bovine Rotavirus (BRV) has been identified as a major cause of neonatal diarrhea in cattle. The study was aimed to determine the prevalence of BRV and to antigenically characterize the G-types of circulating strains in dairy and beef herds in Argentina. A total of 1129 stool samples from diarrheic calves was analyzed from 1994 to 1999. The samples were initially screened for RV by ELISA and PAGE, and then G-typed using monoclonal antibodies (Mab) directed against G1, G2, G3, G6 and G10-specific epitopes. Forty percent (452/1129) of the samples were positive for RV by ELISA, while 24.7 (279/1129) were also positive for PAGE. VP7 was detected in the 70.5 (319/452) of the positive samples using a broadly reactive Mab (C60); 32.6 (104/319) were G6, 15.4 (49/319) were G10, and 6 (19/319) were G1. However, 46.1 (147/319) of the samples remained untypable. Rotavirus diarrhea prevalences were comparable in beef and dairy herds (87.3 and a 74.4, respectively). Finally, G6 was the most prevalent G-type circulating in beef herds while G10 prevailed in dairy herds. A better understanding of RV epidemiology will contribute to the optimization of current vaccines and prevention programs of RV diarrhea in calves.(AU)

Rotavirus bovino grupo A: diagnóstico y caracterización antigénica de cepas circulantes en la República Argentina, 1994-1999. / [Group A bovine rotavirus: diagnosis and antigenic characterization of strains circulating in the Argentine Republic, 1994-1999]

Group A Bovine Rotavirus (BRV) has been identified as a major cause of neonatal diarrhea in cattle. The study was aimed to determine the prevalence of BRV and to antigenically characterize the G-types of circulating strains in dairy and beef herds in Argentina. A total of 1129 stool samples from diarrheic calves was analyzed from 1994 to 1999. The samples were initially screened for RV by ELISA and PAGE, and then G-typed using monoclonal antibodies (Mab) directed against G1, G2, G3, G6 and G10-specific epitopes. Forty percent (452/1129) of the samples were positive for RV by ELISA, while 24.7

(279/1129) were also positive for PAGE. VP7 was detected in the 70.5

(319/452) of the positive samples using a broadly reactive Mab (C60); 32.6

(104/319) were G6, 15.4

(49/319) were G10, and 6

(19/319) were G1. However, 46.1

(147/319) of the samples remained untypable. Rotavirus diarrhea prevalences were comparable in beef and dairy herds (87.3

and a 74.4

, respectively). Finally, G6 was the most prevalent G-type circulating in beef herds while G10 prevailed in dairy herds. A better understanding of RV epidemiology will contribute to the optimization of current vaccines and prevention programs of RV diarrhea in calves.

Campylobacter fetus diagnosis: direct immunofluorescence comparing chicken IgY and rabbit IgG conjugates.

In Argentina Bovine Genital Campylobacteriosis is routinely diagnosed by direct immunofluorescence test. Generally, the hyperimmune sera used for this test are obtained from rabbits and less often from goats. In this work, a chicken egg yolk immunoglobulin (IgY) extract was conjugated and its ability to detect campylobacters with the regular conjugate prepared with rabbit sera was comparatively evaluated. Both conjugates were independently evaluated by two laboratories, named "Azul" (Lab A) and "Balcarce" (Lab B). Animals were immunised with formalin inactivated Campylobacter (C.) fetus cells. Chicken IgY and rabbit IgG were conjugated with fluorescein isothiocyanate and used to comparatively examine strains of C. fetus subspp., other Campylobacter spp. and different bacterial species. Both conjugates had a high percentage rate of detection for C. fetus. IgY had less background due to unspecific fluorescence than IgG. IgY is a cheap, bloodless and very productive method. IgY can replace mammal immunoglobulins for C. fetus diagnosis.