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Abstract

Objectives

To determine tilmicosin concentrations in serum and tissues of rabbits given a single dose of 25 mg of tilmicosin/kg of body weight. To examine the effects of tilmicosin treatment (25 mg/kg, SC) in rabbits with pasteurellosis.

Procedure

After receipt of tilmicosin, healthy New Zealand White female rabbits (n = 3 at each time) were euthanatized at 2, 4, 8, 24, 48, and 72 hours for collection of blood samples and tissue specimens; 4 rabbits served as untreated controls. Rabbits (male and female) with pasteurellosis (n = 42) also were treated. Tilmicosin concentration was determined in serum, lung, and uterine tissues. Rabbits with pasteurellosis were treated with tilmicosin. Response was monitored, using bacteriologic culturing and antibiotic resistance and susceptibility testing, and by scoring clinical signs of disease.

Results

Serum tilmicosin concentration reached 1.91 ±0.18 μg/ml after 2 hours, decreased to 0.77 ± 0.07 μg/ml by 8 hours, and was below minimum inhibitory concentrations for Pasteurella multocida at 24 hours. Terminal half-life in serum was 5.97 hours. Lung and uterus concentrations were 14.43 ± 1.34 and 11.57 ± 0.09 ppm at 2 hours, and were 5.10 ± 1.05 and 8.87 ± 1.66 ppm at 24 hours, respectively. 69% (29/42) of rabbits with pasteurellosis responded favorably in 3 days. Second treatment was required in 31% (13/42), and 5 of these rabbits had clinical signs on day 6; 2 of these 5 had improved. Treatment success rate was 93% (39/42). Of the rabbits that were culture positive on day 0, 35% (6/17) remained positive on day 3. 1 of 6 rabbits was culture positive on day 6.

Conclusion

Tilmicosin (25 mg/kg, SC) was an effective treatment for pasteurellosis in New Zealand White rabbits.

Clinical Relevance

Tilmicosin treatment of pasteurellosis in rabbits is useful in research rabbits and in those destined for meat production. A single dose of antibiotic minimizes stress-associated handling. (Am J Vet Res 1996;57:1180-1184)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To compare the virulence of selected strains of porcine reproductive and respiratory syndrome virus (PRRSV) relative to reproductive performance of pregnant gilts.

Design

16 pregnant gilts (principals) were exposed oronasally to 4 strains (vaccine strain RespPRRS, field strains VR-2385, VR-2431, and NADC-8, 4 gilts/strain) of PRRSV on or about day 90 of gestation. 4 pregnant gilts (controls) were kept under similar conditions, except for exposure to PRRSV. Samples and specimens obtained from gilts, pigs (before ingestion of colostrum), and fetuses were tested for PRRSV and homologous antibody.

Animals

20 pregnant gilts.

Procedure

The virulence of each strain of PRRSV was evaluated mainly on the clinical status of the corresponding litters at farrowing.

Results

Most gilts remained clinically normal throughout the study and farrowed normally at or near the expected farrowing time. All virus strains crossed the placenta of principal gilts to infect fetuses in utero. The number of late-term dead fetuses (which appeared to be the best measure of relative virulence) ranged from 0 for litters of control gilts and gilts exposed to strain RespPRRS, to 38 for gilts exposed to strain NADC-8. All principal gilts became viremic and developed antibody against PRRSV. All strains persisted in alveolar macrophages of at least some principal gilts for at least 7 weeks after exposure.

Conclusion

Strains of PRRSV vary in virulence.

Clinical Relevance

The effects of PRRSV on reproductive performance are strain dependent and this should be considered in making a tentative diagnosis on the basis of clinical observations. (Am J Vet Res 1996;57:834–839)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To develop and apply the liquid-phase blocking sandwich ELISA (BLOCKING-ELISA) for the quantification of antibodies against foot-and-mouth disease virus (FMDV) strains O1 Campos, A24 Cruzeiro, and C3 Indaial.

Design

Antibody quantification.

Sample Population

158 water buffalo from various premises of São Paulo State-Brazil. The sera were collected either from systemically vaccinated or nonvaccinated animals.

Procedure

The basic reagents of BLOCKING-ELISA (capture and detector antibodies, virus antigens, and conjugate) were prepared and the reaction was optimized and standardized to quantify water buffalo antibodies against FMDV. An alternative procedure based on mathematical interpolation was adopted to estimate more precisely the antibody 50% competition titers in the BLOCKING-ELISA. These titers were compared with the virus-neutralization test (VNT) titers to determine the correlation between these techniques. The percentages of agreement, cutoff points, and reproducibility also were determined.

Results

The antibody titers obtained in the BLOCKING-ELISA had high positive correlation coefficients with VNT, reaching values of 0.90 for O1 Campos and C3 Indaial, and 0.82 for the A24 Cruzeiro (P <0.0005). The cutoff points obtained by use of the copositivity and conegativity curves allowed determination of high levels of agreement between BLOCKING-ELISA and VNT antibody titers against the 3 FMDV strains analyzed.

Conclusions

The results characterized by high correlation coefficients, levels of agreement, and reproducibility indicate that the BLOCKING-ELISA may replace the conventional VNT for detection and quantification of antibodies from water buffalo sera to FMDV. (Am J Vet Res 1996;57:840–843)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To identify morphologic differences in ovaries from cows persistently infected with bovine viral diarrhea virus (BVDV) and determine ovarian cell types infected in these cows.

Design

A comparative study of ovaries in cattle persistently infected with BVDV and cattle not persistently infected with BVDV, using morphologic and immunohistochemical analysis.

Animals

6 postpubertal cows persistently infected with BVDV and 6 postpubertal cows not persistently infected with BVDV.

Procedure

Ovaries were compared morphologically by counting the number of normal structures present on 3 histologic sections taken from each ovary. Immunohistochemistry was accomplished, using an indirect, monoclonal antibody-linked, avidin-biotin-peroxidase complex procedure.

Results

Significant (P < 0.01) decrease in the number of tertiary follicles, graafian follicles, atretic follicles, and corpus hemorrhagicum/luteum/albicans was observed in cows persistently infected with BVDV. No difference in numbers of primordial or secondary follicles was observed. Immunostaining of BVDV antigen in luteal cells and macrophage-like cells was evident in ovaries from cows persistently infected with BVDV.

Conclusions

Cows persistently infected with BVDV appear to have significant morphologic changes in their ovaries that suggest reduction in normal ovarian activities. Furthermore, BVDV antigen can be identified in specific ovarian cell types in cattle persistently infected with BVDV.

Clinical Relevance

The changes observed may reduce reproductive performance in cows persistently infected with BVDV, and may be of importance when trying to salvage valuable genetic material from persistently infected cows through embryo transfer. It is yet to be determined whether similar findings are true in cows acutely infected with BVDV. (Am J Vet Res 1996;57:830–833)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To assess shedding of ovine lentivirus (OvLV) in semen of infected rams with or without epididymitis.

Design

Rams 1 and 2 were naturally infected with OvLV. Rams 3-6 were inoculated with OvLV strain 85/ 34. Ram 7 was inoculated with uninfected cell culture supernatatant (OvLV-negative control). 14 weeks after OvLV inoculation, rams 1-3, 6, and 7 were inoculated with Brucella ovis into the epididymis. Ram 4 was a natural case of B ovis epididymitis, and ram 5 was left non-inoculated (Bovis-negative control). Blood mononuclear cells (BMNC) and semen were collected between 0 and 44 weeks after OvLV inoculation.

Animals

Seven 2- to 3-year-old rams.

Procedure

Infective OvLV in BMNC and semen was determined by virus isolation and subsequent OvLV-DNA amplification by polymerase chain reaction (PCR). Bronchoalveolar lavage cells collected after death were used for DNA extraction and PCR amplification.

Results

OvLV was detected in the semen of rams 3 and 6, but only after Bovis inoculation. OvLV was isolated consistently from BMNC of rams 3 and 6, but only occasionally from rams 1, 2, 4, and 5. Leukocytospermia was evident in every ejaculate of all Bovis-infected rams after infection. Semiquantitative PCR determination of OvLV DNA from bronchoalveolar lavage cells revealed the highest OvLV DNA load in rams 3 and 6.

Conclusions

Leukocytospermia and a high virus load in infected animals are important factors that determine shedding of OvLV in semen.

Clinical Relevance

Dissemination of OvLV through contaminated semen could have important implications in the epidemiology and control of this infection. (Am J Vet Res 1996; 57:684–688)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To genetically characterize Clostridium perfringens isolates for association of pathologic type with various diseases.

Design

Prospective study.

Sample Population

2,659 C perfringens isolates from various nonhuman animals species, human beings, and foods.

Procedure

Colony hybridization with DNA probes for 7 toxin (α, β, ε, ι (subunits a and b), θ, μ, and enterotoxin) genes and 1 sialidase gene were performed to group the isolates by pathologic type.

Results

Enterotoxin-negative type-A isolates were the most common (2,575/2,659), were isolated from all sources, and were separated into 5 pathologic types. In cattle and horses with enterotoxemia, essentially only these pathologic types were identified. The enterotoxin-negative isolates of types C or D each had a single pathologic type. Type-C isolates were isolated only from swine with necrotic enteritis and type-D isolates from small ruminants with enterotoxemia, except that 1 type-D isolate was also found from a healthy fish. Type-B or -E isolates were not found. Among the 47 enterotoxin-positive isolates, 5 isolates from sheep or deer were type D and the other 42 were type A. These 42 isolates were grouped into 3 pathologic types: 1 type was isolated from samples of almost all origins, but the other 2 types were found in only 5 fish, 4 human beings, and 1 dog.

Conclusions and Clinical Relevance

Genetic characterization of these isolates allowed identification of 11 different pathologic types. This approach may be useful in molecular diagnosis and prophylaxis of clostridial disease. (Am J Vet Res 1996;57:496–501)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To investigate prevalence of Salmonella enteritidis-positive eggs, excretion of the organism in fecal droppings, and infection of internal organs after oral inoculation of White Leghorn hens with S enteritidis phage type 8.

Animals

30 White Leghorn laying hens.

Procedure

At 25 weeks of age, hens were each inoculated orally with 1010 colony-forming units of S enteritidis, then were observed for 8 weeks.

Results

Salmonella enteritidis Y-8P2 did not cause any clinical signs of disease or decrease in egg production. However, at 1 week after inoculation, 63.9% of the eggs collected from inoculated hens were culture positive for S enteritidis. The organism was isolated from the shell washings, egg shells, yolk, and albumen. A total of 592 eggs from S enteritidis-inoculated hens were examined. Of these eggs, 157 (26.5%) were positive for S enteritidis on external shell washings alone, 17 (2.9%) were positive for S enteritidis internally, and 44 (7.4%) were positive for S enteritidis externally and internally. The percentage of culture-positive eggs gradually decreased between postinoculation weeks 2 and 5, then gradually increased to a high of 76% at week 8. At 3, 7, and 10 days after S enteritidis inoculation, cloacal swab specimens from 3 hens were positive for S enteritidis. Salmonella enteritidis was recovered from ovary, oviduct, liver, and cecal junction from S enteritidis-inoculated hens.

Conclusions

Our results indicated that birds infected with this isolate produced S enteritidis-positive eggs at high frequencies initially, that decreased over time. When S enteritidis antibody began to decrease, reaching geometric mean titer ≤ 40, the frequency of S enteritidis-positive eggs increased. (Am J Vet Res 1996;57:489–495)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine the efficacy of leukotoxin-based Fusobacterium necrophorum vaccines and dietary tylosin in providing protection against experimentally induced hepatic abscesses in steers.

Design

30 steers assigned randomly to 6 treatment groups of 5 steers each: 1, phosphate-buffered saline solution (PBSS; control); 2, PBSS control, fed tylosin (100 mg/steer) daily; 3, inactivated whole-cell culture with oil emulsion adjuvant; 4, culture supernatant (crude toxoid) with oil emulsion adjuvant; 5, semipurified leukotoxoid with oil emulsion adjuvant; and 6, semipurified leukotoxoid with saponin adjuvant.

Procedure

Steers were inoculated SC with emulsified antigen or PBSS on days 0 and 21. Blood samples were collected at weekly intervals to monitor serum antileukotoxin antibody titer. On day 42, all steers were challenge exposed intraportally with F necrophorum culture. Three weeks later (day 63), steers were euthanatized and necropsied to examine liver and assess protection.

Results

Antileukotoxin antibody titers of all vaccinated groups markedly increased from baseline values, and mean titers of vaccinated groups were higher than those of the control and tylosin-treated groups. Steers vaccinated with culture supernatant with oil emulsion adjuvant or semipurified leukotoxoid with saponin adjuvant had the highest mean antibody titers. All 5 steers in the control group developed liver abscesses. Tylosin feeding did not protect steers challenge exposed with F necrophorum intraportally.

Conclusions

Culture supernatant was more protective than whole-cell culture or semipurified leukotoxin against experimentally induced hepatic abscesses. Partial purification of leukotoxin appeared to reduce its protective immunity. (Am J Vet Res 1996;57:483–488)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To establish the effect of dose on persistence of and immune response to Salmonella choleraesuis in swine.

Design

19 Salmonella-free pigs were allotted to 4 groups. Groups 1 (n = 5), 2 (n = 5), and 3 (n = 5) were inoculated intranasally with 109, 106, and 103 colony-forming units of S choleraesuis, respectively. Group 4 (n = 4) served as uninoculated controls.

Procedure

Pigs were monitored for clinical signs of disease and bacterial shedding. Serum and lymphocytes were obtained to measure immune responses. Pigs from groups 1, 2, and 4 were necropsied at postinoculation (PI) weeks 6 and 15. Pigs from groups 3 and 4 were necropsied at PI weeks 6 and 10.

Results

Pigs in group 1 shed S choleraesuis through PI week 15 and were tissue positive at PI weeks 6 and 15. Pigs in group 2 were tissue positive for S choleraesuis until PI week 6 and continued shedding through PI week 9. Salmonella choleraesuis was not recovered at any time from pigs in groups 3 or 4. Pigs in groups 1, 2, and 3 had serum IgG and IgM titers to S choleraesuis lipopolysaccharide and soluble antigens. Pigs in all groups had a lymphocyte response to concanavalin A, and pigs in groups 1 and 2 had a lymphocyte response to S choleraesuis endotoxin. Pigs in group 1 had a lower stimulation index in response to both antigens, indicating some form of lymphocyte immunosuppression.

Conclusions

Persistence of S choleraesuis in host tissues is dose dependent. Short-term persistence can occur after a dose as low as 106 colony-forming units of S choleraesuis. Higher doses result in development of longterm carrier status, which may be related to the observed lymphocyte immunosuppression.(Am J Vet Res 1996;57:313-319)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine whether porcine reproductive and respiratory syndrome virus plaque variants vary in their pathogenicity in causing late-term reproductive failure.

Design

Four groups of 2 sows each at 86 days of gestation were inoculated intranasally with PRRSV small (MN-Hs) and large (MN-HI) plaque variants, field isolate, and cell culture medium, respectively. In addition, 2 sows each at 86 days of gestation were inoculated intranasally or IM with MN-Hs virus.

Animals

14 pregnant sows.

Procedure

Inoculated sows were allowed to deliver at term, and each litter was examined for clinical abnormality and presence of virus.

Results

Two sows infected with MN-Hs virus delivered 14 live and 5 dead pigs, whereas 2 sows infected with MN-HI virus delivered 0 live and 25 dead pigs. Two sows inoculated with a field isolate (MN-W) delivered 10 live and 20 dead pigs. Two control sows had 26 normal fetuses at slaughter at 107 days of gestation. Virus was isolated from 16 (66.7%) of 24 liveborn pigs, 9 (64.3%) of 14 stillborn pigs, and 3 (12.0%) of 25 mummified fetuses of the 6 infected sows. Subsequently, 4 MN-Hs-infected sows delivered 40 live and 11 dead pigs.

Conclusions

Marked difference in the pathogenicity in pregnant sows between porcine reproductive and respiratory syndrome virus strains was documented. The MN-Hs virus is considered to be of low pathogenicity, but the other viruses are highly pathogenic for late-term pregnant sows.(Am J Vet Res 1996;57:320-323)

Free access
in American Journal of Veterinary Research