Experimentally induced pneumonic pasteurellosis: dose-response relationships and protection against natural reinfection in calves

Calves were inoculated intranasally with 2 X 10(6.2) tissue culture infective doses of infectious bovine rhinotracheitis virus, followed in 7 days by intratracheal inoculations with 1 of 4 challenge doses of pathogenic Pasteurella haemolytica. Severity and duration of the ensuing clinical signs of respiratory tract disease were correlated with the challenge dose of bacteria. Calves given 1 X 10(6) colony-forming units (CFU) of bacteria did not develop reliable clinical evidence of disease, whereas those given 1 X 10(8) CFU or 1 X 10(10) CFU of bacteria developed clinical signs of pneumonic pasteurellosis within 12 to 24 hours of bacterial challenge. Severity of clinical signs was equal at the 10(8) and 10(10) doses of bacteria, but duration of clinical signs was greater in calves given the 10(10) dose. Calves given 1 X 10(12) CFU of bacteria developed relatively severe respiratory tract disease in excess of what was necessary for positive clinical detection. Positive correlations were found between the bacterial challenge dose and the height and duration of increased rectal temperature, amount and duration of increases in ocular and nasal discharges, and the subjective evaluation of depressed attitude and appetite. Correlations were not found between challenge dose and respiratory rate or character, or between challenge dose and complete blood cell count. Convalescent calves were resistant to naturally occurring pneumonic pasteurellosis, which caused severe disease in nontreated calves. Adverse effects of P haemolytica were not observed after the first 4 to 15 days after bacterial administration; however, the bacteria were isolated from nasal secretions of convalescent calves 89 to 116 days after bacterial inoculation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of serum amyloid A and surfactant protein D in sera for identification of the clinical condition of horses with bacterial pneumonia

In the present study, the concentrations of serum amyloid A and surfactant protein D in sera were measured to evaluate them for identification of the clinical condition of horses with bacterial pneumonia. The study utilized 185 clinically healthy control thoroughbreds and 9 thoroughbreds for experimental infectious study with S. zooepidemicus. Blood samples were collected from the 185 healthy control thoroughbreds. The 9 thoroughbreds were experimentally infected S. zooepidemicus using an endoscopic injection to a lung lobe and were then observed of clinical conditions. Blood samples were collected before inoculation and on the 1-15th, 22nd, and 29th days after inoculation (follow-up group). The levels of SAA and SP-D in the healthy control thoroughbreds were very low. In the follow-up group, the levels of SAA and SP-D changed in parallel with the horses' clinical condition. The pyrexia observed after bacterial inoculation faded by the 11th day, and the changes in SAA and SP-D occurred simultaneous to disappearance of the clinical signs. Measurement of SAA and SP-D proved useful for monitoring the clinical condition of the horses with bacterial pneumonia. Changes in the SP-D value were preceded by changes in the SAA value. Since the changes in SP-D occurred approximately simultaneous to the changes in the horses' clinical signs, we believe that they reflect the condition of the alveolar membranes. We conclude that measurement of SAA and SP-D in sera is useful for identification of the clinical condition of horses with bacterial pneumonia.     

Pathogenesis of Streptococcus zooepidemicus infection after intratracheal inoculation in llamas

OBJECTIVES: To test whether generalized Streptococcus zooepidemicus infection could be induced by intratracheal inoculation in llamas and to characterize this infection. ANIMALS: 6 test and 3 control llamas. PROCEDURE: Test llamas received 1 of 3 dosages of S. zooepidemicus by intratracheal injection, whereas control llamas received sterile culture medium. Physical examination variables and results of clinicopathologic analyses of blood, peritoneal fluid, and tracheal wash fluid were compared in test llamas between, before, and during the development of bacteremia and with control llamas. Bacteriologic culture was performed on all collected body fluids and tissue specimens that were collected at necropsy. Tissue specimens that were collected at necropsy were examined histologically. RESULTS: Infection induced fever, anorexia, and signs of depression. Five of 6 infected llamas developed specific signs of inflammation in the thorax or abdomen, bacteremia, neutrophilic leukocytosis with toxic changes and high band neutrophil cell counts, hyperfibrinogenemia, and high peritoneal fluid WBC counts and protein concentrations. On development of bacteremia, llamas had significant decreases in serum iron (from 118+/-25 to 6+/-4 microg/ml) and increases in serum glucose (from 131+/-5 to 253+/-48 mg/dl) concentrations. CONCLUSIONS AND CLINICAL RELEVANCE: Streptococcus zooepidemicus spreads rapidly to other body compartments after intratracheal inoculation in llamas. Fever, anorexia, and signs of depression are the most consistent clinical signs, although other signs are possible. Clinicopathologic analysis of body fluids yields evidence of inflammation. Infection by S. zooepidemicus can be proven by bacteriologic culture of body fluids before death or of tissue specimens after death.     

Salmonella enterica serovar typhimurium colonization of the crop in the domestic turkey: influence of probiotic and prebiotic treatment (Lactobacillus acidophilus and lactose)

Acute colonization of the crop of the domestic turkey by Salmonella enterica serovar typhimurium (ST) was examined. The influences of preharvest probiotic and prebiotic treatment with lactobaccilli and lactose on crop colonization with ST were also investigated. Prior to Salmonella challenge, poults received 2.5% lactose and Lactobacillus acidophilus (1.9 x 10(9) organisms/liter) in the only source of drinking water from 1 day old to termination. At 3-wk-old, turkey poults were challenged with ST (1.7 X 10(8) colony-forming units [CFU]/ml) before their natural nocturnal fast to determine the potential effects of supplementation on crop colonization when the crop was engorged and subsequently undergoing emptying. Crop ingesta and tissue were collected at time points 30 min and 4, 8, and 24 hr postchallenge and ST levels were determined. High levels of ST were detected in the crop. For instance, for the poults not receiving lactose or lactobacilli, 30 min after ST challenge, there were 4.4 x 10(7) CFU in the crop ingesta and 5.3 x 10(5) CFU in the crop wall. Ingesta ST levels dropped dramatically to 1.0 x 10(6) CFU after 4 hr as the crop emptied. Crop wall ST levels were steady during the nocturnal crop evacuation. Immunohistochemical staining demonstrated ST in close association with the crop epithelium. Treatment with lactose and L. acidophilus supplementation did not reduce ST colonization.     

Immunogenicity and safety of an attenuated Bordetella bronchiseptica vaccine in pigs

The immunogenicity and safety of an attenuated Bordetella bronchiseptica vaccine for swine atrophic rhinitis (AR) was evaluated in 22 hysterectomy-produced, colostrum-deprived pigs and 18 conventional pigs. None of 8 pigs inoculated at 7 days of age intranasally with greater than or equal to 3 X 10(5) colony-forming units (CFU) of vaccinal strain/pig and 2 of 5 pigs inoculated at 7 days of age intranasally with 3 X 10(4) CFU of the vaccinal strain/pig developed AR after intranasal challenge exposure with a virulent strain at postinoculation week (PIW) 3. The remaining 3 vaccinated pigs and 4 nonvaccinated pigs developed AR. Thirteen pigs were inoculated intranasally with 3 X 10(6) to 3 X 10(9) CFU of the vaccinal strain at 7 days of age. At PIW 12, the pigs were killed and necropsied. None of the pigs had clinical signs of AR and/or pneumonia. Virulence was studied by transmission of vaccinal strain through 3 serial growing passages on the nasal mucosa of a litter of hysterectomy-produced colostrum-deprived pigs. Inoculum (nasal swab samples from 2 pigs 4 days after inoculation with 10(8) CFU of vaccinal strain at 5 days of age) was inoculated into the nasal cavity of 2 nonvaccinated pigs. This procedure was repeated 3 times. After the 1st passage, the vaccinal strain was recovered on postinoculation day 4, but after postinoculation day 4, the vaccinal strain was not recovered until the end of the 3rd passage. Turbinate atrophy or pneumonia was not recognized in these inoculated pigs. The vaccinal strain provided immunogenicity without ill effects.     

The effects of parenteral iron dextran and/or desferrioxamine on the development of experimental pseudotuberculosis in the domestic chicken (Gallus domesticus)

Abstract The development of disease following oral challenge with Yersinia pseudotuberculosis (serotype 11) was compared in four groups of five birds treated with a parenteral dose of 10 mg iron dextran (Imferon), 10 mg of iron dextran plus 10 mg of the chelating agent desferrioxamine (Desferal), 10 mg of desferrioxamine or 10 mg of dextran 2 days before the experiment. Four groups of two birds received the above treatment regimens but no bacterial challenge. In iron dextran treated birds, oral challenge resulted in faecal shedding for the 10 day duration of the experiment, whereas in those birds which received dextran or desferrioxamine alone, the duration of faecal shedding was significantly less. Serological titres to the lipopolysaccharide antigen of the challenge bacteria were also lower in the groups not pretreated with iron dextran. The birds pretreated with iron dextran had diarrhoea and were clinically unwell 2 days following the initial oral challenge. Birds not given iron dextran showed no clinical signs of disease. Histological examination of five selected areas in the liver, spleen and intestine of each bird indicated that birds in the groups treated with iron dextran prior to bacterial challenge had significantly more intestinal lesions than birds in the groups not treated with iron. In contrast, there were significantly more lesions in the spleens of birds not pretreated with iron dextran. There was no evidence of stainable iron in the livers of birds challenged with Y pseudotuberculosis 10 days after an injection of 10 mg of iron dextran. This is in contrast to birds given iron dextran and no bacteria. It was concluded that pretreatment of birds with iron dextran resulted in more severe clinical disease, prolonged faecal shedding with associated intestinal lesions and higher serological titres to bacterial antigen. The number of lesions in the spleen and liver was not necessarily correlated with the severity of clinical disease, and in all infected birds the hepatic iron levels were significantly lower than in the non-infected control birds 10 days after oral challenge. It seems probable that the chicken has a high requirement for iron during infection with Y pseudotuberculosis and mobilises stored and exogenously supplied iron for tissue repair and immunological function.     

The effects of parenteral iron dextran and/or desferrioxamine on the development of experimental pseudotuberculosis in the domestic chicken (Gallus domesticus)

The development of disease following oral challenge with Yersinia pseudotuberculosis (serotype 11) was compared in four groups of five birds treated with a parenteral dose of 10 mg iron dextran (Imferon), 10 mg of iron dextran plus 10 mg of the chelating agent desferrioxamine (Desferal), 10 mg of desferrioxamine or 10 mg of dextran 2 days before the experiment. Four groups of two birds received the above treatment regimens but no bacterial challenge. In iron dextran treated birds, oral challenge resulted in faecal shedding for the 10 day duration of the experiment, whereas in those birds which received dextran or desferrioxamine alone, the duration of faecal shedding was significantly less. Serological titres to the lipopolysaccharide antigen of the challenge bacteria were also lower in the groups not pretreated with iron dextran. The birds pretreated with iron dextran had diarrhoea and were clinically unwell 2 days following the initial oral challenge. Birds not given iron dextran showed no clinical signs of disease. Histological examination of five selected areas in the liver, spleen and intestine of each bird indicated that birds in the groups treated with iron dextran prior to bacterial challenge had significantly more intestinal lesions than birds in the groups not treated with iron. In contrast, there were significantly more lesions in the spleens of birds not pretreated with iron dextran. There was no evidence of stainable iron in the livers of birds challenged with Y pseudotuberculosis 10 days after an injection of 10 mg of iron dextran. This is in contrast to birds given iron dextran and no bacteria. It was concluded that pretreatment of birds with iron dextran resulted in more severe clinical disease, prolonged faecal shedding with associated intestinal lesions and higher serological titres to bacterial antigen. The number of lesions in the spleen and liver was not necessarily correlated with the severity of clinical disease, and in all infected birds the hepatic iron levels were significantly lower than in the non-infected control birds 10 days after oral challenge. It seems probable that the chicken has a high requirement for iron during infection with Y pseudotuberculosis and mobilises stored and exogenously supplied iron for tissue repair and immunological function.     

Bluetongue virus serotypes 20 and 17 infections in sheep: Comparison of clinical and serological responses

The clinical, virological and serological responses of sheep infected with an Australian bluetongue virus (BTV) isolate (serotype 20) were compared to responses in sheep inoculated with an American bluetongue isolate (serotype 17) with which it had shown cross-reactions in serum neutralization tests. In sheep inoculated with BTV 20, clinical signs were very mild and viremia was first detected by day 5; virus was isolated intermittently for a further 2 to 3 days. Neutralizing and precipitating antibodies were first detected in the serum of the sheep between 2 to 3 weeks following inoculation. In contrast, sheep inoculated with BTV 17 showed pyrexia and severe hyperemia of the nasolabial area and oral mucosa from day 7 to 17. Viremia was first detected on day 3 and extended to day 20, while the appearance and titers of serum antibodies was similar in both groups.After challenge with BTV 17 the sheep in both groups remained clinically normal, and virus was not detected in the blood; however, serum neutralizing antibody titers to both viruses increased 2 weeks after challenge and the mean titer of the two groups ranged from 1:250 to 1:640.     

Interferon, fluorescent antibody, and neutralizing antibody responses in sera of calves inoculated with bovine respiratory syncytial virus

Interferon, fluorescent antibody, and neutralizing antibody responses were studied in sera of 9 calves inoculated with bovine respiratory syncytial virus, in relation to viral shedding and clinical signs of disease. The calves (5.5 to 6.5 weeks of age) were assigned to 3 groups. Group I was inoculated once with the virus, and groups II and III were challenge exposed at postinoculation day (PID) 15 or 37. Serum-neutralizing and indirect fluorescent antibody techniques were used to measure antibody responses. The plaque-inhibition technique, using vesicular stomatitis virus, was applied to measure serum interferon titers. The virus was recovered by inoculation of nasal secretions onto cell cultures. Fluorescent antibody was detected in all calves on PID 3, with maximum titers appearing approximately on PID 10. Low neutralizing antibody was detected in most animals on PID 3, and titers peaked approximately 4.5 weeks after inoculation and then decreased. Interferon titers were high in all calves during the early stage of infection, dropped to undetectable amounts by PID 6, and reappeared in low amounts at least 1 week later. All infected calves manifested clinical signs of disease by PID 4 to 9. Clinical signs of disease were not observed after challenge exposure at PID 15 or 37, and anamnestic responses were not detected. Virus was recovered after challenge exposure at PID 15, but not at PID 37.     

Proliferation of Streptococcus zooepidemicus and Pseudomonas aeruginosa within a simulated subpalpebral lavage flushed with equine serum

Objective  To evaluate whether equine serum administered via a simulated subpalpebral lavage system (SPL) supports proliferation of Streptococcus zooepidemicus or Pseudomonas aeruginosa within the tubing.
Procedures  A sterile i.v. catheter with injection cap was inserted into sterilized silicone tubing (Mila^®). To mimic an SPL within the dorsal conjunctival fornix, the tubing was secured to an elevated platform. The tip of the tubing extended from the platform into a vial containing culture medium just inoculated with approximately 1.5 × 10⁸ CFU/mL P. aeruginosa or S. zooepidemicus . To mimic administration of medication, the tubing was infused twice daily with equine serum, sterile saline (negative control), or culture medium (positive control) followed by air. Incubation was at 25 or 37 °C. At 24, 48, and 72 h postinoculation, samples were obtained for bacterial culture from one simulated SPL for each experimental variant. The following sections were cultured: (i) tubing tip previously submerged in the inoculated culture medium, (ii) tubing mid-section, and (iii) tip of the i.v. catheter. The experiment was performed in triplicate.
Results  Streptococcus zooepidemicus or P. aeruginosa were isolated from 100% of the tubing tips. Streptococcus zooepidemicus was isolated from one mid-section flushed with culture medium incubated at 37 °C. All other samples were negative for growth of the inoculated agents.
Conclusions  Streptococcus zooepidemicus and P. aeruginosa did not proliferate within silicone tubing infused with equine serum. These data suggest that topical serum can be safely administered through a superiorly placed SPL in clinical cases.     

Assessment of protective efficacy of live and killed vaccines based on a non-encapsulated mutant of Streptococcus suis serotype 2.

The protective efficacy of a live and killed non-encapsulated isogenic mutant of Streptococcus suis serotype 2 was determined in pigs, and compared with the efficacy of the capsulated wild-type strain. SPF pigs were vaccinated twice intramuscularly at 4 and 7 weeks of age with a dose of 1 x 10(9) formalin-killed CFU of the wild-type (WT-BAC), formalin-killed non-encapsulated mutant (CM-BAC) or live non-encapsulated mutant (CM-LIVE) strain. After 2 weeks, vaccinated pigs and non-vaccinated controls were challenged intravenously with 1 x 10(7) CFU of the homologous, wild-type S. suis serotype 2 strain. Protection was evaluated by clinical, bacteriological, serological and post-mortem examinations. All pigs vaccinated with WT-BAC were completely protected against challenge with the homologous serotype. Pigs vaccinated with CM-BAC were partially protected. Although all pigs vaccinated with CM-BAC survived the challenge, four out of five pigs developed clinical signs of disease for several days. Compared to the WT-BAC and CM-BAC, the CM-LIVE vaccine was less protective. Two out of five pigs vaccinated with CM-LIVE died in the course of the experiment and all of them developed specific clinical signs of disease for several days. The protective efficacy of the vaccines could be associated with serum antibody titers. Antibody titers against cells of wild-type and non-encapsulated mutant strains as well as against muramidase-released proteins (MRP) were high in pigs vaccinated with WT-BAC and CM-BAC. Pigs vaccinated with CM-LIVE showed lower antibody titers. Antibody titers against purified capsular polysaccharides (CPS) of S. suis serotype 2 were only found in pigs vaccinated with WT-BAC. These findings indicate that CPS and other bacterial components of WT-BAC are probably essential for full protection against homologous challenge.     

Serum bactericidal responses to Streptococcus equi of horses following infection or vaccination

An indirect test based on horse blood was used to study bactericidal responses of the horse to Streptococcus equi following infection or vaccination. Bactericidal antibody appeared in convalescent sera between two and four weeks and high titres were usually attained by eight weeks. Infection without clinical evidence of abscessation was also effective in eliciting strong bactericidal responses. Serum bactericidal activity of horses either recovered from strangles or immunised with commercial bacterin had declined eight months after vaccination. However, horses that developed strangles eight to 10 months after vaccination exhibited rapid and substantial increases in serum bactericidal activity. Groups of yearlings immunised with commercial S equi vaccines consisting either of M protein or bacterin developed clinical strangles within six months of vaccination although the majority of the animals had exhibited strong serum bactericidal activity a few weeks before occurrence of the disease. Similarly, a group of seven yearling ponies hyperimmunised with experimental vaccine, rich in M protein, were found to be highly susceptible to an intranasal challenge of 5 X 10(8) colony forming units of S equi, although their sera exhibited strong bactericidal activity at the time of challenge. These observations suggest that the role of serum bactericidal antibody in protection of the horse against strangles has been overrated.     

Bordetella bronchiseptica experimental model development in pigs and efficacy evaluation of a single intramuscular injection of gamithromycin (Zactran® for Swine) against Bordetella bronchiseptica-associated respiratory disease in experimentally infected piglets

In the Bordetella bronchiseptica infection model development study, twenty-eight piglets were inoculated with B. bronchiseptica strain of either canine (10⁹ CFU/ml) or swine (10⁸ and 10⁹ CFU/ml) origin; swine origin strain at 10⁹ CFU/ml was chosen for the efficacy assessment study due to higher incidence and severity of gross and histopathological lesions compared with other strains. To assess efficacy of gamithromycin against B. bronchiseptica, forty piglets were experimentally inoculated on Day 0 and clinical signs were scored as per severity. Animals were then treated either with gamithromycin or saline on Day 3. The Global Clinical Scores in gamithromycin-treated group were consistently lower than the saline-treated control group from Day 4 onwards and were 0 and 40 in the gamithromycin-treated and saline-treated control groups, respectively, on Day 6. Severity and frequency of gross and histopathological observations were significantly lower in gamithromycin-treated animals compared with saline-treated controls. The efficacy of Zactran® for Swine at the label dose for the treatment of B. bronchiseptica–associated respiratory disease was demonstrated based on the faster reduction in clinical signs as early as 1 day post-gamithromycin treatment and based on the significant difference in the severity of macroscopic and microscopic lung lesions 10 days post-gamithromycin treatment.     

Studies of infectivity and pathogenicity of an isolate of Trypanosoma evansi in Yankasa sheep.

The course of experimental infection and pathogenicity of an isolate of Trypanosoma evansi were investigated using eight infected and six uninfected control Yankasa sheep. The sheep were each infected intravenously via the jugular vein with approximately 2.0 x 10(6) T. evansi parasites. The effects of the parasite on body temperature, packed cell volume (PCV), haemoglobin, erythrocytes, total protein, were monitored three times a week for approximately 9 weeks. Body weights were determined once every week for the duration of the experiment. The results showed that all the infected sheep were positive for the parasite. The prepatent period varied between 3 and 6 days. T. evansi produced parasitaemic waves at an average of 8.3 days interval. Two distinct forms of the disease were produced namely, acute (4-14 days postinfection), and chronic (43-59 days postinfection). Anaemia was a distinct feature of the disease. While the mean rectal temperatures were significantly elevated (P < 0.05), the mean values of the haematological parameters of the infected sheep dropped significantly (P < 0.05) compared to the preinfection levels. Observed clinical signs included pale mucous membrane, epiphora, loss of appetite, emaciation, dullness and rough hair coat together with fluctuating pyrexia which in most cases coincided with rise in parasitaemia. It is suggested that the isolate of T. evansi is pathogenic for Yankasa sheep.     

The viability of Campylobacter jejuni on refrigerated chicken drumsticks

Radappertized chicken drumsticks were experimentally contaminated with suspensions of Campylobacter jejuni in two trials. Qualitative analysis on drumsticks with an initial level of contamination of 4.8 X 10(3) CFU/cm2 showed that viability was retained for at least 10 days of storage at either 9 degrees or -12 degrees C. In a second quantitative trial, the level of contamination declined from 9.9 X 10(2) CFU/cm2 to 4.5 X 10(1) CFU/cm2 after 7 days at -20 degrees C. Thereafter, C. jejuni persisted at levels ranging from 1.8 X 10(1) to 0.2 X 10(1) CFU/cm2 through the 26th week of storage. Drumsticks held at 4 degrees C showed a significant decline in count from 9.9 X 10(2) CFU/cm2 to 1.8 X 10(2) CFU/cm2 on day 7. It is concluded that the viability of C. jejuni on chicken parts is maintained under both refrigerated and freezing conditions which approximate commercial storage. This is of significance to the meat industry and consumers.     

Serum haptoglobin: an objective indicator of experimentally-induced Salmonella infection in calves

Experimental models of Salmonella -induced gastroenteritis have previously relied on crude subjective clinical markers of infection to assess disease severity. The aim of this study was to investigate the possibility that changes in serum levels of the acute phase protein, haptoglobin, may be used as an objective, quantitative measurement of infection. Eight 3- to 4-week-old animals were challenged with a mixture of three Salmonella serotypes containing 6 x 10(10)bacteria and compared with five animals given a placebo preparation. Animals were monitored and characteristic clinical symptoms of infection; diarrhoeal scores, morbidity scores and rectal temperature, were recorded. Serum samples, from both animal groups, taken prior to challenge and again on days 1, 3, and 5 post-challenge, were analysed for haptoglobin levels using a direct serum binding assay. Prior to challenge, all 13 animals had normal levels of haptoglobin in their serum. By day 3 post-challenge six of eight animals challenged with Salmonella had abnormal serum haptoglobin levels (median level = 212 microg ml(-1)), while haptoglobin levels remained normal in placebo-challenged animals (median level = 0 microg ml(-1)). The change in haptoglobin levels during the 5-day observation period was statistically significant in the Salmonella -challenged animals (P = 0.0003, H = 16.477). Serum haptoglobin levels showed a statistical correlation with clinical measures of disease severity; diarrhoeal scores (P = 0.0015, H =8. 988), morbidity scores (P = 0.0004, H = 15.711) and rectal temperature (P = 0.0001, Z = 4.304). Thus, serum haptoglobin levels closely reflect the clinical symptoms of infection and are therefore a useful marker of infection severity in salmonellosis in calves.     

Susceptibility of laboratory animals to experimental infection with Ife virus

The susceptibility of rabbits, domestic chickens and albino rats to experimental infection with Ife virus was investigated. Neither pyrexia nor clinical signs of disease were observed in infected rabbits or chickens. Low-grade viraemia (10(1.0) mouse lethal doses per 0.02 ml) occurred in intracerebrally (i.c.) inoculated chicks on the second day post-infection. Complement-fixing antibody was detected on the 14th day post-inoculation in rabbits and on the 7th day in chickens. Infant rats less than 3 and 5 days of age died after subcutaneous (s.c.) and i.c. inoculation, respectively; older rats survived infection. Ife virus titres were highest in the brain following both i.c. and s.c. inoculation.     

Pathogenesis of canine parvovirus enteritis: the importance of viremia

The clinical signs, hematologic changes, serum and fecal virus titers, specific antibody production and the occurrence of histologic lesions were studied in 22 nine-week-old seronegative beagle dogs inoculated by the oral and intravenous route with canine parvovirus. Approximately 30% of the dogs had clinical signs of pyrexia, depression, vomiting, and diarrhea irrespective of the route of inoculation. Events in the dogs inoculated intravenously preceded those in dogs inoculated orally by approximately two days. Only one dog died. Lymphopenia was the most consistent hematologic change. Viremia always preceded the initiation of fecal virus shedding. Viral titers in the serum and feces were significantly greater in symptomatic dogs compared to asymptomatic dogs. Termination of the plasma viremia coincided with the onset of the humoral immune response, but viremia persisted one day longer in symptomatic dogs. The severity of lymphoid tissue and intestinal infection, assessed by tissue immunofluorescence and histology, was also greater in symptomatic dogs. The severity of intestinal disease was highly correlated with the magnitude and duration of viremia.     

Immunologic response and resistance to experimentally induced pneumonic pasteurellosis in cattle vaccinated with various dosages of lyophilized Pasteurella haemolytica

Pasteurella haemolytica was lyophilized in an enriched soybean polypeptone broth. Lyophilization in this medium resulted in a mean 10-fold loss in P haemolytica viability, as opposed to up to a 10(4)-fold loss in viability when other media were used. Lyophilized P haemolytica was reconstituted and used as a live vaccine in 3 experiments. Calves were challenge exposed by transthoracic injection with virulent P haemolytica. In experiment 1, 2 subcutaneous injections (7-day interval between injections) with 5 ml of recently harvested (1 X 10(9) colony-forming units [CFU]/ml) or lyophilized (1 X 10(8) CFU/ml) P haemolytica significantly (P less than 0.001) enhanced resistance against challenge exposure, compared with resistance in calves given saline solution or sterile medium (control calves) or calves vaccinated with lyophilized organisms at a concentration of 1 X 10(6) CFU/ml. In experiment two, 1, 2, or 5 ml of lyophilized P haemolytica (1 X 10(8) CFU/ml) significantly (P less than 0.05) enhanced resistance, compared with resistance in calves given saline solution (control calves). In experiment three, 1 or 2 injections of lyophilized P haemolytica significantly (P less than 0.01) enhanced resistance against challenge exposure, compared with that of calves given saline solution. The mean lesion score for calves given 1 injection was not significantly higher than the mean lesion score for the group given 2 injections. Vaccination with lyophilized P haemolytica vaccine caused significant (P less than 0.05) increases in serum antibody to P haemolytica somatic antigens, to a carbohydrate-protein subunit of the organism, and to leukotoxin.