Kinetics of antibody production and clinical profiles of calves experimentally infected with Listeria monocytogenes

Clinical and serum antibody profiles were studied during oral Listeria monocytogenes infection of calves. No clinical signs, except for pyrexia with mild diarrhoea and staggering gait, were observed in the infected calves. Specific antibodies to listeriolysin O (LLO) appeared as early as day 8 of an oral infection and peaked by days 16-32 of infection. Antibodies to LLO were observed to persist over the period of 126 days observed in the study. LLO being a major virulence factor and capable of inducing a humoral response could therefore be used as an antigen for development of an immunoassay for diagnosis of Listeria monocytogenes infections in animals.     

Prevalence of agglutinating antibodies to Sarcocystis neurona in raccoons, Procyon lotor, from the United States

Equine protozoal myeloencephalitis (EPM) is the most important protozoal disease of horses in North America and it is caused by Sarcocystis neurona. Natural cases of encephalitis due to S. neurona have been reported in raccoons, Procyon lotor. We examined 99 raccoons for agglutinating antibodies to S. neurona using the S. neurona agglutination test (SAT) employing formalin-fixed merozoites as antigen. Raccoons originated in Florida (N=24, collected in 1996), New Jersey (N=25, collected in 1993), Pennsylvania (N=25, collected in 1999), and Massachusetts (N=25, collected in 1993 and 1994). We found that 58 (58.6%) of the 99 raccoons were positive for antibodies to S. neurona using the SAT; 44 of 99 raccoons (44%) had titers of ≥1:500. This prevalence is similar to the reported seroprevalence of 33–60% for S. neurona antibodies in horses from the United States using the Western blot test.     

Hematologic values in calves infected with Sarcocystis cruzi

Calves were inoculated with 2 X 10(5) Sarcocystis cruzi sporocysts. Red cell mass decreased dramatically between Days 21 and 35 post-infection and plasma volume increased concurrently, so that blood volume did not change significantly. Mild reticulocytosis and increased pyrimidine 5' nucleotidase activity in erythrocytes occurred between Days 35 and 42. Antiglobulin tests with anti-bovine IgG, IgM and C3 were negative, with the exception of a positive test for C3 in 1 of 6 infected calves.     

Self-cure in zebu calves experimentally infected with Trypanosoma vivax

The course of an experimental infection of Zebu calves (6-12 months old) with Trypanosoma vivax was studied. Three of eight (38%) infected calves died, two within the first three weeks of infection and the other at 17 weeks. The remaining animals were self-cured. It would appear that self-cure of the infection was related to the ability of the calves to control parasitaemia as well as the severity of anaemia.     

Ostertagia ostertagi in neonatal calves: establishment of infection in ruminating and non-ruminating calves

An experiment was carried out to study the role of the ruminal function in the establishment of Ostertagia ostertagi in neonatal calves. Three groups of calves were fed either milk only (groups A and C), or hay and concentrate in addition to milk (group B) from birth. At the time of infection, ruminal function was negligible in groups A and C, whereas it was well developed in group B. Calves of groups A and B were each given 25,000 normal ensheathed infective larvae of O ostertagi and those of group C were given 25,000 infective larvae exsheathed in vitro. Daily faecal egg output and post mortem worm counts 28 days after infection were higher in calves with well developed ruminal function than those having only negligible ruminal function. In the latter group, exsheathed larvae established at a lower rate than did ensheathed larvae. The results suggest that the degree of development of the ruminal function influences the establishment of O ostertagi.     

Histopathologic and histochemic changes in the small intestine of calves infected with Trichostrongylus colubriformis

The pathologic effects of Trichostrongylus colubriformis on the small intestine of 8-week-old calves were studied. Morphologic and enzymic alterations were confined to the proximal third of the small intestine, which was shown to be the principal habitat of the nematode. Changes in the mucosa varied according to the acuteness of the infection rather than the duration. Villous atrophy, infiltrations of the lamina propria with plasma cells and lymphocytes, infiltrations of glandular tissue with eosinophils, and necrosis and erosions of the surface epithelial cells were present. Enzymic changes were related to the extent of cellular injury. Alkaline phosphatase and leucine aminopeptidase were more severely reduced, while nonspecific esterase and succinic dehydrogenase were less affected. Enzymic activities in the distal areas were nor influenced by the lesions in the proximal region.     

Interleukin-2 and interleukin-10 gene expression in calves experimentally infected with Fasciola gigantica

The gene expression of interleukin-2 and interleukin-10 in calves with a primary infection of Fasciola gigantica was studied. Five calves were infected orally with a dose of 1000 viable metacercariae of F. gigantica and five calves served as uninfected control animals. Expression of two cytokine genes i.e. IL-2 and IL-10 (Th1 and Th2) was measured at 10, 30 and 75 days post-infection (PI) by real-time polymerase chain reaction with the double stranded DNA-binding dye SYBR Green. Interleukin-2 was not detected in the peripheral blood mononuclear cells (PBMCs) of infected or control animals at 10, 30 and 75 days PI, however, IL-10 was present in detectable levels in PBMCs of infected animals at 10, 30 and 75 days PI, with no expression of this cytokine in the control animals. With an increased expression of IL-10 and no expression of IL-2 cytokine gene, the present study suggests that F. gigantica infection in calves evoked Th2 immune response.     

Asymptomatic encephalitis in calves experimentally infected with bovine herpesvirus-5

This study demonstrated that bovine herpesvirus 5 (BoHV)-5 infected calves can develop encephalitis and remain asymptomatic. Seven calves were infected intranasally and monitored for 30 days. Cerebrospinal fluid (CSF) analysis was performed from the onset of neurological signs. Multiple sections of brain and the trigeminal ganglion were submitted to histopathology. Virus detection (PCR and isolation) was performed on CSF and tissues. Four calves developed signs of neurologic disease and died. Three calves remained asymptomatic and were euthanized 30 days post-infection. Cerebrospinal fluid mononuclear pleocytosis occurred in symptomatic and asymptomatic calves. BoHV-5 was isolated and viral DNA was detected in multiple areas of the encephalon of all calves. The viral DNA was detected in the CSF of 2 calves showing neurological signs. Histologically, inflammation was noted in the brain of all calves and confirmed that the encephalitis caused by BoHV-5 may be mild and asymptomatic.     

Efficacy of difloxacin in calves experimentally infected with Mannheimia haemolytica

OBJECTIVE: To determine the efficacy of difloxacin, a novel fluoroquinolone antibiotic, in calves experimentally infected with Mannheimia haemolytica (formerly Pasteurella haemolytica). ANIMALS: Seventy-two 3-month-old Holstein calves. PROCEDURES: Calves were inoculated with M haemolytica intratracheally; after they developed clinical signs of pneumonic pasteurellosis, they were randomly assigned to 1 of 6 groups (n = 12/group). Calves in each group were treated with 10% difloxacin (2.5 or 5 mg/kg of body weight), 5% difloxacin (2.5 or 5 mg/kg), enrofloxacin (5 mg/kg), or saline (0.9% NaCl) solution (control group), once daily for 5 days, and clinical signs were scored daily. On day 15, calves were euthanatized, and the percentage of diseased lung tissue was calculated. Swab specimens of the lungs were submitted for bacterial culture. RESULTS: Mortality rate and percentage of diseased lung tissue were significantly higher and cure rate and average daily gain were significantly lower for control calves, compared with calves in the treatment groups; however, no significant differences were found among treatment groups. Mannheimia haemolytica was isolated from the lungs of 10 control calves and from at least 2 calves in each of the treatment groups. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that difloxacin and enrofloxacin were equally effective for treatment of calves with experimentally induced pneumonic pasteurellosis. However, treatment of infected calves with difloxacin or enrofloxacin may not eliminate the organism.     

Depressed immunoconglutinin responses in calves experimentally infected with Trypanosoma congolense

Contrary to expectation, immunoconglutinin levels failed to rise significantly in calves infected with Trypanosoma congolense. In addition, it was shown that trypanosome infection appeared to inhibit the immunoconglutinin response to Brucella abortus strain 19. The possible reasons for these findings are discussed.     

Stillbirth/perinatal weak calf syndrome: a study of calves infected with Leptospira

Leptospiral infection has been reported in calves which were either stillborn or dead from perinatal weak calf syndrome; 356 such calves were examined for evidence of associations between leptospiral infection and macroscopic, histological and microbiological findings, and the parity of the dam. Calves in which leptospiral antigen was detected in the placenta were significantly lighter by an average of 6 to 10 kg than calves with no antigen in the placenta. Calves infected with Leptospira were more likely to be infected by Actinomyces pyogenes or Bacillus species. No other significant associations were detected. The adrenal gland, lung and placenta were the most useful organs to examine for leptospiral antigen. The placenta was the only antigen-positive tissue 8.9 per cent of the calves submitted with their placenta.