Immunosuppression of lymphocyte blastogenesis in cattle infected with Ostertagia ostertagi and/or Trichostrongylus axei

Twenty 4-month-old calves were infected with O ostertagi and/or T axei and the responses to phytolectins were evaluated. Whole blood cultures were incubated with phytohemagglutinin (PHA), concanavalin A (Con A) and pokeweed mitogen (PWM). The blastogenic response was determined by tritiated thymidine uptake with results presented as counts per minute (cpm), stimulation indices (SI) and a mononuclear cell responsive index determined by dividing the phytomitogen induced cpm by the absolute mononuclear cell number per ul. The control group results were adjusted to 100 percent and changes in the percentage difference by the parasitized calves was determined. There was a decline in lymphocyte responsiveness to PHA beginning at the time of infection. Significant depression of responses to PHA was observed in all parasitized calves 8 weeks after infection although clinical signs of parasitism did not occur. Lymphocyte responses to PW, were not different in infected calves from the control, although the O ostertagi group had significantly higher PWM mean upon than the calves infected with T. axei. A slight depression in response to Con A was also observed at 8 weeks after infection followed by a significant increase after 10 weeks. The immunosuppression appeared to be a feature of gastrointestinal parasitism and related to infections with O. ostertagi and/or T. axei.     

Lesions in lambs experimentally infected with bovine respiratory syncytial virus

Respiratory syncytial virus was inoculated intratracheally into five 1-week-old lambs. Three of the lambs responded clinically with fever, hyperpnea, and listlessness. Pulmonary lesions consisted of multifocal areas of consolidation, with necrosis of individual epithelial cells of the airways and accumulation of necrotic debris, macrophages, and few neutrophils in terminal airways and alveoli. Pulmonary septa in affected areas were infiltrated with numerous macrophages and lymphocytes. Viral particles were seen as buds on epithelial cells and free in bronchioles and alveoli.     

Development of immunity to incoming radiolabelled larvae in lambs continuously infected with Trichostrongylus vitrinus

Infective third stage larvae (L3) of Trichostrongylus vitrinus were radiolabelled with 75 selenium by a method which did not affect their viability. Three groups of six-month-old lambs were infected daily with 1000 L3 for four, eight and 12 weeks, respectively. After each period, one of those groups (n = 5) and a group (n = 4) of worm-free controls were challenged with three consecutive daily doses of 1000 radiolabelled L3, killed 10 days after the first dose, and their worm burdens examined. After four weeks of continuous infection partial immunity to the establishment of challenge L3 was apparent, and by eight and 12 weeks, with the exception of one sheep, there was almost total resistance to incoming worms. Immunity was also expressed as an inhibition of the development of established worms.     

The humoral immune response of lambs experimentally infected with Mycoplasma ovipneumoniae

Using sera from lambs experimentally infected with Mycoplasma ovipneumoniae and Pasteurella haemolytica, the development of a good humoral immune response to M. ovipneumoniae was detected by ELISA. The antibody titres peaked 41 days post-infection and good antibody titres were maintained over the 16-week experimental period. Immunoblotting revealed that antibodies to specific antigens appeared in the sera in a sequential manner, some being seen shortly after infection and others developing only after a substantial time lag. Antibodies were raised against almost all the major antigens detected in one laboratory strain (956/2) and against all antigens previously shown to be conserved in 22 Scottish field isolates of M. ovipneumoniae.     

Intestinal enzyme activity in lambs chronically infected with Trichostrongylus colubriformis: effect of anthelmintic treatment

After twenty weeks of continuous dosing with Trichostrongylus colubriformis larvae substantial, but declining, numbers of worms had persisted in most of the lambs examined, although there were wide inter-individual variations. Mucosal lesions were found in the proximal small intestines of all the infected animals, their severity being directly related to worm burden. Representative brush border enzyme activities analysed in intestinal mucosal extracts from the same lambs showed differing responses. Alkaline phosphatase and glycyl-L-leucine dipeptidase were significantly depleted, whereas maltase activity was only marginally reduced, and leucine aminopeptidase activity was normal. Mucosal acetylcholinesterase activity was significantly elevated in the parasitised animals and, interestingly in view of the postulated role of this enzyme in nematode pathogenicity, the level of activity was directly correlated with individual worm burdens. Intestinal trypsin and chymotrypsin activities were unaffected and the level of superoxide dismutase, an enzyme associated with the inflammatory response, was normal. There were also no consistent changes in the mucosal activities of several enzymes including lactic dehydrogenase, creatine phosphokinase, aldolase, and glutamic oxaloacetate transaminase, whose leakage from damaged or necrotic tissues has been well defined in terms of the concomitant increase in their activity in the circulation. Lambs treated orally with fenbendazole five and/or ten weeks before slaughter either in the presence or absence of continued larval intake, had negligible worm burdens, and showed little evidence of intestinal damage at post mortem. Brush border enzyme levels, with the exception of alkaline phosphatase and, in two cases dipeptidase, were normal in these animals. The activity of alkaline phosphatase was approximately double that in the continuously infected, untreated lambs, but remained markedly lower than in the uninfected controls. The activities of the other enzymes studied, including acetylcholinesterase, were within the control range. In summary, in chronic trichostrongylosis even relatively low nematode burdens were associated with marked pathological and biochemical damage in the intestine with both lesion severity and mucosal acetylcholinesterase activity being directly related to worm numbers. Although morphological integrity was completely restored after anthelmintic treatment, the persistent low activity of brush border alkaline phosphatase coupled with the enzymological findings in untreated, infected animals suggests that recovery of the full functional capability of the intestinal mucosa may take longer.     

Pathogenesis of bovine respiratory syncytial virus in experimentally infected lambs

Twenty-four 6-8-week-old conventionally reared lambs were inoculated intranasally and intratracheally with bovine respiratory syncytial virus. Infected lambs showed mild clinical signs characterized by slight serous nasal discharge, coughing, lachrymation and bronchovascular sounds on the middle part of the lung 5-9 days post-inoculation (PI). Virus was isolated in nasal swabs from 9 of 24 lambs between 3 and 7 days PI. However, virus was recovered from tracheal and lung tissue of all lambs killed between 3 and 11 days PI. Virus-specific antibodies appeared as early 6 days PI but high titres were attained 14-21 days PI. Lungs of lambs killed on different days PI had multifocal areas of consolidation. There was an increase of lymphocytes with a T-suppressor cell marker and a decrease in those with a T-helper marker in lung lavages obtained 5 days PI.     

Pulmonary lesions in lambs experimentally infected with ovine adenovirus 5 strain RTS-42

Twelve lambs were inoculated transtracheally and intranasally with Mastadenovirus ovi 5 strain RTS-42 and killed sequentially. Pulmonary lesions were studied by light and electron microscopy. Four lambs served as sham inoculated controls. Pulmonary lesions consisted of multifocal areas of bronchiolitis and alveolitis associated with necrosis and sloughing of isolated type I and type II alveolar epithelial cells and nonciliated bronchiolar epithelial cells. This was followed rapidly by hyperplasia of the remaining epithelium and repair of the damage. A cellular infiltrate of neutrophils and macrophages began at 2 days after inoculation, peaked at 4 days after inoculation, gradually diminished until minimal at 12 days after inoculation, and was resolved at 21 days after inoculation. Surfactant was abundant and, along with debris, was removed from the alveoli by macrophages. Clinical disease was not seen, but lesions were believed to be sufficient to allow bacteria to colonize the lungs and cause severe disease.     

Evaluation of Cymbopogon schoenanthus essential oil in lambs experimentally infected with Haemonchus contortus

Hematophagous gastrointestinal parasites cause significant economic losses in small ruminant grazing systems. The growing reports of multi-drug resistant parasites call for intensive research on alternative treatments for anthelmintics to help small ruminants cope with these parasites. Two-month-old lambs with mean body weight (BW) of 22.5 kg were experimentally infected with a multidrug-resistant Haemonchus contortus strain. Infected animals were dosed orally with Cymbopogon schoenanthus essential oil to evaluate its anthelmintic potential. Eighteen animals were allocated into three groups of six animals, and each received one of the following treatments: Group 1 - control (10 mL of water), Group 2 - C. schoenanthus essential oil (180 mg/kg BW); and Group 3 - C. schoenanthus essential oil (360 mg/kg BW). Animals received the oil once a day for 3 consecutive days. Lambs were evaluated clinically for blood biochemistry before, at 1, 5, 10, 15 and 20 days after treatment, and then were euthanized to assess the total worm burden. No statistically significant reduction in fecal egg count, packed cell volume or total worm count was observed after treatments. Also, no statistical difference among group means for blood levels of urea, creatinine, albumin, alkaline phosphatase, aspartate aminotransferase and gamma glutamyl transferase was found. Larval development assay (LDA) and egg hatch assay (EHA) were performed from feces of treated animals at 1, 5, 10 and 15 days after essential oil administration. An inhibition in LDA was observed 1 day after the 3-day treatment in larvae from feces of animals treated with 360 mg/kg essential oil. In conclusion, the essential oil at the doses of 180 mg/kg and 360 mg/kg was safe to sheep, but failed as an anthelmintic treatment when applied to young sheep artificially infected with a multidrug-resistant H. contortus strain.     

Infection and immune kinetics of Trichostrongylus axei in calves.

In one experiment, 21 calves were given daily oral immunizing inoculations of 1,000 infective larvae (L3) of Trichostrongylus axei, an abomasal nematode parasites, for 35 weeks. Calves were euthanatized in groups of three every 5 weeks to determine infection kinetics. Worm populations steadily increased through week 30, but the percentage of total inoculum that became established was about the same through week 30. At week 35, the number of worms dropped markedly. In a second experiment, 27 calves given daily oral inoculations of infective larvae were allotted to three groups comprised of three subgroups each: (A), challenge-exposed vaccinated; (B), nonchallenge-exposed vaccinated; and (C), challenge-exposed nonvaccinated. Calves of subgroups A and C were given single challenge inoculums of 200,000 L3 after the 10th, 20th, and 30th weeks. All calves were necropsied 35 days after challenge exposure. When immunity was determined from the equation: [(No. of worms in [(B + C)-A])/No. of worms in [B + C])] X 100, immunity was 35% at 10 weeks, 52% at 20 weeks, and 100% at 30 weeks.