Listeriosis in Sheep: Tick-Borne Fever used as a Model to Study Predisposing Factors

Three groups of 6 months old lambs, each group consisting of 5 animals, were infected experimentally with Ehrlichia phagocytophila (Ep), Listeria monocytogenes (Lm) and Ep/Lm, respectively. All the animals had a period with fever and reduced appetite after infection, and these symptoms were most pronounced in the group with the combined infection (Ep/Lm). One animal in group Lm developed listeric meninigo-encephalitis.Lm was isolated from blood samples from both groups infected with Lm during the first week after infection, and from faecal samples during the first 2 weeks. Lm was also isolated from organs from several animals in these 2 groups at post-mortem examination.Group Ep/Lm developed the highest reciprocal geometrical mean titres and the stromgest delayed hypersensitivity reaction against Lm.After infection, a fall in serum iron and albumin was recorded, and the groups infected with Ep had a substantial fall in neutrophils.The myeloid : erythroid ratio in the bone marrow tended to decrease in Group Ep/Lm after infection.An increase in leucocyte counts and total protein content was found in the cerebrospinal fluid in the 2 groups infected with Lm, The experiment indicates that the blood changes induced by tick-borne fever viz, neutropenia and probably also impaired function of the neutrophils, may predispose for listeric septicaemia, but probably not for listeric meningo-encephalitis.     

Listeriosis in Sheep: Experimental Listeric Infection in Sheep Treated with Various Immunosuppressiva

Four groups of lambs, about 6 months old, were given 4 different immunosuppressiva (prednisolone, cyclophosphamide, niridazole and gestagene hormones), 1 substance to each group. After this treatment the 4 groups together with a 5th group of the same size, were infected with Listeria monocytogenes (Lm).None of the animals developed clinical listeric encephalitis. The level of antibodies differed between the groups. The group not given any immun osuppressivum reached the highest antibody titres, the group given gestagene hormones had the lowest titres and the other groups ranged somewhere inbetween. All the groups except the group treated with niridazole had a strong delayed hypersensitivity reaction against Lm. The effects of the treatment upon some blood components are also described.Further studies are necessary to establish the effect of various immunosuppressiva, especially gestagene hormones.     

Listeriosis in Sheep: Listeria Monocytogenes in Sheep Fed Hay Or Grass Silage During Pregnancy. Immunological State,White Blood Cells,Total Serum Protein and Serum Iron

A comparison was made between a hay fed group, consisting of 23 ewes, and a grass silage fed group of 22 ewes, all pregnant. Excretion of Listeria monocytogenes (Lm) in the faeces and milk, antibody titres in sera and whey and delayed hypersensitivity against Lm, and several blood components were determined. The animals had previously been exposed to Lm, and Lm was isolated from the faeces from several animals when the experiment started.No significant difference in number of excretors between the 2 groups was found during the experimental period. The haemagglutination titres in both sera and whey were low and on the same level in both groups. The titres were higher in animals with 1 foetus than in animals with more than 1 foetus.In the first part of the experimental period the silage group had a reduced number of lymphocytes, lower total serum protein values and higher serum iron values, compared with the hay group.The silage group also had a stronger delayed hypersensitivity reaction against Lm than the hay group, and in the silage group the reaction was significantly stronger in ewes with 3 or more foetuses than in ewes with 1 foetus.In conclusion, the combined effect of some of the changes found in animals fed grass silage may leave them more susceptible to infections.     

Listeriosis in sheep. Listeria monocytogenes excretion and immunological state in healthy sheep.

Listeriosis in sheep. Listeria monocytogenes excretion and immunological state in healthy sheep. Acta vet. scand. 1979, 20, 168–179. — The excretion of Listeria monocytogenes (Lm) in the faeces and milk, and humoral and cell mediated immunity against Lm, were examined in a sheep flock where no cases of listeriosis had occurred during the last 3 years. The investigation was carried out during the indoor season. During the first part of the season 2 of the 10 pregnant, 8 months old lambs excreted Lm in the faeces, but none of the 106 ewes, 2–10 years old. At lambing the organism was isolated from the faeces of 6 of the 10 1 year old lambs and from 64% of the ewes, and from the milk of 1 of the lambs and 41% of the ewes. Nearly all the isolates (98.5%) belonged to serotype 1.Antibody titres against Lm were found in sera and whey by an indirect haemagglutination method. The titres were higher for the ewes than for the hoggs and seemed to be influenced by the number of foetuses the animals carried.Cell mediated immunity was determined by a skin test where delayed hypersensitivity against an antigen prepared from Lm, was measured. Animals fed grass silage had a stronger reaction than animals fed hay, and a stronger reaction was found in animals with ≥ 3 foetuses than in the remainder.The investigation indicates that even in a healthy sheep flock all the animals may be exposed to Lm, and the majority may be latent carriers and excrete this organism in the faeces and milk during periods of stress.     

Clinical, haematological and plasma biochemical changes in specified-pathogen-free (sporozoa) lambs experimentally infected with low numbers of Sarcocystis tenella sporocysts

Two groups of lambs raised free of sporozoan infection were inoculated with Sarcocystis tenella sporocysts and compared with controls. Lambs from Group 1 were inoculated with 5000 sporocysts and those in Group 2 were given 20,000. Transient increases in rectal temperatures occurred between 23 and 39 days post-inoculation (dpi), although the lambs appeared normal and retained their appetites. Packed cell volumes (PCV) of lambs given 20,000 sporocysts decreased dramatically from 28 to 38 dpi after which they slowly returned to near pre-inoculation levels by 99 dpi. The anaemia was normocytic/normochromic. White cell counts (WCC) rose in infected lambs from 49 dpi, reflecting principally an increase in lymphocyte numbers. Plasma albumin of Group 2 decreased at 28 dpi and remained depressed until the experiment was terminated at 99 dpi. Plasma globulin of infected groups increased from 31 (Group 2) and 35 dpi (Group 1). Plasma alkaline phosphatase (ALP) of Group 2 decreased from 28 dpi and remained depressed to 99 dpi. Lactate dehydrogenase (LDH) of Group 2 was elevated at 24 and 28 dpi and from 42 to 78 dpi, while aspartate aminotransferase (AST) of the same group was elevated from 45 to 66 dpi. Creatine kinase (CK) of Group 2 was elevated from 52 to 71 dpi.     

Influence of dietary protein on the pathophysiology of haemonchosis in lambs given continuous infections

Mixed-sex groups of three-month-old Finn Dorset and Dorset Horn lambs were given complete diets containing either high or low protein. A trickle infection with Haemonchus contortus of 200 larvae, given three times a week, began one month later for a 17 week period. Erythrokinetic, metabolic, digestibility and balance studies were conducted with the male lambs during weeks 12 to 14 of the infection. Clinical signs of haemonchosis became evident only in the low protein diet group. The infection was characterised by severe macrocytic anaemia, hypoproteinaemia, hypoalbuminaemia, reduced survival, high egg counts and a significantly greater worm burden. In the high protein diet group many lambs developed resistance to further infection in contrast to the low protein group in which no resistance developed. Live-weight gain was not affected by infection in the high protein diet group but decreased in the lambs given the low protein diet compared with uninfected controls. However, infection did not appear adversely to affect the digestive efficiency, nitrogen retention or iron absorption in either dietary group although loss of appetite occurred in the low protein group. Examination of a sample joint from the carcases showed infection was associated with a marked reduction in muscle mass in lambs given the low protein diet relative to the control animals.     

An experimental study on the pathogenicity of the caprine herpesvirus type 1 (CHV-1).

The pathogenicity of caprine herpesvirus type-1 (CHV-1) in goat kids and lambs was studied. Two experiments were carried out. In the first, two Saanen goat kids and four lambs of a local breed were infected intravenously with the Swiss strain E/CH of the virus. Clinical reaction was severe in the kids, but it was very mild in the lambs. Virus was excreted from the kids in higher titres and longer than in lambs. Virus was also isolated from tissue specimens but only from a kid that died on post inoculation day 4 (PID 4). The gross- and histopathological lesions were more severe in kids. In the second experiment only lambs were used. They were dexamethasone treated and then virus inoculated. A very mild infection developed. The lambs did not shed the virus, neither the virus was isolated from their tissues collected at necropsy. Nevertheless histopathological lesions were seen. In both experiments the animals seroconverted on PID 10.     

The effect of dietary protein on the pathogenesis of acute ovine haemonchosis

Two experiments were conducted to examine the ifluence of dietary proteins on parasite establishment and pathogenesis in Finn Dorset/Dorset Horn lambs infected with Haemonchus contortus. The lambs were introduced to high (169 g) or low (88 g crude protein (CP) kg⁻¹ dry matter (DM)) protein diets at 3 months of age and infected 1 month later with 350 larvae kg⁻¹ body weight (BW). Blood and faecal smaples were collected for analysis and body weights recorded weekly. In the first experiments some of the infected lambs were killed 6 weeks after infection and the remainder 5 weeks later. In the second experimental all the infected lambs were killed 4 weeks after infection.

The results showed that lambs on a low protein diet were less able to withstand the pathogenic effects of infection with 350 H. contortus larvae kg⁻¹ BW than lambs given the higher protein diet. Thus mortality was greater in the low protein group and adverse clinical signs, such as inappetance, weight loss and oedema were osbserved more frequently. This group also had a more severe anaemia, hypoproteinaemia and hypoalbuminnaemia than the high protein group. In contrast, faecal egg counts, total daily faecal egg output and worm burdens were similar in all groups of infected lambs, indicating that the diets did not influence parasite establishment.     

Analysis of the kinetics, isotype and specificity of serum and coproantibody in lambs infected with Cryptosporidium parvum

Enteric cryptosporidiosis was studied in colostrum-deprived lambs each infected at five days old with 10(6) oocysts. The prepatent period was three to five days and faecal oocyst concentration fell below detectable levels by day 16 after infection. Specific IgA, the only isotype detected by immunofluorescent assay in faecal extracts from infected lambs, was first evident on day 10 and titres continued to rise until day 16 of infection in association with declining oocyst output. Specific IgM and IgG antibodies were first detected in serum seven days after infection. No specific antibody was detected in uninfected control lambs. Immunoblotting methods showed that serum antibody and faecal IgA had similar profiles of antigen recognition. Antigens with approximate molecular weights of 180,000, 23,000 and 15,000 were consistent features on immunoblots performed with convalescent sera and faecal extracts. The results suggest that specific IgA in intestinal secretions has an important role in immunity to cryptosporidiosis.     

Effect of Peganum harmala (wild rue) extract on experimental ovine malignant theileriosis: pathological and parasitological findings

Malignant theileriosis of sheep is a highly fatal, acute or subacute disease is caused by the tick-borne protozoan parasite, Theileria hirci. In this investigation ten healthy male lambs aged 5-6 months were randomly divided into two groups, A and B and were kept in isolated tick-proof pens. They were treated for internal and external parasite before commencement of the experiment. The lambs were experimentally infected with T. hirci by placing ticks Hyalomma anatolicum anatolicum infected with T. hirci on them. The ticks used in this survey had originally been isolated from sheep and colonies of them were established in an insectarium. Before and after infection rectal temperatures and clinical signs of the lambs were recorded, blood and prescapular lymph node smears were prepared and examined to determine the extent of the parasitaemia, and blood samples were analyzed to evaluate their haemoglobin (Hb) and packed cell volume (PCV) rates. Three days after the commencement of a febrile reaction and appearance of the schizonts in the lymph node smears, treatment of the lambs in Group A with an extract containing the alkaloids of Peganum harmala (wild rue) was commenced. Group B lambs were kept untreated controls. Before treatment there were no significant differences in the rectal temperature, parasitaemia rate, and the Hb and PCV values between animals in the two groups but after treatment significant differences in these values was detected (P < 0.05). After treatment, the clinical signs and parasites in the lymph node smears of the animals in Group A disappeared and they all animals recovered. These parameters in the animals of Group B progressed until their death. Pathological studies showed the characteristic lesions of theileriosis in lambs in Group B, but not in Group A. The results indicate a therapeutic effect of the alkaloids of P. harmala for treatment of ovine malignant theileriosis.     

Experimental infection of the udder of ewes due to Mycoplasma bovis

Twelve freshly lactating ewes were experimentally infected with 2 Mycoplasma (M.) bovis strains via the teat canal in the left udder. The M. bovis infection produced a febrile clinical mastitis in all infected animals. M. bovis could be re-isolated regularly from the experimentally infected udder halves and the infection spread to the other halves. Some contact animals and 4 suckling lambs became naturally infected. Antibody titres were detected by means of the indirect hemagglutination test in blood sera 2 to 3 weeks post infectionem. The pathological lesions were similar to those of the M. bovis mastitis of cows. By the end of the trial the ewes had recovered from the clinical mastitis.     

Studies on the pathogenicity of bovine herpesvirus type 5 in sheep.

Four Merino lambs were intranasally inoculated with bovine herpesvirus type 5 (BHV-5) reference strain N569. Two lambs were mock-inoculated as negative controls. The virus-inoculated animals developed apathy, inappetence, rhinitis, nasal, ocular and genital discharge, slight diarrhea and neurological disorders, like tremor and salivation. BHV-5 was isolated from the nasal discharge in two of the animals, while the polymerase chain reaction (PCR) detected the virus in all the infected lambs. Two lambs died on post infection day (PID) 13, while the other two infected animals were euthanized on PID 15 and 30. Gross pathological changes were not observed, however, histopathological examinations revealed diffuse nonsuppurative meningo-encephalitis in all infected animals. Viral antigen was detected by immunohistochemistry and viral nucleic acid was revealed by in situ hybridization in the brain of the two lambs, which died on PID 13. The virus was demonstrated by virus isolation and by PCR from different organs of all the infected animals. Slight rise of antibodies was observed in the infected animals from PID 15. The results show that BHV-5 is able to cross the species barrier and may establish infection in sheep.     

Immunity of specific pathogen-free lambs to challenge with an aerosol of Pasteurella haemolytica biotype A serotype 2. Pulmonary antibody and cell responses to primary and secondary infections

Specific pathogen-free (SPF) lambs previously exposed to an aerosol of P. haemolytica biotype A serotype 2 (A2) were immune to subsequent challenge with an aerosol of P. haemolytica A2. Untreated control lambs were not immune to this challenge. The local immune responses of the lung to these challenges were examined. High IgG and IgA titres to P. haemolytica and high levels of opsonizing antibody against P. haemolytica were present in the lung washings from previously infected immune lambs at autopsy, seven days after the second infection. Lung washings from control lambs, 7 days after challenge with P13 virus and P. haemolytica A2, had no IgG titres, very little opsonizing activity but did have IgA titres which were significantly higher than in unchallenged control lambs. The cellular response of animals challenged with P13 virus and P. haemolytica was significantly greater than that of unchallenged controls or of lambs exposed only to P. haemolytica. However, this finding was complicated by the response to P13 virus. Lymphocytes from lung washings of all lambs failed to respond in a lymphocyte stimulation test to phytohaemagglutinin while blood lymphocytes did respond. There was little specific response to P. haemolytica antigen in the test.     

The influence of dietary protein on live bodyweight, degree of anaemia and erythropoietic responses of Scottish Blackface sheep infected experimentally with Trypanosoma congolense

The present study investigated the influence of dietary protein on the intensity of parasitaentia, degree of anaemia and erythropoietic responses, in sheep experimentally infected with Trypanosoma congolense and given either a high protein diet (116 g digestible crude protein [dcp] per day) or a low protein diet (51·5 g dcp per day). It was observed that infected and control animals on the high protein diet grew at similar rates while infected animals on the low protein diet experienced marked retardation of growth compared with their uninfected controls. Dietary protein had no influence on the degree of anaemia that followed infection. Measurement of blood volumes revealed that low protein infected group had significantly lower mean circulating red cell volume than their controls. Ferrokinetic measurements indicated that plasma iron turnover rates (pitr) and ⁵⁹Fe incorporation rates were higher in the high protein infected group than in the low protein infected group, although these differences were not significant. These observations indicate that infected animals on a high protein tended to show greater enhancement of erythropoietic activity that infected animals on low protein diet.     

Effect of Haemaphysalis punctata infestation on growing lambs and rabbits

Lambs infected with adult Haemaphysalis punctata and rabbits infected with nymphs developed a macrocytic normochromic anaemia during seven and six successive infestations, respectively. The anaemia was directly proportional to the degree of infestation but disappeared several days after the termination of infestation. A leucocytosis, due to neutrophilia, was seen in both lambs and rabbits. Rabbits developed a thrombocytosis and reticulocytosis. Infested lambs grew less rapidly than uninfested animals. Signs of tick toxicosis and several other clinical manifestations appeared in both infested sheep and rabbits. Circulating antibodies against salivary antigen of adult H punctata were demonstrated in the sera of infested lambs by the micro-ELISA test. Titres were first detected on day 3 after infestation and increased gradually as infestation progressed. No precipitating antibodies in either infested sheep or rabbits were detected.     

Pathophysiology of ovine trypanosomiasis: ferrokinetics and erythrocyte survival studies.

The haematological changes, erythrokinetics and ferrokinetics of sheep were investigated after infection with Trypanosoma congolense. Following the detection of parasites in blood, the infected sheep developed macrocytic hypochromic anaemia. Studies with 51Cr-red cells, 125I-albumin and 59Fe as ferric citrate 11 weeks after infection revealed that infected sheep had significantly lower mean circulating red cell volumes but higher plasma and blood volumes than control sheep. The infected sheep also had enhanced erythropoietic activity as judged by significantly higher plasma iron turnover rates, faster disappearance of radio-labelled iron and higher iron incorporation rates than control sheep. The rate of disappearance of 51Cr-labelled red cells was greater in infected than in control sheep. It was concluded that the anaemia observed at this stage of infection was due to an increased rate of removal of red cells from the circulation coupled with haemodilution, with no evidence of dyshaemopoiesis.     

Classical and alternative pathway haemolytic activities of ovine complement: variations with age and sex

The classical (CH50) and alternative (ACH50) pathway haemolytic activities of sheep complement were measured with microtechniques. Storage of blood at room temperature (instead of 4 degrees C) before centrifugation and usage of sera stored at -70 degrees C were compatible with complement titration. The effects of age and sex were tested in 303 sera obtained from animals aged between 2 weeks and 3.5 years old. ACH50 titres were low during the first 1.5 months of life then increased to reach the level found in adults at the age of 3 months. Conversely, CH50 titres were very high in suckling lambs, decreased up until the age of 3 months and then increased to reach the adult level at 1 year old. In lambs, the haemolytic complement activity was significantly higher in females than in males.     

Anaemia in housed lambs: effects of oral iron on clinical pathology and performance

An experiment including 39 pairs of housed twin lambs was performed to evaluate the effect of an oral iron supplement (Fe-MAX Starter) on clinical pathology, growth rates and disease occurrence. Significant differences between the iron supplemented group (Fe-group) and the controls were seen, for varying periods of time, for all red blood cell and iron parameters examined. In spite of this, 25% of the iron supplemented lambs had haemoglobin values below 80 g/L 4 weeks after treatment, whereas 33% of the controls had corresponding values 3 weeks after treatment, indicating that one single iron dose was insufficient to prevent iron deficiency anaemia. No significant positive effect on live weights was seen. However, the Fe-group had a poorer daily weight gain during the first week after dosing (p < 0.01), but a better daily gain during the second (p < 0.01) and third weeks. No effects were seen on disease occurrence. An additional trial with iron dextran injections to 5 untreated 21 days old lambs with varying haemoglobin values, revealed a rapid increase in the red cell distribution in anaemic lambs, with production of macrocytic, mainly normochromic erythrocytes. The new erythrocyte population was visible on the cytogram after 2 to 3 days and on the histogram after 5 days.     

Acute phase response to Mycoplasma haemofelis and 'Candidatus Mycoplasma haemominutum' infection in FIV-infected and non-FIV-infected cats

The pathogenicity of Haemoplasma spp. in cats varies with 'Candidatus Mycoplasma haemominutum' (CMhm) causing subclinical infection while Mycoplasma haemofelis (Mhf) often induces haemolytic anaemia. The aims of this study were to characterise the acute phase response (APR) of the cat to experimental infection with Mhf or CMhm, and to determine whether chronic feline immunodeficiency virus (FIV) infection influences this response. The acute phase proteins serum amyloid A (SAA), haptoglobin (Hp) and α-1-acid glycoprotein (AGP) concentrations were measured pre-infection and every 7-14days up to day 100 post-infection (pi) in cats infected with either Mhf or CMhm. Half of each group of cats (6/12) were chronically and subclinically infected with FIV. Marbofloxacin treatment was given on days 16-44 pi to half of the Mhf-infected cats, and on days 49-77 pi to half of the CMhm-infected cats. FIV-infected animals had significantly lower AGP concentrations, and significantly greater Hp concentrations than non-FIV-infected cats when infected with CMhm and Mhf, respectively. Both CMhm and Mhf infection were associated with significant increases in SAA concentrations, while AGP concentrations were only significantly increased by Mhf infection. Mhf-infected cats had significantly greater SAA concentrations than CMhm-infected animals. Both Mhf and CMhm infections were associated with an APR, with Mhf infection inducing a greater response. Chronic FIV infection appeared to modify the APR, which varied with the infecting Haemoplasma species.     

Listeriosis in sheep. Listeria monocytogenes excretion and immunological state in sheep in flocks with clinical listeriosis.

The excretion of Listeria monocytogenes (Lm) in the faeces and milk, and humoral immunity against Lm, were examined in a sheep flock with outbreaks of listeric encephalitis and in a flock with outbreaks of listeric abortion. The encephalitis flock consisted of 86 ewes and 20 hoggs, the abortion flock of 45 ewes and 3 hoggs, all of them pregnant. Faecal excretion rate in the encephalitis flock varied from about 25 % in the first part of the indoor season to nearly zero 1 month later, to about 30 % 1 month before lambing and about 15 % at lambing. About 15 % of the animals also excreted Lm in the milk. Lm 4 was the dominating serotype.In the abortion flock about 2/3 of the animals excreted Lm in the faeces and 1/3 in the milk at lambing. All the isolates belonged to serotype 1, which also was isolated from grass silage and strawbedding samples.In the encephalitis flock ewes with ≥ 3 foetuses had a higher excretion rate than the remainder, while no such differences were found in the abortion flock.Antibody titres against Lm in sera and whey in the encephalitis flock were of the same order as in the healthy flock described in an earlier publication (Grønstøl 1979), except that the highest titres were found in the hoggs. Serum titres from the abortion flock after lambing were significantly higher than in the encephalitis flock, while whey titres were of the same order.Treatment with 2-mercapto-ethanol reduced the titres substantially in sera from the abortion flock, indicating that the antibodies belonged to the IgM-fraction, while only a slight reduction was seen after similar treatment of the whey.