Infected Ewes Research Articles

Maternal transfer of protection from Echinococcus granulosus infection in sheep

Although passive immunity against larval metacestodes of the genus Taenia is well established, the transfer of immunity against Echinococcus granulosus infection has not been demonstrated convincingly. The immune status of newborn lambs born to ewes that had been infected or immunised with E granulosus eggs or oncospheres was investigated. The ewes and their six- to eight-day-old lambs were subsequently challenged. Lambs born to triply infected ewes were 80 per cent protected from a challenge infection whereas lambs born to singly infected ewes were only 45 per cent protected. Lambs born to ewes that had been immunised with preparations of sonicated oncospheres had the lowest levels of immunity. The infected ewes were challenged intramuscularly with activated oncospheres and showed some degree of immunity. Ewes which had received oncospheres solubilised in sodium dodecylsulphate or sonicated oncospheres were protected from subsequent oral challenge by 60 to 66 per cent. Radial immunodiffusion revealed that lambs with statistically significantly lower levels of IgG were more susceptible to challenge. However, the degree of protection did not show a simple relationship to the titre of antibody, as determined by an elisa using a solubilised antigen.

Brain malformations in ovine fetuses associated with the cytopathogenic biotype of bovine viral-diarrhoea virus.

A total of six ewes were intravenously inoculated at between 65 and 68 days of gestation with the Indiana strain of bovine viral diarrhoea virus (BVDV), containing both non-cytopathogenic (ncp) and cytopathogenic (cp) biotypes. Eight transplacentally infected fetuses were sequentially removed from the infected ewes and were found to have inflammatory lesions and malformations of the brain. BVDV RNA was isolated from formalin-fixed, paraffin-embedded brain tissue sections and detected by nested polymerase chain reaction after reverse transcription. The two biotypes of BVDV were distinguished by the fact that a sequence insertion in the RNA of the cp biotype of the inoculum results in larger amplicons. Only RNA from cp BVDV was detected in three of the brains removed up to 14 days post-inoculation (p.i.), and no BVDV RNA was detected after more than 14 days p.i. These findings suggest that, in critical phases of development, cp BVDV may transplacentally infect the ovine fetal brain and cause malformations.

Development and evaluation of an indirect ELISA to detect antibodies to abortion strains of Chlamydia psittaci in sheep sera

A novel indirect enzyme-linked immunosorbant assay (ELISA) for antibodies against abortion strains of Chlamydia psittaci (C. psittaci) has been developed. The antigen used was chlamydial elementary bodies treated sequentially with N-lauroyl sarcosine and n-octyl-β-D-glucopyranoside and finally solubilized with N-lauroyl sarcosine and dithiothreitol. Treating the antigen with sodium periodate after coating of the plates increased the specificity for antibodies to abortion strains. The test was evaluated initially with sera from experimentally infected sheep and an uninfected control group. These sheep were monitored for lambing performance and infection status. When used in conjunction with the indirect micro-immunofluorescence test (MIF), the ELISA was able to identify as negative all twenty-five sera from ewes that had no typical placental lesions and identified as positive twenty of twenty-one sera from infected ewes that had either typical placental lesions or had been found positive by isolation of chlamydia in cell culture. The combination of ELISA and MIF was also able to discriminate correctly groups of sera from six flocks with a history of infection from four known uninfected flocks.

Effects of postpartumTrypanosoma vivaxinfection on feed intake, livevveight changes, milk yield and composition in West African Dwarf ewes and associated lamb growth rates

SUMMARYThe effects of trypanosomiasis on digestible organic matter intake, milk yield and composition, dam liveweight changes during lactation and lamb growth rates were investigated at Ibadan, Nigeria 1991/92, using 20 West African Dwarf sheep nursing single lambs. Although digestibility coefficients were neither affected by infection nor by level of feed intake, organic matter intake during early and late lactation was significantly lower in infected dams. Nitrogen retained in late lactation was lower in infected animals due to reduced feed intake. Mean daily milk yields were not affected by the infection during early lactation; however, during the second half of lactation, average daily milk yields were significantly lower in infected animals than in uninfected controls. Variations in milk component concentrations between experimental groups did not attain statistical significance throughout lactation. While control ewes on a high plane of nutrition (CH) gained 12·1 g/day, infected ewes (IH) and uninfected control ewes on a medium plane of nutrition (CM) lost 45 and 5·4 g/day respectively during lactation. Liveweight gain in the lambs was not affected by infection in the dams.This study demonstrated reduction in feed intake, late lactation milk yield and dam liveweight gain with no adverse effect on digestibility coefficients, milk composition, early lactation milk yield and lamb weight gain duringT. vivaxinfection of lactating ewes.

Effects ofTrypanosoma vivaxinfection during pregnancy on feed intake, nitrogen retention and liveweight changes in West African Dwarf ewes

SUMMARYThe effects of infection withT. vivaxin mid- or late pregnancy on food intake and utilization, liveweight changes, abortion rate and lamb growth rate were investigated in West African Dwarf ewes at lbadan, Nigeria in 1990. Rate of liveweight gain by ewes infected during mid-pregnancy (IMH) was16 g/day compared with 33 and 37 g/day for the uninfected ewes offered medium (CM) or high (CH) plane diets. Although digestibility coefficients were not affected, intake of digestible organic matter was higher in CH ewes than in IMH and CM ewes. Nitrogen retention at mid-pregnancy on a metabolic size basis was higher in CH ewes than in CM and IMH ewes.Lamb birth weight and survival rate were lower in infected ewes. Ewes infected in mid-pregnancy (IMH) and in late pregnancy (ILH) had mean birth weights of 1·4 and 1·0 kg compared with CM and CH ewes, which had mean birth weights of 1·9 and 2·0 kg respectively. Observed survival rates were 63, 15, 75 and 80% for lambs nursed by IMH, ILH, CM and CH ewes respectively. During the first 6 weeks postpartum, lamb growth rate in all groups did not differ. However, during weeks 7–12 postpartum, lambs nursed by IMH ewes had significantly lower growth rates. Weaning weight was also lower in lambs from IMH (5·0 kg) dams than in lambs from CM and CH dams (7·1 kg). Infection during late pregnancy was more severe and all infected ewes lost weight due to reduced feed intake and fever.T. vivaxinfection in sheep is responsible for reproductive wastage, abortion, poor lamb growth and ewe mortality.

Ovine Lentivirus (Maedi-visna Virus) Protein Expression in Sheep Alveolar Macrophages

The expression of gag (p15, p25) and env gene products in ovine lentivirus-infected cells was studied in 20 adult Texel ewes seropositive to maedi-visna virus and 10 seronegative matched controls. Bronchoalveolar lavage was performed to recover alveolar cell pools from which cytocentrifuge preparations were made. Single and double immunocytochemical techniques were applied to study viral replication and coexpression of viral markers with markers for macrophages, lymphocytes, and major histocompatibility complex (MHC) class II. Aveolar macrophages of eight of 20 infected sheep (40%) were positive for viral protein expression. The percentage of positive macrophages varied from < 1% to 12% of the total population of macrophages. Viral protein expression was not detected in lymphocytes or other cell types. A relationship between virus-replicating macrophages and differential expression of MHC class II molecules, upregulated in ovine lentivirus infection, could not be established. Pathology was evaluated in nine infected ewes. Animals with the highest levels of positive cells had moderate or severe lymphoid interstitial pneumonia. However, sheep with similar degrees of lesions had lower percentages of positive macrophages or were negative for viral protein detection. These results support the idea that a partial or even a complete loss in the restriction mechanism of maedi-visna virus in lungs can occur in some individuals.

Brucella ovis infection in two flocks of sheep

Brucella ovis infection could not be eradicated from two flocks of sheep despite serologically testing and culling the infected rams for four years. The hypothesis that the ewes played a major role in the maintenance of the infection in both flocks was investigated by using serological, bacteriological and pathological criteria. Specific antibodies against B ovis were demonstrated in 71 ewes in the two flocks. Forty-four of the seropositive ewes were slaughtered for bacteriological and pathological studies and B ovis was isolated from 16 of them; the uterus was the target organ of the infection, although extrauterine infection was also demonstrated in some of the infected ewes.

Long-Term Study of Toxoplasma gondii Infection in a Swedish Sheep Flock

The infection rate of Toxoplasma gondii was studied during 6 years in a sheep flock in central Sweden. The flock consisted of 165-249 breeding ewes of which 20-35% were lambs less than 1 year old. Most ewes were slaughtered when 5 years old. The sheep were kept indoors from end of September to early May. Lambing took place in March and April. Individual serum samples were collected twice a year, once just before turning the sheep out to pasture in the spring and again after housing in the autumn. Sera were analysed by ELISA for antibodies to T. gondii. The seroprevalence varied between 10% and 45% during the 6 years of observation. Seroconversion was detected predominantly at the autumn sampling, indicating that in most cases infection was acquired at pasture. Subclinical effects of T. gondii infection on lamb weight, litter size, total litter weight and ewe weight were also studied. Lambs born to chronically infected ewes were lighter at birth than those of uninfected ewes, but this disparity was no longer evident at weaning.

An Indirect Microimmunofluorescence Test for Detection of Chlamydial Antibodies in Ovine Fetal Fluids

The objective of this study was to evaluate an indirect microimmunofluorescence test (IMIF) for detection of chlamydial antibodies in serum and/or thoracic fluids of aborted ovine fetuses. One hundred eighty-two ovine fetuses, including 64 fetuses from 40 ewes that were experimentally infected with an ovine abortion strain of Chlamydia psittaci at gestation days 90-100, 10 fetuses from 6 normal ewes, and 108 fetuses selected from those received at the Iowa Veterinary Diagnostic Laboratory, were evaluated in this study. Fetuses from experimentally infected ewes were examined 4-60 days after inoculation. The IMIF findings were compared with the results of complement fixation serology for chlamydiae and concentrations of immunoglobulin (IgG). Chlamydiae-specific antibodies were detected by IMIF in 28 of 38 fetuses infected with C. psittaci. Elevated levels of IgG and IMIF titers > or = 1:8 were consistent findings in ovine fetuses infected with chlamydiae for more than 24 days. IgG levels and titers of chlamydial antibodies increased with maturity of the fetus and duration of chlamydial infection. Chlamydial antibodies were not detected with the complement fixation test. Fluids from ovine fetuses aborted as a result of other causes also were examined, and IMIF results were negative. The results of this study indicate that the IMIF is a useful and relatively rapid test for identification of chlamydial antibodies in ovine fetuses.

Ovine lentivirus induced indurative lymphocytic mastitis and its effect on the growth of lambs.

The effect of the indurative lymphocytic mastitis caused by infection with maedi-visna virus was quantified by comparing the pre-weaning growth of lambs from infected and uninfected ewes under the same conditions. A total of 73 infected, but clinically healthy, ewes and 75 ewes from a maedi-visna virus-free source were purchased to form a new flock; they were all three years old. The ewes were mated and the flock was managed as a normal field flock. Serum samples were taken at regular intervals and tested for antibodies to maedi-visna virus. The lambs were weighed at birth and at 14, 30, 50 and, finally, 80 days old, when they were weaned. The ewes were slaughtered, their udders were examined histologically, and the lesions were assessed by counting the typical lymphocytic follicles. Sixty-six per cent of the ewes that were seropositive at slaughter appeared to have follicles. A statistically significant association was found between the number of follicles in the udder and the reduction in the growth rate of the lambs. Lambs from ewes with the mean number of follicles weighed 1.7 kg less at weaning.

Border Disease Virus Transmitted to Sheep and Cattle by a Persistently Infected Ewe: Epidemiology and Control

In a Swedish sheep flock comprising 202 ewes and 13 rams, a pair of twin lambs born in the spring of 1990 demonstrated signs of border disease (BD) and were persistently infected (PI) with border disease virus (BDV). Investigation showed that BDV had been introduced in the preceding tupping period 5-6 months earlier by a bought-in ewe which, on the basis of immunoperoxidase- and polymerase chain reaction techniques, was shown to be PI with BDV. Only 7 of the ewes, all of which had been in close contact with the PI ewe, seroconverted during the subsequent gestation. Apart from the PI twin lambs the losses caused by BDV were restricted to 2 barren ewes. The twin lambs, the PI ewe and lambs from the other 4 ewes that seroconverted were removed from the flock. The flock was thereafter free from an ongoing infection with BDV as shown by the absence of seroconversion. In addition, 5 heifers in late pregnancy most probably seroconverted to bovine virus diarrhoea virus (BVDV) when kept in close contact with the same PI ewe during the winter of 1989-90. When these heifers were reintroduced to the BVDV-free dairy herd from which they originated, their serum antibody titres ranged between 1:250 and 1:1250. Neither these heifers--not their calves--caused any spread of the infection in the herd, as indicated by the absence of seroconversion in 70 cows. The present investigation shows that in the control of both BDV in sheep and BVDV in cattle, it is important to ensure that the risk of transmission of pestivirus between the 2 species is minimized.

Clinico-serological studies of ovine infectious keratoconjunctivitis in adult ewes experimentally infected with Mycoplasma conjunctivae and/or Staphylococcus aureus

The clinical and serological responses following single and mixed ocular inoculation with Mycoplasma conjunctivae and Staphylococcus aureus to ewes were investigated. Ewes in group II inoculated with M. conjunctivae and S. aureus showed more severe conjunctivitis than ewes in group I which were only inoculated with M. conjunctivae. The third group, inoculated with S. aureus alone, also showed mild conjunctivitis. In all three groups, no keratitis was induced. Although there were no significant differences ( P < 0.05) in the lacrimal and clinical responses to M. conjunctivae between the infected ewes of groups I and II, there were marked sero-conversions post-inoculation. Similarly, the quantification of the background bacterial flora before and during infection including the inoculated S. aureus did not appear to increase the clinical response. It appears that S. aureus may be significant in increasing the clinical response, perhaps in the presence of trauma and reduced ocular resistance.

Lungworm infection in a sheep flock in Maryland

Summary: First-stage larvae of Protostrongylus rufescens were detected in the feces of a ram with diarrhea, anorexia, weight loss, and mucopurulent nasal discharge. Subsequently, a survey was initiated in the experimental sheep flocks maintained at the Agricultural Research Service's Helminthic Diseases Laboratory in Beltsville, Md to determine the extent and effect of infection with the parasite. Five of 31 ewes and 4 of 16 rams were found to be infected with the lungworm. Clinical signs of infection, which ranged from mild to severe, included diarrhea, weight loss, and respiratory distress. Natural transmission of the parasite to parasite-naive lambs grazing on pasture occurred during the course of this study. Three lambs born to infected ewes during this study were not infected, suggesting that there is no vertical transmission. Additionally, cattle grazing the same pastures as infected sheep were not infected with the parasite. Results of this study indicated that Protostrongylus rufescens can cause serious disease in domestic sheep in the United States and should be considered as a differential diagnosis in sheep with nonspecific respiratory tract signs.

Echinococcus granulosus in sheep: Transfer from ewe to lamb of ‘Arc 5’ antibodies and oncosphere-killing activity, but not protection

Fourteen ewes were orally dosed with 2000 E. granulosus eggs at 2 weeks of age, were mated at 19 months, and produced lambs when the cysts were 2 years old. One week after parturition, all 14 ewes had ‘Arc 5’ antibodies in their serum, as did 11 14 of their lambs. Fourteen uninfected ewes were immunized three times before parturition with E. granulosus eggs injected intramuscularly. Cysts grew at the first, or first and second site, but not the third, indicating that the ewes were immune prior to parturition. Most sera from these ewes and their lambs, and from 14 control ewes and their lambs, produced precipitin arcs with hydatid cyst fluid, but no ‘Arc 5’. All lambs were challenged with 500 eggs 2 weeks after birth. At necropsy, cyst numbers within groups ranged from 3 to > 200, but there was no significant difference between the three groups of lambs. The immunized ewes did not pass a protection to their lambs that was effective when the lambs were challenged. ‘Arc 5’ antibodies were induced by prolonged infection with cysts, and were not seen in the sera of ewes immunized with eggs, although the eggs developed into cysts at the injection sites. ‘Arc 5’ antibodies did not protect lambs against infection, and were not correlated with protection in ewes. Subcutaneous injection of oncospheres into four ewes from each group at the time of lamb challenge showed that the immunized ewes were immune to this method of challenge, but the infected and control ewes were not. Ewes and lambs of the immunized group, and to a lesser extent the 2-year-infected group, had in vitro oncosphere-killing capacity in their serum collected 1 week after parturition, while those from the control group did not. Killing capacity in the sera of two hyperimmunized lambs was predominantly in the IgG2 subclass. It would appear that the IgG1 subclass, which is the major immunoglobulin in ewe colostrum, either does not carry protective antibodies, or is not able to participate in killing oncospheres in vivo in young lambs.

Effects of infection with Trypanosoma brucei brucei on different trimesters of pregnancy in ewes

The effects of Trypanosoma brucei brucei infection during the first, second or third trimesters of pregnancy in 13 ewes were studied. All infected ewes were anaemic with the anaemia being most severe, moderate and least in ewes infected in the second, third and first trimesters, respectively. Weight loss occurred in all infected ewes but was most severe in ewes infected in the third trimester. Three of the four ewes infected in the first trimester died without aborting while one aborted and later died. Of the four ewes infected in the second trimester, three died without aborting while one lambed and later died. In the third trimester ewes, one aborted, two lambed and all three later died while one died without aborting. None of the lambs was viable. The control ewe lambed normally. The infection resulted in 16.7% abortion, 100% death and 33.3% neonatal deaths. This study demonstrates that T. brucei brucei has a devastating effect on pregnancy irrespective of the trimester of infection.

Interspecific interactions in naturally acquired nematode communities from sheep abomasum in relation to age of host and season in four areas of Leon (Spain)

The abomasa of naturally infected ewes (407) and lambs (190) from four areas of León were collected weekly over 2 years in the abattoir of León (north-west Spain). The major species and morphs found were Teladorsagia circumcincta and Trichostrongylus axei and to a lesser extent Marshallagia marshalli and Teladorsagia trifurcata. The putative interactions between species were assessed by Euclidian distances based on the results of multivariate analyses. The estimation of interaction was either based on mean intensities of worm burdens or on frequencies of nematode species within individual hosts. The areas, years, seasons and categories of sheep (ewes or lambs) did not influence the interaction estimates. These were not dependent upon the size of worm burden. The majority of interactions were positive. Slight negative interactions were found only with T. circumcincta-T. axei, T. circumcincta-M. marshalli and M. marshalli-T. axei. Positive interactions were recorded between the less frequent species.

Evaluation of a commercial solid-phase enzyme immunoassay for the detection of ovine Chlamydia psittaci.

Diagnostic tests designed specifically for direct (nonculture) detection of Chlamydia psittaci in animal specimens are not available commercially. However, several tests for C. trachomatis, particularly enzyme immunoassays (EIA) utilizing antibodies against Chlamydial lipopolysaccharide (LPS), have been used for this purpose. Chlamydial LPS possesses at least 3 antigenic domains, 2 of which are shared by other gram-negative bacteria and 1 that is common only to members of the genus Chlamydia. l Generally, these tests are less sensitive and specific than Chlamydial isolation in cell culture. Cross-reactions with other gram-negative bacteria have limited the usefulness of some tests. Recently, direct-binding (solid-phase) enzyme immunoassays for detection of C. trachomatis have been introduced. These tests are self-contained, require no special equipment, and yield visual results. In this study, a commercial directbinding monoclonal-based EIAa for the visual detection of Chlamydial antigen in human endocervical, urethral, ocular, and urine specimens was compared with isolation in cell culture for detection of C. psittaci in samples collected from aborting ewes. This test does not depend upon the viability of the organism. The LPS antigen is extracted from the organism and is detected with a monoclonal antibody specific for Chlamydial LPS antigen. Placental vaginal swabs were collected at abortion or lambing from 23 pregnant crossbred ewes that were inoculated intravenously with 1.0 ml of 0.01 M phosphate-buffered saline (PBS) (pH 7.2) containing approximately 10 inclusion forming units of the ovine abortion strain B577 of C. psittaci. Placental swabs for EIA analysis were also collected from ovine placentas submitted to the Iowa State University Veterinary Diagnostic Laboratory, Ames, Iowa. Swabs of abomasal contents, lung, liver, abdominal or thoracic fluids, and conjunctiva were collected from aborted fetuses and weak lambs from experimentally infected ewes, were placed in transport tubes (supplied with the EIA kit), stored at 4 C for 24-48 hours, and tested for Chlamydial antigen by EIA. The EIA was performed according to the manufacturer’s instructions. All reagents, including wash solutions, were provided with the test kit. Representative samples of placental cotyledons and fetal tissues were used for Chlamydial isolation in cell culture and for routine aerobic and anaerobic bacterial isolation. Sixty-one placental specimens (23 experimentally infected and 38 field cases) and 25 vaginal swabs were examined by cell culture and by EIA (Table 1). Compared with isolation in cell culture, the EIA had a

Border disease of sheep--aspects for diagnostic and epidemiologic consideration.

Border Disease (BD) is a condition of newborn sheep that results from congenital infection by a non-cytopathic pestivirus, occurring during the first half of gestation. The variations in expression of the virus directly relate to the age of the fetus at the time of infection. There are four distinct disease syndromes: (1) early embryonic death, (2) abortion and stillbirth, (3) birth of lambs with malformations, and (4) birth of small, weak lambs, lacking characteristic clinical signs, but bearing features of immunosuppression. In the newborn, the BD virus may be recovered from all tissues and teratogenic lesions are found in the endocrine, nervous, skeletal, integumentary and immune systems. These effects of virus infection are manifest in the clinical signs characteristic of the disease, such as tremors, ataxia, hairy birthcoat, low birth weight, facial bone malformations, short-boxy stature, and eye abnormalities. The consequences of the BD compromised immune system is an increased susceptibility to infection, a failure to produce specific antibody to BD virus, and an inability to clear the virus; features characteristic of the immuno-tolerant state. The lifelong shedding and persistence of virus is of epidemiologic importance. The persistently infected BD ewe remains a source of infection for the flock both through horizontal transmission (virus shedding) and congenital transmission (a persistently infected ewe will always bear a BD lamb). Detection of persistently infected individuals within a flock is difficult: clinical signs abate with time and most frequently no antibody to BD is produced.

The intensity of resistance by mature Merino ewes against Haemonchus contortus and Tichostrongylus colubriformis in single‐species and combined‐species infection

Three-year-old, non-lactating and non-pregnant Merino ewes, raised on pasture under a program of strategic treatment with anthelmintic and found to be extremely resistant to "trickle" infection with Haemonchus contortus, were given single-dose infections with either H. contortus or Trichostrongylus colubriformis or both species together. The purpose was to ascertain the intensity of protective immunity against the 2 parasites in sheep with immunity acquired from a presumably slight exposure to infection. To provide a criterion, some infected ewes were immunosuppressed with corticosteroid, dexamethasone. Untreated ewes were extremely resistant to challenge infection with either 15,000 or 150,000 H. contortus or 15,000 T. colubriformis. Surprisingly, when mixed infection was given, egg counts for H. contortus were significantly elevated compared with infection by that species alone. Antibody to antigens from infective larval and adult H. contortus was measured in serum by enzyme-linked-immunosorbent assay (ELISA) during the course of infection. Serum titres against larval antigens were significantly depressed when infections with either H. contortus or T. colubriformis were permitted by immunosuppression with dexamethasone, whereas those against adult antigen were depressed when infection with T. colubriformis was permitted.

Studies on Ostertagia spp. from Greenlandic Sheep: Arrested Development and Worm Length

Studies were conducted to investigate earlier observations that lambs slaughtered in Greenland in late September/early October have relatively few arrested larvae in the abomasal mucosa and that the adult Ostertagia from such lambs are abnormally large. Post mortem examination of naturally infected ewes in mid-winter demonstrated that a significant proportion of their Ostertagia population was hypobiotic at this time of year, while an experimental study showed that considerable numbers of larvae of Greenlandic origin became arrested following cold conditioning for 10 weeks. A comparison of adult Ostertagia of Greenlandic and Britain origins from lambs experimentally infected with larvae cultured under identical conditions demonstrated that the "giant" size of the arctic worms was attributed mainly to environmental rather than genetic influences.