Relative contribution of colostrum from Maedi-Visna virus (MVV) infected ewes to MVV-seroprevalence in lambs

Maedi-visna virus (MVV) seroprevalence associated with consumption of colostrum from seropositive ewes was investigated in 276 housed lambs from birth to 300 days-old. At birth, lambs were allocated to five experimental groups according to the maternal MVV-serological status, source and mode of feeding colostrum (bovine or ovine and bottle fed or suckled from the dam) and type of horizontal MVV-exposure (raised with the dam or separately with other lambs). The risk of being seropositive at 300 days-old was associated with feeding ovine colostrum from seropositive ewes and increased with intake of bottle-fed ovine colostrum and was higher in lambs separated from their dams and raised with other experimental lambs compared to lambs raised with their dams. Approximately 75-87% of ELISA-positive results in lambs that had ovine colostrum was attributable to colostrum itself. However, approximately only 16% of naturally raised and 29-61% of bottle-fed ovine colostrum lambs were ELISA-positive as a result feeding ovine colostrum. These results confirm that ovine colostrum from seropositive ewes can be a major source of MVV but its overall contribution to seroprevalence in natural conditions is relatively low, and shows that horizontal MVV transmission can be an important source of infection in new-born lambs.     

Intestinal uptake of intact maternal lymphocytes by neonatal rats and lambs

Two experiments were conducted using neonatal rats and lambs. The intestinal lumen of neonatal rats was infused with radiolabelled syngeneic lymphocytes, whereas the intestine of lambs was infused with radiolabelled allogeneic maternal lymphocytes. The results of both experiments indicated that radiolabelled cells were absorbed by the intestine as judged by autoradiographic studies of intestinal tissue. Furthermore, in lambs it was possible to show that these cells were transported via the lacteal lymph ducts to the mesenteric lymph nodes. These findings suggest another mechanism by which the lactating ewe may confer immunity to its suckled young.     

实验性流行性腹泻仔猪小肠粘膜上皮细胞及肠系膜淋巴结的超微结构

给8头生后3d的哺乳仔猪经口感染猪流行性腹泻病毒(PEDV)“吉”毒株,于感染后18、30、45和96h各扑杀2头,以透射电镜和扫描电镜观察了小肠粘膜上皮细胞及肠系膜淋巴结的超微结构。结果表明,小肠上皮细胞的病变因感染时间不同而有明显差异。上皮细胞的脱落和残留上皮细胞超微结构的破坏,以感染后30h最严重,病毒在这些上皮细胞内的增殖最显著。感染后45h,见有大量新生上皮细胞修补损伤的肠绒毛。感染后96h,小肠绒毛短缩、粗大乃至发生融合。实验仔猪肠系膜淋巴结内巨噬细胞和淋巴细胞的超微结构均遭到破坏,在巨噬细胞内见有PED冠状病毒粒子。     

PCR detection of colostrum-associated Maedi-Visna virus (MVV) infection and relationship with ELISA-antibody status in lambs

A recent large-scale experimental study showed that bottle-feeding ovine colostrum from seropositive ewes results in high MVV-seroconversion in lambs. In contrast, relatively few lambs that naturally suckled colostrum from seropositive dams seroconverted as a result of it. Furthermore, lambs fed uninfected bovine colostrum readily seroconverted when mixed with ovine-colostrum lambs indicating that horizontal MVV transmission between lambs was efficient. MVV-infection was further investigated in the same samples using two PCR tests targeting sequences in the long-terminal repeats (LTR) and POL MVV genes. PCR-tests confirmed previous serological findings. However, the LTR-PCR was more sensitive and allowed detecting infection earlier than the other tests, including 5-8% of new-born lambs from seropositive dams, providing more evidence that prenatal MVV-infection may be more important than considered. The degree of agreement between PCR and antibody tests in individual samples was low up to 6 months of age and moderate at 10 months-old. Nine percent of lambs were always PCR-negative but seroconverted and 19% of lambs were PCR-positive at least once and did not seroconvert. However, seroconversion was associated with increasing number of times lambs were PCR-positive and ovine colostrum-fed lambs were more frequently PCR-positive than other lambs. The significance of these findings in terms of MVV-infection, epidemiology and control is discussed.     

Variation in the immuno-pathological responses of lambs after experimental infection with different strains of Mycobacterium avium subsp. paratuberculosis

Ruminant infection by Mycobacterium avium subsp. paratuberculosis (MAP) causes a granulomatous inflammatory response in the intestine and associated lymph nodes. Differences either in the affected organs or in the inflammatory infiltrate were observed between species and individuals. Such differences are usually attributed to variations in host immune responses or to inconsistent effects among different MAP strains. To evaluate if different MAP strains induce different immuno-pathological responses in lambs, 28 one-month-old individuals were divided into six groups and inoculated with different MAP strains. Groups 1 and 2 were inoculated with two bovine strains isolated in Argentina that showed different genetic patterns after BstEII-IS900-RFLP (hereafter strains E and A respectively). Group 3 was inoculated with a bovine strain isolated in Spain obtained after a previous step of culture (patterns C1). Group 4 was inoculated with a homogenate of intestinal mucosa of a clinical case affected by the same bovine strain as that of group 3. Group 5 was inoculated with an ovine strain that was directly purified from the intestinal mucosa of a clinical case, and group 6 was kept as control (i.e. no inoculation). Peripheral immune responses were assessed until 150 days post-infection (dpi), when lambs were humanely killed. Pathological studies were performed in tissues from the intestine and lymph nodes. Lesion types and inflammatory infiltrates were examined as indicators of pathogenicity. All the lambs infected with bovine MAP strains showed a common lesion pattern regardless of the strain type. Such pattern was characterized by focal lesions mainly in the mesenteric lymph nodes, the presence of fibrous tissue, and, occasionally, necrosis in the granulomas as well as the presence of numerous giant cells. Differences in lesion severity were observed among groups: lambs from groups 1 and 2 had the highest number of granulomas and the largest lymph node area affected. Lesions in animals from group 5 (infected with an ovine strain) were more severe and occurred mostly in the intestinal lymphoid tissue; necrosis, fibrosis or giant cells were never detected in this group. These results indicate that the MAP strain type induces different pathological responses in lambs.     

Comparison of the pathogenicity for pregnant sheep of Rift Valley fever virus and a live attenuated vaccine

A live attenuated mutant of Rift Valley fever virus, MV P12, was previously shown to be non-pathogenic in young lambs, but capable of producing protective immunity. The studies reported here show that the abortion in sheep caused by an infection with virulent virus is the result of necrosis of the maternal villi and cotyledons arising from an acute inflammation of the maternal caruncles. Pregnant ewes infected with the attenuated mutant virus MV P12 showed none of these lesions in the placenta and gave birth to healthy lambs. Colostrum from ewes infected with MV P12 virus was able to induce protective immunity in the offspring. These data along with previously published results suggest that the mutant virus MV P12 is an excellent candidate for use as a live attenuated veterinary vaccine.     

Neutralization of a transmissible gastroenteritis virus of swine by colostral antibodies elicited by intestine and cell culture-propagated virus.

Cross-protection studies of gilts exposed to 4 transmissible gastroenteritis viruses--Ilinois (field strain), Miller-3, Miller low passage (M-LP), and Miller high passage (M-HP) tissue culture-adapted--indicated that only the gilt vaccinated with Illinois strain was protected, along with its newborn pigs, against challenge exposure with field virus. Similar results were obtained when the 4 viruses were incubated in vitro with colostrum from each of the 4 vaccinated gilts and subsequently used to orally inoculate newborn pigs. However, when the colostrums were used to neutralize M-HP virus in cell cultures, the neutralization titers were similar, indicating that a close antigenic relationship existed among the viruses. Neutralization studies in cell cultures, using immunoglobulin (Ig) fractions derived from colostrums of sows exposed to Illinois and M-HP virus, indicated that Illinois virus elicited more neutralizing activity in IgA than in the IgG fraction and that M-HP virus elicited more IgG than IgA antibody activity. In another study, Illinois virus was treated with these Ig-enriched fractions and then inoculated into the lumen of the jejunum of 3-day-old pigs. Anti-Illinois IgA was the only class of antibody which prevented replication of the Illinois virus in the intestine. Similar intraintestinal inoculations were used to test invasiveness of untreated Illinois and M-HP viruses. It was demonstrated that Illinois virus caused marked effect on the intestine: shortening of the villi, intestinal distension, edema, and presence of accumulated intestinal fluid within 60 hours after inoculation. The M-HP virus grew in the intestinal cells without affecting the length of the villi. The degree of invasiveness of Illinois or M-HP virus may account for the difference in the antibody class elicited in the colostrums.     

The passive transfer of immunity to Taenia ovis in lambs via colostrum

Colostrum from ewes that had been repeatedly exposed to cestode infection, whether or not their immunity was boosted by vaccination with Taenia ovis, transferred a strong immunity to the lambs. Susceptible ewes, not recently exposed to tapeworm eggs, gave no protection to their lambs via the colostrum. There was no evidence that colostrum-deprived lambs were more susceptible to infection with T ovis than lambs that received colostrum from non-immune ewes. Colostrum from naturally immune vaccinated ewes gave good protection to lambs for up to six weeks but thereafter the effect was variable. The immunity that developed in susceptible ewes after vaccination with activated embryos was not passed on to the lambs via the colostrum.     

Pathology of naturally occurring paratuberculosis in water buffaloes (Bubalus bubalis)

Gross and histologic lesions of paratuberculosis were studied in water buffaloes. Small intestines and associated mesenteric lymph nodes of 405 water buffaloes were examined. Of these, 20 animals having visible changes of intestinal thickening, mucosal corrugations, and enlargement of mesenteric lymph nodes exhibited histologic alteration characteristics of mild to moderate granulomatous inflammation. The histologic lesions observed in these animals were classified into 3 grades on the basis of type of cellular infiltration, granuloma formation, and presence of acid-fast bacilli. Grade-1 lesions observed in 8 animals were marked by the presence of scattered epithelioid macrophages amid large number of lymphocytes in the intestinal villi and in the paracortical regions of the associated mesenteric lymph nodes. Another 8 animals classified under grade-2 revealed microgranulomas, infiltration with a larger number of epithelioid macrophages besides lymphocytes in the intestinal villi, and granulomas in the mesenteric lymph nodes. Grade-3 lesions observed in 4 animals were characterized by the presence of epithelioid granulomas and giant cells in the intestines and the mesenteric lymph nodes. The Ziehl-Neelsen's stained tissue sections revealed acid-fast bacilli in grade-3 and -2 animals and acid-fast granular debris in grade-1 animals. Among these 20 buffaloes, 14 (70%) were positive in the IS900 specific polymerase chain reaction and 6 (30%) were positive in the bacterial culture.     

Intestinal lesions in specific-pathogen-free lambs associated with a cryptosporidium from calves with diarrhea

Small and large intestines of seven specific pathogen-free lambs infected with cryptosporidia from calves with diarrhea were examined by scanning and transmission electron microscopy and by light microscopy. The small intestine was infected in all the lambs, and the cecum and colon in three. Small intestinal alterations were severe villous atrophy and dilatation of the crypts of Lieberkühn. Epithelial cross-bridging between contiguous villi caused much villous fusion. Epithelial cells constituting the bridges were connected by desmosomal junctions, and were continuous with the epithelial coverings of the associated villi. The lamina propria was heavily infiltrated with neutrophil leukocytes. Infected crypts in cecum and colon were dilated and devoid of mucus-secreting cells, while the ridges between crypts were hypertrophied, and the lamina propria was infiltrated by neutrophils. Cell vegetations with adherent bacteria were present in the surface intestinal epithelium of two lambs infected for 11 and 14 days, respectively. No adherent bacteria were seen in any site in lambs killed up to six days post-inoculation.     

Lymphocyte localization in lymph nodes of pubescent, prepartum, and postpartum sheep

It is generally accepted that lymphocytes associated with the mammary mucosal immune system of non-ruminants may be largely derived from gut-associated lymphoid tissue (GALT). The relationship between the mammary immune system and the GALT of ruminants has not been clearly defined. To address this question, we examined patterns of lymphocyte localization in sheep by 51Cr-labeled lymphocytes following infusion back into donor ewes. We found that lymphocytes taken from mammary lymph nodes of pubescent ewes returned preferentially to mammary nodes, while in prepartum and postpartum ewes, mammary node cells localized equally well in mammary and mesenteric lymph nodes. In contrast, ileal mesenteric lymph node cells from pubescent ewes localized equally well in mammary and mesenteric nodes, but in prepartum and postpartum ewes, localization in mammary nodes was markedly reduced. Comparison of the homing patterns of mammary, mesenteric, and peripheral lymph node cells indicated that mammary node cells behaved similarly to peripheral, rather than mesenteric node cells. This information may be relevant to the extent of communication between the gut and mammary gland in ruminants.     

Transfer of humoral and cell-mediated immunity via colostrum in pigs

The first aim of our study was to obtain information on the transmission of antigen-specific antibodies from colostrum to respiratory tract mucosa in piglets. The second aim was to confirm the biological relevance of the presence of lymphocytes in colostrum and the already described fact that these cells can penetrate the intestinal barrier and "colonize" peripheral blood and lymphatic tissues of piglets. Therefore, we performed an experiment in which sows were immunized with a model antigen Keyhole Limpet Hemocyanin and their piglets were euthanized at different intervals after birth and colostrum intake. Colostrum, bronchoalveolar lavage fluid and blood samples were collected for serological detection of antigen-specific antibodies. Lymphocytes isolated from peripheral blood and lymphatic tissues (mesenteric and tracheobronchial lymph nodes and spleen) of piglets were in vitro activated with the antigen. We found that colostrum-derived antibodies can cross into the respiratory tract mucosa. Furthermore, we found that antigen-specific lymphocytes were detectable in mesenteric lymph nodes and peripheral blood, but very rarely in spleen and tracheobronchial lymph nodes.     

The histopathologic diagnosis of subclinical Johne's disease in North American bison (Bison bison)

The morphologic changes of subclinical Johne's disease in North American Bison (Bison bison) are characterized by microgranulomas composed of epithelioid macrophages and individual multinucleate giant cells of Langhans'-type occasionally containing individual cytoplasmic acid-fast bacilli compatible with Mycobacterium avium paratuberculosis. The microgranulomas are best visualized in the mesenteric lymph nodes of infected subclinical animals. Macrophages that can be confused with infection-associated epithelioid macrophages in the mesenteric lymph nodes are pigment-carrying cells from the intestinal tract. Mesenteric lymph node biopsy may be a useful diagnostic tool for detection of mild subclinical infection in individual ruminants from herds of unknown infection status. The biopsy may also be useful for Johne's disease surveillance during test-and-cull programs.     

Development of a new monoclonal antibody to ovine chimeric IgE and its detection of systemic and local IgE antibody responses to the intestinal nematode Trichostrongylus colubriformis

The J558L cell line, previously transfected with the ovine Cepsilon gene, was induced to secrete a chimeric IgE protein composed of the ovine heavy chain and a mouse light chain with MW of approximately 80 and 26 kDa, respectively. After purification, the chimeric protein was used to immunise BALB-c mice and monoclonal antibodies (mAbs) were generated. The mAb 2F1, which had greatest anti-IgE activity in preliminary screens, was chosen for further characterisation and an examination of systemic and local IgE responses to the intestinal nematode, Trichostrongylus colubriformis. The chimeric IgE protein was not recognised in enzyme linked immunosorbent assay (ELISA) by mAbs raised against ovine IgG1, IgG2, IgA or IgM. However, 2F1 was highly specific to the chimeric IgE protein, and did not cross-react with ovine IgG1, IgG2 or IgA. Western blot analysis also showed that 2F1 and secretory IgA (sIgA) did not cross-react, and that 2F1 and the anti-IgA mAb identified different MW bands from colostrum (approximately 200 and 400 kDa, respectively). 2F1 bound to mucosal mast cells (MMC) isolated from the intestines of lambs infected with T. colubriformis, but cultured bone marrow-derived mast cells (BMMC) required prior incubation with the chimeric IgE protein for this binding to occur. Distinctive staining of plasma cells and putative mast cells were observed using 2F1 on immunohistological sections of mesenteric lymph node and jejunum.ELISA incorporating 2F1 was able to detect >0.4 ng chimeric protein. Total IgE in ovine colostrum and intestinal homogenates was quantified using a capture ELISA, with known amounts of chimeric protein used to produce a standard curve. Colostrum from outbred Merino ewes had 0.55-11.05 ng ml(-1) total IgE, and their lambs, at necropsy after infection with a total of 18,000 T. colubriformis infective larvae over a 9-week period, had 45-620 ng g(-1) total IgE in intestinal tissue. Compared to genetically susceptible lambs, antigen-specific levels of IgE were significantly higher in genetically resistant lambs after infection with 4500 T. colubriformis infective larvae (TcL3) per week for 9 weeks (161.4 versus 44.8 geometric mean titres; P=0.043). In western blots, distinctive bands (19-21 and 27 kDa) from T. colubriformis larval antigen were differentially recognised by IgE, as identified by 2F1, in intestinal homogenates from genetically resistant animals.These results have demonstrated the value of 2F1 for quantification of IgE responses in samples derived from ovine fluids and tissues using ELISA, western blots and immunohistology. In this respect, it recognises native ovine IgE and does not require pre-treatment of the sample with denaturing agents or ammonium sulphate.     

Studies on transmission of maedi virus to lambs

Lambs born to 5 ewes in 3 successive years were studied for presence of maedi virus and its antibodies. In the middle of the first-year pregnancies the ewes and the only ram of the colony were inoculated with maedi virus. No antibodies or viraemia could be detected in the lambs at birth. After sucking colostrum, antibodies appeared in the lambs of the ewes which themselves were seropositive, and reached their peak in a few days. Maternal antibodies disappeared within 12 weeks in all the lambs. Neutralizing antibodies were demonstrated in the colostrum and their content declined rapidly after lambing. Virus was isolated from the milk of 2 ewes in the third year of the studyIn the first year the spread of maedi virus was demonstrated to only 1 of the lambs, but in the other 2 years maedi virus was detected in tissues of half of the lambs sacrificed at 3–12 weeks of age. It was concluded that lambs born to chronically infected ewes are readily infected, indicating excretion of virus by ewes. The study yielded no information on the specific routes of transmission, except for the finding of the virus in milk of 2 ewes in the third year of the study. No evidence was obtained of transplacental transmission of maedi.     

Does sward height grazed by ewes in mid- to late-pregnancy affect indices of colostrum intake by twin and triplet lambs?

AIMS: To determine if sward height grazed by ewes in mid- to late-pregnancy affects subsequent indices of colostrum intake by twin and triplet lambs, and the extent of the variation in colostrums intake between twin and triplet litter-mates. METHODS: Blood samples were collected from 75 twin and 46 triplet litters, respectively, 24-36 h after birth. Samples were not collected from lambs that died before this age. Lambs were born to ewes which had grazed one of four sward heights (2, 4, 6 and 8 cm) during mid- to late-pregnancy. Serum samples were analysed for gamma-glutamyl transferase (GGT) activities and glucose concentrations. The number of lambs present at weaning was used to determine lamb survival rate. RESULTS: GGT activities of lambs born to ewes that grazed swards 2 cm high were lower than those born to ewes that grazed swards 4 and 6 cm high (p=0.053 and p=0.037, respectively). Glucose concentrations were higher in twin than triplet lambs (p=0.003) and in lambs born to ewes grazed on swards 6 cm high than those born to ewes grazed on swards 2 cm high (p=0.033). These differences were not evident after correction for differences in birthweight. There was significant (p<0.001) variation within litter-mates for GGT activities and glucose concentrations in both twins and triplets. The blood constituent status of lambs that died before the 24-36 h collection period is not known. However, lambs which died after this period had significantly lower GGT activities (p=0.009) and glucose (p=0.010) concentrations at the time of sampling than those which survived. CONCLUSIONS: Farmers should ensure twin- and triplet-bearing ewes in mid- to late-pregnancy are grazing at least 4 cm of herbage to ensure colostrum intake of lambs in the postpartum period is not adversely affected.     

Maedi-visna control in sheep. I. Artificial rearing of colostrum-deprived lambs

A field trial to study the practicability and efficacy of maedi-visna control in sheep by artificial rearing of lambs was carried out during the lambing season of 1979. Lambs were immediately separated from the dams at birth, deprived of ovine colostrum, and reared isolated from the parent flock. Bovine colostrum was given instead of maternal colostrum. Eleven farms participated in the experiment. All flocks were severely infected with maedi-visna virus: 63-100% of the ewes were seropositive as demonstrated by ELISA. Artificially reared lambs were serologically tested and positives culled at the age of 6, 12, 18, 24, 30 and 36 months. Only very few positives were found: 1/389, 1/376, 0/337, 1/223, 1/192 and 0/144, respectively. The first two sero-positive lambs occurred in one flock, and it could be ascertained that both had mistakenly been given ovine colostrum probably containing maedi-visna virus. No explanation, other than sub-optimal hygiene and isolation, could be found for the two sero-positive sheep that turned up in another flock at 24 and 30 months of age although, transplacental infection cannot be entirely excluded. It is concluded that artificial rearing of ovine colostrum-deprived lambs is an effective and practicable method for the control of maedi-visna in sheep. The method appears particularly useful when valuable genetic material has to be salvaged.     

Effect of aflatoxin on susceptibility of hamsters to Mycobacterium paratuberculosis.

After oral administration of Mycobacterium paratuberculosis to hamsters, the organism passed the epithelial barrier of the intestine, and infection was established in the small intestine and mesenteric lymph nodes. The addition of aflatoxin to the ration of hamsters did not increase their susceptibility to M paratuberculosis but, rather, seemed to decrease susceptibility to the bacillus. Hamsters not treated with aflatoxin and infected with M paratuberculosis had higher bacterial counts in intestinal tract and mesenteric lymph node on necropsy than did infected hamsters that had been treated with aflatoxin. Aflatoxin-treated hamsters grew slowly, had an unthrifty appearance, and developed lesions of megalocytosis regardless of whether they were infected with M paratuberculosis.     

Repetitive abortion in Neospora-infected ewes.

Pregnant ewes inoculated with cultured Neospora caninum tachyzoites in 1995, 1996, or 1995 and 1996 aborted or delivered weak or clinically normal lambs in 1996. Nine of 11 ewes in the study had previously produced infected lambs or fetuses after being experimentally infected in 1995. Fetuses and lambs produced in 1996 showed histologic lesions and zoites indicative of Neospora. Serologic responses and production of infected fetuses/lambs indicated systemic neosporosis in the ewes during gestation, although tachyzoites could not be cultured from maternal tissues. The repetitive infection of fetuses, and resulting clinical and histopathologic findings in the present study are similar to those reported in naturally infected cattle, adding to the already established similarities of neosporosis between sheep and cattle.     

The effect of a natural maedi-visna virus infection on the productivity of South African sheep

A cohort study was conducted in order to measure the effect of the chronic indurative lymphocytic mastitis caused by the South African strain of maedi visna virus (MVV) on the pre-weaning growth of lambs born either of naturally infected or uninfected ewes kept under similar conditions. Fifty naturally infected ewes as well as another 40 from a maedi-visna-free source to be used as control animals, were purchased and kept in separate flocks which were managed in a similar way. All the ewes were of the same breed and 3-4 years old. During the adaptation period, and through the mating, pregnancy and lactation periods they were periodically monitored for the presence of MVV serum antibodies. The lambs were weighed at birth and thereafter every 2 weeks until the age of 90 days, when they were weaned. The ewes were then slaughtered, and their udders examined histologically and the number of lymphocytic follicles were counted and assessed. Although the calculated values indicated a correlation between the number of follicles in the udder and the reduction in the growth rate of the lambs, this was not statistically significant. Similarly, despite higher counts of lymphoid follicles in the udders of sero-positive ewes as compared to those that were sero-negative and the lower ewe productivity indexes in infected ewes, no statistically significant differences were found in the indexes of ewes in different follicle categories.