Preweaning mortality in piglets in loose-housed herds: etiology and prevalence.

Preweaning mortality in piglets is a welfare issue, as well as an ethical and economic concern in commercial pig farming. Studying the causes of preweaning mortality and their prevalence is necessary to reduce losses. Preweaning piglet mortality was investigated in a field study including 347 sows from 14 loose-housed Norwegian piglet-producing herds. A total of 5254 piglets were born in these herds during the study period, and 1200 piglets were necropsied. The cause of death was based on pathoanatomical diagnosis (PAD). Preweaning mortality of all piglets in the study was 23.4%, including 6.3% stillborn. The two main causes of preweaning mortality in live-born piglets (n=4924) were trauma (7.1%) and starvation (2.7%). Piglets dying of an infection accounted for 2.0%. Among the necropsied piglets (n=1200), 29.1% had died due to trauma, 26.8% were categorized as stillborn and 11% had died of starvation. Piglets that had died of trauma, had a mean time of death of 1 lactation day (LD 1), ranging from LD 0 to LD 21. The mean time of death of piglets that died due to bacterial infection was LD 9, ranging from LD 0 to LD 31, with Escherichia coli accounting for most infections found in necropsied piglets. Farmers were able to identify death by trauma in piglets, but were less able to identify death due to hunger. Most piglets that died in the preweaning period, died of trauma. Surprisingly, this included large and well-fed piglets. The second most prevalent cause of preweaning mortality was starvation. Improved monitoring may reveal piglets with low body mass index, and additional nutrition may contribute to increase the survival rate.

Intestinal strictures, fibrous adhesions and high local interleukin-10 levels in goats infected naturally with Mycobacterium avium subsp. paratuberculosis.

This study describes pathological findings and their association with the production of interferon (IFN)-γ and interleukin (IL)-10 in goats infected naturally with Mycobacterium avium subsp. paratuberculosis (MAP). Twenty-seven goats were subjected to pathological examination. More than half of the animals had severe, diffuse, transmural granulomatous enteritis, often with abundant acid-fast bacilli (AFB), which was most evident in the proximal jejunum. Jejunal strictures and fibrous, peritoneal adhesions were findings that are not often reported in animals with paratuberculosis. Immunohistochemical labelling of IL-10 was seen within diffuse, granulomatous lesions and this may have prevented optimal local IFN-γ production and exacerbated the disease. However, since IFN-γ production was detected in cells from blood, jejunum and jejunal lymph nodes of goats with severe lesions by enzyme-linked immunosorbent assay, intracellular labelling and in-situ hybridization, the up-regulation of IL-10 might have been a consequence rather than a cause of the severe disease. The IL-10 labelling was co-localized with major histocompatibility complex (MHC) class II(+) cells, but rarely with CD4(+) cells. Comparable numbers of CD4(+) and CD8(+) T cells were recruited to both severe, diffuse lesions and small to moderate granulomatous lesions, while few T cells expressing the γδ form of the T-cell receptor were associated with both types of lesions.

Characterization of macrophages and occurrence of T cells in intestinal lesions of subclinical paratuberculosis in goats.

The granulomatous lesions of subclinical paratuberculosis of goats were examined with emphasis on phenotypic characteristics of macrophages and the presence of different subpopulations of T cells. The macrophages in the granulomatous lesions were morphologically homogeneous in histological sections but showed varying expression of the macrophage marker CD68 (a glycoprotein found mainly in late endosomal and lysosomal membranes) and varying acid phosphatase activity. The lesional macrophages showed decreased expression of complement receptor 3 and major histocompatibility complex proteins, which are markers associated with phagocytosis and antigen-presentation, respectively. The granulomas showed low proliferation activity as measured by the proliferation-associated protein Ki-67, indicating that most cells were recruited to the lesions. Few apoptotic cells were demonstrated by the TUNEL technique, suggesting a low cell turnover in the lesions. CD4(+) T cells constituted the main T-cell population among the CD68(+) macrophages in the granulomatous lesions, and few CD8(+) T cells and gamma delta T cells were observed within the lesions, suggesting the limited ability of these cells to influence the granulomatous lesions in caprine subclinical paratuberculosis. Both WC1(+) and WC1(-) gamma delta T cells were present in the small intestinal wall, but the latter were the more numerous. No difference in the numbers of these cells was observed between the subclinically infected animals and control animals.

In vitro responses to purified protein derivate of caprine T lymphocytes following vaccination with live strains of Mycobacterium avium subsp paratuberculosis.

Live attenuated vaccines provide protection against intestinal lesions in goats infected with Mycobacterium avium subsp. paratuberculosis. To examine the role of different T lymphocyte subsets in the development of this protective immunity, CD4(+), CD8(+) and gamma delta T cell receptor (TCR)(+) cells from peripheral blood of goat kids vaccinated with live attenuated strains of M. a. paratuberculosis were studied. After in vitro stimulation with purified protein derivate, the expression of gamma-interferon (IFN-gamma) and the activation marker interleukin-2 receptor (IL-2R) was analysed by flow cytometry. A depletion experiment was performed, where the phenotypes and IL-2R expression was studied after stimulation of cultures depleted of a T lymphocyte subpopulation. Close to all of the IFN-gamma producing cells were of the CD4(+) subset, while only a small number were CD8(+) cells. The gamma delta TCR(+) cells were highly activated, but did not produce IFN-gamma after in vitro stimulation. Depletion of CD4(+) cells lead to a decrease in the percentage of total gamma delta TCR(+) cells and gamma delta TCR(+)IL2-R(+) cells. Removing the gamma delta TCR(+) cells increased the relative numbers of CD4(+), but not the CD4(+)IL-2R(+) cells. Insight into the in vitro recall responses of T cell subsets from animals vaccinated with live paratuberculosis vaccines is essential in the development of more efficient vaccines.

Lesions in subclinical paratuberculosis of goats are associated with persistent gut-associated lymphoid tissue.

The organized gut-associated lymphoid tissue (the Peyer's patches [PPs] of domestic ruminants) is an important site of lesions caused by Mycobacterium avium subsp. paratuberculosis. To investigate the association between PP morphology and the lesions of paratuberculosis in goats, two experiments were performed. Five healthy kids aged 4-5 weeks were examined and the morphology of organized lymphoid tissue in the small intestine was described. Morphological similarities were observed between the ileocaecal-valve PP (ICVPP) and the jejunal PPs (JPPs), with pear-shaped follicles, large submucosal interfollicular T-cell areas, and many intraepithelial leucocytes in the follicle-associated epithelium. The ileal PP (IPP) consisted of elongated follicles, small T-cell areas and few intraepithelial leucocytes. The association between these three locations of PPs and lesions of paratuberculosis was then studied in seven goats inoculated with M. a. paratuberculosis at 5-8 weeks of age and killed 2 years later, while in the subclinical phase of infection. Gross lesions were recorded in five animals and microscopic lesions were observed in the intestine and mesenteric lymph nodes of six animals. The lesions in the small intestine were mainly located in the PPs of the mid-jejunum (JPPs) and ICVPP. Lesions were not present in the intestinal segments that had contained IPP, which had undergone involution during the first 12-18 months of life. These observations indicate that the persistent organized lymphoid tissue in the JPPs and ICVPP, but not the involuted IPP, sustains the development of granulomatous inflammation due to paratuberculosis during the subclinical phase of infection.

Localisation of CD25+ cells and MHCII+ cells in lymph nodes draining Mycobacterium avium subsp. paratuberculosis vaccination granuloma and the presence of a systemic immune response.

Vaccination of goat kids against paratuberculosis protects against lesions and clinical disease. The systemic cellular response was studied in goat kids 3-9 weeks after vaccination. Peripheral blood cells showed increased interferon-gamma production and expression of interleukin-2 receptor (CD25) after stimulation with Mycobacterium avium subsp. paratuberculosis antigens. The lymph node draining the vaccination granuloma was studied three weeks after vaccination in a parallel group of goat kids. In deep cortex, MHCII+ cells were observed surrounded by CD4+ T-cells, while follicular hypertrophy and hyperplasia were prominent in the subcapsular region and along connective tissue trabecula. Comparison of the local and systemic immune responses revealed an inverse relationship between CD25+ T-cells in the lymph node deep cortex and cells in peripheral blood that up-regulate CD25 upon in vitro stimulation, suggesting that activated and regulatory T-cells in the local lymph node influence the level of circulating antigen-specific T-cells following vaccination against paratuberculosis in goats.

Subclinical paratuberculosis in goats following experimental infection. An immunological and microbiological study.

An experimental oral infection of goats with a caprine isolate of Mycobacterium a. subsp. paratuberculosis was used to investigate immunological and bacteriological events during the subclinical phase of infection. Seven goats at 5-8 weeks of age were given a bacterial suspension in milk-replacement three times weekly for 9 weeks. Six animals were kept as controls. Cellular recall responses against M. a. paratuberculosis were analysed by means of a lymphocyte proliferation test, an IFN-gamma assay and an IL-2 receptor assay. All inoculated animals had detectable CMI responses from 9 weeks post-inoculation and through the 2 years of study, although the responses were highest during the first year. Antibodies against M. a. paratuberculosis could be detected from weeks 15-20 in four of the seven animals, and one additional animal became antibody positive at week 35, while two inoculated animals did not produce significant antibody titres during the experiment. At about 1-year post-inoculation, two animals became faecal shedders, while two others started to excrete bacteria into faeces about 2 years post-inoculation. The appearance of M. a. paratuberculosis in faeces was not associated with a decline in cellular responses as far as could be assessed using the current methods for measuring CMI. Pathological lesions due to M. a. paratuberculosis infection and presence of bacteria were recorded in the intestine and/or mesenteric lymph nodes of five animals while lymph node changes suggestive of paratuberculosis were observed in one animal. Only the two animals with no signs of an active infection at necropsy showed a considerable decline in the cellular parameters during the last year of the study, particularly in the IFN-gamma assay. The two animals with the highest levels of M. a. paratuberculosis responsive CD8+ lymphocytes in the circulation about 1-year post-inoculation had no detectable lesions in the distal ileum and colon at necropsy, while high numbers of gammadelta T-cells responsive to M. a. paratuberculosis in the circulation were associated with disseminated lesions in the distal ileum and colon.

Disseminated Mycobacterium celatum (type 3) infection in a domestic ferret (Mustela putorius furo).

A 4-year-old male ferret (Mustela putoriusfuro) had a 6-month history of weight loss and gradual development of depression and coughing. Necropsy findings included pale gray tissue around the distal trachea, multiple nodules in the lungs, a single nodule in the stomach wall, gray foci in the liver, and enlarged lymph nodes. Histologic examination revealed multifocal to coalescing granulomatous inflammation in the trachea, lungs, stomach, liver, and lymph nodes, with acid-fast bacteria in epithelioid cells and macrophages. The acid-fast bacteria were identified as Mycobacterium celatum (type 3) using DNA sequence analysis of the 16S ribosomal DNA gene. M. celatum is a recently described mycobacterium isolated mainly from immunocompromised humans. This is the first report of M. celatum infection in an animal.