Signalment:  

3-year-old, male, Tokara (Japanese native) goat (Capra hircus domesticus).Four goats and nine sheep were kept in a zoological garden. The present case was born at the garden in 2006, and the zoo staff noticed that the goat showed decreased appetite and weight loss from January 2009. He had intermittently excreted soft feces since May 2009 and overt diarrhea was noted in October of the year. He died in November 2009.

Gross Description:  

The carcass was in poor nutritional condition and post mortem autolysis was mild. The oral mucosa and conjunctiva were pale white. The liver diffusely showed centrilobular congestion and periportal white discoloration, such as in nutmeg liver. There was a foreign body (tight handkerchief) in the content of rumen. Numerous white small foci due to mucosal thickening, approximately 2 mm in diameter, were visible from serosa of the small intestine. About 50% of lung lobes, mainly in both cranial lobes, were dark red, wet and consolidated.

Histopathologic Description:

Liver: The liver showed severe interlobular, periportal, and intralobular infiltration of macrophages, epithelioid cells and a small number of lymphocytes. There was atrophy, degeneration and loss of the hepatocytes adjacent to the foci due to the extensive invasion of the macrophages. Mild proliferation of bile duct and arterioles was noted in expanded portal area. Hemosiderin-laden macrophages (Kupffer cells) were scattered in sinusoids throughout the parenchyma. The Ziehl-Neelsen stain showed a massive presence of acid-fast rod shaped bacilli in the epithelioid cells. Additionally, epithelioid cells diffusely infiltrated and proliferated in lamina propria mucosae of the ileum and colon. Epithelioid cell aggregates were occasionally observed around the vessels and lymphatics under the serosa. Similar foci were also noted in the mesenteric adipose tissue. These epithelioid cells also contained numerous acid-fast rod shaped bacilli in the cytoplasm. Obvious necrosis and mineralization could not be found in any granulomatous foci.

Morphologic Diagnosis:  

Liver: Hepatitis, granulomatous, multifocal to coalescing, marked, with numerous intrahistiocytic acid-fast bacilli.

Lab Results:  

Tissues from this goat were not examined microbiologically. After the necropsy, monitoring study in the herd was performed for Mycobacterium avium subsp. paratuberculosis (MAP) with johnin reaction, complement fixation (CF) test, and the isolation from feces five times in all for 5 months. MAP was not isolated from any animals, but 6 sheep were positive in both johnin reaction and CF test.

Condition:  

Johne's Disease

Contributor Comment:  

Paratuberculosis, or Johnes disease, caused by MAP infection mainly occurs in domestic ruminants and is responsible for considerable economic losses all over the world.(2,5) The disease has been spontaneously recognized in pigs, free-ranging and captive wild ruminants, camelids, and rarely in equids and captive primates. Speculation exists that Johnes disease is zoonotic and associated with Crohns disease in human beings, although MAP has still not been accepted as the cause of the human disease.

MAP is very resistant to environmental stressors, particularly in regions with acid soils. The bacterium enters the M cells that cover the intestinal Peyers patches, and ingested bacteria are subsequently phagocytized by macrophages.(2) In cattle, susceptibility to infection is greatest in the first 30 days of life, although clinical disease does not usually develop until 2-5 years of age. The progression from asymptomatic to clinical Johnes disease is associated with a decrease in peripheral cell-mediated immunity and increasing production of non-protective IgG1 antibodies.(7,8) The disease is clinically characterized by untreatable diarrhea accompanied by progressive weight loss and hypoproteinemia. The characteristic gross lesion in the symptomatic cattle is chronic segmental thickening of the ileum, mesenteric lymphadenopathy, and lymphangitis. Histologically, cattle usually have non-caseating granuloma in the affected bowel and lymphoid tissues.(2)

Although the pathogenesis of Johnes disease in small ruminants is assumed to be similar to that in cattle, there are several differences in clinical signs and pathology. Sheep and goats reveal emaciation and hypoproteinemia, but overt diarrhea is unusual.(2,5) In sheep, goats, and deer, enteric gross lesions are often mild, with little obvious thickening, and no transverse ridges.(2,4)

Two main pathological forms of the intestinal lesion have been described in symptomatic sheep.(3,9) The first form is multibacillary or lepromatous, in which macrophages filled with numerous mycobacteria are the main inflammatory cells. The second form is paucibacillary or tuberculoid, in which the inflammatory infiltrate is composed of lymphocytes and few macrophages and caseous necrosis and calcification may be observed. It is difficult to find acid-fast mycobacteria in macrophages in the latter form. It is uncertain whether the two distinct forms represent sequential or divergent stages. Asymptomatic sheep may have small granulomas in the interfollicular and basal areas of ileal Peyers patches, usually with no visible intracellular organisms.(9)

Corpa et al.(4) characterized the intestinal lesions of caprine tuberculosis in four categories: focal, diffuse multibacillary, diffuse lymphocytic, and diffuse mixed. Histological classification for sheep was valid for goats, and the lower frequency of focal lesions in goats compared to sheep appears to indicate that the former species has only limited ability to control the infection. In this species, granulomatous lesions are likely to be more severe in the jejunum than in the ileum although the distribution could not be found in this case. Currently, the similar histological classification is applicable also in bovine paratuberculosis.(6)

The ileum of the present case showed diffuse multibacillary lesions. The monitoring study in remaining sheep and goats supported the histological diagnosis. Previously, focal granulomas have been seen in lymph nodes elsewhere in the body, liver, lung, spleen, and other organs in symptomatic sheep and goats.(2-4) However, the amount of macrophagic infiltrates in the liver was unusual.

JPC Diagnosis:  

Liver: Hepatitis, portal and random, histiocytic, diffuse, marked with numerous intrahistiocytic acid-fast bacilli.

Conference Comment:  

The pathogenesis of Mycobacterium avium ssp. paratuberculosis (MAP, Johnes) is assumed to be similar in cattle and sheep. The greatest susceptibility to infection is within the first 30 days of life. Infection occurs when MAP is ingested, taken up by M cells overlying intestinal Peyers patches, and transported to resident macrophages. The bacteria localize in the mucosa and draining lymph nodes; rarely in small ruminants, MAP-associated lesions can be found in the walls of blood vessels, meninges, liver and spleen.(2) These disseminated lesions are thought to result from irregular lymphogranulomatous foci; affected animals typically have a negative response to intradermal johnin testing.(2)

Mycobacteria species utilize a complex interplay of virulence factors and the host immune system to evade being killed. The chart below, adapted from Weiss and Souza,(10) summarizes the mechanisms by which MAP suppresses monocyte-macrophage microbicidal response:

Organism Factor	Cell Pathway	Mechanism	Result
Man-LAM	TLR2-MAPK-p38	IL-10 overexpression	Decreased: IL-12, IL-8, and TNF-α, MHC class II, apoptosis, phagosome acidification, and organism killing
Man-LAM	IL-10-mediated	Decreased: IL-12, IL-8, and TNF-α expression	Attenuation of: 1. Inflammatory response 2. Th 1-type immune response
Man-LAM	IL-10-mediated	Decreased MHC class-II expression	Decreased antigen presentation
Unknown	IL-10-mediated; decreased TNF-α	Decreased apoptosis	Increased cell Survival
Man-LAM	IL-10-mediated; TLR2-MAPK-p38 signaling	Decreased phagolysosome fusion and acidification	Increased organism survival

Interleukin 10, as noted in the chart above, plays a pivotal role in the MAP-directed immune modulation; a brief review of IL-10 follows. IL-10 is produced by a variety of cells, including T regulatory lymphocytes, Th 2 lymphocytes, and dendritic cells. The primary function of IL-10 is to direct the immune system to a Th 2-type immune response by enhancing Th 2 activity and suppressing Th 1 activity; Th 1 suppression is accomplished by inhibiting macrophage IL-12 production. Antigen presentation by dendritic cells is decreased through IL-10 mediated down-regulation of MHC class-II.(1)

As commented by the contributor, the distribution and extent of the histiocytic infiltrate in the liver is striking. While most participants interpreted the lesion as consistent with Mycobacterium avium subsp. paratuberculosis infection, they were nevertheless impressed by the number of infiltrating macrophages filled with acid- fast bacilli. A similar histopathologic presentation is reported in dogs infected with M. avium-intracellulare complex (MAC), as exemplified by Wednesday Slide Conference 2009 Conference 5 Case 1, and in the absence of special stains may result in the histologic interpretation of histiocytic neoplasia or a sarcomatous lesion, rather than an infectious process.

References:

1. Ackermann MR. Acute inflammation; Chronic inflammation and wound healing. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 4th ed. St. Louis, MO: Elsevier; 2007:149,157-160.
2. Brown CC, Baker DC, Barker IK. Alimentary system. In: Maxie MG, ed. Jubb, Kennedy and Palmers Pathology of Domestic Animals. 5th ed., vol. 3. Philadelphia, PA: Elsevier Ltd; 2007:222-225.
3. Clark CJ. The pathology and pathogenesis of paratuberculosis in ruminants and other species. J. Comp. Pathol. 116:217-261, 1997
4. Corpa JM, Garrido J, Garc+�-�a Mar+�-�n JF, P+�-�rez. Classification of lesions observed in natural cases of paratuberculosis in goats. J Comp Pathol. 2000;122:255-265.
5. Gelberg HB. Alimentary system. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 4th ed. St. Louis, MO: Elsevier; 2007:372-374.
6. Gonz+�-�lez J, Geijo MV, Garc+�-�a-Pariente C, et al. Histopathological classification of lesions associated with natural paratuberculosis infection in cattle. J Comp Pathol. 2005;133:184-196.
7. Koets A, Rutten V, Hoek A, et al. Progressive bovine paratuberculosis is associated with local loss of CD4+ T cells, increased frequency of γδ T cells, and related changes in T-cell function. Infect Immune. 2002;70:3856-3864.
8. Kurade NP, Tripathi BN, Rajukumar K, Parihar NS. Sequential development of histologic lesions and their relationship with bacterial isolation, fecal shedding, and immune responses during progressive stages of experimental infection of lambs with Mycobacterium avium subsp. paratuberculosis. Vet Pathol. 2004;41:378-387.
9. P+�-�rez V, Gac+�-�a Mar+�-�n JF, Badiola JJ. Description and classification of different types of lesions associated with natural paratuberculosis infection in sheep. J Comp Pathol. 1996;114:107-122.
10.Weiss DJ, Souza CD. Modulation of mononuclear phagocyte function by Mycobacterium avium subsp. paratuberculosis. Vet Pathol. 2008;45:829-841.

Click the slide to view.

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3-1. Liver

3-2. Liver

3-3. Liver

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