Spontaneous Listeric Encephalitis and Neuritis in Sheep

Abstract

Abstract. Sixteen of 17 sheep with spontaneous listeric encephalitis had neuritis characterized by diffuse and focal intrafascicular and perineural accumulations of lymphocytes, plasma cells, macrophages and neutrophils in one or more cranial nerves. Nine sheep had extensive trigeminal neuritis which was usually unilateral. Brain lesions were mainly in the stem and were foci of macrophages or neutrophils or both, malacia, neutrophilic neuronophagia, vascular cuffing, and meningitis. Lesions in the brain and trigeminal ganglia were most severe on the same side as the affected trigeminal nerve. Gram-positive bacilli were in proximal parts of cranial nerves in foci of inflammatory cells and occasionally in morphologically intact nerve fibers. Organisms in the brain were in phagocytes in areas of inflammation and in scattered neurons and axons. The results were consistent with centripetal migration of the infectious agent along one or more branches of the trigeminal nerve to the brain and dissemination in the brain stem occurring, at least partly, along fiber tracts. Intraaxonal movement of bacteria probably is a mechanism involved in the pathogenesis of this disease.Listeriosis in sheep may be manifested as abortion, neonatal septicemia, or neurologic disease. The neurologic syndrome (circling disease) occurs mainly as a sporadic encephalitis of adult sheep, is frequently fatal and rarely occurs concurrently with either of the other two syndromes.Listeric encephalitis in sheep is characterized by microabscesses, focal gliosis and perivascular cuffing. Although there are reports of a few cases of diffuse meningoencephalitis [20], the lesions usually are confined to the brain stem, especially the pons and medulla oblongata. This regional distribution is not consistent with a hematogenous route of infection [12], which usually results in disseminated lesions in the cerebrum as well as the brain stem. Focal invasion of brain parenchyma via a nonvascular route could explain partially the distribution. Lesions in the proximal parts of branches of the trigeminal nerve occur in the spontaneous disease in sheep, cattle and goats. It has been suggested that the infective organism reached the brain by migration along these nerves [1, 2,24]. Other studies in sheep did not show extensive inflammation of trigeminal nerves [5] and migration of infection along nerves was not considered likely. In addition, reports of isolation of Listeria monocytogenes from visceral organs of several sheep with spontaneous listeric 297

Listeria monocytogenes infection in ruminants: Is there a link to the environment, food and human health? A review

“…Most commonly, Listeria CNS infections in ruminants occur as rhombencephalitis, i.e. primarily affect the brainstem, and only exceptionally as meningitis or meningoencephalitis (Charlton and Garcia, 1977). This is in contrast to humans, where CNS infections most often manifest as diffuse meningitis and meningoencephalitis, and less commonly as rhombencephalitis or abscesses in the cerebrum and cerebellum (Mylonakis et al, 1998;Bartt, 2000).…”

“…In humans, it is assumed that L. monocytogenes passes the gastrointestinal barrier and spreads haematogenously to the brain (Nikitas et al, 2011;Disson and Lecuit, 2012). In ruminants, there are indications that the pathogen enters the cranial nerves via the oral epithelium or conjunctivae (Charlton and Garcia, 1977). Moving within the axons, it reaches the brain stem and spreads further to other regions of the brain via axonal pathways (Oevermann et al, 2010a;Madarame et al, 2011).…”

Spontaneous Listeric

“…Also, the predominant type of inflammatory cell (macrophage or neutrophil) varies between different brains [4]. In light microscopic studies, bacteria occurred more frequently in neutrophils than macrophages [4]. No reason was found for this apparent greater phagocytosis by neutrophils.…”

“…The proportion of macrophages to neutrophils in these inflammatory foci varies greatly in the same brain. Also, the predominant type of inflammatory cell (macrophage or neutrophil) varies between different brains [4]. In light microscopic studies, bacteria occurred more frequently in neutrophils than macrophages [4].…”

“…Viruses also may spread within the brain via neuronal processes [7]. A recent study of listeric encephalitis in sheep suggested that bacteria migrated along peripheral nerves to the brain and that migration in the brain occurred, at least partly, along fiber tracts [4]. A few neurons and neuronal processes contained organisms which suggested that neuronal cytoplasm is a vehicle for movement of the infectious agent…”