On epidemic tremor of chickens, avian encephalomyelitis in newborn chickens. 1. Suggestion of a new name for the disease

Abstract

Neurohistopathological investigation was carried out on the brains and spinal cordsof 105 newborn chicks which, judging from epidemiological aspects, symptoms, andhistopathological findings, were believed to have been infected with a disease identicalwith what had been reported under the name avian encephalornyelitis. The resultsobtained are summarized as follows.1) MaterialsThe materials used for the investigation consisted of 105 chicks which had beencollected from 11 poultry farms (named A -K), as recorded in Table 1. The birds werefrom 5 to 42 days old and were broiler chicks of foreign-produced strains. In all ofthem, except four, weakness or paralysis of the legs was recogrnized as the mainsymptom. Tremor in the head and neck was found only in a few of them.2) Histopathological findings of brains and spinal cordsa) Degeneration of nerve cells (Figs. 1810) : This change was observed mosteasily and clearly in large ntotor nerve cells. The nerve cells swelled, and their cytoplasmwas stained pale, showing a homogeneous feature. The Nissl substance disappeared inmost part, altlrough it frequently remained in the periplreral areas of tlte cell bodies.There were often enlargement and peripheral migration of the nucleus in these cells.It may be said that suclx changes were in progress in the process of degeneration. In thefinal stage, the nerve cells formed an irregular-shaped mass or a shrunken mass stainedwell with eosin. Irn this way, the dernsity of nerve cells became very low in the nuclearareas, such as the ventral horns of the cervical and [urnbar en[arc>ement of the spinalcord, which otherwise were to be rich in large unotor nerve cells. The process ofdegeneration of small nerve cells seemed to be fundamentally identical with that oflarge nerve cells. On the whole, however, the frequency of appearance of affected nervecells was usually low.b) Activation of neuroglias: The activation of neuroglias was very dull, ascompared with the changes of the nerve cells, especially the large nerve cells wlaichshowed outstanding features of degeneration. In fact, the neuroglias were almost in-different to the degeneration of large nerve cells. On the other hand, a feature namedneuronophagy occurred here and there to degenerated small nerve cells, but it was notso important as the other Iesions. Rather than that, the sparse accumulation of micro-glial cells scattered in the groutad substance attracted more attention. On that occasiondegenerated nerve cells could, or could not, be demonstrated near the cellularaccumulation.c) Appearance of wandering cells: This finding was also infrequent. It was animpressive feature, however, that plasma cells had infiltrated here and there into theground substance of gray matter.d) Vascular changes (Figs. lIsI6) : There was a slight Iesion in which a fewplasma cells had infiltrated into perivascular spaces. This Iesion needed attention.Vascular alteration was a [esion of small blood vessels observed in older birds, whichexhibited a cellular accumulation, thick or thin, surrounding a part of the blood vessel.The cellular elements recognizecl were mainly histiocytes, lymphocytes, and plasma cells.Moreover, microglial cells were oftern fottnd in such lesion. Such vascular lesionsappeared in no particular areas.3) Distribution and severity of affected nerve cells and neurogliasLesions were investigated in all parts of the brain.and spiztal cord, and comparedas systematically as possible. Tlte results are sltown in Table 2.a) Large nerve cells: In view of the cellular constrtuction, the areas coming intoquestion were Nucleus (N.) isthmi, pars magnocellularis, N. ruber, Nn. ocu[omotoriidorsalis et ventralis, N. reticularis pontis caudalis, pars gigantocellularis, and variousnuclei in the ventral horns of the spinal cord. Judging from the distribution andseverity, the cervical and lumbar enlargement of the spinal cord attracted an over-whe[ming attention, followed by N. [the rest omitted]