Tuberculosis of the Central Nervous System in Macaca Mulatta*

Brit. vet.

J.

(1963), liS, 393

TUBERCULOSIS OF THE CENTRAL NERVOUS SYSTEM IN MACACA M ULATTA* Three cases with vertebral and dural involvement By J. R. M.

INNES

Biology Department, Brookhaven National Laboratory, Upton, New York

Wherever colonies of monkeys are maintained for research, tuberculosis still constitu tes the major disease problem, and if monkeys are housed in batches it can ravage a colony. Further, in experimental work with monkeys, the disease can be a wrecker of profitable results and make for a total waste of the money, time and effort expended on experiments. Publications exemplifying the importance of tuberculosis, and the necessity of eradicating it in monkey colonies, are worth mentioning again here. Habel (1947) reported that about one-third of all monkeys received in the National Institutes of Health, Bethesda, Maryland, U .SA., developed tuberculosis and gave unequivocal evidence on the rapidity with which 'it spread. Ten years later, Haberman & Williams (1957) in the same institution found the situation was still serious; they found 101 cases of tuberculosis in 615 necropsies on Macaca mulatta but no cases in 93 cynomolgus monkeys (which does not mean the latter kind are immune). Benson, Fremming & Young (1955) described an epidemic of the disease, in another laboratory in the U.S.A., which necessitated the disposal of the entire colony of over 200 monkeys. In the 1930's, Schroeder (1 938a,b), from the results of a questionnaire sent out in the U.S.A., estimated that the average death rate from tuberculosis in imported monkeys was about ten per cent per annum, and that about 80 per cent of all deaths were due to this disease. In many well-run zoological gardens the disease appears to have been brought under control, but the general situation regarding its incidence in imported monkeys kept in certain kinds of scientific institutions may not seem to have improved. In laboratories which use huge numbers, the problem has been fully appreciated and some have established their own independent methods of capture and delivery without dealers. In one commercial institution in the U.S.A. which uses some 6,0009,000 monkeys a year, reactors are now less than 1 per cent and stock monkeys are conditioned for 3-6 weeks. The mortality has been about 11 per cent in gang cages and 2-3 per cent in individual cages. The major problem concerns laboratories which experiment on smaller numbers (up to a hundred or so a year) for speciallong-telm work, and which have neither the space nor facilities to conduct extensive screening, testing and conditioning of monkeys in quaran*Research carried out at Brookhaven National Laboratory under the auspices of the U.S. Atomic Energy Commission.

394

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tine, and must get their animals from dealers. In this type of laboratory, for example devoted to neurophysiology, to observations on behaviour, to ablation studies and to the use of the stereotaxic instrument, non-familiarity of the observers with what are problems in pathology may perhaps be conducive towards perpetuation of infection. The pathology and pathogenesis of tuberculosis in monkeys have occupied the attention of many investigators. No data of any great importance have, however, been added to the literature on these aspects since the superb study by Scott & Beattie (1928), which should be read by all interested in the simian disease. The article also contains an account of the normal anatomy of the lymphatic channels and nodes in the thorax and abdomen, a knowledge of which helps to explain much about the mode of spread of visceral tuberculosis in monkeys. All the important contributions on the pathology and pathogenesis of tuberculosis in simian primates are given by Francis (1958), Ruch (1959) and by van Bogaert and Innes (1962) . Some of the most informative original studies, quoted in the above sources, are those by Kalbfleisch & Nohlen (1929), Scott (1930), Nieberle (1932), Krishnan (1936), Schleussing (1936), Urbain (1941)as well as the papers by Scott and Beattie, Habel, Haberman and Williams already mentioned. In summary, what we see in the simian disease is an analogy to primary tuberculosis in children, with its frequent and different forms of early generalization (see Scott and Beattie for comparisons between monkeys and children), or what was once seen in adult human populations in certain parts of the world after they had contact with infection for the first time. Chronic isolated tuberculosis (phthisis) of the human adult is never seen in apes or monkeys. It is obvious, looking at the general picture of many advanced cases, that bacillaemic invasion of the blood stream from arterial and venous lesions must cause repeated attacks of miliary tuberculosis. Lesions affecting the intima and media of arteries and veins are common enough in monkey tuberculosis (see illustration of such a lesion in the longitudinal sinus in van Bogaert and Innes, 1962, Fig. IV.51 D). Consequently, one would wonder why the nervous system ever escapes if monkeys are allowed to live out the full natural course of the disease. The answer may lie in the fact that sufficient search, including neuropathological study, may not be possible or may not be made in the average routine simian necropsy. The literature contains only very few reports. In the Bunge Institute, Antwerp, where Dr. Ludo van Bogaert and his staff have been conducting detailed neuropathological studies of simian primates for over 30 years, more than 50 cases have been catalogued to which the present three cases can be added. Histologically, in the simian disease there is progressive central caseation, rarely calcification, with tissue reaction around in which epithelioid cells predominate and Langhans' giant cells can be either absent, rare or very numerous. With sufficiently assiduous search in Ziehl-Neelsen-stained sections, acid-fast mycobacteria can be identified in variable numbers; sometimes they are scanty and sometimes extremely numerous. However, not all such epithelioid

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and giant cell lesions with central necrosis in monkeys are necessarily tuberculous. Similar nodular foci have been seen in the liver, lungs and spleen in which it was impossible to identify acid-fast mycobacteria. To call these lesions pseudotuberculosis simply obscures the real issues. The possible confusion of gross tuberculous lesions with those associated with lung mites was discussed by Innes, Colton, Yevich & Smith (1954); histologically, there can be no mistake. There may be variations in susceptibility between the different kinds of apes and monkeys, but the Macaca mulatta tops the list in incidence of reported cases, which must be due partly to the fact that it is the commonest species used experimentally. Francis ( 1958) stated that out of the 123 records of typing of cultures of Mycobacterium tuberculosis recovered from monkey cases, 89 were identified as the human variety, 28 bovine, and 6 avian. The idea has therefore persisted that monkeys do not acquire infection in their natural habitat, but only do so when they first come into contact with human sources, and thereafter they spread infection to other monkeys. In earlier times, when no care was taken to feed milk only from cows known to be in tuberculosis-free herds, alimentary infection by the bovine type of bacilli must have been a potential source of infection. That it is not necessary for monkeys to acquire infection only by repeated body contact with others is clearly proved by the fact that the three cases reported here had been kept in separate cages and under excellent care for 26 months, 33 months, and 24 months, respectively, after receipt from the dealer. Tuberculosis in monkeys never lasts as long as this, and we must not forget the hazards attached to human health in attendants who are unwittingly handling infected animals. The present report of three cases of tuberculosis in monkeys in which there was contiguous involvement of the spine and dura mater in two, and presumptively so in the third, is of interest in several directions. First there is the fact that clinical diagnosis in monkeys is usually very superficial. Secondly, it emphasizes the intrinsic difficulties of accurate clinical neurological diagnosis in simian primates, and thirdly, it may bring out that the central nervous system is probably involved more commonly than is appreciated.

REPORT ON THREE CASES OF TUBERCULOSIS WITH INVOLVEMENT OF A

THORACIC

VERTEBRA,

CONTIGUOUS

EXTENSION

TO

THE

DURA

MATER AND RESULTANT SPINAL CORD COMPRESSION

All three monkeys had been tuberculin tested (once) many months previously, and were old animals. Two (cases I and 2) had been used in experiments involving production of seizures by Metrazol (pentylenetetrazol) and carbon dioxide; Case 3 had been exposed to X-irradiation (3500 rads) of the right cerebral hemisphere one month before being killed. All animals had been under daily clinical observation and periodic electroencephalographic recordings had been made. This is a good example, therefore, where much

BRITISH VETERINARY JOURNAL, IIg, 8

time and effort had been wasted on animals which must manifestly have been infected for months. All three animals had a similar clinical history. Appetite was first adversely affected, physical activity then became diminished, loss of condition ensued and then occurred the onset of motor weakness which finally progressed to gradually worsening flaccid paralysis of the lower limbs. All three animals were killed after the onset of the paralysis-Cases I and 3 after one month and Case 2 after two months. Radiographs of the vertebral column and chest were available and in each of these there was a focus of lessened density around thoracic vertebrae 8-10. At necropsy, each monkey showed severe generalized tuberculosis of the viscera of the thorax and abdomen. Histological examination of infected organs revealed the presence of typical lesions of tuberculosis and no difficulty was encountered in identifying acid-fast mycobacteria by the Ziehl-Neels en stain. In Cases I and 3, the vertebral column was taken out and fixed intact before the spinal cord was removed; in Case 2 only the spinal cord was available for examination, but radiographs had been made of the whole animal. In all three an almost identical epidural lesion was present. Between the 8th-loth thoracic vertebrae, an elongated caseous lesion (tuberculoma) was attached to the dura mater, which in turn was contiguous with a caseous focus in the adjacent thoracic vertebrae (proved by necropsy in two, and presumptively in one from the X-ray picture). The spinal cord with dura mater was sliced every 2-3 mm. through the lesion and for about 3 em. above and below it. Tissues were embedded in paraffin and sections were stained by a large variety of methods, including that of Ziehl-Neelsen. The lesions are illustrated in Figs. 1-5. In Cases I and 2' the lesion was confined to the dura mater and epidural space; in Case 3, the effect of compression was very severe and there was actual spread of the tuberculous infection to spinal white matter. The possibility is that originally infection had spread from a regional focus of tuberculosis in a thoracic lymph node to a vertebra and from thence to the vertebral canal and dura mater. Why the same region was involved in each case is a matter of speculation. The cause of the slowly developing lower limb paralysis is obviously explained. Histologically, the lesions found in the spinal cord are identical with those well-recognized in simian tuberculosis, as the plates show.

DISCUSSION

It is of comparative interest that in children neural tuberculosis (see Rich, 1952) takes the form of (1) disseminated miliary meningeal tuberculosis, (2) focal caseous plaques, (3) acute exudative inflammatory meningitis, or (4) proliferative meningitis. In human beings, the meningitis (mostly base of brain) usually results from discharge of bacilli into the meningeal spaces following rupture of a caseous focus in the brain substance. Whereas in human brains the above forms of tuberculosis are most frequently observed, and tuberculoma rarely, the situation is reversed in Macaca mulatta.

PLATE I

Fig . 1 a. Case 1 (P.NI .No. 108 /6 1) . A. Thoracic vertebra 10 • 8. Tra nsve rse sect ion . Caseating tuber culosis of the bod y a nd a r ch, with dest ructio n of the bo n e a nd invas ion of ver te bral cana l (top ), and con tig uous infecti o n to cl ura m ater (Fi g. 2). x 80 (BNL Neg. No. 5-502-62).

Fig. 1 b . High power o f a rea from A. Epi t helioid a nd m any La ngh a ns' gia n t cells a t peripher y of caseation. Luxo l-fas t blue a ncl PAS stains. x 200 (BN L Neg. No . 5-499-62 ) . Inn es, Brit. vet . J. , II9. 8 E2

PLATE II

Fig.

2.

Spinal cord, w ith ventral fi ssure at bottom. Same case as Fig. I. Dura m a te r intact, a nd no extension of the infec tion to spin a l cord substa nce. M ass ive caseat ing e pidural tuberculoma, ventro-I aterally, which was contiguous with lesion shown in Fig. I. Secondary degeneration in th e wh ite matter from compression. Luxol-fast blu e and PAS. x 11 ·5 (BNL Neg. No. 5-5 0 4- 62 ) .

Fig. 3.

Spinal cord, Case 2 (P.AI. No . 4/62 ) . Identi cal les ion to that in Fig. 2 but is dorso la teral. From X-ray pic ture it was a lso a contiguous on e with vertebra. Luxol-fas t blue. x 11 ·5 (BNL Neg. No. 5-503-62) .

Fig. 4.

Spinal cord, Case 3. Identical lesion to oth ers shown, and contiguous with tuber culosis of the adjacent vertebra. Compression effe ct on spinal cord was more severe than others, a nd infection had spread in to the white matter. Haematoxylin and eos in x 11·5 (BNL Neg. No. 9-274-62 ) .

Inn es, Brit. vet.

J. , II9, 8

PLATE III

Fig. 5 .

Same case as Fig. I a nd 2. Hi gh power of area in latter. Epidural tuberculoma on the right, separated by subarachnoid space from spinal cord on left; area through ventral fissure and artery. Luxol-fast blue and PAS. x 80 (BNL Keg. No. 5-498-62 ).

In nes, Brit. vet. ]., 119, 8

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Isolated and conglomerate tuberculoma (and the latter is but a later sequel to the former) in cerebral hemispheres are illustrated by van Bogaert & Innes (1962, Fig. IV. 51 , page III). The lesions caseate rapidly. Two of the present monkey cases are really examples of PoU's disease, and the third one is .presumptively so. We return to the problem of neurological (clinical) diagnosis in monkeys, to which theme van Bogaert has devoted much attention for some 30 years. He has depicted (van Bogaert, 1962) the difficulties encountered and the important signs to be observed in neurological cases (proved by him after necropsy). Manifestly, from what van Bogaert says, much time must be spent periodically in observing apes and monkeys when they are at rest, active, eating, and with other animals. Where animals are confined in small cages little of any neurological value can be learned, at least in the incipient stages of any disease involving the brain or spinal cord. Once there is motor weakness and paresis affecting different parts, animals can be turned loose in a room and much more learned by objective findings, and by testing reflexes as enumerated by van Bogaert. In the neurological sense, van Bogaert found the following clinical syndromes in simian primates with tuberculosis: progressive cachexia with psychic changes, lassitude and somnolence; sudden death without any specific clinical picture (and that is a common enough experience); sudden epileptic attacks without any premonitory signs; one case of progressive paraplegia in flexion, and two cases with Jacksonian-type epilepsy. The cases reported here all showed lower limb paralysis of a progressive nature, and in the third case tuberculosis was suspected, although not proved until after death. Clinically these monkeys could not possibly have been differentiated from others suffering from spontaneous leucoencephalomyelosis with predominating spinal lesions, or from experimental monkeys in which there was massive damage due to the delayed effect of experimental X-irradiation on the spinal cord. This is important for there is no doubt that lesions due to the spontaneous leucoencephalomyelosis (van Bogaert) are more frequent than generally believed (see Pitcock, 1962).

SUMMARY

Tuberculosis is still the major disease problem which must be controlled in monkey colonies kept for experimental research. Spread of infection to the central nervous system in the early generalization stage is more common than the literature indicates. Over 50 cases have been catalogued in the material of the Bunge Institute, Antwerp (collection of Dr. Ludo van Boga,e rt). The clinical neurological picture is a varied one. In monkeys with neurological signs, evident either with no general changes or concomitant with wasting, the possibility of neural tuberculosis being present should be borne in mind. In contrast to the pathologica l picture which occurs in post-primary generalization of tuberculosis in children, tuberculoma is the commonest lesion in neural disease of monkeys, and not diffuse proliferative or exudative meningitis.

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