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Cerebrospinal Nematodiasis with Focal Encephalomalacia as a Cause of Paralysis of Beavers (Castor Canadensis) in the Dublin Zoological Gardens
Br. vet. J. (rg66),
122,
285
CEREBROSPINAL NEMATODIASIS WITH FOCAL ENCEPHALOMALACIA AS A CAUSE OF PARALYSIS OF BEAVERS (CASTOR CANADENSIS) IN THE DUBLIN ZOOLOGICAL GARDENS By W. R.
KELLY
Veterinary College, University College, Dublin
and
J.
R. M. INNES
Bionetics Research Laboratories, Falls Church, Virginia
SUMMARY
Fatal paralysis has occurred in beavers in the Dublin Zoological Gardens for some years, and it has been found impossible to raise this species to maturity. Immature worms or larvae which are probably ascarids appear to be the cause of a focal malacia of the brain and almost certainly account for the neuroparalytic signs. We have no idea what are the natural hosts of these parasites. The case adds to a growing list of diseases which are caused by helminth parasites migrating to the central nervous system of a great variety of mammalian hosts. · One of us (WRK) has observed for some years that it had been impossible to raise to maturity beavers (Castor canadensis) born in the Zoological Gardens of Dublin. The animals appeared normal at birth but at variable times up to three months (in most cases between 7-14 days of age) they developed motor weakness and inco-ordination of the hind limbs, progressing to involve the fore limbs. There was a tendency to fall to one side or another, and in some animals there was interference with normal head movements. All three siblings of one litter showed such neurologic signs within two weeks of birth. Initially, it was considered, but not proved on superficial clinical grounds, that the disease was nutritional in origin. The idea was discarded subsequent to the examination of one brain. PATHOLOGY
Portions of the brain and spinal cord were received by one of us (JRMI) already fixed in formol saline. Some coronal slices were embedded in paraffin and stained by various neuropathological techniques; other parts were examined as squeeze preparations under the dissection microscope (see Anderson,
BRITISH VETERINARY JOURNAL,
122,
7
Ig6sa, for the technique, although similar methods have been used for years by other workers). In the stained sections, there was patchy encephalitis involving the cerebellum and many vessels in the grey and white matter showed perivascular cuffs of cells with occasional eosinophils (Fig. I). The cuff sometimes was but one layer thick. In parts of the cerebral cortex there were microglial nodules near a malacic focus with some liquefaction in the centre; in and around there were gitter cells, some astrocytic reaction and a few eosinophils. In the centre there were cross sections of two immature nematodes or larvae (Fig. 2), identified as ascarids. The squeeze preparations failed to reveal the presence of other worms which would have been essential for identification of helminth species. DISCUSSION
It is unfortunate that the nervous system of several beavers could not be examined. However, in one beaver with a history of paralysis, the cerebral focus with worms can certainly explain the neuroparalytic signs, and is another example of cerebrospinal nematodiasis caused by ascarid larvae whose natural host might be yet another mammalian species. There is a full discussion on this topic in the chapter on helminth infections of the nervous system in Innes & Saunders ( 1962). The theme was promulgated that under certain conditions - which are totally inexplicable helminth parasites transmitted to unnatural hosts are strangely attracted to invade the central nervous system (and eye). In their wandering they produce sometimes eosinophilic meningitis and one or more areas of focal malacia (which is simply traumatic damage) which forms the anatomic substratum of a variety of clinical neurologic conditions. There are abundant records now proving that the concepts defined above apply to diseases (sometimes enzootic) in a great variety of mammalian hosts spread all over the globe, affecting sheep, goats, horses, deer, elk, moose and reindeer. There is also quite a range of helminth species now identified in addition to Setaria digitata, which was the first to be incriminated by Japanese workers who carried out the research study on paralyzed sheep in Korea. Anderson (I g6sb) contributed a brilliant study on Pneumostrongylus tenuis (previously designated Elaphostrongylus tenuis) whose natural host is the white tailed deer, Odocoileus virgianus; he showed that this worm migrates directly to the central nervous system and remains there in association with the dura mater and its vessels after a prolonged developmental period in neural parenchyma. Eggs and larvae only are carried to the lungs from the nervous system by haematogenous paths. In this species of deer neurological signs are rare, but Anderson in an experimental study with moose showed that in this host (unnatural, abnormal or inadequate) the worms produced neuroparalytic signs associated with malacic lesions in brain or spinal cord. Recently, Richter & Dradel (1965) have recorded cases of cerebrospinal nematodiasis in ground hogs in Pennsylvania.
PLATE I
Fig. 1. Cerebral cortex, beaver. Malacic focus contammg cross-sections of two ascarid larvae. Gitter cells and astrocytic reaction around. H . E.
Fig. 2. High power of parasite seen on the right of Fig. 1. H. E. The lateral alae are features of ascaroidal larvae.
Kelly and Innes, Br. vet. J. ,
122,
7
CAUSE OF PARALYSIS OF BEAVERS ACKNOWLEDGEMENTS
One of us (WRK) thanks a member of his staff, Dr. F. B. Halpin, for examination of sections of the spinal cord in the initial stages of the work. We are also indebted to Dr. Paul Weinstein, Acting Chief of the Laboratory of Parasitic Diseases, National Institutes of Health, Bethesda, Maryland, for his help m examination on the squeeze preparation in our search for worms. REFERENCES
ANDERSON, R . C. (1965a). Path. Vet., 2, 36o. ANDERSON, R. C. (1965b). Cerebrospinal nematodiasis (Pneumostringylus tenuis) in North American cervids. Trans. Thirtieth North American Wild and Natural Resources, Wildlife Management Institute, Washington 5, D. C. INNEs, J. R. M. & SAUNDERS, L . Z . (1962). Comparative Neuropathology, pp. 540 et seq. New York: Academic Press. RicHTER, C. B. & KRADEL, D. C. (1965). Am. ] . vet. Res., 25, 1230. (Accepted for publication 21 April, 1966)
122,
285
CEREBROSPINAL NEMATODIASIS WITH FOCAL ENCEPHALOMALACIA AS A CAUSE OF PARALYSIS OF BEAVERS (CASTOR CANADENSIS) IN THE DUBLIN ZOOLOGICAL GARDENS By W. R.
KELLY
Veterinary College, University College, Dublin
and
J.
R. M. INNES
Bionetics Research Laboratories, Falls Church, Virginia
SUMMARY
Fatal paralysis has occurred in beavers in the Dublin Zoological Gardens for some years, and it has been found impossible to raise this species to maturity. Immature worms or larvae which are probably ascarids appear to be the cause of a focal malacia of the brain and almost certainly account for the neuroparalytic signs. We have no idea what are the natural hosts of these parasites. The case adds to a growing list of diseases which are caused by helminth parasites migrating to the central nervous system of a great variety of mammalian hosts. · One of us (WRK) has observed for some years that it had been impossible to raise to maturity beavers (Castor canadensis) born in the Zoological Gardens of Dublin. The animals appeared normal at birth but at variable times up to three months (in most cases between 7-14 days of age) they developed motor weakness and inco-ordination of the hind limbs, progressing to involve the fore limbs. There was a tendency to fall to one side or another, and in some animals there was interference with normal head movements. All three siblings of one litter showed such neurologic signs within two weeks of birth. Initially, it was considered, but not proved on superficial clinical grounds, that the disease was nutritional in origin. The idea was discarded subsequent to the examination of one brain. PATHOLOGY
Portions of the brain and spinal cord were received by one of us (JRMI) already fixed in formol saline. Some coronal slices were embedded in paraffin and stained by various neuropathological techniques; other parts were examined as squeeze preparations under the dissection microscope (see Anderson,
BRITISH VETERINARY JOURNAL,
122,
7
Ig6sa, for the technique, although similar methods have been used for years by other workers). In the stained sections, there was patchy encephalitis involving the cerebellum and many vessels in the grey and white matter showed perivascular cuffs of cells with occasional eosinophils (Fig. I). The cuff sometimes was but one layer thick. In parts of the cerebral cortex there were microglial nodules near a malacic focus with some liquefaction in the centre; in and around there were gitter cells, some astrocytic reaction and a few eosinophils. In the centre there were cross sections of two immature nematodes or larvae (Fig. 2), identified as ascarids. The squeeze preparations failed to reveal the presence of other worms which would have been essential for identification of helminth species. DISCUSSION
It is unfortunate that the nervous system of several beavers could not be examined. However, in one beaver with a history of paralysis, the cerebral focus with worms can certainly explain the neuroparalytic signs, and is another example of cerebrospinal nematodiasis caused by ascarid larvae whose natural host might be yet another mammalian species. There is a full discussion on this topic in the chapter on helminth infections of the nervous system in Innes & Saunders ( 1962). The theme was promulgated that under certain conditions - which are totally inexplicable helminth parasites transmitted to unnatural hosts are strangely attracted to invade the central nervous system (and eye). In their wandering they produce sometimes eosinophilic meningitis and one or more areas of focal malacia (which is simply traumatic damage) which forms the anatomic substratum of a variety of clinical neurologic conditions. There are abundant records now proving that the concepts defined above apply to diseases (sometimes enzootic) in a great variety of mammalian hosts spread all over the globe, affecting sheep, goats, horses, deer, elk, moose and reindeer. There is also quite a range of helminth species now identified in addition to Setaria digitata, which was the first to be incriminated by Japanese workers who carried out the research study on paralyzed sheep in Korea. Anderson (I g6sb) contributed a brilliant study on Pneumostrongylus tenuis (previously designated Elaphostrongylus tenuis) whose natural host is the white tailed deer, Odocoileus virgianus; he showed that this worm migrates directly to the central nervous system and remains there in association with the dura mater and its vessels after a prolonged developmental period in neural parenchyma. Eggs and larvae only are carried to the lungs from the nervous system by haematogenous paths. In this species of deer neurological signs are rare, but Anderson in an experimental study with moose showed that in this host (unnatural, abnormal or inadequate) the worms produced neuroparalytic signs associated with malacic lesions in brain or spinal cord. Recently, Richter & Dradel (1965) have recorded cases of cerebrospinal nematodiasis in ground hogs in Pennsylvania.
PLATE I
Fig. 1. Cerebral cortex, beaver. Malacic focus contammg cross-sections of two ascarid larvae. Gitter cells and astrocytic reaction around. H . E.
Fig. 2. High power of parasite seen on the right of Fig. 1. H. E. The lateral alae are features of ascaroidal larvae.
Kelly and Innes, Br. vet. J. ,
122,
7
CAUSE OF PARALYSIS OF BEAVERS ACKNOWLEDGEMENTS
One of us (WRK) thanks a member of his staff, Dr. F. B. Halpin, for examination of sections of the spinal cord in the initial stages of the work. We are also indebted to Dr. Paul Weinstein, Acting Chief of the Laboratory of Parasitic Diseases, National Institutes of Health, Bethesda, Maryland, for his help m examination on the squeeze preparation in our search for worms. REFERENCES
ANDERSON, R . C. (1965a). Path. Vet., 2, 36o. ANDERSON, R. C. (1965b). Cerebrospinal nematodiasis (Pneumostringylus tenuis) in North American cervids. Trans. Thirtieth North American Wild and Natural Resources, Wildlife Management Institute, Washington 5, D. C. INNEs, J. R. M. & SAUNDERS, L . Z . (1962). Comparative Neuropathology, pp. 540 et seq. New York: Academic Press. RicHTER, C. B. & KRADEL, D. C. (1965). Am. ] . vet. Res., 25, 1230. (Accepted for publication 21 April, 1966)