Abstract
1. When this investigation was begun in 1935, relatively
little was known about the Swayback other than it was a form of
lamb 'paralysis". These studies established the pathological
nature of the disease for the first time and as a result caused
it to be viewed in an entirely-new light, and thus placed it
on sounder basis for further important work. •
2. Swayback is a nervous disorder of new-born and young
lambs of different breeds occurring in many parts of England,
Scotland and Wales. The same disease occurs in Australia and
New Zealand and probably corresponds to conditions which have
occurred in South America, Sweden, South Africa and India. The
incidence in Britain varies annually and may be as high as 90
per cent. of the lambs born on any one affected farm. In some
areas (e.g. Derbyshire) the disease is enzootic. •
3. The symptoms are those of a spastic paralysis of the
limbs with resultant inco- ordination and occasionally blindness;
the disease is progressive in most cases with a fatal termination. •
4. The pathology is characterised by a diffuse symmetrical
demyelination of the cerebrum varying in extent in different
cases from small foci in the centrum ovale to gross demyelination
of the whole hemispheres. Liquefaction and cavitation is a common
end stage of the lesion. Secondary degeneration of the motor
tracts in the cord is always present. The disease is a degenerative
disorder bearing some resemblance to Schilder's disease in
man and is of ante-natal origin. •
5. Bacteria and /or viruses are not concerned in the
aetiology; "Swayback" is analagous in this respect to the
demyelinating disorders in man, monkey and the dog. •
6. The causal agent causes no obvious disturbance in the
health of the ewe but exerts a pathogenic effect on the foetus or
young lamb. In the latter this agent has a specific affinity for
the cerebral myelin and/or for the mechanism or cells responsible
for the laying down of myelin which it destroys with singular
rapidity. •
7. The suggestion that a disturbance of copper metabolism
in the pregnant ewes was concerned in this way with the aetioloty
was subsequently investigated. Chemical analyses of the blood
and body tissues of "Swayback" lambs and their mothers show lower
Cu values compared with suitable controls. The remarkable prophylactic
value of Cu is clearly proved as a result of a large scale
field experiment carried out in Derbyshire. The exact role which
the trace element plays in the aetiology is not, however, understood
as it is apparent from the Cu analyses of the pastures that
the disease is not a Cu deficiency per se. Until more is known
about function of copper and its relation to myelin metabolism,
the pathogenesis may not be easily explained. specific anaemic
complication in the mother is not part of the syndrome and swayback
is not thus a blood-brain complex parallel with pernicious
anaemia and subacute combined degeneration in man.
