December, 1956]
ABSTRACTS
287
A difference in mortality following challenge dose of virus was seen between
lines from the various matings. The line raised from the family with the highest pre-
challenge mortality showed a most rapid increase in deaths as compared with the
line from the low-mortality-rate family. Great differences in the percentage of
mortality were shown to occur between chicks challenged in warm battery room and
those challenged under brooder-house conditions. There was 31 per cent mortality
in the former case and 88.5 per cent to 96.6 per cent in the latter.
To explain family differences in mortality following challenge with a standard
dose of virus, the possibility of existence of a specific mechanism in either aiding or
preventing the transport of virus in which red cells appear to play some role, has
been suggested. (C. R.).
On the invasion of the central nervous system by nematodes—I. The incidence
and pathological significance of nematodes in the central nervous system.
SPRENT, J. F. A. (1955). Parasitology, 45 (1, 2): 31-40.
T HE author reviews the available literature dealing with the incidence of
nematodes in the central nervous system and discusses the pathological signifi-
cance of nematode infection in relation to the central nervous system.
A wide variety of nematode species like ascarids, filariids and strongyles, parti-
cularly their larval and immature stages, are known to invade the tissue of the brain
and spinal cord as well as the meningeal spaces of animals and human beings, some
manifesting violent nervous symptoms while others apparently producing no sym-
ptoms at all. The direct pathological changes resulting from invasion of the central
nervous system are probably due to the traumatic effect of the nematode parasite,
and are found to vary in their extent and nature, depending upon the size, the route
of migration and the activity of the species involved. The relatively small larvae
of Toxocara sp. may wander in the brain without producing sufficient damage to
provoke symptoms, while larger larvae such as those of Ascaris spp. and filariids do
sufficient damage during their migrations to cause definite derangement of the central
nervous system. The pathological changes, which may or may not be seen in close
association with the invading organism, may be diffused or focal, and may include
haemorrhage, degenerative changes, cellular infiltration and glial proliferation.
Nematodes entering the maningeal spaces may cause severe nervous symptoms by
compression of the spinal cord, by distension and thrombosis of blood vessels of the
spinal cord, by destruction of the meninges, or by meningeal haemorrhage.
Nervous symptoms are also found to be associated with nematode infections
outside the central nervous system where there is no evidence that the parasite had
invaded the central nervous system and where the symptoms tend to disappear after
anthelmintic treatment. The occurrence of toxins in such infections offers no satis-
factory explanation for the nervous symptoms while there is experimental evidence
to prove that the pathogenesis may be allergic in origin.
The possibility that the nematodes entering the central nervous system may
carry viruses present in the other parts of the host's body, thus facilitating a secondary
invasion of the central nervous system, is also discussed. (C.T.P.).