The host- parasite relationship of a hybrid strain of
domestic rabbit, Or ctola,gus cuniculus, and the ruminant
nematode Trichostronrylus colubriformis was studied.
The main techniques used to follow the infections were
faecal egg counts, live weight gains, worm counts at
autopsy, haematology and serum biochemistry.
The newly -weaned rabbit was found to be a moderately
good host for the nematode. Most animals developed
patent infections and worm egg production was of
varying size and duration. The sex of the host
appeared to have little influence on the numbers of
worms establishing or on the subsequent course of the
infections. Adaptation of the parasite to the rabbit
by successive passage through 16 senerations indicated
that total egg production by the worms increased over
the first three generations, dropped in the fourth, rose
up to the seventh and then stabilised. Further
evidence for such adaptation was provided by an
experiment in which it was shown that the total egg
production by a fifth generation rabbit -adapted strain
of the worm was significantly greater than that of a sheep strain.
Doses as high as 15,000 infective larvae of either
strain of the worm did not appear to be very pathogenic
in the rabbit and acute disease was produced on only
three occasions. The most consistent clinical sign
was anorexia. Most animals showed only transient
clinical signs of disease or none at all and a true
chronic trichostrongyliasis as described in sheep and
goats was never seen.
An age -related resistance was observed in rabbits
aged 13 weeks and older and this was manifested mainly
by a reduction in the numbers of worms reaching the
Most newly- weaned rabbits eventually developed
acquired resistance to a primary infection and expelled
their worm burdens apparently in a self -cure reaction.
_bout this time a transient eosinophilia often
accompanied by a basophilia occurred in the peripheral
blood. After this the rabbits were resistant to a
challenge infection which they ejected within 12 days.
A similar blood response was seen during the first 11
days of this infection. However a minority cf rabbits
failed to self -cure after their primary infections and
these rabbits were not then resistant to a challenge
infection. No blood response was observed in these or
in worm -free controls. during a primary infection.
Experience of primary infections, chemically
abreviated after 12 days by thiabendazole did not appear
to give the rabbits the ability to resist a challenge
infection but the results were inconclusive because of
interference by age resistance.
No variation from the normal was observed in the
serum proteins of rabbits infected with the nematode.
The current theories relating to the function of
the eosinophil and basophil leucocytes of mammals are
discussed and possible roles for these cells in the
mechanism of the self -cure reaction to T.colubriformis
in the rabbit are suggested. It is pointed out that
the rabbit -T.colubriformis host- parasite relationship
affords a useful system for studying the phenomenon of
It is also noted that the pathogenicity and
immunology of T.colubriformis infections in the rabbit
are different to those in the guinea pig.