Fróðskaparrit - 31.12.2000, Blaðsíða 186

190
PARASITES IN SHEEPIN THE FAROEISLANDS
matode found all over the world. The
prevalence was very high in this study, and
the macroscopic changes in sheep lungs
normally associated with this nematode in-
fection are very well known in the Faroe Is-
lands. (Fig. 27). Pneumonic signs are
rarely observed in combination with Muel-
lerius infection, thus, the pathogenic effect
on sheep is considered low.
Dictyocaulus filaria is also a nematode
that, according to this study, seems to be
wiđespread. This lung parasite is consid-
ered to be more pathogenic than Muellerius
capillaris. Clinical symptoms as coughing
in conjunction with D.filaria infections are
commonly seen.
Flukes in the liver
The common liver fluke is found in tem-
perate areas and in high altitudes in the
tropics and subtropics. In the Faroe Is-
lands, Fasciola hepatica has been de-
scribed as a very common sheep parasite
(Liitzen and Bovien, 1934). In the present
study, flukes were only found in one lamb,
and these were early immature stages, 1-4
mm in length. Bearing in mind the life cy-
cle of F. hepatica and the systematic use of
flukicides, it was not expected that the inci-
dence would be high in lambs. The devel-
opment of the F. hepatica larvae, both in the
environment and in the intermediate host, is
dependent on temperature and humidity.
Minimum temperature required for
miracidia to infect the intermediate host is
5-6°C, and the optimum is in the range be-
tween 15 and 26°C (Christensen and
Nansen, 1976). For development of both F.
hepatica larvae and its intermediate host.
Lymnaea truncatula, a mean day/night
temperature of at least 10°C is needed
(Kassai, 1999). In the Faroe Islands, the
highest mean temperatures at sea level are
reached in July and August, 10.3 and
10.5°C, respectively, (Fig. 28), and in alti-
tudes higher than 100 metres the tempera-
tures never reach a mean temperature above
10.0°C. Consistent with this, L. truncatula
has not been found at altitudes higher than
100 metres in the Faroe Islands (Jensen et
al., 1928-1971). It is expected that with
these climatic conditions the development
from egg to infective metacercaria will be
only just possible in the Faroe Islands, and
that development may take a relatively long
time.
Faecal examinations -
epidemiological studies
Strongvle tvpe eggs
No attempt was made to differentiate be-
tween these eggs, as they may be from any
of the following nematodes, identified in
this study: Teladorsagia spp., Tri-
chostrongylus spp., Trichuris ovis, and
Chabertia ovina. If one compares the egg
numbers with the post mortem examina-
tions described above, it is likely that the
majority of these eggs belonged to Telador-
sagia spp. and Trichostrongylus spp. The
egg counts were generally higher in lambs
than in ewes. The autumn mean epg count
in lambs was 651 and in ewes 219. It fell to
around 90 epg in both lambs and ewes in
winter and then rose to 1,066 in lambs and
539 in ewes in the spring (Fig. 4). The fall
in epg in the winter is likely to be due to in-
creased resistance and the anthelmintic