| dc.description.abstract | In order to assess if there are any differences
on the susceptibility and changes in the reproductive
function of various varieties of the Small East
African goats to tryapanosomiasis, 10 adult normocyclic
females aged between 2-3 years from tsetse-free and
tsetse-endemic areas of East Africa (MorOgoro, Arusha,
Lambwe Valley and Imbo) were experimentally infected
with Trypanosoma congolense strain (EATRO-1753). When
the study was terminated 24 weeks later, distinct
variety susceptibilities were noted.
Morogoro goats were the most tolerant, followed
by Arusha, Lambwe Valley and Imbo goats in that order.
The Imbo goats, from a tsetse-free area, had the
highest parasitaemia, most severe anaemia, marked
emaciation and 70% mortality. The Morogoro goats
from a tsetse-endemic area, had milder infection with
lower parasitaemia, smaller weight losses, less severe
anaemia and lower (30%) mortality. The Lambwe and
Arusha goats (from tsetse-endemic areas) were intermediate
in susceptibility to the Morogoro (resistant)
and Imbo (susceptible) goats.
Although changes in the reproductive function
of the infected goats followed the same pattern for
the first 3 months, this difference disappeared
later, as all the goats became acyclic. Irregular
and predominantly shorter (P<O.05) oestrous cycles
were observed in all the infected goats before cessation
at the second cycle in Imbo goats and fourth cycle in
Morogoro and Lambwe goats. A significant decrease
(P<O.Ol) in the mean monthly plasma progesterone and
oestradiol-17S, peak luteal progesterone, as well as
in preovulatory oestradiol-17S values were observed
within the second, third and fourth cycles post infection,
respectively. Decline in hormonal values was, however,
lower in the Morogoro than in other infected goats
at least for the first 2 months of infection (P<O.05).
Remarkable increase in connective tissue in the
ovaries and decrease in the number of primordial and
primary follicles were observed in all the infected
goats, and those developing became atretic at the
tertiary stage. This resulted in the lack of corpora
luteaformation. The pituitary gland of the infected
goats revealed reduced degranulation of the basophils
and little acini secretions, and slight hypertrophy
of the acidophils.
In the adrenals, the zona fasciculata were
markedly hypertrophied in some areas and slightly
atrophied in others. Extensive atrophy and degeneration
of the thyroid gland was evident in most infected
goats and plasma thyroxine (T4) levels were concomitantly
reduced in all the infected goats throughout the
experimental period.
It is concluded that, there are differences in
susceptibility to trypanosomiasis in different
varieties of Small East African goats. The higher
resistance found in the tsetse fly endemic areas
may have evolved as a genetic selection following
prolonged exposure to various strains of trypanosomes.
Though this increased resistance may influence the
degree of initial damage of the reproductive and
other endocrine glands, prolonged presence of
trypanosomes even at a low level in the blood stream
may exacerbate any underlying diseases.
The evidence obtained in this study indicates
that, the hypothalamus may be the initial target of
trypanosomiasis, reducing its liberins and thereby
impairing the pituitary gland. This results in
panhypopituitarism which in turn impairs the function
of target glands including cessation of reproductive
functions and damage of the thyroid and adrenal
glands.
It was also evident that, clinical tolerance is
correlated with residual fertility; that is the
greater the tolerance, the greater the retention of
residual fertility and vice versa. | en |
