| dc.description.abstract | Heartwater is a rickettsial disease of
ruminants primarily cattle, sheep and goats
transmitted by several species of Amblyomma
ticks. It is prevalent throughout Africa
south of the Sahara wherever the vector ticks
are found in association with livestock. The
disease syndrome is characterised by fever,
nervous, intestinal and pulmonary disorders.
The mechanism of .i.mmun i,ty of heartwater has
not been clearly understood.
Cowdry (1925) identified Cowdria ruminantium
as the causative agent of heartwater. He observed it
In the endothelial cells of the ruminant
host and in the epithelial gut cells of the
vector tick Amblyomma habreum. He then
observed that c. ruminantium replicated
exclusively in the endothelial cells of
ruminant host. This observation was supported
by Jackson and Neitz (1932) and Pienaar (1970).
Du Plessis (1910, 1975) however, added another
dimension to the replication of c. ruminantium
when he reported that the c.ruminant lymph nodes
were the primary site of replication and that
the ruminant endothelial cells were the
secondary site. Be also found that the
organism as it occurred in lymph nodes did
nothave,a limiting membrane compared to the
form occurring in vascular endothelial cells.
A comprehensive study on the clinical
pathology has been done by Ilemobade and
Blotkamp (1978). The ultrastructural studies
on the organism will broaden our understanding
of the pathogenesis of the disease heartwater.
The alm of the present study was to
elucidate further the ultra-structural
appearance of the organism c. ruminantium in
the two sites of replication. The findings
would then help in the understanding of the
growth of the organism and may be useful to
the immunological studies of heartwater disease.
Attempts to confirm the organism in a blood
smear have been unsuccessful. In vitro attempts
a.t the culturing of ruminantium has to
date been difficult.
Twenty sheep and twenty goats were used
in this study. They were bought from Kiambu
which is known to be a heartwater free area,
brought to the Faculty of Veterinary Medicine
Kabete and housed In groups of four. They
were then allowed to adjust to the stall
feeding for two weeks, ear tagged, dewormed
and then bled for baseline values for another
week.
The stabilate of C. ruminantium (in
10 ml aliquots) was obtained from Veterinary
Research Laboratories at Kabete where it
had been stored in liquid nitrogen (-196oC).
The stabilate was thawed immediately in a
water ba t h (37oC) and inoculated into three test
animals. Subsequent passage was carried out
from one animal to another by intravenous
inoculation of whole blood with the donor and
recipient animals standing side by side.
Clinical examinations were done in the
morning between 7-8 a.m., noting demeanour,
rectal temperature, heart and respiratory rates,
digestive system, appearance of mucous
membranes and changes in locomotor and
nervous systems.
The average incubation period was found
to be eight days for both sheep and goats
following artificial inoculation. The disease
was 100% fatal in goats while mortality in
sheep was much lower (40%). The disease
syndrome wa acute to peracute in goats and
subacute to acute in sheep. Respiratory
and nervous disorders were the two most
marked signs seen terminally.
Blood for haematology was obtained for
red cells counts (RBC), white cell counts
(WBC) both total and differential, haemoglobin
(HB) and packed cell volume (PCV). The
erythrocyte indices were later calculated to
determine the mean corpuscular volume (MCV)
a.n.dmean corpuscular haemoglobin concentration
(MCBC) .
Blood for serum biochemistry was obtained
for Aspartate amino transferase (AST), Blood
urea nitrogen (BUN) total protein content
(TP), albumin and globulins.
MCBC was found to have dropped significantly
in test goats compared to controls
with the maximum drop coinciding with the
period of peak fever reaction. MCHC in
sheep and lymphocytes in both species were
found to have insignificant difference in
both controls and test animals. WBC, RBC,
HB, PCV and MCV were found to be significantly
higher in controls of both specles compared
to the test animals. AST, BUN and TP were founa
to be significantly higher in test animals
compared to controls during the same period
of study.
Blood was also processed for study
using the light and electron microscopes to
confirm the presence of the organism.
Nine animals were sacrificed at various
stages of the disease to obtain organ tissues
for electron microscopic studies. Nine other
animals were allowed to run the heartwater
disease syndrone to death , Standard necropsy
procedures were used for all the animals
sacrificed or dying after the full course of
the disease syndrome. The histopathological
sections, including brain squash smears and
impression smears were prepared routinely.
Histopathological sections were stained with
haematoxylin and eosin (H&E) while squash and
impression smears were stained with Giemsa.
The maln gross lesions were pulmonary oedema,
petechial haemorrhages in various organs,
hydropericardium and hydrothorax.
Histopathology mainly revealed, cellular
infiltration in various organs, congestion and
haemorrhages. Little gross pathology was
observed in the brain except for mild
congestion and oedema.
Impression smears of the lungs, various
internal lymph nodes and spleen showed
cytoplasmic, intranuclear and perinuclear
presence of the organism. Free forms of the
highly pleomorphic organism were also observed.
Brain squash smears revealed the typical
c. ruminantium mbrulae in endothelial cells
and were used for confirmation of the disease
in all cases.
Electron microscopy showed perinuclear
attachment of the organism in the lymphocytes
and reticular cells of lymph nodes. The forms
found in these cells did not have limiting
membranes and seemed to be budding from the
nucleus. The buffy coat showed possible
organisms which were phagocytosed by circulating
-
macrophages. The endothelial cells revealed
forms previously reported which were bound
in a limiting membrane and which seemed to divide
by binary fission.
The most important finding which has
not been reported before was the observation
of intranuclear and perinuclear replication
of the organism. From this study it was
concluded that previous attempts to culture
the organism in vitro had been difficult
because of the two stage life cycle, the first
of which requires the host cell nucleic material. | en |
