THE PHYSIOLOGY OF THE TICK RHIPICEPHALUS APPENDICULATUS IN RELATION TO THE TRANSMISSION OF THEILERIA PARVA
THE PHYSIOLOGY OF THE TICK RHIPICEPHALUS APPENDICULATUS IN RELATION TO THE TRANSMISSION OF THEILERIA PARVA
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Date
1998-03
Authors
KIBUUKA SEBITOSI, ESTHER NALUGGA
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Abstract
The factors within the tick vector R. appendiculatus that influence the
development and transmission of the parasite Theileria parva were investigated
and found to include the blood meal, phenoloxidase, enzymes, hormones and
lectins. The cattle blood meal, when fractionated into cells and plasma
components by centrifugation and provided to ticks in vitro, indicated that
plasma alone negated the development and infectivity of T. parva to bovine
lymphocytes leading to only 0.07% infections of T. parva in the peripheral blood
lymphocytes, cells showed 1.02% , whole blood revealed 20% while the ticks fed
in vivo on rabbits produced the highest infection (67.9%). For the first time in
vitro infections of lymphocytes was carried out by sporozites obtained from ticks
fed in vitro.
Lectins were detected in the haemolymph, gut and salivary glands from
partially fed female adult R. appendiculatus and R. pulchellus. The gut lectins
were agglutinated by several vertebrate erythrocytes, the highest being rabbit
with a titre of 4096. No agglutination was observed when common domestic
cattle, goat and sheep cells were used. The gut lectin was inhibited by fetuin,
D(+) galactosamine and D(-) manosamine while the haemolymph lectin was
inhibited best by xylose, N-acetyl galactosamine and B-D-fructose. The role of
lectins investigated by feeding the carbohydrates and glycoproteins that
inhibited agglutination to ticks in vitro, to ticks together with infected blood,
revealed reduced or no infections in the salivary glands. Ticks fed upon
immunised rabbits immunised with the lectins had also reduced infection rates
(50%) compared to control (80%) which implied that these lectins were
involved in the control of the development of T. parva. Anti-sera to lectins
raised by immunising rabbit and mice with red blood cells to which an
immunogen had been adsorbed reacted with purified piroplasms and bound the
shizont stages of this parasite opening a new avenue in the possible intervention
of Theileriosis at the piroplasm stage and underscoring the role of lectins in the
development of this parasite. The digestive gut cells and lining and salivary
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gland type III acini from the ticks fed upon these immunized rabbits were
damaged an indication that the antibody traversed the gut, reaching target
organs and remained functionally active.
Subjection of these lectins to enzyme treatments before agglutination
assays revealed the lectins to be proteins, most likely glycoprotein in nature. The
haemolymph was thermo-labile above 40 C, affected by freezing and thawing
treatments shown by the reduction in agglutination properties, while the gut
lectin was thermal stable, and withstood temperatures up to 80 °C. Optimum
haemagglutination depended upon neutral pH conditions and the agglutination
activity was C 2+/ Mg2+ dependent.
Among the hormone effects on ticks, topical application of ecdyson on
ticks significantly reduced the moulting time as well as the engorgement weights.
In vitro feeding of 20 hydroxyecdyson and juvenile hormones resulted into
various responses among which was the significant reduction of engorgement
weights of nymphs, moulting time and infection rates. The deleterious effects of
hormones on ticks should be further investigated.
Enzymes particularly trypsin and protease were detected in the guts and
not in the salivary glands using casein gel as substrate and results showed that
there were higher levels in the infected females. These enzymes were blood meal
induced and peaked at least 48 hr following a blood meal. The phenoloxidase
system in Rappendiculatus, activated by methanol, indicated significantly low
levels of phenoloxidase in the haemolymph, compared to insects (locusts) and
Amblyoma variegatum. At least 95% of the phenoloxidase activity occurred in
the plasma and was highest among the infected ticks indicating that infection
with T. parva altered the normal levels if this enzyme activity and suggesting
that the system may be involved in the "self" and "non self" recognition among
ticks.
Scanning electron microscopy revealed that the salivary glands had a
"grape like" appearance with type I and II acini having smooth surfaces unlike
the type III which were bigger and had sculptures. The infected type III acini
were bigger and had diffuse surface structures. The type III acini had
distinguished morphological features which did not exist in the other cells
implying that the possible mechanism of entry of kinetes into the e cells was
most likely specific receptors at the site of entry into these cells, coupled with
chemical attraction as revealed by the glycogen deposits and was unlikely to be
by chance as earlier suggested.
The investigations revealed the lectins should be looked at as possible
immunogens in the blocking of transmission of T. parva as well as anti- tick
interventions in the future of theileriosis control.
Description
A DISSERTATION PRESENTED TO THE DEPARTMENT OF PARASITOLOGY AND
ENTOMOLOGY FACULTY OF VETERINARY MEDICINE, AHMADU BELLO
UNIVERSITY, ZARIA, NIGERIA, IN FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY IN VETERINARY ENTOMOLOGY
PARASITOLOGY AND ENTOMOLOGY DEPARTMENT,
FACULTY OF VETERINARY MEDICINE,
AHMADU BELLO UNIVERSITY, ZARIA,
NIGERIA. MARCH, 1998
Keywords
PHYSIOLOGY,, RHIPICEPHALUS,, APPENDICULATUS,, TRANSMISSION,, THEILERIA PARVA