STUDIES ON TROPICAL THEILERIOSIS IN TURKEY
Tropical theileriosis, Theileria annulata infection, is the
most important disease of cattle in Turkey and is a major threat to
the high yielding exotic cattle introduced into the country in
order to improve the productivity of local breeds. A vaccination
programme, using locally produced vaccine, has operated for several
years but despite these efforts to control the disease the
importance of tropical theileriosis in Turkey is increasing. The
inability to control the disease is related to lack of
epizootiological knowledge and incorrect targeting of the vaccine.
The present study (STD2A 170), funded by the European
Union, and coordinated by Professor C.G.D. Brown, CTVM, University
of Edinburgh was undertaken with the aims of improving the
epidemiological understanding of tropical theileriosis in selected
areas of Turkey by the use of sero-epidemiological methods and the
study of tick transmission patterns of T.annulata in four species;
Hyalomma anatolicum anatolicum, H.a. excavatum, H.detritum and
H.marginatum, widely distributed in Turkey. Stocks of T.annulata
isolated from clinical cases of tropical theileriosis in villages
in Central and Eastern Anatolia were isolated in tissue culture and
cryopreserved for further study which included characterisation by
biochemical methods.
The epidemiology of tropical theileriosis in central
Anatolia Turkey was investigated over a four year period by
serology, identification of carrier animals, clinical disease and
the analysis of tick species. The infection rates in ticks and
their biology was investigated in an attempt to explain infection
and disease patterns and the levels of Theileria annulata infection
in the region. Four tick species, Hyalomma anatolicum anatolicum,
H.a. excavatum, H.detritum and H.marginatum were identified as
vectors of T.annulata in Central Anatolia. The disease coincided
with the feeding of adult ticks in late spring / early summer
related to an increase in temperature. Female ticks were found to
lay eggs in summer with the hatching and development of larvae
followed by feeding and the moult into nymphs in late summer /
early autumn. The nymphs then fed on carrier cattle in autumn when
there is no disease and over wintered: either as engorged nymphs,
in which case T.annulata remains as zygotes in the nymph and
develops into sporoblasts and sporozoites the following year in
spring when temperatures increase and the nymphs moult into adults;
or as adults to which the nymphs may moult in autumn, with the
concomitant development of T.annulata into sporoblasts and
sporozoites.
Over four years the sero-epidemiology of the disease around
Ankara was studied using the indirect fluorescent antibody test on
sera collected from cattle and compared with blood smears to detect
piroplasms in order to determine the extent of T.annulata
infection. Two pilot studies were carried out at the State
Veterinary Laboratory at Pendik; the first describes the isolation
and cryopreservation of cell lines isolated from the Aydin region
of western Turkey; the second a preliminary study on the
clonability of the Pendik T.annulata vaccine cell line.
The phenotypic diversity of stocks of T.annulata isolated
from cattle with clinical tropical theileriosis around Ankara in
central Anatolia and Elazig in eastern Anatolia was examined. This
was done by isoenzyme analysis, of glucose phosphate isomerase
(GPI), lactate dehydrogenase (LDH) and hexokinase (HK). The GPI
assays were carried out on piroplasms isolated directly from
animals, on schizonts grown in cell culture from infected animals
and occasionally on sporozoites obtained from ticks feeding on
experimentally infected animals. The T.annulata parasites isolated
from clinical cases showed polymorphism with respect to GPI
isoenzymes which appeared to arise from various combinations of
parasite populations. The GPI pattern of the vaccine cell lines at
Pendik showed a simple triplet pattern, reflecting a decrease in
the number of populations present. LDH piroplasm patterns were
identical for the 10 or so stocks examined, indicating that it
could be a species-specific marker. The variation of GPI patterns
was followed for two stocks over a period of two years during
cattle-tick passage. Differences were found in the banding
patterns in the bovine host, the tick vector and in tissue culture
conditions but a stable isoenzyme profile was the norm.
In vivo transmission studies were carried out on the Ankara
stock of T.annulata and the clones derived from it. The parent
stock and clones were initially used to infect calves, then ticks
fed on these calves to assess the infectivity of each clone for
ticks. GPI patterns were used to trace the parasite through ticks
and cattle. The clones and parent stock induced protection in
cattle following mild disease. Ticks fed on the cattle were not
able to pick up a proportion of the clones, representing important
biological differences between these clones. The virulence of the
clones appeared to be enhanced by passage through the tick.
The infection rates in four species of Hyalomma ticks which
occur widely in central Anatolia were compared with respect to
their ability to pick up T.annulata piroplasms from experimentally
infected calves. All species of ticks were infected by the
parasite with no significant differences. The efficacy of the
Pendik theileriosis vaccine was assessed in a series of
experiments. Protection afforded by various doses, was compared
with that provided by the standard vaccination dose of 107 cells
against challenge with virulent heterologous stocks. This study
showed that, with an attenuated and cryopreserved vaccine such as
this a large cell dose was necessary to ensure protection.
For further information contact:
Professor Fahri Sayin
Faculty of Veterinary Medicine
University of Ankara, Diskapi
06110 Ankara Turkey
OR
Professor C.G.D. Brown
Centre for Tropical Veterinary Medicine
University of Edinburgh
Easter Bush, Roslin
Midlothian EH25 9RG
Scotland
