Page 207 - The Veterinary Laboratory and Field Manual 3rd Edition

176 Susan C. Cork and Mani Lejeune

4 Centrifuge for 10 min and pour out the super- diseases caused by haemoparasites
natant. in ruminants
5 Add a drop of Methylene Blue stain to the
sediment and mix gently. Theileriosis
6 Place two drops of this stained sediment on a Theileriosis has been recorded in Africa, Asia,
glass slide and examine under microscope for North America and parts of Europe and is trans-
microfilaria. mitted by a number of tick vectors (for example,
Hyalomma sp., Rhipicephalus sp., Haemaphysalis
sp.). Bos indicus cattle tend to be more resistant
Immunological tests than European breeds, although this may be

due to resistance to the tick vectors. There are
There are a number of serological tests (for a number of species of Theileria (T. parva, T. ori-
example, complement fixation [CFT], agglutina- entalis, T. mutans, T. sergenti and so on) some of
tion, FAT and ELISA – see Chapter 6) currently which cause a non-persistent and mild clinical
available for the diagnosis of haemoparasitic disease. Theileria mutans (benign bovine theile-
diseases, however, the interpretation of the test riosis) can be transmitted by Amblyomma sp. and
results requires experience and knowledge of the Haemaphysalis sp. ticks. Theileria annulata (syn.
epidemiological pattern of the disease(s) in a T. dispar) causes tropical theileriosis in cattle
given area. Many animals will have antibodies to (also known as Mediterranean Coast fever), this
haemoparasites without developing clinical dis- is transmitted by Hyalomma sp. ticks. In Africa,
ease and low titres may imply a level of immunity Theileria parva, transmitted by Rhipicephalus
from past exposure. If the disease is endemic in appendiculatus ticks, is the cause of ECF. ECF is
an area it is important to gather information characterized by lymph node enlargement, high
about the ‘normal’ titres expected from healthy temperature, weakness, emaciation and a high
animals. This allows the laboratory to determine death rate. Theileria sp. parasitize red and white
a ‘cut off’ level above which serological titres blood cells and can be found in lymph nodes and
will be considered positive for animals in that the spleen. The life cycle of Theileria sp. involves
area. The results of any serological tests need to development in the tick vector. The incubation
be evaluated with reference to the clinical signs period may take up to 40 weeks depending upon
exhibited in the animals sampled. There are also the species and environmental conditions, but
tests available to look for antigenic material in for most it is 1–3 weeks.
tissues or smears (for example, immunofluores- In sheep and goats Theileria hirci causes a
cence, see Chapter 6). Survey work to assess the disease similar to ECF in cattle. Theileria hirci
prevalence of haemoparasites in livestock usu- causes moderate disease and is transmitted by
ally includes detailed evaluation of the number Hyalomma sp. ticks. Theileria ovis causes mild dis-
and type of arthropod (that is, tick or insect) ease and is transmitted by Rhipicephalus sp. and
vectors in the area. The species of arthropods Haemaphysalis sp. ticks.
found locally can have some predictive value for
the risk of exposure to arthropod borne diseases LIFE cycLE
although the mere presence of a potential vector Theileria infected ticks may remain infected for a
does not always imply that the disease can be number of months. Developmental stages of par-
effectively transmitted (see Chapter 14 – vector asites occur in the tick and these pass through
borne diseases). the stages (larva, nymph and adult) of the tick life
cycle (trans stadial) but there is no transovarial

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