Page 211 - The Veterinary Laboratory and Field Manual 3rd Edition

180 Susan C. Cork and Mani Lejeune

the host species and the host immune response. nodes are enlarged and the spleen and liver are
In Africa, the Trypanosomes most commonly enlarged and soft. The muscles appear pale and
infecting cattle include Trypanosoma congolense, the blood watery with evidence of haemorrhages
T. brucei and T. vivax. Infections with more than on the pleural surfaces and pericardium. Smears
one species of Trypanosome are common. The of lymph nodes or spleen may be made for indi-
clinical disease associated with Trypanosomes is rect fluorescent antibody tests or a brain crush
often referred to as ‘nagana’. Nagana is a zulu smear may be submitted to the laboratory. Ante-
word meaning ‘to be depressed’. In general, the mortem diagnosis can be made on clinical signs
incubation period is 1–3 weeks but it can be up and the epidemiological profile but will need
to 2 months for less virulent strains. The clini- to be confirmed by examining stained (thick
cal signs observed are variable. In cattle, chronic and thin) blood smears (Figure 3.36). These
Trypanosomosis presents as an elevated temper- should be taken from the ear vein of animals in
ature, weakness and a loss of appetite followed the early stages of the disease when a fever is
by a reduction in milk production in lactating present. Whole blood may be collected for labo-
animals. Anaemia may develop along with diar- ratory animal tests (sub-inoculation of blood in
rhoea and swollen lymph nodes. In the final rats (T. congolense, T. brucei) or in other labora-
stages of the disease emaciation may become tory animals) or for isolation of trypanosomes.
severe and fluid swelling may appear along the A haematocrit centrifuge is used to concentrate
belly and dewlap (oedema). In pigs and horses the trypanosomes in the buffy layer of the blood
the disease is often acute and animals usually die (the white cells).
shortly after a period of high temperature.
controL and PrEvEntIon
Trypanosomosis requires the control of the
Other trypanosomes
insect vector (regular spraying with insecticides,
Trypanosoma evansi causes a serious disease known controlled clearing of bush and use of fly traps).
as Surra in horses and camels. Although T. evansi If possible, the movement of susceptible live-
can infect other species it is often asymptomatic stock into infected zones should be prevented.
but in horses and camels it can be fatal with fever, Treatment of exposed livestock with anti-proto-
anaemia, oedema and neurological signs develop- zoal drugs can be effective in preventing clinical
ing prior to death. Surra occurs in North Africa, disease but these usually need to be repeated
Central and South America, Southern Russia (consult the nearest veterinary officer for current
and parts of Asia. It is thought that T. evansi is recommendations). In some areas disease-resis-
transmitted by biting flies and also vampire bats tant cattle have been bred (or have evolved),
(in Central and South America). Another pro- for example, the West African N’Dama breed
tozan, Trypanosoma equiperdum (Dourine) causes which seems to be resistant to ticks and other
an acute venereal disease in horses and donkeys, parasites.
treatment is rarely successful. In some cases, it is possible to predict which
vector borne diseases may be present in an
dIaGnoSIS area by evaluating the climate, vegetation and
Diagnosis may be confirmed at necropsy topographical features. Figure 3.37 outlines the
although the gross findings may be similar to broad global climatic zones and zoogeographic
those of other chronic diseases in cattle and areas. These factors, along with the presence of
acute septicaemia in horses/pigs. The carcass suitable hosts (wild or domestic animals), deter-
is usually emaciated and anaemic. The lymph mine which arthropods will thrive in an area and

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