Page 194 - The Veterinary Laboratory and Field Manual 3rd Edition

Parasitology 163

Table 3.6b Classification of classification, development and
rickettsiae. rickettsia are non-motile, life cycles
gram-negative, highly pleomorphic
bacteria that can be present as cocci In common with other living organisms, pro-
or rods and are often transmitted by tozoa are classified according to the Linnaean
arthropod vectors. system characterized by a species and a genus
name. Recent developments in genetic profiling
Order Family Genus and scientific studies of parasite life cycles have
Rickettsiales Rickettsiaceae Rickettsia resulted in a number of changes to the names
Coxiella given to many protozoal organisms. Table 3.6a
Ehrlichia/ provides an overview of the classification of
Cowdria some protozoal species of veterinary impor-
Bartonellaceae Bartonella tance. The life cycles of some common protozoa
are illustrated in Figures 3.31–3.34; the termi-
Anaplasmataceae Anaplasma
nology is quite complex and in some cases the
Eperythrozoon
predominant clinical signs seen in the infected
host will depend on the presence of concurrent
disease as well as the immune response of the
Sample collection for haemoparasites is outlined host to the parasite.
in Section 3.6.
In some protozoal diseases, for example,
toxoplasmosis (see Figure 3.32), the oocysts are 3.5 Protozoal diseases
only found in the faecal material of the defini-
tive host (that is, the cat). To detect infection There are a variety of protozoal species
in intermediate (rat, sheep) or abnormal hosts (Cryptosporidia sp., Cystoisospora sp., Eimeria sp.,
(humans) serological tests are used to detect Giardia sp., Entamoeba sp.) that may be associated
antibodies to Toxoplasma gondii. In most cases with diarrhoea in animals, some are obligate
two blood samples taken two weeks apart pathogens but many are relatively harmless in
would be necessary to distinguish between pre- healthy adults and only become pathogenic in
vious exposure and current infection (that is, a severely debilitated individuals. Clinical signs,
rising titre for IgG antibodies indicates current for example, blood tinged mucoid diarrhoea
infection, see Chapter 6). Alternatively, check- associated with Eimeria sp., may be severe in
ing for IgM antibodies can indicate an ongoing young animals and non-immune adults espe-
infection. Some protozoal organisms are highly cially where stocking rates are high and hygiene
motile (for example, Trichomonas sp. that can is poor. Other protozoa such as Trypanosoma sp.
cause infertility in cattle). These organisms can and Leishmania sp. can cause severe systemic
be seen in fresh smears prepared from scrapings disease which may be fatal in some cases. Early
of infected tissues such as vaginal mucus or diagnosis and treatment is important. In this sec-
preputial washings. tion the cause, prevention and control of some
common protozoal diseases will be discussed. It
is not within the scope of this book to cover all
of the important protozoal diseases in detail so
we have chosen some common organisms which
illustrate the key approach to diagnosis and

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