Page 217 - The Veterinary Laboratory and Field Manual 3rd Edition

186 Susan C. Cork and Mani Lejeune

mites). Samples should be placed into sealed The distribution of ticks and other arthro-
labelled containers. If there is to be a delay in pods depends on a number of environmental and
examination it is preferable to fix the specimens climatic factors. Owing to changes in land use
using preservatives such as 70% alcohol. If the and climate the distribution of some arthropod
specimens are to be used for museum collec- species, including ticks, is changing. Studies on
tions, or for display, it is advisable to consult an tick distribution and abundance can give good
entomologist to determine the best way to fix predictive information about the likely occur-
the specific parasites which are collected because rence of specific tick-borne diseases in an area.
some fixatives alter the colour and/or size of the Tick survey work should be done using strict
specimen. guidelines with an agreed sampling protocol.
Skin and hair samples may also be examined The latter would usually include whole body
for the presence of fungal hyphae. Fungal spe- tick counts along with pasture tick counts to
cies such as Trichophyton sp. and Microsporum sp. assess the number of ticks present in the envi-
may cause ‘ringworm’. Ringworm is not a ‘para- ronment. Data from such studies can be used for
site’ but it is a skin infection which can resemble the development of vector distribution maps and
ectoparasite infestation causing irritation, red for risk assessments. Disease modelling, which
skin and hair loss especially if there is a second- engages the expertise of epidemiologists, clima-
ary bacterial infection (see Chapter 4, section 4.6 tologists, disease specialists and entomologists,
and Chapter 10, Tables 10.7 and 10.8). has become a very useful tool for establishing
surveillance and disease prevention programs
for vector borne diseases in many parts of the
3.8 Ticks and tick-borne diseases world.
There are two main types of tick, the
Ticks are common worldwide and are responsible Argasidae (soft ticks: no scutum) and the
for transmitting a wide range of micro-organ- Ixodidae (hard ticks: scutum present). These
isms including haemoprotozoa (for example, are distinguished by the presence or absence of
Babesia spp. and Theileria spp.), Rickettsia (for a hard outer scutum on the dorsal aspect of the
example, Anaplasma spp.), bacteria (for exam- body. In the Ixodid species the scutum covers
ple, Borrelia spp.) and viral diseases (louping ill, most of the dorsal surface of the male tick but
various encephalidities) (see Table 3.9). not of the fed female tick (Figure 3.39). Ticks
Ticks can be collected directly from the ani- exist as eggs, larval, nymph and adult forms. The
mal host and fixed in 70% alcohol or in 10% larval forms have three pairs of legs like insects
formal saline prior to examination under a dis- (Figure 3.40). The nymphs and adults have four
secting microscope. Try to make sure that the pairs of legs. Some tick species have a single host
head and mouthparts of the tick are removed and others have several different hosts during
along with the body. Swabbing the skin where their life cycle. Ticks feed on blood and swell
the tick is attached with alcohol and waiting a to many times their original size as they feed.
few minutes may help. Collected ticks should Heavy tick infestations in young animals may
be stored in labelled glass or plastic vials and cause anaemia. In ticks which feed on multiple
should be accompanied by information about hosts, the larval, nymph and adult ticks drop
the host (species, breed, age, sex, recent ecto- off each host after feeding and then begin the
parasite treatment, general health and so on), next stage of development in the environment
the location (altitude/latitude of the area) and (Figure 3.41). In ticks which feed on a single
the date when the ticks were collected. host the tick progresses through each stage of

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