Page 532 - The Veterinary Laboratory and Field Manual 3rd Edition

Arthropod vectors and arthropod-borne diseases 469

Pathogen Tick species distribution Vertebrate hosts diagnostic methods
Crimean-Congo Hyalomma Two or three hosts
Haemorrhagic dromedari Hares, small rodents
Fever (Nairovirus) (larvae)
Hares, small rodents,
large ungulates
(nymphs)
Camels, cattle, sheep,
goat, horse (adults)
reovirus
Colorado Tick Dermacentor North America Three hosts Serology (ELISA)
Fever (Coltivirus) andersoni (west) Small mammals PCR
(larvae, nymph) IF staining of blood
Large mammals smears
(adults)
Note: For the most up to date guidelines on testing for specific diseases in livestock species check the online edition of the OIE
Manual of Diagnostic Tests and Vaccines for Terrestrial Animals http://www.oie.int/standard-setting/terrestrial-manual/access-
online/.
* Emerging pathogen – https://cdn.ymaws.com/www.nzva.org.nz/resource/resmgr/docs/other_resources/Theileria_Handbook1.pdf

Tick life cycles usually include a larval, one The method of sampling used is determined
(most hard ticks) or several (most soft ticks) by tick ecology as well as disease ecology con-
nymphal and an adult stadium. Life cycles can siderations. Figure 14.2 gives an example of a
be up to several years long. One method for the workflow for setting up a tick sampling protocol.
collection of ticks can be from the environment, In most cases, arthropod-borne viruses are
where ticks rest (soft ticks) or search for a new only detectable from the blood of a vertebrate
host. Environmental sampling is commonly host for a short time and the peak of viremia
achieved by flagging, a technique where a white coincides with a febrile stage. After this initial
piece of cloth is dragged through a specified area, viremia, virus isolation can be attempted from
and ticks waiting for a host in the environment cerebrospinal fluid (for viral encephalitises),
attach to the cloth. Ticks are then counted and lymph nodes, or the spleen, but detection rates
abundance can be calculated. Traps baited with are much lower. An exception to this is the
carbon dioxide (compressed air or dry ice, alone Orbivirus family, which remain detectable in
or combined with pheromones) are another peripheral blood for a long duration after infec-
method that targets adult ticks in the search of tion, since they adhere to erythrocytes. For
a blood meal. It requires ticks to actively seek a example, ungulates for period of up to 60 days
carbon dioxide source rather than just dropping (Bluetongue virus) and equines up to 40 days
off from the vegetation. (African Horse Sickness Virus).
Another possible technique is the collection The most common diagnostic methods for
of ticks from the vertebrate host, which targets virus detection are DNA/RNA amplification by
females that are in the process of blood feed- PCR or quantitative real-time PCR, as well as
ing. This method additionally gives information virus isolation by cell culture or the inoculation
about the tick burden, the species preference of embryonated eggs.
and the variety of tick species on a targeted ver-
tebrate host.

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