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BOOK REVIEW
Durden, L. A., and J. E. Keirans. 1996. Nymphs of
the Genus Ixodes (Acari: Ixodidae) of the United States: Taxonomy,
Identification Key, Distribution, Hosts, and Medical/Veterinary
Importance. Entomological Society of America (Thomas Say Publications
in Entomology); Lanham, MD. iv + 95 p. ISBN 0-938522-57-4. Paperback.
$13.20 (ESA members), $22.00 non-members, from ESA Sales, 9301
Annapolis Rd., Lanham, MD 20706-3115. Add $2.50 per volume for
postage and shipping ($3.50 to foreign addresses).
There are about 670 species of hard ticks (Ixodidae)
belonging to 13 genera. Out of those, more than a third-234 species-belong
to a single genus-Ixodes. Members of this genus are distributed
world-wide and include documented and suspected vectors of an
extensive list of viral, bacterial and protozoan agents of human
and animal diseases. Also, several species of this genus can cause
tick paralysis in their hosts. All Ixodes ticks that have been
tested so far appear to be capable of acquiring and transmitting
agents of animal and human diseases. Therefore, one can say that
the genus Ixodes have the highest epidemiological and veterinary
significance among Acari. It attracted profound attention by the
medical and scientific communities in the late 1930’s, at the
time of the discovery of Russian spring-summer tick-borne encephalitis.
Our knowledge about the importance of diseases transmitted by
Ixodes spp. to public health has grown greatly since then. Concurrently,
it has been recognized that closely related species of ticks possess
markedly different susceptibility to certain tick-borne pathogens,
and play different roles in their natural circulation. Yet, those
species that are capable of acquiring and transmitting pathogens
in turn differ in their aggressiveness toward humans, and therefore
have dissimilar significance as a source of infection for humans
and domestic animals.
In the late 1950’s, it was found that one of the
major vectors of Russian tick-borne encephalitis (TBE), previously
considered to be a single species, indeed presented a complex
group. There are several species of ticks phylogenetically close
to Ixodes persulcatus which dwell in a huge territory of Southern
Siberia, Far East, and Middle Asia. One of those species-I. pavlovskyi-appears
to have a wide geographical range, and sometimes reaches a high
abundance in active foci of TBE. Still, because of its ecological
peculiarities I. pavlovskyi plays a notably different role in
epidemiology and epizootiology of TBE than I. persulcatus. In
the USA, ticks I. dentatus, I. spinipalpis, and I. neotomae are
competent vectors of the Lyme disease spirochete. However, they
rarely attack humans, and therefore pose a lot lesser threat to
human health than I. scapularis or I. pacificus. These are just
a few of the available examples of the importance of careful identification
of tick species for both practical and scientific purposes.
The reviewed book presents the first practical guide
for identification of the Ixodes spp. nymphs since 1945. It includes
all 34 species of the genus Ixodes considered to be resident in
the United States. The authors introduce their book with a short
morphological description of an Ixodes sp. nymph which makes the
usage of the guide possible for an inexperienced person. The following
comprehensive key to nymphal stages of all U.S. species contains
references to scanning electron micrographs for further help with
the identification. In the species accounts, the authors have
included micrographs of characteristic features of each species,
chronological listings of synonymies, geographical distribution,
and known host records. They also provide synopses of the known
medical and veterinary importance in the United States of each
species. The 148 cited references alone present valuable information
to those interested in learning about tick distribution, and tick-borne
diseases in the U.S. The format and concise information included
in this book make it useful to medical and veterinary practitioners,
as well as to specialists studying ectoparasites of vertebrates.
Michael Levin
Yale School of Medicine
Dept. of Epidemiology and Public Health
60 College St., P. O. Box 208034
New Haven, CT 06520-8034