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identification keys to adult forms of large stomach worms (Haemonchus) of
ruminants of North America, the most important nematode pathogens of sheep in
southeastern United States and of cattle in warm, moist pastures. The keys
employed newly discovered characters of the synlophe (surface cuticular ridges)
and permit the morphological identification of single adult specimens of either
sex for the first time.
Developed first phylogenetic classification of nematodes of the
family Trichostrongylidae which includes most of the economically important
nematode parasites of ruminants. This new classification of the subfamilies for
the first time established monophyly for the family and subfamilies of these
important groups, a prerequisite for further studies on their evolution.
Developed diagnostic probes specific for species of
Trichinella. Species and subspecific populations from domestic hosts and
wildlife can be identified without costly, time-consuming animal infections.
This work revolutionized the identification of Trichinella, which cannot
be identified morphologically, and contributed greatly to an understanding of
the epidemiology of this important parasite of swine and other domestic animals
Developed diagnostic probes for species of the genera
Ostertagia, Haemonchus, Cooperia and Nematodirus. The probes can
be used for any developmental stage in the life cycle of the parasite including
difficult to identify eggs and larvae. The results may lead to the development
of cow-side diagnostic kits to determine the presence and intensity of
infections in individual animals. This provides a means to tailor
treatment to individual animals reducing the cost and the risk of environmental
damage or the development of resistance to drugs.
Developed the Arctic Refugium Hypothesis which postulated that
the Arctic and Subarctic were regions of evolutionary diversification rather
than net extinction during the last million years. The hypothesis provides a
framework for evaluating evolutionary relationships between hosts and parasites
in the Holarctic, and is the focus of broad based studies in biodiversity.
Following the discovery of Nematodirus
battus in sheep, the recently introduced pathogen was redescribed and
APHIS personnel were trained for a nationwide survey of sheep. Five populations
of this species from worldwide localities were studied using DNA sequences in an
effort to determine the source of the importation and elucidate the mysterious
history of this nematode that appeared as a serious pathogen of sheep in England
in 1950 and was subsequently identified in Norway, The Netherlands, France, and
in 1985 in the US and Canada. Results of the DNA studies indicate the
probability of a European origin for the nematode and importation to the US
Provided phylogenetic resolution among species of Taenia,
economically and medically important tapeworms of humans and domesticated hosts.
This information is critical to understanding the role of humans as hosts for
these tapeworms. These data will be of significance in medicine and veterinary
practice in providing more critical diagnostics and for understanding patterns
of life cycles and host relationships for these species.
Developed a National Plan for Parasite Collections that proposed
the development of collections of frozen parasite tissue and a database of
available parasite germplasm. The demand for such parasite specimens is growing
rapidly, but no such collections or databases have been developed. Developing
such resources at existing parasite collections would use existing structures to
provide new services to parasitologists and broaden the user community of the
collections. The database of the U.S. Parasite Collection has been made
available on the Internet.
Discovered and described a new pathogenic nematode from ostriches in
North Carolina and Texas in a collaborative project with the College of
Veterinary Medicine, North Carolina State University and the Texas Veterinary
Medical Center, Texas A&M University. Nematodes may cause significant losses
of valuable ostriches in the rapidly growing ratite industry in the United
States. The nematode was apparently imported with ostriches from Africa
and is now widespread in North America. This information is important to
scientists, producers and the Animal and Plant Health Inspection Service who are
interested in controlling the nematode and in preventing future importations of
Paired subcuticular glands with microscopic surface pores have been
discovered near the vulva of female Trichostrongyloid nematodes and they are
being investigated as a possible source of a sex attractant for male nematodes.
The discovery was made during microscopic studies required to identify the
economically important nematodes. If the new organ is determined to be a source
of a sex attractant, a biological control might be developed that could reduce
the cost of controlling the nematodes in meat and dairy animals. Such a
biological control would be of considerable interest to producers, especially in
organic and sustainable agricultural systems.
Collaborated with researchers in Scotland and Australia to identify
nematode parasites of horses to be used to develop molecular probes that will
permit nematode eggs in the feces of horses to be identified. The probes will be
powerful research tools for determining which species are drug resistant or most
pathogenic, for evaluating antiparasitic drugs and biological control agents,
and for identifying the species causing larval cyathostomiasis, an emerging
disease of horses.
Discovered a common synlophe pattern among genera of the Haemonchinae
that significantly advanced the utility of this morphological character for
identification and classification of these important nematode parasites of
cattle, sheep, goats and deer. The Haemonchinae includes 3 genera, Haemonchus,
Mecistocirrus and Ashworthius, commonly referred to as large stomach worms that
cause significant production losses due to morbidity, mortality, cost of
treatment and suboptimal use of contaminated pastures. The new information
improved the ability of scientists to identify endemic and exotic species that
threaten farmed ruminants. This information is essential to evaluate biological
and chemical treatment and control agents, determine the importance of reservoir
hosts such as wildlife, evaluate emerging or recently imported pathogens and to
prevent the importation of others. .
Developed an international standard taxonomy for the strongylid
nematode parasites of horses. Led an international team that revised and
improved the standard system of names used for all research to diagnose and
control the most pathogenic nematode parasites of horses. The information is
essential for progress in developing diagnostic probes, biological control
agents and antiparasitic drugs for larval cyathostomiasis, an emerging disease
of horses worldwide.
Discovered a cryptic species of abomasal nematode in North
American ruminants. This discovery and description of a new species of
medium stomach worm, of the genus Teladorsagia, clearly indicates that
we do not yet have a basic understanding of the species diversity of nematode
pathogens in domestic and wild ruminants in North America. The new species
was recognized on the basis of DNA sequence differences and comparative
morphology. Previously, the long-spicule forms of medium stomach worms in
domestic and wildlife species were believed to belong to a single species.
This work is critical to understanding the interface between domestic and wild
ruminants, and the potential for emerging disease related to these parasites
within the context of global change.