presentation, with 1 dog lost to follow-up.
Our work represents a novel case series, with outcome information, on dogs outside of the US (Canada) with detected hookworm, A caninum , anthelminticresistance markers. Before our study, there
are beginning to fail because of the development of anthelminticresistance in parasites. Anthelminticresistance among gastrointestinal tract nematodes of small ruminants has been documented in many countries, with multidrug resistance becoming a
Objective—To determine prevalence of resistance to
all anthelmintics that are commonly used to treat gastrointestinal
nematodes (GINs) in goats.
Procedure—On each farm, goats were assigned to 1
of 5 treatment groups: untreated controls, albendazole
(20 mg/kg [9.0 mg/lb], PO, once), ivermectin (0.4
mg/kg [0.18 mg/lb], PO, once), levamisole (12 mg/kg
[5.4 mg/lb], PO, once), or moxidectin (0.4 mg/kg, PO,
once), except on 3 farms where albendazole was
omitted. Fecal samples were collected 2 weeks after
treatment for determination of fecal egg counts
(FECs), and percentage reductions were calculated
by comparing data from anthelmintic-treated and
control groups. Nematode populations were categorized
as susceptible, suspected resistant, or resistant
by use of guidelines published by the World
Association for the Advancement of Veterinary
Results—Resistance to albendazole was found on 14
of 15 farms, and resistance to ivermectin, levamisole,
and moxidectin was found on 17, 6, and 1 of 18 farms,
respectively. Suspected resistance to levamisole and
moxidectin was found on 4 and 3 farms, respectively.
Resistance to multiple anthelmintics (albendazole and
ivermectin) was found on 14 of 15 farms and to albendazole,
ivermectin, and levamisole on 5 of 15 farms.
Mean overall FEC reduction percentages for albendazole,
ivermectin, levamisole, and moxidectin were 67,
54, 94, and 99%, respectively.
Conclusions and Clinical Relevance—Anthelmintic
resistance in GINs of goats is highly prevalent in the
southern United States. The high prevalence of resistance
to multiple anthelmintics emphasizes the need
for reexamination of nematode control practices.
(J Am Vet Med Assoc 2003;223:495–500)
Objective—To determine the prevalence and clinical
implications of anthelmintic resistance in cyathostomes
Animals—80 horses on 10 farms in a 5-county region
of northeast Georgia.
Procedure—On each farm, horses were stratified in
descending order according to pretreatment fecal egg
count (FEC), blocked into groups of 4, and then randomly
assigned to 1 of 4 treatment groups: no treatment
(controls), and treatment with pyrantel
pamoate, fenbendazole, or ivermectin. Fecal samples
were collected 24 hours prior to treatment and 2, 4,
and 6 weeks after treatment for determination of
FEC. Mean percentage of reduction in FEC was then
calculated for each treatment group. For horses from
each farm, the efficacy of each anthelmintic was categorized
on the basis of mean percentage of reduction
in FEC at 2 weeks after treatment (< 80% reduction
= ineffective; 80 to 90% reduction = equivocal;
and > 90% reduction = effective).
Results—Pyrantel pamoate was effective at reducing
FEC in horses from 7 farms, ineffective in horses from
2 farms, and equivocal in horses from 1 farm.
Fenbendazole was ineffective at reducing FEC in horses
from 9 farms and equivocal in horses from 1 farm.
Ivermectin was effective at reducing FEC in horses
from all 10 farms.
Conclusions and Clinical Relevance—Results suggest
that cyathostome resistance to fenbendazole is
highly prevalent, and resistance to pyrantel pamoate
is high enough to warrant concern. Resistance to ivermectin
was not detected. On the basis of these data,
it appears that ivermectin continues to be fully effective
in horses. However, too few farms were used in
this study to determine the prevalence of cyathostome
resistance to ivermectin. Therefore, the efficacy
of ivermectin should continue to be monitored closely.
(J Am Vet Med Assoc 2001;218:1957–1960)
contortus . 3,4 Although the use of these products has often been effective at controlling parasitism by H contortus in the short term, marked anthelminticresistance has been documented 1,5 in recent decades because overuse or underdosing has
Objective—To determine prevalence of anthelmintic
resistance in cyathostome nematodes of horses in
the southern United States.
Animals—786 horses on 44 farms and stables in
Georgia, South Carolina, Florida, Kentucky, and
Procedure—Fecal egg count (FEC) reduction tests
were performed on 44 large farms and stables. Horses
on each farm were treated with an oral paste formulation
of fenbendazole, oxibendazole, pyrantel pamoate,
or ivermectin at recommended label dosages. A mixed
linear model was fitted to the percentage reduction in
FEC, accounting for differences among farms, states,
ages, treatments, and treatment by state interactions.
Results—By use of a conservative measure of resistance
(< 80% reduction), the percentage of farms with
anthelmintic-resistant cyathostomes was 97.7%, 0%,
53.5%, and 40.5% for fenbendazole, ivermectin, oxibendazole,
and pyrantel pamoate, respectively. Mean percentage
reductions in FEC for all farms were 24.8%,
99.9%, 73.8%, and 78.6% for fenbendazole, ivermectin,
oxibendazole, and pyrantel pamoate, respectively.
Pairwise contrasts between states for each treatment
revealed that in almost all instances, there were no significant
differences in results between states.
Conclusions and Clinical Relevance—The prevalence
of resistance found in this study was higher than that
reported previously, suggesting that anthelmintic resistance
in equine cyathostomes is becoming a major problem.
Furthermore, data from these 5 southern states,
which are geographically and physiographically distinct,
were remarkably similar. This suggests that drug resistance
in cyathostomes is highly prevalent throughout
the entire southern United States and probably nationwide.
(J Am Vet Med Assoc 2004;225:903–910)
The primary aim of this article is to provide an overview of several selected skin conditions in livestock species. Topics include ectoparasites in alpacas, antler velvet in reindeer, immune-mediated disease in goats, ectoparasites in pigs, Culicoides allergic dermatitis and parapox infection in sheep. When dealing with skin disease in livestock, it is important to collect a detailed history and undertake a thorough clinical examination to include the axilla, groin, limbs and feet. While the diagnosis will often be anticipated from the history and presentation, it is important to consider a differential diagnosis list and appropriate diagnostic testing before embarking on a poly-pharmacy approach to “rule out” causes of disease. This is particularly important where morbidity is high and the livestock of perceived high value to the keeper/owner, such as goats and small-breed pigs, or when the skin condition is long standing/chronic. Ideally, the management plan should sequentially clarify the role of microbial infection and then ectoparasites before considering less common allergic and autoimmune conditions. Skin cytology is an invaluable in-house diagnostic method that can support the findings of culture. Taking skin samples for histopathology and possibly culture may prove valuable once other diagnostic methods have been explored. Given the need to protect the use of parenteral antimicrobials, topical antimicrobial therapies can be deployed successfully. The repeated use of macrocyclic lactones (avermectins) must be balanced in terms of the risks of promoting anthelmintic resistance versus controlling or eradicating the ectoparasites that have, ideally, been specifically identified.
Effective control of strongyles, particularly cyathostomes, is becoming increasingly difficult in horses as anthelminticresistance becomes more commonly recognized. Only 3 drug groups, the benzimidazoles, avermectins, and pyrantel salts, have
observations of shortened ERPs in more contemporary compounds (macrocyclic lactones). 3–5 Anthelminticresistance is an inherited trait passed from adult parasites to their offspring, and genetic reversion to susceptibility was shown to not occur in a 40-year