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Abstract

Objective—To determine prevalence of heartworm infection among healthy, client-owned cats in the lower peninsula of Michigan.

Design—Cross-sectional prevalence study.

Animals—1,348 healthy cats examined at private veterinary practices throughout the lower peninsula of Michigan.

Procedure—Sera were tested by use of an ELISAbased antigen test kit to determine infection and 2 commercially available antibody detection kits to determine exposure. A questionnaire was used to collect data to assess risk factors associated with infection.

Results—25 cats had positive results for heartworm antigen, yielding an observed prevalence of 1.9%. Neither antibody test was reliable or provided reproducible results, and neither yielded positive results for more than 20% of the antigen-positive heartworminfected cats. Multivariate regression indicated that cats from southeastern Michigan and cats ≥ 2 years old had a higher risk of infection.

Conclusions and Clinical Relevance—Results indicated that most (80%) heartworm-infected cats in the lower peninsula of Michigan were from the southeastern part of the state, a pattern that closely paralleled the prevalence of heartworm infection in dogs. Therefore, knowledge of the regional prevalence of heartworm infection in dogs may be useful in assessing the risk of infection in cats. Results also suggested that currently available in-clinic heartworm antibody detection kits have limited utility in the diagnosis of heartworm infection in cats. (J Am Vet Med Assoc 2000;217:857–861)

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective

To test the possible role of endothelial cells in mediating fade of norepinephrine-induced constriction and the effect of heartworm infection on these responses.

Design

Rings of pulmonary vein from control and heartworm-infected dogs were constricted with norepinephrine (10−5.5 M) and followed over 65 minutes. Time profiles were established by measuring active tension every 2 minutes for the first 10 minutes, then every 5 minutes for 15 minutes, then every 10 minutes for 40 minutes. Time profiles were done in pulmonary vein rings with and without endothelial cells, and in the presence and absence of N-nitro-L-arginine methyl ester (L-NAME; nitric oxide synthase inhibitor), mefenamic acid (cyclooxygenase inhibitor), or methylene blue (guanylate cyclase inhibitor).

Animals

12 noninfected control and 11 heartworm-infected dogs.

Results

Pulmonary vein constricted with norepinephrine spontaneously loses tension (fades) over time. Fade was not different between control and heartworm-infected dogs. In pulmonary vein from control dogs, methylene blue decreased fade while L-NAME and mefenamic acid did not. In pulmonary vein from heartworm-infected dogs, L-NAME and methylene blue significantly decreased fade, but mefenamic acid did not.

Conclusion

Nitric oxide, but not cyclooxygenase products, mediates fade of norepinephrine-induced constriction in pulmonary vein from heartworm-infected dogs. In control dogs, neither nitric oxide nor cyclooxygenase products appear to be involved in fade. We conclude that in canine pulmonary vein, fade of norepinephrine-induced constriction is mediated, in part, by endothelial cells.

Clinical Relevance

Altered production of endothelium-derived relaxing factors may be important in the pathogenesis of heartworm disease.

Free access
in American Journal of Veterinary Research

Summary

Endothelium-dependent relaxation of canine femoral artery in vivo is depressed in dogs infected with Dirofilaria immitis (heartworms). In vitro, endothelium-dependent relaxation of aorta from rat is depressed in the presence of adult heartworms or heartworm-conditioned media. The depression of relaxation is attributable, in part, to a low molecular weight, biologically active product that is released by the adult parasites. Because heartworms reside in the right heart and pulmonary arteries, biologically active factors produced by the parasites could circulate and alter endothelial cell function. The hypothesis that filarial factors in serum from heartworm-infected dogs depress endothelium-dependent relaxation was tested. Rings of thoracic aorta from rats were constricted by use of norepinephrine, and cumulative dose-response relationships to methacholine and nitroglycerin were evaluated in the presence of serum from heartworm-infected dogs or serum from noninfected (control) dogs. Nitroglycerin relaxation was not different; however, methacholine relaxation was significantly depressed in rings exposed to serum from heartworm-infected dogs when compared with that of controls. These results supported the hypothesis and suggested that circulating filarial factors have the potential to influence the behavior of any endothelial cell surface.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To determine whether therapeutic riding resulted in higher levels of stress or frustration for horses than did recreational riding and whether therapeutic riding with at-risk individuals was more stressful for the horses than was therapeutic riding with individuals with physical or emotional handicaps.

Design—Observational study.

Animals—14 horses in a therapeutic riding program.

Procedure—An ethogram of equine behaviors was created, and horses were observed while ridden by 5 groups of riders (recreational riders, physically handicapped riders, psychologically handicapped riders, atrisk children, and special education children). Number of stress-related behaviors (ears pinned back, head raised, head turned, head tossed, head shaken, head down, and defecation) was compared among groups.

Results—No significant differences in mean number of stress-related behaviors were found when horses were ridden by recreational riders, physically handicapped riders, psychologically handicapped riders, or special education children. However, mean number of stress-related behaviors was significantly higher when horses were ridden by the at-risk children.

Conclusions and Clinical Relevance—Results suggest that for horses in a therapeutic riding program, being ridden by physically or psychologically handicapped individuals is no more stressful for the horses than is being ridden in the same setting by recreational riders. However, at-risk children caused more stress to the horses, suggesting that the time horses are ridden by at-risk children should be limited both daily and weekly.

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine the effects of a therapeutic riding program on psychosocial measurements among children considered at risk for poor performance or failure in school or life and among children in special education programs.

Design—Observational study.

Population—17 at-risk children (6 boys and 11 girls) and 14 special education children (7 boys and 7 girls).

Procedure—For the at-risk children, anger, anxiety, perceived self-competence, and physical coordination were assessed. For the special education children, anger and cheerfulness were measured, and the children's and their mothers' perceptions of the children's behavior were assessed. Measurements were made before and after an 8-session therapeutic riding program.

Results—For boys enrolled in the special education program, anger was significantly decreased after completion of the riding program. The boys' mothers also perceived significant improvements in their children's behavior after completion of the program.

Conclusions and Clinical Relevance—Results suggest that an 8-session therapeutic riding program can significantly decrease anger in adolescent boys in a special education program and positively affect their mothers' perception of the boys' behavior.

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To develop a direct assay to measure platelet surface-associated immunoglobulins (PSAIg) in dogs and to determine whether the assay is useful in the diagnosis of immune-mediated thrombocytopenia (IMT).

Animals—20 healthy dogs were used to develop reference intervals, and 23 dogs with IMT and 17 with non-IMT were used to evaluate the clinical use of this assay.

Procedure—After optimization of platelet collection and assay conditions, concentrations of PSAIg were measured, using radiolabeled staphylococcal protein A (SpA) and polyclonal antibodies against canine IgG (anti-γ) and IgM (anti-µ). Concentrations of PSAIg were expressed as the percentage of radiolabeled immunoglobulin detector bound.

Results—Cut-off values (mean + 3 SD) were as follows: SpA, 1.1%; anti-γ, 1.3%; and anti-µ, 3.5%. Values greater than these cut-off values were considered positive. Values determined by use of radiolabeled SpA for all dogs with IMT were greater than the cut-off value; values were considered high positives (> 5 times cut-off value) for 22 of these 23 dogs. Although 9 of 17 dogs with non-IMT also had PSAIg concentrations greater than the cut-off value, values were considered high positives for only 3 of these 9 dogs.

Conclusion and Clinical Relevance—The immunoradiometric assay developed is a reliable and sensitive method to detect PSAIg in dogs. However, to obtain accurate results, optimum temperature, time, and storage conditions must be used. Detection of increased concentrations of PSAIg in dogs presumed to have non-IMT should alert clinicians to reconsider an immune-mediated basis for the thrombocytopenia. (Am J Vet Res 2002;63:124–136)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine whether cattle persistently infected with bovine viral diarrhea virus (BVDV) that lack virus detectable in serum by use of the immunoperoxidase microtiter assay (IPMA) can transmit the virus to susceptible herdmates and determine prevalence of these cattle.

Design—Clinical trial and serologic survey.

Sample Population—2 cattle and 1,952 blood samples.

Procedure—A persistently infected cow in which virus could not be detected in serum was housed with a BVDV-seronegative steer. Blood and nasal swab specimens were tested via virus isolation and serum virus neutralization. Parallel WBC preparations and sera from blood samples of 1,952 adult cows were screened for BVDV by use of IPMA.

Results—The steer seroconverted to BVDV within 4 weeks of contact with the cow. Virus was detected in sera and WBC of 5 adult cows that were verified as persistently infected by retest 3 weeks later. Cattle persistently infected with BVDV in which virus could not be detected in both serum and WBC by use of IPMA were not found.

Conclusion and Clinical Relevance—Cattle persistently infected with BVDV in which virus cannot be detected in serum by use of IPMA may serve as virus reservoirs for infecting susceptible cattle. Persistent infection was detected at a prevalence of 0.26%. Screening adult cattle by use of IPMA on serum samples appears to be a reliable means of detecting persistent infection with BVDV. Prevalence of cattle persistently infected with BVDV that have negative results of IPMA on serum is extremely low. (J Am Vet Med Assoc 2001;219:629–631)

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective

To test the effect of thiacetarsamide and melarsomine on vascular responses in isolated rings of pulmonary artery from heartworm-infected dogs.

Animals

18 heartworm-infected dogs.

Procedure

Isolated rings of pulmonary artery from heartworm-infected dogs were randomly treated with thiacetarsamide (30 μg/ml) or melarsomine dihydrochloride (30 μg/ml) for 30 minutes; untreated rings from the same dog served as control. Cumulative dose-response relations to norepinephrine, nitroglycerin, and methacholine were determined.

Results

Norepinephrine-induced constriction was not altered by treatment with either thiacetarsamide or melarsomine. Treatment with thiacetarsamide depressed nitroglycerin-induced relaxation, compared with values for untreated control rings and rings treated with melarsomine. Treatment of rings with thiacetarsamide or melarsomine depressed methacholine-induced relaxation, compared with values for untreated rings. Histologic examination of rings indicated that treatment with thiacetarsamide or melarsomine resulted in loss of endothelial cells.

Conclusion

Endothelial cell loss as a direct drug effect may be responsible for impaired endothelium-dependent relaxation in pulmonary artery from heart-worm-infected dogs. Thiacetarsamide appears to have additional effects on vascular smooth muscle, which may explain why fewer complications are observed in dogs treated with melarsomine.

Clinical Relevance

Melarsomine may be a safer drug than thiacetarsamide and could be a better treatment for dogs with heartworm infection. (Am J Vet Res 1997;58:389–393)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To test the effect of heartworm infection on agonist-induced constriction of canine pulmonary artery and vein in vitro.

Procedure

Cumulative concentration-response relations to norepinephrine, serotonin, histamine, prostaglandin F2α, and the thromboxane A2 analog U-44069 were determined, using isolated rings of pulmonary artery and vein from control and heartworm-infected dogs. To determine the role of endothelial cells in histamine constriction, some rings were denuded of endothelial cells in both artery and vein.

Animals

Noninfected control and heartworm-infected dogs.

Results

There was no difference in constriction response to norepinephrine, serotonin, prostaglandin F2α, or U44069 of pulmonary artery or vein from control or heartworm-infected dogs. Histamine-induced constriction of pulmonary artery from heartworm-infected dogs was not different from control values, however, when endothelial cells were removed from control, but not heartworm-infected pulmonary artery, histamine-induced constriction was enhanced. Histamine-induced constriction of pulmonary vein from heartworm-infected dogs was significantly depressed, compared with that of control pulmonary vein. However, removal of endothelial cells in pulmonary vein from heartworm-infected, but not control dogs significantly increased constriction.

Conclusion

Heartworm infection alters histamine-induced constriction responses of pulmonary artery and vein. These changes may reflect high circulating histamine concentrations in heartworm-infected dogs, compared with that in controls. Increased circulating histamine concentrations in vivo could bring about decreased sensitivity of histamine receptors or decreases in the number of receptors expressed.

Clinical Relevance

Mast cells and histamine may be important factors in altered endothelium-mediated responses associated with heartworm disease. (Am J Vet Res 1997;58:394–397)

Free access
in American Journal of Veterinary Research

Abstract

Objective—To determine whether viral involvement with platelets obtained from cattle persistently infected (PI) with bovine viral diarrhea virus (BVDV) is associated with altered platelet function or decreased platelet counts.

Sample Population—Platelets obtained from 8 cattle PI with BVDV and 6 age-, sex-, and breed-matched uninfected control cattle.

Procedure—Manual platelet counts were determined, and platelet function was assessed through optical aggregometry by use of the aggregation agonists ADP and platelet-activating factor. Identification of BVDV in serum and preparations of purified platelets was determined by use of virus isolation tests.

Results—No significant difference in platelet counts was detected between cattle PI with BVDV and control cattle. In response to the aggregation agonists, maximum aggregation percentage and slope of the aggregation curve were not significantly different between cattle PI with BVDV and control cattle. We isolated BVDV from serum of all PI cattle and from purified platelets of 6 of 8 PI cattle, but BVDV was not isolated from serum or platelets of control cattle.

Conclusions and Clinical Relevance—Isolation of BVDV from platelets in the peripheral circulation of cattle immunotolerant to BVDV does not result in altered platelet function or decreases in platelet counts. (Am J Vet Res 2005;66:1738–1742)

Full access
in American Journal of Veterinary Research