Comparison of anthelmintic activity of pyrantel, praziquantel, and nitazoxanide against Anoplocephala perfoliata in Horses

Three anthelmintics were compared for efficacy in reducing the egg production of Anoplocephala perfoliata in a herd of central Texas horses. Two trials were run, 1 in mares and the other in weanlings that were diagnosed as being infected with Anoplocephala by recovery of eggs in 5 g of feces with sugar centrifugation. Each animal was evaluated twice before treatment and again twice following treatment (at weeks 2 and 4 after treatment). The criteria for infection were the recovery of eggs on at least 1 occasion before treatment and the finding of eggs on 1 day following treatment. The mares were treated 1 time with either pyrantel pamoate at 13.2 mg/kg, nitazoxanide at 100 mg/kg, praziquantel at 1.23 mg/kg or remained as untreated controls. The weanlings were treated with pyrantel at 13.7 mg/kg nitazoxanide at 100 mg/kg or remained as untreated controls. The percentage reduction of patient infection in mares after treatment with pyrantel was 83%, with nitazoxanide was 78%, and with praziquantel was 83% and in controls was 17%. There was a 75% reduction of patient weanlings treated with pyrantel or nitazoxanide and a 17% reduction in untreated controls. The reduction of infection in all horses treated with any drug was significantly different from controls. All of the drugs were somewhat effective in the control of Anoplocephala, and there were no differences among the drugs in their effectiveness.

Introduction

Anoplocephala perfoliata, the lappeted tapeworm, is an inhabitant of the intestine of equids. Adult tapeworms attach to the intestinal mucosa at the ileocaecal valve and, when present in large numbers, cause edema and hypertrophy of the ileum. The disease manifest by this infection may be inapparent or may give rise to colic (abdominal pain) in the horse apparently from mechanical obstruction or intussusception of the small intestine into the caecocolon.^{1, 2, 3, 4, 5, 6, 7 and 8} The prevalence of infection is geographically variable^{9, 10, 11, 12 and 13} but appears to be increasing,¹⁴ with a much higher rate of infection found with necropsy as opposed to fecal observations. Horses become infected by the ingestion of infected orbatid mites in pastures. Orbatid mites, the intermediate hosts, are predatory and are found in decaying organic material, such as leaf litter. Horses of all ages are infected, but there are lower numbers of clinical cases in horses older than 4 years of age.⁴ The intensity of infection is highest in the late summer and autumn.^{8 and 12} Anthelmintics with reported efficacy against A perfoliata include pyrantel pamoate at 13.2 mg/kg,¹⁰ pyrantel tartrate at 2.6 mg/kg for 30 days,¹⁵ pyrantel embonate at 38 mg/kg,¹⁶ and praziquantel at 1 to 2 mg/kg.^{17 and 18} Nitazoxanide has not been evaluated for Anoplocephala but was included in the trial because of its effects against nematodes and tapeworms in humans.¹⁹ Because Anoplocephala infections may cause disease and there is a perception that current anthelmintics may not be as effective as in the past, a study was done to compare anthelmintics to lower the intensity of fecal egg counts in a herd of horses in central Texas.

Materials and methods

Quarter horse mares and weanlings from a single herd were evaluated with 5 g of feces with a sucrose double centrifugation test to determine whether eggs of Anoplocephala were present.²⁰ Feces from each individual horse were evaluated twice, once approximately 2 weeks before treatment and again on the day of treatment. If Anoplocephala eggs were found on either date, the horse was considered to have positive results. Within each group (mares or weanlings), the treatment selection was randomly allocated as the horses were restrained for treatment. Fecal samples were again evaluated at 14 and 28 days after treatment for the presence or absence of eggs on either day.The dose for each individual horse was determined by chest girth weight tape at the time of treatment. The treatments were as follows: pyrantel pamoate (Strongid-T, Pfizer Animal Health, Exton, Pa) at 13.7 mg/kg via nasogastric intubation (12 mares, 8 weanlings), nitazoxanide oral paste (Nitazoxanide, Idexx Laboratories, Westbrook, Me) at 100 mg/kg (9 mares, 8 weanlings), praziquantel (Droncet injectable, Bayer Corp, Shawnee Mission, Kan) at 1.23 mg/kg via nasogastric intubation (6 mares), and untreated controls (6 mares, 6 weanlings). A 1-tailed Fisher exact test was used to compare rates of infection before and after treatment. If a mare or foal did not have positive results before treatment, it was not evaluated in this study.

Results and discussion

No abnormal clinical signs were seen after treatment with any of the products. Treatment was administered to several additional animals with each product, but they were not included in the analysis if they did not have positive results on 1 of the 2 evaluations before treatment, hence, the different numbers of horses in treatment groups.None of the horses in the trial exhibited clinical signs associated with the infection of A perfoliata. However, before the trial, a mare from the infected herd exhibited signs of colic and Anoplocephala eggs were detected in the feces. Examination of the remainder of the herd gave impetus to the study.Mean egg counts before and after treatment are given in the Table.The presence of strongylate and Parascaris eggs in weanlings served as a control of the methodology of evaluation. The difficulty of finding Anoplocephala eggs has been recognized by several authors,^{5, 8, 13, 14 and 21} but the authors also recognize that when there were greater numbers of parasites there was increased egg production. Therefore, finding of eggs with fecal flotation indicated that there were 20 worms or more. However, there appears to be no correlation between the number of worms and egg counts once the detection threshold is reached,²² so the criterion for evaluation was the presence of eggs in the feces before treatment compared with after treatment. Although mean egg counts were not compared, the number of eggs in each infected horse was less after treatment in all groups compared with untreated controls (Table). The method of evaluation used in this study cannot be equated to those of critical^{10 and 16} or control¹⁴ studies in which horses are killed so that all worms are detected. However, the use of clinical studies to compare compounds is useful in detecting which anthelmintics are likely to be of value against geographically distinct populations of worms. Admittedly, more sampling may have increased the number of horses with positive results, both before and after treatment.     

Thecoma in a mare

A 4-year-old crossbred Thoroughbred mare was referred to the University of Tehran Veterinary Medical Teaching Hospital for evaluation of a mass in the pelvic cavity. The mare had been partially anorectic and pyrexic. On clinical examination, the mare was thin and depressed, with body temperature of 38°C, a pulse rate of 38 beats/minute, and a respiratory rate of 10 breaths/minute. Palpation per rectum revealed a large, smooth and tense mass in the anterior part of the pelvic cavity. Ultrasound examination confirmed the presence of a soft tissue mass with a thick wall. The inner surface of the mass had a villous-like appearance. The stroma of the mass was mottled, with accumulation of speckled and hypoechoic to slightly hyperechoic fluid. Hormone assays revealed low serum concentration of testosterone. Serum progesterone concentration indicated that active luteal tissue and serum estradiol concentration was 24 pg/ml. On histological examination, the sections from the tumor were composed of oval- or spindle-shaped cells loosely arranged in diffuse sheets or irregularly interlacing fascicles. On the basis of these histological findings, the large tumor mass of the left ovary was considered to be a thecoma. To our knowledge, the details of the clinical, ultrasonographic, endocrinologic, and histologic findings of this tumor in the mare have not been described in the veterinary literature.     

Primary meningeal T-cell lymphoma in a harbor seal (Phoca vitulina).

A 15-year-old female harbor seal (Phoca vitulina) was referred to the Nantes Veterinary School, Nantes, France, with a clinical history of anorexia, seizures, and left hemiplegia. Cerebrospinal fluid analysis revealed large numbers of neoplastic lymphoid cells. After injection of a contrast agent into the cerebrospinal space, radiographs demonstrated an asymmetry of the right lateral ventricle. Necropsy examination revealed a marked edema of the right frontal lobe, extending to the basal nuclei and thalamus in the brain. Histological examination of the brain revealed leptomeningeal lymphoma. Immunohistochemical labeling demonstrated that the neoplasm was of T-cell origin. No significant macroscopic or microscopic lesions were observed in the other organs examined, including lymphoid organs. This is the first report of primary leptomeningeal lymphoma in a harbor seal.     

Surgical repair of a peritoneopericardial diaphragmatic hernia in a pregnant dog

Objective: To describe the surgical repair and pre‐ and postoperative management of a peritoneopericardial diaphragmatic hernia (PPDH) in a pregnant dog. Case summary: A pregnant dog was presented for vomiting, lethargy, and pale mucous membranes. Pulsus paradoxus was noted on physical examination. The dog was diagnosed with a PPDH via thoracic radiographs, abdominal ultrasound, and an echocardiogram. The hernia was surgically repaired and the dog received supportive medical care until the puppies were old enough to be delivered via cesarean section. The mother and all puppies survived. New or unique information provided: This is the first report that describes the surgical repair and postoperative management of a PPDH in a pregnant dog.     

Lack of agreement between thermodilution and echocardiographic determination of cardiac output during normovolemia and acute hemorrhage in clinically healthy, anesthetized dogs

Objective and hypothesis: To determine whether or not there is agreement between the thermodilution and echocardiographic measurement of cardiac output (CO) during normovolemia and acute hemorrhage. The hypothesis was that there will be agreement between echocardiographic measurement of CO (ECO) and thermodilution measurement of CO (TDCO) during normovolemia and acute hemorrhage. Design: CO was measured by both thermodilution and echocardiography during α‐chloralose anesthesia in dogs before and 15 and 30 minutes following acute arterial hemorrhage. Setting: Laboratory investigation. Animals: Eighteen clinically healthy dogs, weighing 20–25 kg, anesthetized with α‐chloralose. Interventions: Acute arterial hemorrhage of approximately 50% of the total blood volume. CO was measured by thermodilution and echocardiography before and 15 and 30 minutes following hemorrhage. Measurements and main results: Acute hemorrhage resulted in a significant decrease in CO. There was a lack of agreement between the 2 methods to measure CO at each time and at all anatomic points of measurement in the aorta and pulmonary artery. Conclusion: There is a lack of agreement between the 2 methods; thus, determination of CO by echocardiography may not be a clinically useful tool following hemorrhage in dogs.     

Baclofen intoxication in a dog successfully treated with hemodialysis and hemoperfusion coupled with intensive supportive care

Objective: To describe a case of confirmed baclofen intoxication in a dog that was successfully treated with hemodialysis and hemoperfusion (HD/HP) and to report the serum baclofen kinetics. Case summary: A 2.5‐year‐old, 23 kg, spayed female Brittany Spaniel‐mix was treated after ingesting 21‐52 mg/kg of baclofen. The dog was comatose and was receiving manual ventilation at the time of presentation. Extracorporeal HD/HP was started 10 hours after admission. Within 3 hours of starting HD/HP the dog began initiating breaths and was extubated 18 hours after admission. Serial serum samples that were obtained during the first 24 hours of hospitalization were later analyzed for baclofen concentrations. The dog had elevated creatine phosphokinase and liver enzymes that correlated with an agitated recovery period. The dog had thrombocytopenia that resolved by 10 days after presentation. New or unique information provided: HD/HP shortened the baclofen serum elimination half‐life from 5 to 1.5 hours in the initial 2 hours of treatment. The intrinsic elimination rate constant (K_intr) for this dog was 0.138/hour and the total elimination rate constant (K_tot) during the first 2 hours of HD/HP treatment was 0.458/hour. In this dog, HD/HP was an effective method for rapidly decreasing serum baclofen concentration after an acute overdose.     

Partial pressure of end-tidal CO2 sampled via an intranasal catheter as a substitute for partial pressure of arterial CO2 in dogs

Objective: To demonstrate correlation and clinical usefulness of the partial pressure of end‐tidal CO₂ (ETCO₂) measurement by nasal catheter placement in sedated dogs with and without concurrent nasal oxygen administration as a substitute for partial pressure of arterial CO₂ (PaCO₂). Design: Prospective, cross‐over trial. Setting: University of Saskatchewan veterinary research laboratory. Animals: Six cross‐breed dogs with a mean (±SD) weight of 29.1±4.03 kg. Interventions: All dogs were sedated with 5 μg/kg medetomidine intravenously (IV) and an arterial catheter was placed in a dorsal pedal artery for removal of blood for gas analysis. A nasal catheter was placed in the ventral meatus and connected to a capnometer for ETCO₂ measurements in all dogs. Dogs receiving supplemental nasal oxygen had a second nasal catheter placed in the contralateral naris. Measurements and main results: In the group without nasal oxygen supplementation, the ETCO₂ measurement underestimated (negative bias) the PaCO₂ by ?2.20 mmHg with limits of agreement (95% confidence interval) of ?5.79, 1.39 mmHg. In the group receiving oxygen supplementation, ETCO₂ measurement underestimated (negative bias) the PaCO₂ by ?2.46 mmHg with limits of agreement (95% confidence interval) of ?8.42, 3.50 mmHg. Conclusions: The results of this study demonstrate that ETCO₂ monitoring via a nasal catheter provides a clinically acceptable substitute to arterial blood gas analysis as a means of monitoring ventilation in healthy, sedated dogs. The limits of agreement were within acceptable limits with and without concurrent insufflation of oxygen.     

Malignant pheochromocytoma presenting as a bradyarrhythmia in a dog

Objective: To describe a case of atrioventricular block and syncope secondary to systemic hypertension in a dog with malignant pheochromocytoma. Case Summary: A 13‐year‐old spayed female mixed‐breed dog presented following an acute onset of collapse. The dog was hypertensive and had paradoxical high‐grade second‐degree atrioventricular block with concurrent syncope. Initial emergent therapy included a nitroprusside infusion for the systemic hypertension and vagolytic therapy for the bradyarrhythmia. A left adrenal mass was seen on abdominal ultrasound and was further characterized by MRI. Following medical stabilization with phenoxybenzamine and propantheline, a left adrenalectomy was performed. Histological diagnosis was consistent with a malignant pheochromocytoma. Following tumor removal there has been no further hypertension, atrioventricular block or syncope. Unique information provided: This is the first documented case of a malignant pheochromocytoma presenting as syncope secondary to hypertension induced atrioventricular block.