Comparison of nucleic acid amplification, serology, and microbiologic culture for diagnosis of Rhodococcus equi pneumonia in foals.

Recently, a technique was described for amplification of Rhodococcus equi-specific chromosomal and vapA DNA from blood and tracheal wash fluids. It was hypothesized that this technique would be more sensitive than standard culture techniques or serology for diagnosis of R. equi pneumonia in foals. Tracheal wash fluid, nasal swabs, whole blood samples, and serum samples from 56 foals with pneumonia were analyzed. Final clinical diagnosis was determined by the attending clinician on the basis of final interpretation of all available information about each foal, including clinical presentation, diagnostic test results, response to therapy, and outcome. Clinical diagnosis was used as a final reference standard for calculation of sensitivity, specificity, and predictive values for PCR, serology using an agar gel immunodiffusion test, and tracheal wash fluid culture. PCR of tracheal wash fluid using primers that recognized the vapA virulence plasmid of R. equi had a diagnostic sensitivity of 100% and specificity of 90.6%. Sensitivity and specificity were 57.1 and 93.8%, respectively, for standard microbiologic culture of tracheal wash fluid and 62.5 and 75.9%, respectively, for serology. PCR of tracheal wash fluid is more sensitive and specific for diagnosis of R. equi pneumonia than are other available diagnostic tests.

Characterization of a coronavirus isolated from a diarrheic foal.

A coronavirus was isolated from feces of a diarrheic foal and serially propagated in human rectal adenocarcinoma (HRT-18) cells. Antigenic and genomic characterizations of the virus (isolate NC99) were based on serological comparison with other avian and mammalian coronaviruses and sequence analysis of the nucleocapsid (N) protein gene. Indirect fluorescent-antibody assay procedures and virus neutralization assays demonstrated a close antigenic relationship with bovine coronavirus (BCV) and porcine hemagglutinating encephalomyelitis virus (mammalian group 2 coronaviruses). Using previously described BCV primers, the N protein gene of isolate NC99 was amplified by a reverse transcriptase PCR (RT-PCR) procedure. The RT-PCR product was cloned into pUC19 and sequenced; the complete N protein of NC99 (446 amino acids) was then compared with published N protein sequences of other avian and mammalian coronaviruses. A high degree of identity (89.0 to 90.1%) was observed between the N protein sequence of NC99 and published sequences of BCV (Mebus and F15 strains) and human coronavirus (strain OC43); only limited identity (<25%) was observed with group 1 and group 3 coronaviruses. Based on these findings, the virus has been tentatively identified as equine coronavirus (ECV). ECV NC99 was determined to have close antigenic and/or genetic relationships with mammalian group 2 coronaviruses, thus identifying it as a member of this coronavirus antigenic group.

Clinical application of a polymerase chain reaction assay in the diagnosis of pneumonia caused by Rhodococcus equi in a horse.

Diagnosis of pneumonia caused by Rhodococcus equi can be made more rapidly by use of a polymerase chain reaction (PCR) assay than by use of conventional bacteriologic culture techniques. Use of a PCR assay aids in the differentiation between virulent and avirulent strains of R equi, and the assay may be used to identify R equi in feces and soil of breeding farms.

Oxytocin release and its relationship to dihydro-15-keto PGF2alpha and arginine vasopressin release during parturition and to suckling in postpartum mares.

Pituitary blood was collected from the intercavernal sinus in five mares before and during parturition, and in nine mares immediately after parturition to investigate oxytocin patterns during parturition and early lactation, and to determine the relationship between oxytocin, prostaglandin and arginine vasopressin during parturition. In four mares in which sample collection began at least 6 h before rupture of the chorioallantois, a significant increase (P < 0.05) in PGF(2alpha) concentration was detected before a significant increase in oxytocin concentration. Cross-correlation analysis of log-transformed oxytocin and PGF(2alpha) concentrations revealed a significant correlation (P < 0.05) at a 6 min lag period, indicating that in the 2 h before delivery of the foal, an increase in prostaglandin was followed 6 min later by an increase in oxytocin. A significant effect of suckling on oxytocin release by the mare was detected in only two of nine mares, when oxytocin concentrations were evaluated 0-3 min after suckling. When foals were prevented from sucking for 1 h, by being either muzzled (n = 2) or separated from the mare (n = 2), there was no significant association between resumption of suckling and oxytocin release by the mare. The results of these studies show that: (i) oxytocin secretion from the maternal posterior pituitary gland begins before, or in association with, the onset of the second stage of labour, and that prostaglandin increases in the peripheral circulation before oxytocin release; and (ii) suckling is not significantly related to oxytocin release in mares.

Pharmacokinetics of enrofloxacin administered intravenously and orally to foals.

OBJECTIVE: To determine the pharmacokinetics of enrofloxacin administered IV and orally to foals. ANIMALS: 5 clinically normal foals. PROCEDURE: A 2-dose cross-over trial with IV and oral administration was performed. Enrofloxacin was administered once IV (5 mg/kg of body weight) to 1-week-old foals, followed by 1 oral administration (10 mg/kg) after a 7-day washout period. Blood samples were collected for 48 hours after the single dose IV and oral administrations and analyzed for plasma enrofloxacin and ciprofloxacin concentrations by use of high-performance liquid chromatography. RESULTS: For IV administration, mean +/- SD total area under the curve (AUC0-infinity) was 48.54 +/- 10.46 microg x h/ml, clearance was 103.72 +/- 0.06 ml/kg/h, half-life (t1/2beta) was 17.10 +/- 0.09 hours, and apparent volume of distribution was 2.49 +/- 0.43 L/kg. For oral administration, AUC0-infinity was 58.47 +/- 16.37 microg x h/ml, t1/2beta was 18.39 +/- 0.06 hours, maximum concentration (Cmax) was 2.12 +/- 00.51 microg/ml, time to Cmax was 2.20 +/- 2.17 hours, mean absorption time was 2.09 +/- 0.51 hours, and bioavailability was 42 +/- 0.42%. CONCLUSIONS AND CLINICAL RELEVANCE: Compared with adult horses given 5 mg of enrofloxacin/kg IV, foals have higher AUC0-infinity, longer t1/2beta, and lower clearance. Concentration of ciprofloxacin was negligible. Using a target Cmax to minimum inhibitory concentration ratio of 1:8 to 1:10, computer modeling suggests that 2.5 to 10 mg of enrofloxacin/kg administered every 24 hours would be effective in foals, depending on minimum inhibitory concentration of the pathogen.

Primary hyperparathyroidism caused by a functional parathyroid adenoma in a horse.

A 14-year-old Arabian gelding had weight loss and anorexia of 3 weeks' duration. Results of repeated laboratory tests revealed persistent hypercalcemia and serum phosphorus concentration that was within or less than the reference range. Parathyroid hormone concentration was high. Histologic examination of specimens obtained at necropsy revealed parathyroid adenoma. A diagnosis of primary hyperparathyroidism attributable to a functional parathyroid adenoma was made. Abnormalities in calcium and phosphorus concentrations were similar to those seen with primary hyperparathyroidism in dogs, in which this syndrome is best described. Primary hyperparathyroidism should be considered to be a potential cause of hypercalcemia in horses in which other more common causes of hypercalcemia, such as humoral hypercalcemia of malignancy, nutritional secondary hyperparathyroidism, chronic renal failure, vitamin D toxicosis, and bony or granulomatous disease, are ruled out.

Concentrations of amino acids in plasma from 45- to 47-week gestation mares and foetuses (Equus caballus).

Concentrations of 16 of 24 amino acids in plasma of foetuses were significantly higher, while four of 24 were lower, than their concentration in maternal plasma. The higher foetal concentrations of amino acids in plasma are similar to other species, with some exceptions, and suggest that equine placenta actively transports and concentrates amino acids into the umbilical circulation. Concentrations of nine of 24 amino acids were significantly lower in plasma from the umbilical artery compared to plasma from the umbilical vein, while no significant differences were present between maternal artery and vein plasma. The umbilical venous-arterial difference in concentrations of amino acids in plasma suggests the foetus extracts amino acids from the umbilical circulation for catabolism or protein synthesis, as in other species.

The endocrinology of parturition in the mare.

The endocrinology of late gestation and parturition in the mare has been described, but unlike other domestic animal species, the factors that initiate parturition in the mare have not been elucidated. In contrast to ruminant species, maternal estrogen and progesterone concentrations do not change markedly, and a well-defined fetal cortisol surge is not observed just prior to parturition in the mare. Parturition is associated with large increases in prostaglandin and oxytocin concentrations, which induce uterine contractions and delivery of the foal. There are many methods of inducing parturition in term mares, but the most popular and safest method is through the administration of low-dose oxytocin.

Hemodialysis for treatment of oxytetracycline-induced acute renal failure in a neonatal foal.

Acute renal failure in a 4-day-old foal secondary to oxytetracycline toxicosis was treated by hemodialysis. Oxytetracycline had been administrered as treatment for forelimb flexor tendon contracture. Conservtive treatment with fluids, furosemide, and dopamine partially alleviated serum electrolyte concentration imbalances, but was ineffective in promoting diuresis or decreasing azotemia. Three hemodialysis treatments over 4 days were administered, after which the clinical appearance of the foal improved, and biochemical and electrolyte values returned to within reference ranges. The nephrotoxic potential of oxytetracycline should be considered prior to its administration. Hemodialysis may be a treatment option in management of acute renal failure in foals that are nonresponsive to conservative medical treatment.

Cutaneous fungal flora in twenty horses free of skin or ocular disease.

The fungal flora of the hair and underlying skin from 2 sites was examined qualitatively in 20 horses free of skin or ocular disease. Fungi were isolated from both the hair and the underlying skin of all 20 horses. Twenty-two genera regarded commonly as saprophytes were identified and an additional 2 fungi resembled the perfect state of the cutaneous pathogenic genera Microsporum and Trichophyton. Cladosporium spp, Penicillium spp, and Rhizopus spp were the most frequently isolated saprophytes. In general, similar fungi were isolated from the hair and underlying skin, and differences were not noted in isolates from the saddle and rump regions.

Acquired immunodeficiency in a seven-year-old horse.

A 7-year-old horse with no previous history of illness was determined to have a systemic infection of Rhodococcus equi. Rhodococcus equi was isolated from blood, tracheal fluid, and feces. Lymphopenia, failure to respond to concanavalin A and phytohemagglutinin lymphocyte stimulation testing, decreased concentrations of immunoglobulin (Ig)M, IgA, and IgG, low R equi antibody titer, histologic depletion of lymphoid tissue, and a failure to respond to antigenic stimulation led to the conclusion that both humoral and cell-mediated immunity were compromised. No cause for the acquired immunodeficiency could be determined.

Tracheal rupture in two horses.

Two horses were admitted for evaluation of diffuse SC emphysema. Diagnosis of ruptured trachea was made by tracheoscopy and radiography. The tracheal cartilages were not involved in either case. One of the defects was small and responded to medical management. The other defect was large and was apposed surgically. Both horses recovered without complications.

Skeletal disease in a hypothyroid foal.

Hypothyroidism was diagnosed in a 5-month-old Thorough-bred colt by clinical and clinico-pathology examinations, thyroid stimulating hormone response test and by microscopic evaluation of the thyroid gland. Skeletal lesions included delayed appearance of ossification centers and delayed development of bone in cartilage models, delayed closure of epiphyseal plates, transverse trabeculation in metaphyses, osteochondrosis dissecans and subchondral cysts.

Interaction of oestradiol and gonadotrophin-releasing hormone on LH release in the mare.

Acyclic mare given oestradiol for 3 days to simulate the preovulatory plasma oestradiol surge showed a non-significant 37% decrease in plasma LH during treatment. When GnRH analogue injections were given with oestradiol on Days 1--3, oestradiol had no effect on each GnRH-induced LH increase, but LH increases were more prolonged following subsequent GnRH injections on Days 4--7 when oestradiol was no longer being given. A much greater prolongation of LH release occurred when the course of GnRH injections was commenced after oestradiol treatment ceased; the LH response was almost identical to the prolonged periovulatory LH surge of the normal cycle. Therefore, it appears that the timing of the oestradiol surge, in relation to other hormonal events, is critical in inducing the uniquely prolonged periovulatory LH surge of the mare.