In vitro and in vivo modulation of the equine immune response by parapoxvirus ovis.

REASON FOR PERFORMING STUDY: While immune modulators are used routinely in equine medicine, their mechanism of action is not always known. OBJECTIVES: To determine the effect of a commercial preparation of inactivated parapoxvirus ovis (Orf virus; PPVO) on cytokine gene expression by equine peripheral blood mononuclear cells (PBMC) both in vitro and in vivo. METHODS: PBMC were prepared from 6 mixed-breed yearlings and cultured in vitro with PPVO with or without Concanavalin A (Con A) for 24 h. Effects on the expression of IFNalpha, IFNbeta IFNgamma, TNFalpha and IL-18 were analysed by real time quantitative PCR (RT-PCR). In addition, 12 yearling horses were treated with PPVO and whole blood RNA samples were prepared at regular intervals to assess effects on in vivo cytokine gene expression. Six of those yearlings were later treated with saline and served as treatment controls. Nine additional yearlings were injected intradermally with a single dose and their injection sites biopsied at 24 and 48 h for cytokine expression. RESULTS: In vitro culture of PBMC with PPVO led to a significant increase in IFNalpha and IFNbeta gene expression compared to mock-stimulated cultures. In addition, expression of IFNgamma and TNFalpha was significantly higher in PBMC stimulated with PPVO and Con A, than those stimulated with Con A alone. No changes were observed in IL-18 gene expression in vitro. Treatment of horses with a 3-dose regimen of PPVO resulted in elevation of IFNgamma gene expression, which was detected 24 h after the first dose and declined thereafter. Intradermal inoculation led to increased expression of IFNgamma along with IFNbeta, IL-15 and IL-18. CONCLUSIONS: Together these results indicate that PPVO stimulated IFNgamma production both in vitro and in vivo. Increased cytokine expression could account for its immunomodulatory activity. POTENTIAL RELEVANCE: The absence of adverse reactions and clear indications of increased expression of cytokine gene expression supports previous clinical uses for this immune modulator in those situations when increased expression of IFNgamma is warranted.

The cellular perspective on mammary gland development: stem/progenitor cells and beyond.

Study of the mammary gland at the stem cell level is necessary for understanding mammary gland development. Knowledge of mammary gland development and growth is the first step toward formulating strategies to improve milk production. The success of these strategies requires an understanding of the dynamics of adult stem cells and their progeny in the development of the bovine mammary gland. The stem cell lineage pathway begins with adult stem cells and ends with the production of terminally differentiated cells. The progression of adult stem cells along the mammary gland stem cell lineage pathway requires the coordination of many events. One important event in this process is cell differentiation. This differentiation process evolves with a gradient appearance of cell organelles progressing from stem cells to terminally differentiated cells. To dissect differentiation, mechanisms that regulate stem cells to differentiate toward a particular cell fate must be identified. Ultrastructural characteristics assist in distinguishing cells in various stages of differentiation in the mammary gland cell lineage pathway. Cells in the lineage pathway can become either epithelial cells or myoepithelial cells. Epithelial cells function in the production and secretion of milk, whereas myoepithelial cells assist epithelial cells in milk secretion. This review focuses on current concepts regarding adult stem cells and the recent progress on bovine mammary gland stem/progenitor cell development and differentiation. Multistep strategies that incorporate manipulation of the mechanisms influencing lineage choices in the mammary gland will produce beneficial effects on mammary gland development and milk production.

Effects of niacin on biliary lipid output in the rat.

The mechanisms for the hypocholesterolaemic action of niacin (nicotinic acid) were examined in rats administered niacin at a dose of 400 mg/kg body wt/day for either 2 or 4 weeks. Another group of rats were administered diosgenin, an inhibitor of acyl-CoA:cholesterol acyltransferase, as a 1% (w/w) supplement in the diet for 7 days. Both agents produced small increases in bile flow rates (up to 40%) and mild hepatotoxicity evidenced by small increases in serum transaminase activities. Niacin treatment for 2 or 4 weeks lowered serum cholesterol concentrations by 13% or 29%, respectively, with the greatest decrease occurring in the low density lipoprotein fraction. This was accompanied by relatively large increases in biliary cholesterol output (114% and 130% after 2 and 4 weeks treatment, respectively) with smaller increases in the biliary output of phospholipid (18% and 45%) and bile acid (26% and 14%). Diosgenin treatment increased serum cholesterol by 29% and increased the biliary output of cholesterol, phospholipid and bile acid by 800%, 10% and 45%, respectively. Thus, both agents increased the cholesterol saturation of bile (100% by niacin, 500% by diosgenin). Cholesterol and phospholipid in fistula bile from control rats were present in lamellar and micellar forms. Niacin treatment did not alter the physical form of biliary lipids whilst diosgenin caused the appearance of vesicular lipid in fistula bile. Thus, increased biliary secretion of cholesterol explains, at least in part, the hypocholesterolaemic action of niacin. In addition, since aggregation of biliary vesicles is involved in cholesterol gallstone formation in humans, the non-appearance of vesicular material in fistula bile from niacin-treated rats may be of some importance.

Experimental inoculation of foals and pigs with an enterotoxigenic E. coli isolated from a foal.

Hemolytic E. coli strain 807-13, O149:NM:K88(STb+, LT+), was isolated from the feces of a neonatal diarrheic foal. E. coli 807-13 was examined for adhesion to brush border membranes (BBM) from foals, adult horses and pigs, and its pathogenicity was assessed in neonatal foals and pigs. E. coli 807-13 did not adhere to equine BBM but adhered to pig BBM. It did not cause diarrhea nor did it colonize the intestinal epithelium of 3 colostrum-deprived and 3 suckled foals challenged at 24 h of age. Acute ulcerative gastritis and acute suppurative gastritis were observed in 2 colostrum-deprived challenged foals, and acute neutrophilic enteritis was observed in 1 colostrum-deprived and in 1 suckled challenged foal. No similar histopathologic lesions were detected in the control foals. Both gnotobiotic and suckled pigs developed diarrhea after challenge exposure to E. coli 807-13 and the intestinal epithelium of the pigs was colonized. Histopathologic evidence of gastritis and enteritis among the foals indicated some complicity of E. coli 807-13 in foal enteric disease.

Characterization of Escherichia coli isolated from healthy dogs.

Five month old dogs from a Midwestern research kennel occasionally developed bloody diarrhea after shipment to other facilities. As previous diagnostic efforts failed to reveal any potential pathogens in feces from normal and diarrheic dogs, Escherichia coli was investigated for select virulence properties that may contribute to the occurrence of bloody diarrhea. Fecal swabs from 52 healthy dogs were examined for E. coli. Two hundred and sixty E. coli-like colonies were screened by PCR for the attaching and effacing (eae) gene, Shiga toxin (stx) genes, and the heat-stable enterotoxin type A (sta) gene. One hundred forty two of the 260 E. coli-like colonies (54.6%) from 43 dogs were eae or sta positive; and 60 of the eae and/or sta positive isolates were examined further. Among the 60 isolates, 23 (38.3%) possessed the eae gene, 32 (53.3%) possessed the sta gene, and five (8.3%) possessed both eae and sta genes (eae+/sta+). Of the 60 isolates, six sta+ and one eae+/sta+ isolates were hemolytic. When examined in the suckling mouse assay, five of six sta+ isolates and three of four eae+/sta+ isolates gave gut-to-remaining carcass ratios > or =0.083, indicating expression of heat-stable enterotoxin. These enterotoxin-producing isolates belonged to serogroups O42, O170, and O-negative.

Characterization of Escherichia coli isolated from foals.

Serotype, biotype, antibiogram, hemolysin production, fimbrial hemagglutinins, select toxin genes (STb, STaP, LT, slt1 and slt2) and the attaching effacing (eae) gene were determined for 99 foal strains of E. coli. E. coli from diarrheic and normal foals could not be distinguished by serotype, biotype, or antibiogram. Differences (P < or = 0.05) were observed in hemolysin production (11.5% vs 0%) and the expression of mannose-resistant hemagglutinins (23% vs 13%) among E. coli from diarrheic and healthy foals, respectively. Three of the E. coli strains from diarrheic foals were positive with probes for slt genes and one was positive for STb and LT genes. One strain from a healthy foal possessed the STb gene. As determined by the polymerase chain reaction, 8 strains possessed the eae gene. Seven of the 8 strains were from diarrheic foals and one eae-positive strain was from a healthy foal. The slt-positive strains did not possess eae genes and the eae-positive strains did not possess slt genes. These results indicate that enterotoxigenic strains of E. coli are not implicated in any substantial degree in sporadic foal diarrhea. However, the identification of slt-positive and eae-positive strains in foal feces indicate the presence of potentially virulent strains among foals.

Characterization of eae+ Escherichia coli isolated from healthy and diarrheic calves.

Strains of Escherichia coli from 101 healthy and 114 diarrheic calves were screened by PCR for the eae (intimin) gene and Shiga toxin genes (stx). Each eae+ and eae/stx+ strain was examined for antimicrobial susceptibility, enterohemolysin activity, and the somatic O antigen was determined. An immunoassay was used to detect Shiga toxin antigens for the eae/stx+ E. coli. Significantly more (p = 0.005) of the healthy calves carried eae+ and eae/stx+ E. coli in their feces when compared to strains from diarrheic calves. Moreover, Shiga toxin antigens were detected significantly more (p = 0.001) often among the eae/stx+ strains from healthy calves when compared to eae/stx+ strains from diarrheic calves. However, significantly more (p = 0.001) of the eae+ and eae/stx+ strains from diarrheic calves were resistant to at least one of the antimicrobials tested, and the strains from diarrheic calves had a significantly (p = 0.05) higher rate of antimicrobial resistance to at least two different antimicrobial classes. No significant difference (p> or =0.05) was detected among the eae+ and eae/stx+ strains from healthy and diarrheic calves for enterohemolysin production. Serogroups O-negative, O5, O26, and O111 were predominate among both healthy and diarrheic calves.

Distribution of SP- and CGRP-like immunoreactive nerve fibers in the lower respiratory tract of neonatal foals: evidence for loss during development.

The lungs of neonatal foals contain many nerves immunoreactive for substance P and calcitonin gene-related peptide. These nerves are closely associated with the epithelium, bronchial and pulmonary vessels and the airway smooth muscle of all intrathoracic airways, including non-cartilaginous bronchioles. Activation of sensory nerves in the respiratory epithelium could thus potentially affect, via local axon reflexes, vascular and respiratory smooth muscle in neonatal equine airways. Nerves immunoreactive for these peptides are much more widely distributed within the lung than in adult horses; they may thus play a trophic role before birth, or contribute to the post-natal adaptation to breathing.

An outbreak of fetal and neonatal losses associated with the diagnosis of bovine viral diarrhea virus.

A severe outbreak of dairy herd pregnancy wastage was investigated. At the beginning of the outbreak, a total of 121 lactating cattle were pregnant and considered to be at risk. Overall, 33.1% of the population at risk aborted, while 25.6% gave birth to calves that either died during the early neonatal period or demonstrated signs compatible with congenital defects (abnormal births). A laboratory diagnosis of bovine viral diarrhea virus (BVDV) infection was made in two surviving neonatal calves with symptoms of cerebellar hypoplasia and blindness. An on-farm investigation was conducted to determine if the abortions and abnormal births were associated with BVDV infection. The rate of abortions versus abnormal births was biphasic when graphed by the date of occurrence. The cases of abortion occurred early in the outbreak and were followed by the neonatal losses. Within the population at risk, the mean values for gestational age at the beginning of the outbreak were different between the subpopulations described by gestational outcome. The outcome of each pregnancy that existed at the beginning of the outbreak was determined. Classifications included normal birth (birth of a normal calf), abnormal birth (a neonatal loss of the type described above), abortion, and continued gestation (normal, uncompleted pregnancy). The average gestational age at the time of the index case (the first cases of pregnancy wastage) for these four pregnancy outcome classfications was 142.0, 106.2, 86.7 and 31.3 days, respectively. Reasons for assuming that this outbreak was related to BVDV are discussed.

Sensory innervation of the navicular bone and bursa in the foal.

The sensory innervation of the navicular bone (os sesamoideum distale) and its suspensory ligaments [ligamenta sesamoidea collateralia (CSL) and ligamentum sesamoideum distale impar or distal sesamoidean impar (DS-impar) ligament] and the navicular bursa (podotrochlearis) was examined in the neonatal foal using immunocytochemistry. With antisera raised to substance P (SP) and human calcitonin gene-related peptide (CGRP), immunoreactive nerves were demonstrated to innervate the CSL and navicular bursa. Within CSL, and SP- and CGRP-like nerves were present in the synovial lining of the navicular bursa, appearing to reach the surface lining. These nerves appeared to enter the CSL and navicular bursa via the abaxial regions of the foot. Both peptides were present in the deep digital flexor tendon (DDf) along the palmar border of the navicular bursa, as well as in the DS-impar ligament. More nerve fibres were present in the dorsal part of CSL bordering the distal interphalangeal joint than was observed palmarly in CSL along the navicular bursa. Both peptides were observed to innervate the cartilage canals within the navicular bone. In terms of relative densities of immunoreactive SP- and CGRP-like peptides, the CSL dorsally and the DS-impar ligament had the highest relative densities of nerve fibres followed by the navicular bone, the palmar aspect of CSL and the DDf tendon bordering the navicular bursa. These results are discussed in relationship to local anaesthetic injections into the navicular bursa.

Amantadine and equine influenza: pharmacology, pharmacokinetics and neurological effects in the horse.

Amantadine is an antiviral agent effective against influenza A viruses. We investigated 1) the antiviral efficacy, 2) analytical detection, 3) bioavailability and disposition, 4) pharmacokinetic modelling and 5) adverse reactions of amantadine in the horse. In vitro, amantadine and its derivative rimantadine suppressed the replication of recent isolates of equine-2 influenza virus with effective doses (EDs) of less than 30 ng/ml. Rimantadine was more effective than amantadine against most viral isolates; we suggest a minimum plasma concentration of 300 ng/ml of amantadine for therapeutic efficacy. In vivo an i.v. dose of amantadine 15 mg/kg bwt produced mild, transient CNS signs which were no longer apparent after 30 min. Amantadine administered at a dose of 15 mg/kg bwt was established as the maximum safe single i.v. dose. However, if repeated i.v. administration of amantadine is required no more than 10 mg/kg bwt t.i.d. should be used. The maximal safe plasma concentration of amantadine was not evaluated but is probably greater than 2000 ng/ml and possibly greater than 4000 ng/ml. On the other hand, horses with lower seizure thresholds, or those on medications that lower seizure thresholds, may be at increased risk of amantadine-induced seizures, which show few premonitory signs and are rapidly fatal. After i.v. administration of amantadine 10 mg/kg bwt, the disposition kinetics were well fitted by a 2-compartment open model. The estimated peak plasma concentration after this dose was about 4500 ng/ml, the volume of distribution at steady-state (Vdss) was (mean +/- s.d.) 4.9 +/- 1.9 l/kg bwt and the beta phase half-life was 1.83 +/- 0.87 h. Computer projections of plasma amantadine concentrations after i.v. administration of amantadine at a dose of 10 mg/kg bwt t.i.d. at 8 h intervals suggest peak plasma concentrations of 4000-5000 ng/ml and troughs of less than 300 ng/ml will be achieved. Amantadine administered orally at 10 mg/kg bwt and 20 mg/kg bwt showed mean oral bioavailability of about 40-60% and a plasma half life of 3.4 +/- 1.4 h; however, there was substantial inter-animal variation in bioavailability. Projections based on the kinetics observed in individual animals suggest that some animals readily maintain effective plasma concentrations of amantadine after oral administration of 20 mg/kg bwt t.i.d. On the other hand, animals in which amantadine is poorly bioavailable may require up to a 6-fold (120 mg/kg bwt) increase in the oral dose to achieve effective blood concentrations. Withholding food for 15 h did not reduce these inter-animal differences in bioavailability. Our results showed that simple dosing with oral amantadine will not yield effective plasma concentrations in all animals. While i.v. administration yielded more reproducible plasma concentrations, care should be taken to see that the seizure threshold is not exceeded. In acute situations, i.v. administration (5 mg/kg bwt) every 4 h should maintain safe and effective plasma and respiratory tract concentrations of amantadine.

Efficacy of a cold-adapted, intranasal, equine influenza vaccine: challenge trials.

A randomised, controlled, double-blind, influenza virus, aerosol challenge of horses was undertaken to determine the efficacy of a cold-adapted, temperature sensitive, modified-live virus, intranasal, equine influenza vaccine. Ninety 11-month-old influenza-naïve foals were assigned randomly to 3 groups (20 vaccinates and 10 controls per group) and challenged 5 weeks, 6 and 12 months after a single vaccination. Challenges were performed on Day 0 in a plastic-lined chamber. Between Days 1 and 10, animals were examined daily for evidence of clinical signs of influenza. Nasal swabs for virus isolation were obtained on Day 1 and Days 1 to 8 and blood samples for serology were collected on Days 1, 7 and 14. There was no adverse response to vaccination in any animal. Following challenge at 5 weeks and 6 months, vaccinates had significantly lower clinical scores (P = 0.0001 and 0.005, respectively), experienced smaller increases in rectal temperature (P = 0.0008 and 0.0007, respectively) and shed less virus (P<0.0001 and P = 0.03, respectively) over fewer days (P<0.0001 and P = 0.002, respectively) than did the controls. After the 12 month challenge, rectal temperatures (P = 0.006) as well as the duration (P = 0.03) and concentration of virus shed (P = 0.04) were significantly reduced among vaccinated animals. The results of this study showed that 6 months after a single dose of vaccine the duration and severity of clinical signs were markedly reduced amongst vaccinated animals exposed to a severe live-virus challenge. Appropriate use of this vaccine should lead to a marked reduction in the frequency, severity and duration of outbreaks of equine influenza in North America.

A new modified live equine influenza virus vaccine: phenotypic stability, restricted spread and efficacy against heterologous virus challenge.

Flu Avert IN vaccine is a new, live attenuated virus vaccine for equine influenza. We tested this vaccine in vivo to ascertain 1) its safety and stability when subjected to serial horse to horse passage, 2) whether it spread spontaneously from horse to horse and 3) its ability to protect against heterologous equine influenza challenge viruses of epidemiological relevance. For the stability study, the vaccine was administered to 5 ponies. Nasal swabs were collected and pooled fluids administered directly to 4 successive groups of naïve ponies by intranasal inoculation. Viruses isolated from the last group retained the vaccine's full attenuation phenotype, with no reversion to the wild-type virus phenotype or production of clinical influenza disease. The vaccine virus spread spontaneously to only 1 of 13 nonvaccinated horses/ponies when these were comingled with 39 vaccinates in the same field. For the heterologous protection study, a challenge model system was utilised in which vaccinated or naïve control horses and ponies were exposed to the challenge virus by inhalation of virus-containing aerosols. Challenge viruses included influenza A/equine-2/Kentucky/98, a recent representative of the 'American' lineage of equine-2 influenza viruses; and A/equine-2/Saskatoon/90, representative of the 'Eurasian' lineage. Clinical signs among challenged animals were recorded daily using a standardised scoring protocol. With both challenge viruses, control animals reliably contracted clinical signs of influenza, whereas vaccinated animals were reliably protected from clinical disease. These results demonstrate that Flu Avert IN vaccine is safe and phenotypically stable, has low spontaneous transmissibility and is effective in protecting horses against challenge viruses representative of those in circulation worldwide.

Pharmacokinetic evaluation of ceftiofur in serum, tissue chamber fluid and bronchial secretions from healthy beef-bred calves.

Ceftiofur is a new broad spectrum cephalosporin marketed for the treatment of acute bovine respiratory disease. In this investigation ceftiofur was administered by intramuscular injection, at 24 h intervals, to healthy beef-bred calves for four days at dosages of 2.2 and 4.4 mg/kg of body weight, with 4 wk intervals between dosing regimens. Serum, tissue chamber fluid (TCF), and bronchial secretion (BS) concentrations of ceftiofur were measured by microbiological assay after the first and fourth dose of each dosing regimen. Peak serum concentrations (Cmax) of 8.8 micrograms/mL and 17.3 micrograms/mL were obtained approximately 2 h (Tmax), the time of mean peak concentration) after single injections of 2.2 mg/kg and 4.4 mg/kg, respectively. The Cmax was increased approximately twofold following multiple doses of 2.2 mg/kg (Cmax = 13.1 micrograms/mL) and 4.4 mg/kg (Cmax = 24.1 micrograms/mL). Ceftiofur accumulated slowly into TCF and peak concentrations were found to be approximately 14% of those observed in serum after the first dose and approximately 24% after multiple dosing. Concentrations of ceftiofur in BS were obtained rapidly with peak concentrations reaching 45% of the serum Cmax after the first dose. After multiple dosing the Cmax for BS was approximately 25% of the serum Cmax. This study found that both the 2.2 mg/kg and 4.4 mg/kg dosing regimens resulted in continuous serum, TCF and BS concentrations of ceftiofur that exceeded the minimal concentration required to inhibit the bacteria most frequently isolated from calves with acute bovine respiratory disease.

Breath hydrogen concentration and small intestinal malabsorption in calves.

Breath hydrogen concentrations were measured to assess intestinal carbohydrate malabsorption in preruminating calves. Oral administration of 1.25 g of lactulose (a nonabsorbable carbohydrate)/kg to calves produced breath hydrogen concentrations significantly (P less than 0.001) higher than values determined after calves were fed milk and before the treatment was given. This indicates that, in the calf, fermentation of nonabsorbed carbohydrates results in increased breath hydrogen values. To induce small intestinal malabsorption, chloramphenicol was administered orally at 50 mg/kg, 2 times a day, to 5 calves for 3 days. Before therapy was started, each calf was fitted with a duodenal cannula to facilitate collection of intestinal mucosal biopsy samples during treatment. Chloramphenicol therapy significantly (P less than 0.001) increased breath hydrogen concentrations from those values measured after calves were fed milk alone. Concurrently, chloramphenicol administration significantly decreased intestinal villous length (P less than 0.001) and D-xylose absorption (P less than 0.05), compared with those values before treatment was given. These results demonstrate that decreased intestinal absorptive capacity is associated with an increase in breath hydrogen concentrations and that breath hydrogen may be useful in evaluating malabsorption in calves with naturally occurring enteric disease.

Malabsorption of vitamin A in preruminating calves infected with Cryptosporidium parvum.

Serum retinol, retinyl palmitate, and total vitamin A concentrations, and jejunoileal morphology were examined in neonatal calves infected with Cryptosporidium parvum. Group-1 calves served as noninfected controls and, after an adjustment period, were given 50 ml of saline solution i.v. every 12 hours for 6 days. Group-2 calves were inoculated with 10(7) C parvum oocysts and, after the onset of diarrhea, were given 50 ml of saline solution i.v. every 12 hours for 6 days. Group-3 calves were inoculated with 10(7) C parvum oocysts and, after the onset of diarrhea, were treated with difluoromethylornithine (DFMO, 200 mg/kg of body weight i.v., q 12 h) for 6 days. Group-4 calves were naturally infected with C parvum. Jejunoileal biopsy specimens were excised from calves of groups 1-3 at 3 and again at 15 to 16 days of age. During the course of diarrhea and 3 days after saline or DFMO administration, water-miscible retinyl palmitate was administered orally (2,750 micrograms/kg) to each calf in each group. Cryptosporidium parvum infection was associated with significant (P < or = 0.05) reduction in postadministration serum retinol, retinyl palmitate, and total vitamin A concentrations in calves of groups 2, 3, and 4. Cryptosporidium parvum infection caused significant (P < or = 0.05) reduction in villus height. Decreased villus height, villus blunting and fusion, and attenuation of the intestinal mucosa were associated with reduced absorption of vitamin A, as indicated by lower peak postadministration retinyl palmitate concentration in C parvum-infected calves. Intravenous administration of DFMO to group-3 calves did not improve retinol absorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and therapeutic efficacy of rimantadine in horses experimentally infected with influenza virus A2.

OBJECTIVE: To determine pharmacokinetics of single and multiple doses of rimantadine hydrochloride in horses and to evaluate prophylactic efficacy of rimantadine in influenza virus-infected horses. ANIMALS: 5 clinically normal horses and 8 horses seronegative to influenza A. PROCEDURE: Horses were given rimantadine (7 mg/kg of body weight, i.v., once; 15 mg/kg, p.o., once; 30 mg/kg, p.o., once; and 30 mg/kg, p.o., q 12 h for 4 days) to determine disposition kinetics. Efficacy in induced infections was determined in horses seronegative to influenza virus A2. Rimantadine was administered (30 mg/kg, p.o., q 12 h for 7 days) beginning 12 hours before challenge-exposure to the virus. RESULTS: Estimated mean peak plasma concentration of rimantadine after i.v. administration was 2.0 micrograms/ml, volume of distribution (mean +/- SD) at steady-state (Vdss) was 7.1 +/- 1.7 L/kg, plasma clearance after i.v. administration was 51 +/- 7 ml/min/kg, and beta-phase half-life was 2.0 +/- 0.4 hours. Oral administration of 15 mg of rimantadine/kg yielded peak plasma concentrations of < 50 ng/ml after 3 hours; a single oral administration of 30 mg/kg yielded mean peak plasma concentrations of 500 ng/ml with mean bioavailability (F) of 25%, beta-phase half-life of 2.2 +/- 0.3 hours, and clearance of 340 +/- 255 ml/min/kg. Multiple doses of rimantadine provided steady-state concentrations in plasma with peak and trough concentrations (mean +/- SEM) of 811 +/- 97 and 161 +/- 12 ng/ml, respectively. Rimantadine used prophylactically for induced influenza virus A2 infection was associated with significant decreases in rectal temperature and lung sounds. CONCLUSIONS AND CLINICAL RELEVANCE: Oral administration of rimantadine to horses can safely ameliorate clinical signs of influenza virus infection.

Isolation of enterotoxigenic Escherichia coli from a foal with diarrhea.

Enterotoxigenic Escherichia coli was isolated from a 3-day-old foal with diarrhea. The isolate was distinguished from nonpathogenic E coli by determining the presence of pili and enterotoxin production. A standard slide agglutination test was performed, using pooled antisera that contained antibodies against K99 and F41 pilus antigens, K87 capsular antigen, and 0101 somatic antigen. Agglutination of the antisera occurred in the presence of the isolate. Piliation was verified by use of negative-contrast electron microscopy. Further, the isolate produced a heat-labile enterotoxin-like antigen that cross-reacted with a reagent containing formalin-treated, heat-killed Staphylococcus aureus (cowan 1 strain) bearing anti-cholera antibodies. On the basis of the aforementioned procedures and the absence of other identifiable enteric pathogens, we believe that E coli was responsible for causing diarrhea in the foal.

Adenovirus-associated pneumonia and hepatitis in four llamas.

This report focuses on the diagnostic laboratory and necropsy findings in 4 llamas with adenovirus-associated hepatitis or pneumonia. In the 2 young llamas, clinical illness was characterized by chronic respiratory tract disease. In the 2 adult llamas, clinical illness was characterized by neurologic signs and a history of respiratory tract disease. Histologic examination, electron microscopy, virus isolation, and fluorescent antibody results indicated that adenovirus infection was associated with disease in all 4 llamas.

Investigation of an epizootic of bovine viral diarrhea virus infection in calves.

Eight of 19 calves born to bovine viral diarrhea virus (BVDV)-negative and -immunocompetent dams were determined to be infected with a noncytopathic strain of BVDV. Six of the 8 calves had diarrhea and 2 had no clinical signs of disease. In 3 euthanatized calves, lesions consistent with mucosal disease were found throughout the gastrointestinal tract, and the virus was isolated from the spleen, lymph nodes, and small intestine. In 5 calves, BVDV was isolated from mononuclear cells in blood samples obtained 21 days apart, indicating persistent infection. The virus was not isolated from sera obtained from 2 calves, with chronic nonclinical infections, that had neutralizing antibody titers > or = 1:512 against bovine viral diarrhea-Singer virus and titers > or = 1:256 against the persistent BVDV. Twenty-one days after vaccination with a vaccine that contained inactivated noncytopathic and cytopathic biotypes of BVDV, 4 of 5 persistently infected calves had neutralizing antibody titers < or = 1:4 against the bovine viral diarrhea-Singer virus and their persistent virus. Prior to vaccination, 2 of 11 virus-negative calves had neutralizing antibody titers < or = 1:128 against the bovine viral diarrhea-Singer virus, and after vaccination, only 1 virus-negative calf had a titer < or = 1:512. At 149 days after revaccination and prior to weaning, 4 virus-negative calves had neutralizing antibody titers < or = 1:512 (range, 1:16 to 1:384). Under the specific conditions in this herd, we were not able to detect a beneficial effect of vaccination.(ABSTRACT TRUNCATED AT 250 WORDS)