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PubMed2006

Comparing an experimental agent to a standard agent: relative merits of a one-arm or randomized two-arm Phase II design.

BACKGROUND: Phase II clinical trials in cancer are used to assess whether a new agent has sufficiently promising efficacy to proceed on to a larger definitive study comparing the new agent to a standard agent. PURPOSE: A crucial issue in determining the usefulness of a one-arm design is the uncertainty of the historical response rate of the standard therapy. Therefore, we contrast the usual one-arm design of a Phase II trial with a randomized two-arm design that uses the same number of patients. METHODS: We use simulations and analytical approximations to compare the two designs under a range of realistic values for the historical rate uncertainty and a range of treatment effects. We also extend the simulation model to compare the efficiency of the two designs in settings where multiple Phase II studies are used to make decisions about moving on to a Phase III study. RESULTS: For a one-arm design the probability of correctly identifying an effective experimental agent tends to be at least 0.7 in the cases considered, with the corresponding value for a randomized two-arm design within 0.05-0.10 above or below the one-arm design. An increase in total sample size from 30 patients to 80 patients tends to increase the probability of correctly identifying an effective experiment agent more in the two-arm design than the the one-arm design, particularly when the uncertainty in the historical response rate is large. LIMITATIONS: These results for binary response measures are derived from the specific scenarios and assumptions considered in the simulation study and may not apply to situations outside the range considered. CONCLUSIONS: We find that a one-arm design is preferred for small sample sizes, but a two-arm design may be preferred with larger sample sizes or if the uncertainty in the historical response rates is large.

Antineoplastic Agents↗

PubMed1990

[Studies on porphyrin related compounds and tumor tissue affinities. I. Synthesis of a carrier for tumor imaging agent, bifunctional chelating agent coupled porphyrin (ATN-2)].

A carrier for a new tumor imaging agent, a bifunctional chelating agent (BCA)-coupled porphyrin (ATN-2), has been synthesized from protoporphyrin dimethyl ester in 4 steps. At first, the hydrobromination of protoporphyrin dimethyl ester is carried out to obtain a monobromo derivative. The derivative is treated with ethylene glycol. The resulting porphyrin has an ether group at the either 7- or 12-position of the ring. Metallation with GaCl3 of the porphyrin having a ethylene glycol residue affords Ga-metalloporphyrin. Final condensation of the metalloporphyrin with diethylenetriaminepentaacetic acid (DT-PA) gave BCA-coupled porphyrin (ATN-2). The chelation of ATN-2 with 111InCl3 easily afforded [111In]ATN-2. This agent was used for imaging transplantable pancreatic carcinoma in Syrian golden hamster at 72 h after postinjection. The efficacy of the new agent was compared with that of [67Ga]citrate. The images with [111In]ATN-2 were found to be clearer than those with [67Ga]citrate. Therefore, ATN-2, a carrier for 111InCl3, seems to be more useful for tumor imaging agents.

Animals↗

PubMed2005

Update on antimicrobial agents: new indications of older agents.

The discovery of newly recognised pathogens and the emergence of antimicrobial resistance have led to the development of new antimicrobial agents or to new indications for older agents. The indications have continued to increase because of new discoveries on the older agents' antimicrobial and non-antimicrobial activities. Macrolides and tetracyclines have received attention for their non-antimicrobial properties and potential use in chronic inflammatory disorders. Doxycycline, minocycline and trimethoprim-sulfamethoxazole regained interest for their activity against methicillin-resistant Staphylococcus aureus, whereas colistin has regained interest for its activity against multiple drug-resistant, Gram-negative pathogens (i.e., Pseudomonas aeruginosa). Despite the recent development of new antimicrobial agents, older and less costly agents maintain an important role today in the treatment of infectious diseases.

Animals↗

PubMed1980

Effect of nosiheptide as a feed additive in chicks on the quantity, duration, prevalence of excretion, and resistance to antibacterial agents of Salmonella typhimurium; on the proportion of Escherichia coli and other coliforms resistant to antibacterial agents; and on their degree and spectrum of resistance.

In the first experiment two groups (B and D) each of ten, 15-day-old chicks were fed for 33 days a diet supplemented with nosiheptide (20 g/t) and 2 groups (A and C) of 10 each a diet without medication. Groups A and B were inoculated with Salmonella typhimurium, var. copenhagen (variant resistant to nalidixic acid of the strain DVR 101) 5 days after treatment was started. At intervals of 2, 4, 6, 8, 10, 12, 14, 21, and 28 days postinoculation the following data were collected: the number of salmonella excreted per gram of feces, their duration and prevalence of excretion, and the proportion of salmonella resistant to 9 antibacterial agents commonly used in human and veterinary medicine, as well as their degree and spectrum of resistance. In the second experiment two groups of 10 chicks each were fed either a basal diet (control group) or a diet supplemented with nosiheptide at 20 g/t (treated group). Immediately before and at the end of treatment, the proportions of fecal coliforms, particularly E. coli, which were resistant to 11 commonly used antibacterial agents, and their degree and spectrum of resistance were determined in the 2 groups of chicks. All the strains isolated before treatment started were E. coli sensitive to the 11 antibacterial agents. The strains isolated at the end of treatment were coliforms otherthan E. coli (40% in the control group, 32% in the treated group) and E. coli (60 and 68%, respectively). Coliforms other than E. coli were, as is usual, resistant to ampicillin and sensitive to the other antibacterial agents. The E. coli strains were either sensitive to all the antibacterial agents or resistant to tetracycline and furazolidone (51.8% in the control group, 34.1% in the treated group), or resistant to furazolidone alone (3.7% in the control group, 5.8% in the treated group). In both experiments these determinations showed no appreciable differences between treated and untreated chicks.

Animal Feed↗

PubMed1999

Synergistic effects of new chemopreventive agents and conventional cytotoxic agents against human lung cancer cell lines.

Non-small cell lung cancer (NSCLC) cells have constitutively high expression of cytosolic phospholipase A2 (cPLA2) and cyclooxygenase (COX) 2. These NSCLC cells also have increased prostaglandin expression (PGE2). Many lung cancers also express 12-lipoxygenase RNA and 12-lipoxygenase protein and biosynthesize 12(S)-hydroxyeicosatetraenoic acid, which correlates with their metastatic potential. Several studies have demonstrated that COX-1 and COX-2 inhibitors could inhibit the in vitro growth of human lung cancer cell lines. In this report, we evaluated the growth-inhibitory effects of sulindac sulfide, a COX-1 and COX-2 inhibitor; exisulind (sulindac sulfone), a novel proapoptotic agent that does not inhibit COX enzymes; and nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor on human lung cancer cell lines. We compared these effects with those of 13-cis-retinoic acid, a chemoprevention agent, and with the cytotoxic chemotherapeutic agents paclitaxel and cisplatin, alone or in combination. Our goal was to develop new chemoprevention and treatment strategies. Each of the six agents tested inhibited the in vitro growth of three NSCLC and three SCLC cell lines at the highest concentration. Paclitaxel was the most potent agent (IC50 = 0.003-0.150 microM); sulindac sulfide, NDGA, and 13-cis-retinoic acid had intermediate potency (IC50 = 4-80 microM), and cisplatin and exisulind were the least potent (IC50 = 150-500 microM). Combination studies showed synergistic interactions for sulindac sulfide, exisulind, and NDGA with paclitaxel, cisplatin, and 13-cis-retinoic acid, regardless of drug-resistance phenotype. At high concentrations, the combination of 13-cis-retinoic acid and each of the five other drugs resulted in a strong synergistic effect. These studies provide a rationale for chemoprevention (exisulind +/- retinoic acid +/- NDGA) and therapeutic (exisulind +/- paclitaxel +/- cisplatin) studies in patients at risk for, or with, lung cancer.

Antineoplastic Agents↗

PubMed1990

Beta-blocking agents and positive inotropic agents in the therapy of chronic heart failure.

Positive inotropic stimulation of the failing cardiac muscle seems to be useful, if certain requirements are met: (a) there is some cardiac contractile reserve left, (b) the positive inotropic agent of choice is able to mobilize this contractile reserve, and (c) peripheral vascular resistance is not increased permanently by this agent. On the other hand, the physiological response (i.e., positive inotropic effect) to circulating catecholamines in heart failure is decreased or even absent due to receptor desensitization and an alteration of guanine nucleotide-binding proteins (increased Gi). It has been proved that functionally active beta-adrenoceptors may be restored by treatment with beta-adrenoceptor antagonists. However, these agents necessarily will have negative inotropic effects in the failing cardiac muscle, if the force of contraction is largely dependent on a permanent stimulation by catecholamines and if there are no spare beta-adrenoceptors. To clarify these as-yet unresolved problems, we have determined the contractile reserve as well as its utilization by positive inotropic agents in human cardiac muscles of failing and nonfailing hearts. The number and functional activity of cardiac glycoside receptors, beta-adrenoceptors, and alpha-adrenoceptors were measured as well as the positive inotropic and negative inotropic effects of partial agonists. Furthermore, we have accumulated evidence that, in fact, there are no spare beta-adrenoceptors in the human cardiac muscle. The lack of spare beta-adrenoceptors has consequences for the therapeutic approach in patients with heart failure. At least initially, the administration of beta-adrenoceptor-blocking agents to patients with heart failure depending on agonist-induced stimulation will lead to a worsening of cardiac function. If this situation can be tolerated, however, the subsequent restoration of functionally active beta-adrenoceptors after beta-blockade may lead to restored physiological regulation of force of contraction by norepinephrine.

Adrenergic beta-Antagonists↗

PubMed2002

[The guideline how to use the antimicrobial agents--the guidance how to use the antimicrobial agents].

In regard to reconsider the way of antimicrobial agent, it has given the guideline which is how to use the antimicrobial agent to be protected the occurrence of drug resistant bacteria and how to use it safety. This writing omit the way of thinking about the proper use, the safety use, and the prevention for hospital acquired infections by this reference. What the proper use for antimicrobial agent is. The basic idea as the proper use for antimicrobial agent is 1. to heal a patient(individual-defense), 2. not to increase drug resistant bacteria(group-defense), 3. to be utilizable for a medical resource mostly. In the choice of antimicrobial agent for the individual situation, we have to think about 1. (to heal a patient) seriously first, and then, of course, we recognize the point of view for 2. and 3. has a good balance in this way.

Anti-Bacterial Agents↗

PubMed1987

Newer cardiac agents: antiarrhythmics and antianginal agents.

This article has briefly summarized the physiologic effects, pharmacokinetics, adverse effects, drug interactions, and methods of analysis for the newer cardiac agents. Methods of analysis for these newer agents are primarily chromatographic types, such as gas-liquid or high-pressure liquid chromatography. Conspicuously absent from methods of analysis for these agents are the newer immunologic methods such as RIA or enzyme-linked assays. This deficiency in methodology is due to several factors. Cross-reactivity between metabolites and parent compounds is often a problem with antibody-based assays, and several of these agents have metabolites that reach concentrations equivalent to that of the parent drug. Several of the newer antiarrhythmics are structurally related not only to each other but also to older agents such as lidocaine. Overcoming this cross-reactivity would be necessary before these assays could be used in patients being converted from intravenous lidocaine to the newer oral preparations. With the development of monoclonal antibody techniques, the need for close therapeutic monitoring of several of the drugs, and the increased emphasis on restraining costs in the clinical laboratory, the newer immunologic methods may soon be introduced in the United States.

Angina Pectoris↗

PubMed2002

Vascular targeting agents enhance chemotherapeutic agent activities in solid tumor therapy.

The utility of combining the vascular targeting agents 5,6-dimethyl-xanthenone-4 acetic acid (DMXAA) and combretastatin A-4 disodium phosphate (CA4DP) with the anticancer drugs cisplatin and cyclophosphamide (CP) was evaluated in experimental rodent (KHT sarcoma), human breast (SKBR3) and ovarian (OW-1) tumor models. Doses of the vascular targeting agents that led to rapid vascular shutdown and subsequent extensive central tumor necrosis were identified. Histologic evaluation showed morphologic damage of tumor cells within a few hours after treatment, followed by extensive hemorrhagic necrosis and dose-dependent neoplastic cell death as a result of prolonged ischemia. Whereas these effects were induced by a range of CA4DP doses (10-150 mg/kg), the dose response to DMXAA was extremely steep; doses < or = 15 mg/kg were ineffective and doses > or = 20 mg/kg were toxic. DMXAA also enhanced the tumor cell killing of cisplatin, but doses > 15 mg/kg were required. In contrast, CA4DP increased cisplatin-induced tumor cell killing at all doses studied. This enhancement of cisplatin efficacy was dependent on the sequence and interval between the agents. The greatest effects were achieved when the vascular targeting agents were administered 1-3 hr after cisplatin. When CA4DP (100 mg/kg) or DMXAA (17.5 mg/kg) were administered 1 hr after a range of doses of cisplatin or CP, the tumor cell kill was 10-500-fold greater than that seen with chemotherapy alone. In addition, the inclusion of the antivascular agents did not increase bone marrow stem cell toxicity associated with these anticancer drugs, thus giving rise to a therapeutic gain.

Animals↗

PubMed2001

Novel liver macromolecular MR contrast agent with a polypropylenimine diaminobutyl dendrimer core: comparison to the vascular MR contrast agent with the polyamidoamine dendrimer core.

As MRI contrast agents, more hydrophobic molecules reportedly accumulate in the liver and thus are potentially useful as liver MRI contrast agents. In this study, a generation-4 polypropylenimine diaminobutane dendrimer (DAB-Am64), which is expected to be more hydrophobic than the generation-4 polyamidoamine dendrimer (PAMAM-G4D), was used to synthesize a conjugate with 2-(p-isothiocyanatobenzyl)-6-methyl-diethylenetriaminepentaacetic acid (1B4M) [DAB-Am64-(1B4M-Gd)(64)] for complexing Gd(III) ions. This DAB conjugate quickly accumulated in the liver and its characteristics were studied and compared with those of a PAMAM conjugate [PAMAM-G4D-(1B4M-Gd)(64)], which is known to be a useful vascular MRI contrast agent, in regard to its availability as a liver MRI contrast agent. DAB-Am64-(1B4M-Gd)(64) accumulated significantly more in the liver and less in blood than PAMAM-G4D-(1B4M-Gd)(64) (P < 0.001). Contrast-enhanced MRI with DAB-Am64-(1B4M-Gd)(64) was able to homogeneously enhance liver parenchyma and visualize both portal and hepatic veins of 0.5 mm diameter in mice. In conclusion, DAB-Am64-(1B4M-Gd)(64) is a good candidate for a liver MRI contrast agent.

Animals↗

PubMed1992

Actions and cross-reactivity of antiallergic agents and a calcium channel antagonist on rat peritoneal mast cells. Difference in the action mechanisms and cross-reactivity among the agents.

The actions of the antiallergic agents, disodium chromoglycate (DSCG), tranilast and ketotifen, and of a calcium channel antagonist, nicardipine, and cross-reactivity among the agents were examined by observing the inhibition of 45Ca uptake and histamine release in rat mast cells stimulated by antigen and compound 48/80 (comp. 48/80). 1) All agents inhibited 45Ca uptake and histamine release in mast cells stimulated by antigen. The inhibition of 45Ca uptake by the antiallergic agents paralleled the inhibition of histamine release, while nicardipine inhibition of 45Ca uptake was stronger than its inhibition of histamine release. 2) The action of DSCG on 45Ca uptake and histamine release was significantly decreased in cells stimulated with antigen and phosphatidylserine (PS), while tranilast inhibition of histamine release was not affected by the addition of PS despite a significant decrease in the inhibition of 45Ca uptake. 3) The inhibitory effect of DSCG and tranilast was significantly lower in mast cells stimulated by comp. 48/80 than in the cells stimulated by antigen. 4) Tachyphylaxis was observed in cells re-exposed to DSCG and tranilast following previous exposure to the agents. 5) Cross-reactivity was found between DSCG and tranilast.

Animals↗

PubMed1983

Disinfection studies with two strains of mouse-passaged scrapie agent. Guidelines for Creutzfeldt-Jakob and related agents.

A variety of disinfection procedures were tested on two strains of scrapie agent, treated either as brain macerates (autoclaving) or as 10% homogenates (chemical treatments). It is suggested that a given treatment should produce a titre loss, of both strains of scrapie, of at least 10(4) units before it be regarded as useful for the disinfection of the agents of scrapie and Creutzfeldt-Jakob disease (CJD). By this criterion, treatment at room temperature with about 4% Hycolin (0.6% chlorinated phenols), 0.2% permanganate, 5% Tego (dodecyl-di(aminoethyl)-glycine) or 5% sodium dodecyl sulphate (SDS) are unsuitable. However, data indicate that SDS might be used to reduce the heat stability of scrapie agent. Hypochlorite (Sterilex) was the only satisfactory chemical reagent tested. At least 10(4)-10(5) units of infectivity were lost by treatment with hypochlorite containing 1,000 ppm available chlorine after a 4-16 h exposure, or containing 10,000 ppm available chlorine after a half-hour exposure. The latter result points to the use of concentrated hypochlorite (about 2% available chlorine; approximately 20% Sterilex) to decontaminate surfaces. We suggest that the cleaning action of SDS, or other strong detergents, might also help to decontaminate surfaces, but studies on this are needed. Autoclaving at 126 degrees C for 1-2 h reduced titres by 10(3)-10(7) units, depending on the strain of agent. However, total disinfection of brain containing high titres of infectivity was approached only at 136 degrees C when titre losses of about 10(6) units were obtained by autoclaving for 4-32 min. Further studies are needed before we can make simple, general recommendations for the disinfection of CJD agents in hospital practice.

Animals↗

PubMed1992

A comparison of nonionic, low-osmolality radiocontrast agents with ionic, high-osmolality agents during cardiac catheterization.

BACKGROUND: Nonionic, low-osmolality radiocontrast agents are used frequently because they are believed to be safer than ionic, high-osmolality agents, but they are also more expensive. We conducted a randomized trial to compare the incidence of adverse events after the administration of ionic, high-osmolality and of non-ionic, low-osmolality radiocontrast agents during cardiac angiography. METHODS: We compared the need to treat patients for adverse reactions and the frequency and severity of specific hemodynamic, systemic, and symptomatic side effects in two groups of patients randomly assigned to receive either ionic, high-osmolality or nonionic, low-osmolality radiocontrast material, and also in 366 patients who could not be randomized. RESULTS: Treatment for adverse events was required in 213 of 737 patients who received high-osmolality contrast agents (29 percent) but in only 69 of 753 patients who received nonionic agents (9 percent) (95 percent confidence interval for the percent difference, 15.9 to 23.6 percent). Hemodynamic deterioration and symptoms also occurred more often in the high-osmolality group, as did severe or prolonged reactions (2.9 percent, as compared with 0.8 percent in the nonionic group; P = 0.035). The severe reactions were largely confined to patients with severe cardiac disease. Multivariate analysis showed that the presence of severe coronary disease and unstable angina were predictors of clinically important adverse reactions. If all the patients in our randomized trial had been given nonionic contrast material, the incremental cost per procedure would have been $89. CONCLUSIONS: Nonionic, low-osmolality contrast material is better tolerated during cardiac angiography than ionic, high-osmolality contrast material. Since cost constraints may prevent the universal use of nonionic contrast material, its selective use in patients with severe cardiac disease could be considered.

Contrast Media↗

PubMed1982

Infection with delta agent in Sweden: introduction of a new hepatitis agent.

To investigate the epidemiology of infection with delta (delta) agent in a Swedish city, 181 chronic carriers of hepatitis B surface antigen (HBsAg) and 599 patients with acute, self-limited hepatitis B were analyzed for delta antigen and antibody to delta antigen (anti-delta). The study covered the period from 1970 to 1981. The delta agent was found to have been introduced to this population in 1973. Markers of infection with delta agent were almost exclusively found in intravenous drug addicts and their close contacts. The proportion of drug addicts who were chronic HBsAg carriers with anti-delta increased with time and reached 72% in 1979-1981. An episode of acute hepatitis was frequently seen in connection with seroconversion to anti-delta. Among the domestic cases of acute, self-limited hepatitis, no simultaneous infections with hepatitis B virus and delta agent were found before 1975. From 1975 to 1980, between 18% and 44% of the drug addicts with acute hepatitis B were also infected with delta agent.

Antibodies, Viral↗

PubMed1975

Multiple sclerosis-associated agent: transmission to animals and some properties of the agent.

In confirmation and extension of observations by Carp and his associates, brain tissue and sera from patients with multiple sclerosis (MS) were found to harbor an agent which induces a transitory depression in polymorphonuclear leukocytes (PMN) in mice as well as in rats, hamsters, and guinea pigs. All of eight MD brains contained this agent at titers as high as 10(-9)/g of brain tissue. The agent was found in MS sera at titers up to 10(-3)/ml of serum, but its presence depended to some extent on the clinical status of the patients; it was observed more frequently in sera of patients with active disease (73%) thatn in sera of patients with quiescent disease (31%). Control brain tissues or sera failed to induce PMN depression. The apparently MS-associated agent (MSAA) passed through 50-nm but not 25-nm membrane filters (Millipore Corp.) and was largely sedimented at 105,000 X g but not at 50,000 X g for 1 h. It multiplied to high titers in the central nervous tissue of the inoculated animals and could be serially transmitted from animal to animal by passage of brain homeganates. Various observations and considerations appear to preclude that MS-associated agent represents an indigenous animal virus. Although its role in MS remains to be determined, it should be considered a candidate for the etiology of this disease.

Animals↗

PubMed1997

Adverse events with radiographic contrast agents: results of the SCVIR Contrast Agent Registry.

PURPOSE: To determine prospectively the incidence of adverse events in angiography related to contrast agents, and the relative incidence of events with use of high-osmolality contrast agents (HOCAs) and low-osmolality contrast agents (LOCAs) and to ascertain if risk factors can help identify increased risk of an adverse event and patients likely to benefit from use of LOCAs. MATERIALS AND METHODS: From 26 high-volume institutions, data were collected on every patient who underwent angiography from July 1, 1990, to June 30, 1992. Information included demographic and risk factors, general medical status, previous administration of contrast media, procedural information, occurrence and characteristics of all adverse events up to 12 hours after procedures, and relation to contrast agents, treatment, and outcome. RESULTS: In 60,891 patients, there were 75,616 studies, 56% with nonionic LOCAs, 8% with the ionic LOCA, and 36% with HOCAs. Most major risk factors correlated with an increased incidence of adverse events related to contrast media. Incidence of these adverse events varied with type of procedure, with a higher incidence associated with cardiac and interventional procedures. Overall adverse events related to contrast media and those for which treatment was necessary were significantly increased (P < .001) with use of HOCAs for all but arterial interventional procedures. Serious adverse events were not different between the two classes of agents except for cardiac procedures. Previous reaction to contrast medium was the most important risk factor in prediction of an adverse event. CONCLUSION: The safety benefit of use of LOCAs is limited. Patients most likely to benefit are those with a previous reaction or more than one other major risk factor. Selective use of LOCAs is an appropriate strategy.

Adverse Drug Reaction Reporting Systems↗

PubMed1996

Comparison of the therapeutic effects of the beta-blocking agent bisoprolol and the calcium-blocking agent diltiazem in patients with heart failure due to dilated cardiomyopathy.

Beta-blocking agents reduce mortality and improve symptoms in patients with dilated cardiomyopathy (DCM). There have been reports that diltiazem, a calcium-blocking agent, is also effective in such patients. We prospectively compared the effects of the beta-blocking agent bisoprolol with those of the calcium-blocking agent diltiazem in 18 patients (11 males and 7 females, age 14 to 68) with DCM. The 18 patients, (10 in New York Heart Association functional class III and 8 in class IV) were randomly assigned to 2 groups. Bisoprolol was administered as the first drug in 10 patients and diltiazem was administered in 8. Cross-over to bisoprolol was also performed in 3 patients. At the end of the study, among the 13 patients who had been given bisoprolol, 9 showed a good response (efficacy rate: 69%). In contrast, only 3 of the 8 patients who received diltiazem showed a good response (efficacy rate: 37.5%). Among the patients in NYHA class III, all 7 (100%) who were treated with bisoprolol responded but only 2 of the 4 (50%) treated with diltiazem responded (p < 0.05). Among the patients in class IV, 2 of 6 (33%) responded to bisoprolol and 1 of 4 (25%) responded to diltiazem (not significant). These results suggest that diltiazem, like bisoprolol, has a beneficial effect in patients with DCM, with a greater effect in class III patients. However, we conclude that diltiazem should usually be used as a second choice to improve heart failure in DCM, and as the first medication only in those with contraindications to beta-blocking agents.

Adolescent↗

PubMed1979

Infectious bursal agent vaccination of chicks from infectious bursal agent-vaccinated dams.

Chicks from infectious bursal agent-vaccinated broiler breeders were vaccinated with a commercial infectious bursal agent vaccine at intervals after hatching. Bursas from some of these chicks were examined for infectious bursal agent-specific fluorescence four days after vaccination and bursas from others were examined for histological lesions of infectious bursal disease 21 days after vaccination. Serological studies were conducted to determine if active immunity to infectious bursal agent followed vaccination. Chicks failed to develop immunity if their levels of maternally-derived serum neutralizing antibody were in excess of approximately log(2) 7 at the time of vaccination. When antibody titres fell below this level, vaccination usually resulted in infectious bursal agent virus replication in the bursa and consequential bursal damage but was followed by development of active immunity.

Animals↗